cellular level of organization...module 3.1: cellular differentiation produces specialized cells...

Lecture Presentation by

Lori Garrett

3Cellular Level of

Organization

© 2018 Pearson Education, Inc.

Section 1: Introduction to Cells

Learning Outcomes

3.1 Describe the cell theory and the process of cellular

differentiation.

3.2 Describe a body cell and its organelles, including

the structure and function of each.

3.3 Describe the structural and functional features of

the plasma membrane.

3.4 Differentiate among the structures and functions of

the cytoskeleton.


Section 1: Introduction to Cells

Learning Outcomes (continued)

3.5 Describe the ribosome and smooth and rough

endoplasmic reticula, and indicate their specific

functions.

3.6 Describe the Golgi apparatus, and indicate its

specific functions.

3.7 Describe the structure of a mitochondrion, and

explain the significance of mitochondria to cellular

function.


Module 3.1: Cellular differentiation produces specialized cells

Typical cell

Smallest living unit in the body

~0.1 mm in diameter

Could not be examined until invention of microscope

in 17th century


Module 3.1: Introduction to Cells

Cell theory

1. Cells are building blocks of all plants and animals

2. All new cells come from division of preexisting

cells

3. Cells are smallest living units that perform all vital

physiological functions



Cell cooperation

Each cell maintains homeostasis at cellular level

Coordinated activities of cells allow homeostasis at

higher organizational levels

All cells are descendants from a single cell: the

fertilized ovum

At fertilization, zygote forms

• Fertilized ovum contains genetic potential to become

any cell

• First cell divisions create smaller parcels of cytoplasm



Cellular differentiation

Regional differences in original ovum cytoplasm

means now different composition of cytoplasm in

resulting daughter cells

Cytoplasmic differences affect DNA in daughter cells

and cause specific genes to turn on or off

• Result is specialization of cells

• Process of gradual specialization is called cellular

differentiation

• Specialized cells form tissues of the body


Cell differentiation


Module 3.1: Review

A. Describe the cell theory.

B. Identify the cell from which all the cells of your

body are descendants.

C. Define cellular differentiation.

Learning Outcome: Describe the cell theory and

the process of cellular differentiation.


Module 3.2: Cells are the smallest living units of life

Body fluid distribution

Cells surrounded by watery medium called

extracellular fluid

• Called interstitial fluid (interstitium, something

standing between) in most tissues

Fluid inside cell is intracellular fluid or cytosol

Cell plasma membrane separates cell contents

(cytoplasm) from extracellular fluid


Module 3.2: The cell and its organelles

Basic cell structure

Surrounded by a plasma membrane

Contains cytoplasm

• Material of varying consistency found between cell

membrane and nuclear membrane

• Subdivided into:

– Cytosol (intracellular fluid)—the fluid part of cytoplasm

– Organelles (“little organs”)—intracellular structures

with specific functions



Organelles

Divided into membranous

and nonmembranous

Nonmembranous

• Not completely enclosed

by membranes

• In direct contact with

cytosol

Membranous

• Enclosed in a

phospholipid membrane

• Isolated from cytosol



Peroxisome

STRUCTURE:

• Vesicles containing

degradative enzymes

FUNCTION:

• Break down organic

compounds

• Neutralize toxic

compounds



Lysosome

STRUCTURE:

• Vesicles containing

digestive enzymes

FUNCTION:

• Break down organic

compounds and

damaged organelles or

pathogens



Microvilli

STRUCTURE:

• Membrane extensions

containing

microfilaments

FUNCTION:

• Increase surface area

for absorption



Golgi apparatus

STRUCTURE:

• Stacks of flattened

membranes (cisternae)

containing chambers

FUNCTION:

• Store, alter, and

package synthesized

products



Nucleus

STRUCTURE:

• Fluid nucleoplasm

containing enzymes,

proteins, DNA, and

nucleotides

• Surrounded by double

membrane called

nuclear envelope

FUNCTION:

• Controls metabolism

• Stores and processes genetic information

• Controls protein synthesis



Endoplasmic reticulum

(ER)

STRUCTURE:

• Network of

membranous

sheets and channels

FUNCTION:

• Synthesizes secretory

products; stores and

transports within cell;

detoxifies drugs and

toxins



Endoplasmic reticulum

(ER) (continued)

• Smooth ER

– No attached

ribosomes

– Synthesizes lipids

and carbohydrates

• Rough ER

– Attached ribosomes

– Modifies/packages

newly synthesized

proteins



Ribosomes

STRUCTURE: RNA

and proteins

• Fixed: attached to

endoplasmic reticulum

• Free: scattered in

cytoplasm

FUNCTION:

• Synthesize proteins



Mitochondrion

STRUCTURE:

• Double membrane

• Inner membrane

contains metabolic

enzymes

FUNCTION:

• Produces 95 percent

of cellular ATP



Cytoskeleton

STRUCTURE:

• Proteins organized into

fine filaments or slender

tubes

• Centrosome

– Organizing center

containing pair of

centrioles

FUNCTION:

• Strengthens and

supports cell

• Moves cellular structures and materials within the cell


Module 3.2: Review

A. Distinguish between the cytoplasm and cytosol.

B. Identify the membranous organelles, and

describe their functions.

C. Describe the functions of the cytoskeleton.

D. Describe the external environment of most of

the body’s cells.

Learning Outcome: Describe a body cell and its

organelles, including the structure and function of

each.


Module 3.3: The plasma membrane isolates the cell from its environment and performs varied functions

Plasma membrane—selectively permeable barrier

separating inside of cell from extracellular fluid

Controls:

• Entry of ions and nutrients

• Elimination of wastes

• Release of secretions


Module 3.3: Plasma membrane

Composed of:

Phospholipid bilayer

Proteins

1. Integral

2. Transmembrane

3. Peripheral

4. Glycocalyx—layer formed by superficial membrane

carbohydrates


Plasma membrane



Phospholipid bilayer

Measures 6–10 nm

Two layers of phospholipids

• Hydrophilic heads at

membrane surface

• Hydrophobic tails facing

each other on the inside

Phospholipids interspersed

with cholesterol molecules

• Cholesterol has hydrophilic and hydrophobic

portions (amphipathic)

• Functions to “stiffen” the plasma membrane



Proteins

Integral proteins

• Part of cell membrane and cannot be removed

without damaging cell

• Often span entire cell membrane (these are called

transmembrane proteins)

• Can transport water or solutes

Peripheral proteins

• Attached to cell membrane inner or outer surface

• Easily removable

• Fewer than integral proteins

• May have regulatory or enzymatic functions



Plasma membrane components

Glycocalyx

Components of complex molecules

• Proteoglycans (carbohydrates with protein attached)

• Glycoproteins (protein with carbohydrates attached)

• Glycolipids (lipids with carbohydrates attached)

Functions

• Cell recognition

• Binding to extracellular structures

• Lubrication of cell surface



Plasma membrane

functions

Physical isolation

Regulation of exchange

with external environment

Sensitivity to environment

Structural support

Lipid bilayer provides

isolation

Proteins perform most

other functions


Module 3.3: Review

A. Which structural component of the plasma

membrane is mostly responsible for isolating a cell

from its external environment?

B. List the general functions of the plasma membrane.

C. Which type of integral protein allows water and

small ions to pass through the plasma membrane?

D. What characteristics of phospholipids accounts for

their packing into a double layer?

Learning Outcome: Describe the structural and

functional features of the plasma membrane.


Module 3.4: The cytoskeleton plays both a structural and a functional role

Cytoskeleton

Functions as cell’s skeleton

Provides internal protein framework

Gives cytoplasm strength and flexibility

Components include:

1. Microfilaments

2. Intermediate filaments

3. Microtubules


Module 3.4: The cytoskeleton

Microfilaments

6 nm in diameter

(smallest cytoskeletal

element)

Typically composed of

actin

Commonly at periphery

of cell



Microfilaments (continued)

Microvilli

• Finger-shaped extensions

of cell membrane

• Have core of

microfilaments to stiffen

and anchor

• Enhance surface area

of cell for absorption

Terminal web

(microfilaments inside

plasma membrane in cells

forming a layer or lining)



Intermediate filaments

7–11 nm in diameter

Strongest and most

durable cytoskeletal

elements



Microtubules

~25 nm in diameter

Hollow tubes built from globular protein tubulin

Largest components of cytoskeleton

Extend outward from centrosome (near nucleus)



Centrioles

Composed of

microtubules (9 groups

of triplets)

Two in each

centrosome

Control movement of

DNA strands during cell

division

• Cells without centrioles

cannot divide

– Red blood cells

– Skeletal muscle cells



Cilia

Long, slender plasma

membrane extensions

Motile cilia common in

respiratory and

reproductive tracts

• Microtubules

surrounding a central

pair

• Anchored to cell surface

with basal body


Motile cilia beat rhythmically



Cilia (continued)

Primary cilium functions as sensor

Flagella are longer than cilia and beat in a wavelike

fashion


Module 3.4: Review

A. List the three basic components of the

cytoskeleton.

B. Which cytoskeletal component is common to

both centrioles and cilia?

C. What is the function of motile cilia?

D. Which cytoskeletal structure is found only in

males?

Learning Outcome: Differentiate among the

structures and functions of the cytoskeleton.


Module 3.5: Ribosomes and endoplasmic reticulum

Ribosomes

Responsible for protein synthesis

Two subunits (1 large, 1 small) containing special

proteins and ribosomal RNA (rRNA)

• Must join together before synthesis begins



Ribosomes (continued)

Free ribosomes

• Throughout cytoplasm

• Manufactured proteins enter cytosol

Bound or fixed ribosomes

• Attached to rough endoplasmic reticulum

• Synthesize proteins for export out of cell



Endoplasmic reticulum (ER)

Network of intracellular membranes continuous with

nuclear envelope, which surrounds nucleus

Forms hollow tubes, sheets,

and chambers (cisternae,

singular, cisterna, reservoir

for water)

Synthesizes and stores

proteins, lipids, and

carbohydrates



Two types of endoplasmic reticulum (ER)

1. Smooth (SER)

• Lacks ribosomes

• Cisternae are often tubular



Two types of endoplasmic reticulum (ER)

(continued)

2. Rough (RER)

• Has attached (fixed) ribosomes

• Modifies newly synthesized proteins

• Exports those proteins to Golgi apparatus

Proportion of SER to

RER depends on the

cell and its functions



Polypeptide formation in RER

Polypeptide synthesized on attached ribosome

• Growing chain enters cisterna of RER

Polypeptide assumes secondary/tertiary structures

Completed protein may become enzyme or

glycoprotein

Products not destined for RER are packaged into

transport vesicles

• Deliver products

to Golgi apparatus


Module 3.5: Review

A. Describe the immediate cellular destinations of

newly synthesized proteins from free ribosomes

and fixed ribosomes.

B. Compare and contrast the structure of SER and

RER.

C. Why do certain cells in the ovaries and testes

contain large amounts of SER?

D. The ER is connected to and continuous with what

other organelle in the cell?

Learning Outcome: Describe the ribosome and smooth

and rough endoplasmic reticula, and indicate their

specific functions.


Module 3.6: The Golgi apparatus is a packaging center

Golgi apparatus (Golgi complex)

Functions

1. Renews or modifies plasma membrane

2. Modifies or packages secretions into secretory

vesicles for release from cell (exocytosis)

3. Packages special enzymes within vesicles for use in

cytosol (lysosomes)

Typically consists of 5–6 flattened discs (cisternae)

May be more than one apparatus in a cell

Situated near nucleus


Module 3.6: Golgi apparatus

Golgi apparatus process

1. Transport vesicles filled with proteins and/or

glycoproteins from rough ER arrive at cis face

(“receiving side”) of Golgi apparatus.

2. Transport vesicles fuse, forming new cisternae.

Enzymes in Golgi apparatus modify arriving

products.

3. Products modified and re-packaged as they

move toward trans face (“shipping side”).

4. Finalized products packaged in secretory

vesicles and released from trans face.


Golgi apparatus process



Golgi apparatus products

1. Membrane renewal vesicles

• Add to plasma membrane

• Allow alteration of plasma membrane properties,

changing sensitivity and functions of cells

2. Secretory vesicles

• Contain hormones or enzymes for extracellular

release

3. Lysosomes

• Contain digestive enzymes for intracellular use



Lysosomes

Vesicles that isolate digestive processes from the

rest of the cytoplasm

Three basic functions

1. Fusion with another organelle and digestion of

contents

2. Fusion with another vesicle containing fluid or solid

extracellular materials and digestion of contents

3. Release of digestive enzymes within the cytoplasm

when cell is injured or dying, resulting in autolysis

(enzymes destroy cytoplasm)

– Leads to “suicide packets”—name for lysosomes


Lysosomes



Membrane flow

Continuous movement and exchange of materials

between organelles using vesicles

Can replace parts of cell membrane to allow cell to

grow, mature, or respond to changing environment

In an actively secreting cell, the entire membrane

surface can be replaced in 1 hour.


Module 3.6: Review

A. List the three major functions of the Golgi

apparatus.

B. What do lysosomes contain?

C. Describe three functions of lysosomes.

Learning Outcome: Describe the Golgi apparatus,

and indicate its specific functions.


Module 3.7: Mitochondria are the powerhouses of the cell

Mitochondria (mitos, thread + chondrion, granule)

Produce energy (ATP) for cells

Vary in number per cell depending on cell’s energy

requirements (more energy needs = more

mitochondria)

• Mitochondria account for 30 percent of the heart

cardiac muscle cells

• Red blood cells have no mitochondria

Contain their own DNA (mtDNA) and ribosomes


Module 3.7: Mitochondria

Mitochondrial double membrane

Outer membrane surrounds organelle

Inner membrane contains folds called cristae

• Inner membrane encloses liquid called matrix

• Cristae increase surface area exposed to matrix

• Metabolic enzymes in matrix catalyze reactions

providing energy for cellular function


Cut-away view of mitochondrion organelle


Mitochondrion organelle



Steps of ATP production

1. Glycolysis (glycos, sugar -lysis, a loosening)

• Occurs in cytosol

• 1 glucose → 2 pyruvate

• Pyruvate absorbed into mitochondria

2. In mitochondrial matrix:

• CO2 removed from pyruvate

• Enters citric acid (or TCA, tricarboxylic acid) cycle

– Systematically removes CO2 and hydrogen atoms



Steps of ATP production (continued)

3. Enzymes and coenzymes use hydrogen atoms to catalyze ATP from ADP

• Also forms H2O

4. ATP leaves mitochondrion


ATP Production



Aerobic metabolism or cellular respiration

ATP production that requires oxygen

Occurs in the mitochondria

Much more efficient than ATP production without

oxygen (e.g., glycolysis)

Produces about 95 percent of ATP needed by cell

• Remaining 5 percent produced by enzymatic

reactions in the cytoplasm


Module 3.7: Review

A. Describe the structure of a mitochondrion.

B. Most of a cell’s ATP is produced within its

mitochondria. What gas do mitochondria require

to produce ATP, and what gas results?

C. What does the presence of many mitochondria

imply about a cell’s energy requirements?

Learning Outcome: Describe the structure of a

mitochondrion, and explain the significance of

mitochondria to cellular function.


Section 2: Structure and Function of the Nucleus

Learning Outcomes

3.8 Describe the role of the nucleus in maintaining

homeostasis at the cellular level.

3.9 Describe the functions of the cell nucleus, and

distinguish between chromatin and a

chromosome.

3.10 Discuss the nature of the genetic code, and

summarize the process of protein synthesis.

3.11 Summarize the process of transcription.

3.12 Summarize the process of translation.


Module 3.8: The nucleus is the control center for cellular homeostasis

Nucleus

Usually largest cellular structure

Control center for cellular operations

• Can direct synthesis of >100,000 different proteins

• Genetic information coded in sequence of nucleotides

• Determines cell structure and function

Usually only one per cell

• Exceptions

– Skeletal muscle cells have many

– Mature red blood cells have none

o Because of no nucleus, they disintegrate within

3–4 months© 2018 Pearson Education, Inc.

Module 3.8: Role of the nucleus

The nucleus directs cellular responses to

environmental (ECF) changes

Short-term adjustments

• Enzyme activity changes

Long-term adjustments

• Changes in enzymes

produced

• Changes in cell structure

from changes in structural

proteins

• Often occur as part of

growth, development,

and aging


Module 3.8: Review

A. How is genetic information coded in the cell?

B. How many nuclei do most body cells contain?

C. Describe why the nucleus is said to be the

control center for the cell.

Learning Outcome: Describe the role of the

nucleus in maintaining homeostasis at the cellular

level.


Module 3.9: The nucleus contains DNA, RNA, organizing proteins, and enzymes

Nuclear structures and functions

Nuclear envelope

• Separates nucleus from cytoplasm

• Double membrane

– Perinuclear space (peri-, around)

o Space between layers

Nuclear pores

• Passageways that allow chemical communication

between nucleus and cytoplasm

• Movement of ions and small molecules regulated by

proteins at the pores

• Account for about 10% of the surface of the nucleus


Module 3.9: Contents of the cell nucleus

Nucleoplasm

• Fluid contents of nucleus

• Contains network of fine filaments for structural

support

• Also contains ions,

enzymes, nucleotides,

and small amounts

of RNA and DNA



Nucleoli (singular, nucleolus)

Transient nuclear organelles

Composed of RNA,

enzymes, and proteins

(histones)

Assemble RNA subunits

Most prominent in cells

manufacturing large

amounts of proteins

• Examples: liver, nerve,

muscle cells



DNA in the nucleus

Stores instructions for protein synthesis

Strands in nucleus coiled, allowing much to be

packed in small space

• Wrap around histone molecules forming

nucleosomes

• Loosely coiled

(chromatin) in

nondividing cells

• Tightly coiled

(chromosomes)

in dividing cells



DNA during cell division

Starts by becoming tighter and more complex,

forming chromosomes

Two copies of each chromosome held together at

centromere

23 paired chromosomes in somatic (general body)

cells

• One each from

mother/father

Carry instructions for

proteins and RNA

Also some regulatory and unknown functions


Module 3.9: Review

A. Describe the contents and the structure of the

nucleus.

B. What molecule in the nucleus contains instructions

for making proteins?

C. How many chromosomes are contained within a

typical somatic cell?

D. The total length of the DNA within a human cell

nucleus is approximately 2 meters. How does the

DNA fit into the relatively small space of a human

nucleus, which ranges some 6–10 µm in diameter?

Learning Outcome: Describe the functions of the cell

nucleus, and distinguish between chromatin and a

chromosome.© 2018 Pearson Education, Inc.

Module 3.10: Protein synthesis involves DNA, enzymes, and three types of RNA

DNA

Long parallel chains of

nucleotides

Chains held by hydrogen

bonds between

nitrogenous bases

Four nitrogenous bases

1. Adenine (A)

2. Thymine (T)

3. Cytosine (C)

4. Guanine (G)


Module 3.10: The genetic code and protein synthesis

DNA (continued)

Genetic information stored in sequence of base pairs

• Known as the genetic code

• Triplet code

– Sequence of three nitrogenous bases (triplet)

– Specifies single amino acid

Gene

• Functional unit of heredity

• Contains all the DNA nucleotides to produce a specific

protein

• Size varies (~3003000 nucleotides)



Steps in protein synthesis

1. Gene activation

• Removal of histones and DNA uncoiling

2. DNA strands separate



3. Enzymes assemble nucleotides into a single

strand of messenger RNA (mRNA)

• Complementary base pairing matches DNA

nucleotide sequence with new mRNA sequence

(A-U; G-C)

• Series of three RNA nucleotides called a codon

– Each codon codes for specific amino acid

4. mRNA leaves nucleus

through nuclear pores



5. At a ribosome in the cytoplasm, codons of mRNA

bind to anticodons (triplets of corresponding

nucleotides) on transfer RNA (tRNA)

6. tRNA carries a specific amino acid (associated

with specific anticodon)



7. Ribosomal RNA (rRNA) of the ribosome strings

amino acids together


Protein synthesis


Module 3.10: Review

A. What is a gene?

B. Why is the genetic code described as a triplet

code?

C. List the three types of RNA involved in protein

synthesis.

D. Which type of RNA links the genetic information

in the nucleus with the cytoplasmic sites of

protein synthesis?

Learning Outcome: Discuss the nature of the

genetic code, and summarize the process of

protein synthesis.


Module 3.11: Transcription encodes genetic instructions on a strand of RNA

Transcription (“to copy” or “rewrite”)

Takes place in the nucleus

Production of RNA from DNA template

All three types of RNA are formed


Module 3.11: Transcription

Steps of transcription

1. Gene activation

• Occurs at control

segment or promoter

(1st segment of gene)

• Only template strand

of DNA used to

synthesize RNA




2. Beginning of

assembly

• RNA polymerase

(enzyme) binds to

promoter

• Begins assembly of

mRNA strand




(continued)

3. Continuation of mRNA strand

• RNA polymerase promotes

hydrogen bonding between

nucleotides on DNA template

strand and complementary RNA

nucleotides in nucleoplasm

– Example: (DNA triplet TAC =

mRNA AUG)

• Nucleotides connected by

covalent bonding




(continued)

4. Transcription ends

• Stop codon reached

• mRNA detaches

• Complementary DNA

strands reassociate (with

hydrogen bonding

between complementary

base pairs)



Final processing of mRNA

Initial strand of mRNA called

immature mRNA or

pre-mRNA

Before leaving nucleus,

mRNA requires additional

processing

• Introns (noncoding sequences) removed

• Remaining coding segments (exons) spliced together

• Changing the “editing” can produce mRNA for

different proteins


Module 3.11: Review

A. What is transcription?

B. Define DNA template strand.

C. Name the substrates and product in the

enzymatic reaction catalyzed by RNA

polymerase.

D. What process would be affected if a cell could

not synthesize the enzyme RNA polymerase?

Learning Outcome: Summarize the process of

transcription.


Module 3.12: Translation builds polypeptides as directed by an mRNA strand

Translation

Formation of a linear chain of amino acids from an

mRNA strand

“Translates” genetic information from nucleic acids

to proteins

Occurs in cytoplasm on ribosomes

Three phases

1. Initiation

2. Elongation

3. Termination


Module 3.12: Translation

Steps of translation

1. Initiation phase

• mRNA binds to small ribosomal subunit near the

P site

• tRNA binds to P site and to start codon on mRNA

strand

– Binding occurs between mRNA codons and tRNA

complementary anticodons

• Small and large ribosomal subunits interlock around

mRNA strand forming initiation complex

• Additional tRNA binds to A site

– More than 20 kinds of tRNA

– Each carries an amino acid


Initiation phase



Steps of translation (continued)

2. Elongation

• Ribosomal enzymes remove amino acid from tRNA at

P site and attach it to tRNA in A site

• Ribosome links amino acids forming dipeptide

• Ribosome moves to next codon on mRNA strand

• tRNA from P site moves to E site and is released

– This tRNA can go bind to another amino acid

• More tRNAs arrive, match codon to anticodon, and

continue forming polypeptide


Elongation



Steps of translation

(continued)

3. Termination

• Stop codon on mRNA

• Recognized by protein

releasing factor

• Ribosomal enzyme breaks

bond between polypeptide

and tRNA in P site

• Ribosomal subunits

detach

– Leaves intact mRNA and

new polypeptide



Translation

Produces a typical protein in ~20 seconds

mRNA can interact with other ribosomes and

produce more proteins

Multiple ribosomes can attach to a single mRNA

strand to quickly produce many proteins


BioFlix: Protein Synthesis


Module 3.12: Review

A. What is translation?

B. The nucleotide sequence of three mRNA

codons is AUU-GCA-CUA. What is the

complementary anticodon sequence for the

second codon?

C. During the process of transcription, a nucleotide

was deleted from an mRNA sequence that

coded for a protein. What effect will this deletion

have on the amino acid sequence of the

protein?

Learning Outcome: Summarize the process of

translation.


Section 3: How Substances Enter and Leave the Cell

Learning Outcomes

3.13 Contrast permeable, selectively permeable, and

impermeable membranes.

3.14 Explain the process of diffusion, and identify its

significance in the body.

3.15 Explain the process of osmosis, and identify its

significance in the body.


Section 3: How Substances Enter and Leave the Cell

Learning Outcomes (continued)

3.16 Describe carrier-mediated transport and its role in

the absorption and removal of specific

substances.

3.17 Describe vesicular transport as a mechanism for

facilitating the absorption or removal of specific

substances from cells.


Module 3.13: The plasma membrane is a selectively permeable membrane

Permeability

Property determining which substances can enter or

leave cytoplasm

• Freely permeable

– Any substance can pass (not found in living cells)

• Selectively permeable

– Some substances cross

• Impermeable

– No substances can pass (not found in living cells)

Plasma membrane must allow some movement in

and out of cells to enable intercellular

communication and coordination© 2018 Pearson Education, Inc.

Module 3.13: Permeability of membranes



Selectively permeable membranes

Permit free passage of some materials and restrict

others

1. Characteristics of material to pass

– Size

– Molecular shape

– Lipid solubility

– Electrical charge

– Other factors

2. Characteristics of cell membrane

– What lipids and proteins present

– How components are arranged



Types of membrane transport

1. Passive (do not

require ATP)

• Diffusion

• Carrier-mediated

transport

2. Active (require ATP)

• Vesicular transport

• Carrier-mediated

transport


Module 3.13: Review

A. Define permeability.

B. Identify three different types of membranes

based on permeability.

C. Distinguish between passive and active

processes of membrane passage.

D. What kinds of molecules are involved in both

active and passive processes of membrane

passage.

Learning Outcome: Contrast permeable, selectively

permeable, and impermeable membranes.


Module 3.14: Diffusion is passive movement driven by concentration differences

Diffusion

Net movement of a substance from higher

concentration to lower concentration.

Concentration gradient

• Concentration difference when molecules are not

evenly distributed

At an even distribution, molecular motion continues

but no net movement


Module 3.14: Diffusion

Diffusion (continued)

Slow in air and water but important over small

distances



Movement of water and solutes across plasma

membrane: Selectively restricted diffusion

Movement across lipid portion of membrane

• Examples: lipids, lipid-soluble molecules, soluble

gases

Movement through membrane channel

• Examples: water, small water-soluble molecules, ions

Movement using carrier molecules

• Example: large molecules


Diffusion across a plasma membrane


EXTRACELLULAR

FLUID


Factors that influence diffusion rates

Distance

• Shorter distance = faster diffusion

Molecule or ion size

• Smaller size = faster diffusion

Temperature

• Higher temperature = faster diffusion

Concentration gradient

• Steeper gradient = faster diffusion

Electrical forces

• Attraction of opposite charges (+,–)

• Repulsion of like charges (+,+ or –,–)


Module 3.14: Review

A. Define diffusion.

B. Describe the colliding molecules in the figure

below (with the sugar cube in water).

C. Identify factors that influence diffusion rates.

D. How would a decrease in the oxygen

concentration in the lungs affect oxygen

diffusion into the blood?

Learning Outcome: Explain the process of

diffusion, and identify its significance in the body.


Module 3.15: Osmosis is the diffusion of water molecules across a selectively permeable membrane

Osmosis (osmos, a push)

Net diffusion of water across a membrane

Maintains similar overall solute concentrations

between the cytosol and extracellular fluid

Osmotic flow

• Movement of water driven by osmosis


Module 3.15: Osmosis

Osmosis (continued)

Osmotic pressure

• Indication of force of pure water moving into a

solution with higher solute concentration

• Hydrostatic pressure

– Fluid force

– Can be estimate of osmotic pressure when applied to

stop osmotic flow


Water movement through a selectively permeable membrane



Osmolarity and tonicity

Osmolarity (osmotic concentration)

• Total solute concentration in an aqueous solution

Tonicity

• Effect of osmotic solutions on cell volume

• How a solution affects a cell



Three effects of tonicity

1. Isotonic (iso-,

same tonos, tension)

• Solution that does not

cause osmotic flow

across membrane




(continued)

2. Hypotonic

• Causes osmotic flow into

cell

• Example: swelling and

hemolysis (hemo-,

blood + lysis, loosening)

of red blood cell




(continued)

3. Hypertonic

• Causes osmotic flow out

of cell

• Example: shriveling and

crenation of RBCs


Effects of tonicity



Importance of tonicity vs. osmolarity

Administering large fluid volumes to patients with

blood loss or dehydration

• If administered solution has same osmolarity as ICF

but higher concentrations of individual ions/molecules

– Diffusion of solutes may occur across cell membrane

– Water will follow through osmosis

– Cell volume increases

Normal saline often administered in emergency

• 0.9 percent or 0.9 g/dL of NaCl

• Isotonic with blood


Module 3.15: Review

A. Describe osmosis.

B. Describe osmotic pressure, and state in which

solution below it is greater.

C. Contrast the effects of a hypotonic solution and

a hypertonic solution on a red blood cell.

D. Some pediatricians recommend using a 10

percent salt solution to relieve nasal congestion

in infants. Explain the effects this treatment

would have on the cells lining the nasal cavity.

Would it be effective?

Learning Outcome: Explain the process of

osmosis, and identify its significance in the body.


Module 3.16: In carrier-mediated transport, integral proteins facilitate membrane passage

Carrier proteins

Transport hydrophilic or large molecules across cell

membrane

Many move specific molecules through the plasma

membrane in only one direction

Some move more than one substance in the same

direction (cotransport)

Some move more than one substance in opposite

directions

• Process called countertransport

• Carrier called an exchange pump


Module 3.16: Carrier-mediated transport

1. Facilitated diffusion

Requires no ATP

Passive transport (moves from high concentration to

low concentration)

Carrier binds to molecule, then changes shape to

move molecule across membrane

Rate of transport limited

by number of available

carrier proteins

• Once all carrier proteins

saturated, no increase

in rate of transport



2. Active transport

Active process requiring

energy molecule or ATP

Independent of

concentration gradient

Examples:

• Ion pumps (Na+, K+,

Ca2+, and Mg2+)

• Sodium–potassium

ATPase

– Exchanges 3

intracellular sodium ions

for 2 extracellular

potassium ions© 2018 Pearson Education, Inc.


3. Secondary active transport

Transport mechanism itself does not require ATP

Cell often needs ATP to maintain homeostasis

associated with transport

Movement for one of two substances follows

concentration gradient

Example:

• Sodium and

glucose

cotransporter


A&P Flix: Membrane Transport


Module 3.16: Review

A. Describe the process of carrier-mediated transport.

B. What two factors limit the rate of facilitated diffusion

across a plasma membrane?

C. What do the transport processes of facilitated

diffusion and active transport have in common?

D. During digestion, the concentration of hydrogen

ions (H+) in the stomach contents increases to

many times that in cells lining the stomach. Which

transport process could be responsible?

Learning Outcome: Describe carrier-mediated transport

and its role in the absorption and removal of specific

substances.


Module 3.17: In vesicular transport, vesicles selectively carry materials into or out of cell

Vesicular transport

Materials move across cell membrane in small

membranous sacs called vesicles

• Sacs form at or fuse with plasma membrane

Two major types (both require ATP)

1. Endocytosis

– Importing extracellular substances into vesicles called

endosomes

2. Exocytosis

– Movement of wastes or secretory products from

intracellular vesicle to outside the cell


Module 3.17: Vesicular transport

Receptor-mediated endocytosis

Brings specific molecules into cell using receptor

molecules on membrane surface

a. Target molecule (ligand) binds to receptor



Receptor-mediated endocytosis (continued)

b. Plasma membrane folds around receptors bound to

ligands, forming pocket that pinches off

c. Endosome called clathrin-coated vesicle forms




d. Vesicle fuses with lysosomes




e. Ligands freed from receptors and enter cytoplasm




f. Lysosome detaches from vesicle




g. Vesicle fuses with plasma membrane again


Receptor-mediated endocytosis



Pinocytosis (“cell drinking”)

Formation of endosomes with ECF

No receptor proteins involved

Brings fluid and small molecules into cell



Phagocytosis (“cell eating”)

Produces phagosomes containing solids

No receptors involved

Cytoplasmic extensions

(pseudopodia) surround

object and bring it

into cell

Only specialized

cells (phagocytes

or macrophages)

perform phagocytosis



Exocytosis—functional opposite of endocytosis

Vesicle contents are released to extracellular

environment


Module 3.17: Review

A. Describe endocytosis.

B. Describe the three types of endocytosis.

C. Describe exocytosis.

D. Some white blood cells engulf bacteria and

bring them into the cell. What is this process

called?

Learning Outcome: Describe vesicular transport as

a mechanism for facilitating the absorption or

removal of specific substances from cells.


Section 4: Cell Life Cycle

Learning Outcomes

3.18 Distinguish between interphase and cell division

in the cell cycle.

3.19 Describe interphase, and explain its significance.

3.20 Describe the process of mitosis and its role in the

cell life cycle.

3.21 Clinical Module: Discuss the relationship

between cell division and cancer.


Module 3.18: Interphase and cell division make up the life cycle of a cell

Life starts as a single cell

At maturity, roughly 75 trillion cells in the body

Cell division—form of cellular reproduction

• Responsible for initial increase in cell number

• Essential to continued development and survival

Cells have varying life spans and abilities to divide

• Often genetically controlled death occurs (apoptosis)

Cell life cycle ends when cell dies


Module 3.18: Cell life cycle

Two types of cell division

1. Mitosis

• 2 daughter cells produced

• Each with 46 chromosomes

2. Meiosis

• Produces sex cells

• Each with only 23 chromosomes



Mitosis

Form of cellular

reproduction

Division of single cell

produces pair of

daughter cells

• Half the size of parent

cell

• Grow to size of original

cell before dividing



Divisions of cell life cycle

1. Interphase (nondividing period)

• Cell performs normal activities



Divisions of cell life cycle (continued)

2. Cell division

• Begins with mitosis

– Distribution of identical copies of chromosomes

to each daughter cell

• Ends with cytokinesis (division of the cytoplasm)


Module 3.18: Review

A. Explain why cell division is important.

B. Define apoptosis.

C. When does cell division begin and end?

Learning Outcome: Distinguish between interphase

and cell division in the cell cycle.


Module 3.19: During interphase, the cell prepares for cell division

Division of interphase

Somatic (body) cells spend most of their lives in

interphase

For cells not preparing to divide, they stay in:

• G0 phase

– Performing normal cell functions

– Examples:

o Skeletal muscle cells and most neurons

Stay in this phase forever

o Stem cells

Never enter G0

Divide repeatedly


Module 3.19: Interphase

For cells preparing to divide,

interphase divided into:

G1 phase

• Normal cell functions,

cell growth, duplication

of organelles, protein

synthesis

S phase

• DNA replication, synthesis

of histones and other

proteins to allow duplication of chromosomes

G2 phase

• Last minute protein synthesis and centriole replication



DNA replication process

DNA helicase

• Unwinds DNA strands

• Disrupts hydrogen bonds between bases

DNA polymerase

• Binds to exposed bases

• Promotes bonding between current DNA strand and

complementary nucleotides in nucleoplasm

• Covalently links nucleotides together



DNA replication process (continued)

DNA polymerase (continued)

• Works only in one direction

– One polymerase works continuously along one strand

toward “zipper” forming the leading strand



DNA replication process (continued)

DNA polymerase (continued)

• Works only in one direction

– One polymerase works away from “zipper” forming the

lagging strand

o As “unzipping” occurs, another polymerase binds

closer point of unzipping

o Two new DNA segments spliced together with DNA

ligases

• Two identical DNA strands formed


DNA replication


A&P Flix: DNA Replication


Module 3.19: Review

A. Describe interphase, and identify its stages.

B. A cell is actively manufacturing enough

organelles to serve two functional cells. This

cell is probably in what phase of interphase?

C. What enzymes must be present for DNA

replication to proceed normally?

D. DNA replication occurs during what two cellular

processes?

Learning Outcome: Describe interphase, and

explain its significance.


Module 3.20: Mitosis distributes chromosomes before cytokinesis separates the daughter cells

M phase of cell cycle

Includes mitosis and cytokinesis

Mitosis

• Division and duplication of the cell’s nucleus

• Divided into four stages:

1. Prophase

2. Metaphase

3. Anaphase

4. Telophase

Cytokinesis

• Division of cytoplasm


Module 3.20: Mitosis

Interphase—DNA replicated, DNA is loosely coiled

and no visible chromosomes



Phases of mitosis

1. Prophase (pro-, before)

• Nuclear envelope

disintegrates

• Chromosomes coil and

become visible under light

microscope

• Replicated centrioles move

to poles

– Astral rays (extend from

centrioles)

– Spindle fibers (interconnect

centriole pairs)



Phases of mitosis

(continued)

1. Prophase (continued)

• Each copy of chromosome

called chromatid

– Pair connected at

centromere

– Raised region

(kinetochore) at

centromere attaches to

spindle fibers



Phases of mitosis

(continued)

2. Metaphase (meta,

after)

• Chromosomes align

at metaphase plate



Phases of mitosis

(continued)

3. Anaphase (ana-, apart)

• Centromere splits

• Chromatids separate

• Chromatids drawn toward

opposite sides along

spindle apparatus



Phases of mitosis

(continued)

4. Telophase (telo-, end)

• Cells prepare to enter

interphase

• Cytoplasm constricts

along metaphase plate

(cleavage furrow)

• Nuclear membranes

re-form

• Nuclei enlarge

• Chromosomes uncoil to

chromatin



Cytokinesis (cyto-, cell +

kinesis, motion)

Begins with formation of

cleavage furrow

Continues through

telophase

Completion marks end of

cell division


A&P Flix: Mitosis


Module 3.20: Review

A. Define mitosis, and list its four stages.

B. What is a chromatid, and how many are present

during normal mitosis in a human cell?

C. What would happen if spindle fibers failed to

form in a cell during mitosis?

Learning Outcome: Describe the process of mitosis

and its role in the cell life cycle.


Module 3.21: CLINICAL MODULE: Tumors and cancer are characterized by abnormal cell growth and division

Cancer

Illness that disrupts normal rates of cell division

Characterized by permanent DNA sequence

changes (mutations)

Most common in tissues with actively dividing cells

• Examples: skin, intestinal lining

Cancerous cells compete with normal cells for

resources

Usually begins with single abnormal cell


Module 3.21: CLINICAL MODULE: Tumors and cancer

Tumor (neoplasm)

Mass or swelling produced by abnormal cell growth

and division

1. Benign tumor

– Cells remain within original tissue

– Seldom a threat

– Can be removed surgically

if necessary



Malignant tumor

Cells divide rapidly

Released chemicals stimulate blood vessel

growth (angiogenesis) to tumor area



Malignant tumor (continued)

Accelerated growth due to blood vessel growth and

supply to the area

Tumor spreads to surrounding tissue by invasion

Cells migrate to other areas and establish new

tumors (called metastasis)



Malignant cells disrupt

function

No longer perform original

functions or:

Perform functions in an

abnormal way

Example:

• Malignant tumor of thyroid gland produces abnormal

amounts of thyroid hormone

Cancer cells compete with normal cells for space and

nutrients


Module 3.21: Review

A. Define cancer.

B. What is a benign tumor?

C. Define metastasis.

D. How does angiogenesis aid tumor growth?

Learning Outcome: Discuss the relationship

between cell division and cancer.


cellular level of organization...module 3.1: cellular differentiation produces specialized cells...

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