Cell TheoryCell Theory Cells are the building blocks of the human

body 4 concepts of the cell theory:

Cells are the building blocks of all plants and animals

Cells are the smallest functioning units of life Cells are produced through the division of

preexisting cells Each cells maintain homeostasis

The Study of Cells and Their The Study of Cells and Their AnatomyAnatomy

Cytology – the study of the structure and function of cells The 2 most common methods used to study cell and tissue

structure are light microscopy and electron microscopy Anatomy:

Extracellular fluid – watery medium surrounding cells In tissues it’s called interstitial fluid

Plasma (Cell) membrane – separates the cell contents (cytoplasm) from extracellular fluid

Nucleus – control center for cellular operations Cytoplasm subdivides into:

Cytosol – liquid in cell Organelles – intracellular structures

Copyright © 2010 Pearson Education, Inc. Figure 3.2

Secretion beingreleased from cellby exocytosis

Peroxisome

Ribosomes

Roughendoplasmicreticulum

Nucleus

Nuclear envelopeChromatin

Golgi apparatus

NucleolusSmooth endoplasmicreticulum

CytosolLysosome

Mitochondrion

CentriolesCentrosomematrix

Cytoskeletalelements• Microtubule• Intermediate filaments

Plasmamembrane

Plasma MembranePlasma Membrane General functions include:

Physical isolation A physical barrier that separates the inside of the cell from

the extracellular fluid Regulation of exchange with the environment

Controls the entry of ions and nutrients, the elimination of wastes, and the release of secretions

Sensitivity to the environment Contains a variety of receptors that enable the cell to

recognize and respond to specific molecules in the environment

Structural support For tissues

Copyright © 2010 Pearson Education, Inc. Figure 3.3

Integralproteins

Extracellular fluid(watery environment)

Cytoplasm(watery environment)

Hydrophilic head ofphospholipid molecule Glycolipid

Cholesterol

Peripheralproteins

Bimolecularlipid layercontainingproteins

Inward-facinglayer ofphospholipids

Outward-facinglayer of phospholipids

Carbohydrate of glycocalyx

Glycoprotein

Filament of cytoskeleton

Hydrophobictail of phospholipid molecule

Plasma MembranePlasma Membrane Membrane Lipids

The phospholipids in a plasma membrane lie in 2 distinct layers: (phospholipid bilayer) Phosphate heads: polar and hydrophilic Fatty acid tails: nonpolar and hydrophobic

The hydrophobic tails won’t associate with water or charged molecules, allowing the plasma membrane to act as a physical barrier Lipid-soluble molecules, oxygen, CO2, etc. are able to cross Ions and water-soluble compounds cannot

Membrane Proteins The most common of these membrane proteins span the width of the

membrane 1 or more times and are known as transmembrane proteins May function as receptors, channels, carriers, enzymes, anchors, and

identifiers Membrane Carbohydrates

Carbs form complex molecules with proteins and lipids on the outer surface of the membrane

Function as cell lubricants and adhesives, receptors for extracellular compounds, and form part of a recognition system from attacking the body’s cells and tissues

Diffusion and FiltrationDiffusion and Filtration The permeability of the plasma membrane is the property that

determines precisely which substances can enter or leave the cytoplasm. If nothing can cross a membrane, it’s impermeable

If any substance can cross without difficulty, it’s freely permeable

Plasma membranes are selectively permeable

Based on size, charge, shape, solubility Movement is either passive or active

Passive – move ions or molecules across the plasma membrane without any energy expenditure by the cell Diffusion

Osmosis Filtration

Active – require that the cell expend energy, usually in the form of ATP

DiffusionDiffusion The net movement of molecules from an area of

relatively high concentration to an area of relatively low concentration The different areas create a concentration gradient Movement happens until the gradient no longer exists

Diffusion Across Plasma Membranes An ion or molecule can independently diffuse across a

plasma membrane by either: Moving across the lipid portion of the membrane Passing through the channel protein in the membrane

Diffusion ability depends on lipid solubility and size

OsmosisOsmosis The diffusion of water across a membrane Because dissolved solute molecules occupy space that would

otherwise be taken up by water molecules, the higher the solute concentration, the lower the water concentration As a result, water molecules tend to flow across a membrane

toward the solution containing the higher solute concentration, because this movement is down the concentration gradient for water molecules

Three characteristics of osmosis that are important to remember: Osmosis is the diffusion of water molecules across a membrane Osmosis occurs across a selectively permeable membrane that is

freely permeable to water but is not freely permeable to solutes In osmosis, water flows across a membrane toward the solution

that has the higher concentration of solutes, because that is where the concentration of water is lower

Osmosis (cont.)Osmosis (cont.) The osmotic pressure of a

solution is an indication of the force of water movement into that solution as a result of solute concentration

Pushing against a fluid generates hydrostatic pressure Can be either isotonic (no

net movement), hypotonic (water flows in and swells the cell and lyse), or hypertonic (water flows out of the cells and causes shriveling called crenation)

FiltrationFiltration In this passive process, hydrostatic pressure forces

water across a membrane If solute molecules are small enough to fit through

membrane pores, they will be carried through with the water

Filtration across specialized blood vessels in the kidneys is an essential step in the production of urine

Carrier-Mediated TransportCarrier-Mediated Transport Requires the presence of specialized membrane proteins It can be passive (no ATP required) or active (ATP

dependent), depending on the substance being transport and the nature of the transport mechanism

In CMT , membrane proteins bind specific ions or organic substrates and carry them across the plasma membrane

Passive = high conc. to low conc. Active = low conc. to high conc.

Countertransport – when one substance is moved into a cell while the other is moved out

Cotransport – 2 substances are moved into or out of a cell at the same time

Carrier-Mediated Transport (cont.)Carrier-Mediated Transport (cont.) Facilitated Diffusion

Used when essential nutrients are insoluble in lipids and too large to fit through membrane channels. Passively transported across the membrane by carrier proteins First, the molecule binds to a receptor site on the carrier protein. Then

the shape of the protein changes, moving the molecule to the inside of the plasma membrane, where it is released into the cytoplasm

Active Transport In this case, the high energy bond in ATP provides the energy needed to

move ions or molecules across the membrane Despite the energy cost, this transport has one great advantage : it isn’t

concentration gradient dependent All cells have ion pumps that actively transport Na+, K +, Ca2+, and Mg2+

across plasma membranes either in or out of the cell. If one kind of ion is moving in and another is moving out it is called an exchange pump Exchange pumps mainly function in maintaining cell homeostasis Sodium-potassium exchange pump

Lipid-insoluble solutes (such as sugars or amino acids)

Carrier-mediated facilitated diffusion via a protein carrier specific for one chemical; binding of substrate causes shape change in transport protein

Vesicular TransportVesicular Transport Involves the movement of materials within small

membranous sacs called vesicles Always an active process 2 major categories:

Endocytosis – the packaging of extracellular materials in a vesicle at the cell surface for import into the cell 3 types: receptor-mediated endocytosis (involves the formation

of small vesicles at the membrane surface to import substances), pinocytosis (“cell drinking”, the formation of small vesicles filled with extracellular fluid), and phagocytosis (“cell eating”, produces vesicles containing solid objects that may be as large as the cell itself)

Exocytosis – the functional reverse of endocytosis. In exocytosis, a vesicle created inside the cell fuses with the plasma membrane and discharges its contents into the extracellular environment Ejected material may be a secretion or waste product

The CytosolThe Cytosol Cytoplasm is a general term for material inside the

cell including the cytosol and the organelles Cytosol is the intracellular fluid , which contains

dissolved nutrients, ions, soluble and insoluble proteins, and waste products

It differs from extracellular fluid in that: Contains a higher concentration of potassium ions and a

lower concentration of sodium ions Has a high concentration of dissolved proteins Usually contains small quantities of carbohydrates and

large reserves of amino acids and lipids

The OrganellesThe Organelles Internal structures that perform specific functions essential

to normal cell structure, maintenance, and metabolism Cytoskeleton – internal protein framework of various threadlike

filaments and hollow tubules that gives the cytoplasm strength and flexibility Microfilaments, intermediate filaments, and microtubules

(anchors major organelles) Microvilli – small, finger shaped projections of the plasma

membrane on the exposed surfaces of many cells. Increase surface area for absorption

Centrioles, Cilia, and Flagella Centrioles – cylindrical structure composed of short

microtubules Cilia – relatively long, slender extensions of the plasma

membrane. Undergo active movements that require ATP Flagella – move a cell through surrounding fluid, rather than

moving the fluid past a stationary cell

The Organelles (cont.)The Organelles (cont.) Ribosomes – manufacture proteins using information provided

by DNA. Can be either free or fixed Proteasomes – remove and recycle damaged or denatured

proteins and for breaking down abnormal proteins The Endoplasmic Reticulum (ER) – a network of intracellular

membranes connected to the membranous nuclear envelope surrounding the nucleus. 4 major functions: snythesis of proteins, carbs and lipids, storage of synthesized molecules/materials, transport of materials, and detoxification Smooth ER and Rough ER: ratio depends on cell function

Golgi Apparatus – consists of a set of 5 or 6 flattened membranous discs. Main functions: modification and packaging of secretions, renewal or modification of the PM, and packaging of special exzymes. Creates lysosomes, secretory vesicles, and membrane renewal vesicles

The Organelles (cont.)The Organelles (cont.) Lysosomes – filled with digestive enzymes. Perform

cleanup and recycling functions within the cell Peroxisomes – smaller than lysosomes and carry a

different group of enzymes. Absorb and break down fatty acids and other organic compounds

Mitochondria – small organelles that provide energy via ATP bonds for the cell. Have a double membrane

Nucleus – control center for cellular operations. Stores all the information needed to control the synthesis of more than 100,000 different proteins. Determines both the structure of the cell and the and the functions it can perform by controlling which proteins synthesized, under what circumstances, and in what amounts

Transcription and TranslationTranscription and Translation Transcription – the production of mRNA from a single strand of DNA

Takes place in the nucleus Steps:

RNA polymerase binds to the promoter of a gene Promotes the synthesis of an mRNA strand using complementary nucleotides A sequence of 3 nitrogenous bases along the new mRNA strand represents a codon

that corresponds to a triplet on the gene At the DNA “stop” signal the mRNA detaches

Translation – the assembling of a protein by ribosomes, using the information carried by the RNA molecule Takes place in the cytoplasm Steps:

Begins at the “start” codon of mRNA (AUG) with the attachment of the first tRNA carrying an amino acid

The small and large ribosomal subunits join together to enclose the mRNA A second tRNA arrives, carrying a different amino acid, and binds to the next codon Ribosomal enzymes remove AA1 from its tRNA and attach it to AA2 with a peptide

bond This continues until it reaches the “stop” codon, where the strand detaches

Nuclearpores

mRNA

Pre-mRNARNA Processing

Transcription

Translation

DNA

Nuclearenvelope

Ribosome

Polypeptide

1

2

3

4

Leu

Leu

Energized by ATP, the correct aminoacid is attached to each species oftRNA by aminoacyl-tRNA synthetaseenzyme.

Amino acid

tRNA

Aminoacyl-tRNAsynthetase

G A A

tRNA “head”bearinganticodon

Psite A

siteE

site

Ile

Pro

A AU U UC C C

CG G

G

Largeribosomalsubunit

Smallribosomalsubunit

Direction ofribosome advancePortion of mRNA

already translated

Codon15

Codon16

Codon17

Nucleus

mRNA

Released mRNA

Nuclearmembrane

Nuclear pore

RNA polymerase

Templatestrand ofDNA

After mRNA synthesis in thenucleus, mRNA leaves the nucleusand attaches to a ribosome.

Translation begins as incomingaminoacyl-tRNA recognizes thecomplementary codon calling forit at the A site on the ribosome. Ithydrogen-bonds to the codon viaits anticodon.

As the ribosome moves alongthe mRNA, and each codon isread in sequence, a new aminoacid is added to the growingprotein chain and the tRNA inthe A site is translocated to theP site.

Once its amino acid is releasedfrom the P site, tRNA is ratchetedto the E site and then released toreenter the cytoplasmic pool,ready to be recharged with a newamino acid. The polypeptide isreleased when the stop codon isread.

G A A

UU

A

SECOND BASE

UUGUUAUUCUUU

Phe

Leu

CUGCUACUCCUU

Leu

AUAAUCAUU

Ile

GUGGUAGUCGUU

Val

UCGUCAUCCUCU

Ser

CCGCCACCCCCU

Pro

ACGACAACCACU

Thr

GCGGCAGCCGCU

Ala

UACUAU

Tyr

CAGCAACACCAU

His

Gln

AAGAAAAACAAU

Asn

Lys

GAGGAAGACGAU

Asp

Glu

UGCUGU

Cys

Trp

CGGCGACGCCGU

Arg

AGGAGAAGCAGU

Ser

Arg

GGGGGAGGCGGU

Gly

UAA Stop UGA Stop

AUG Met orStart

UAG Stop UGG

U C A G

GACU

GACU

GACU

GACU

U

C

A

G

Cell Life CycleCell Life Cycle The duplication of a cell’s genetic material is called DNA replication, and

nuclear division is called mitosis (only in somatic cells) Sex cells = meiosis

Stages: Interphase – where cells spend most of their lives, an interval of time in which they

perform normal functions Four subphases:

G1 (gap 1)—vigorous growth and metabolism G0—gap phase in cells that permanently cease dividing S (synthetic)—DNA replication G2 (gap 2)—preparation for division

Stage 1 – prophase – begins when the chromosomes become visible, each with two chromatids joined at a centromere. Centrosomes separate and migrate toward opposite poles. Mitotic spindles and asters form

Stage 2 – metaphase – chromatids move to a narrow central plate called the metaphase plate

Stage 3 – anaphase – shortest phase, chromatids separate and begin moving to the poles of the cell

Stage 4 – telophase – the cell prepares to return to interphase. Nuclear membrane forms and chromosomes uncoil

Cytokinesis – the cytoplasmic division that forms 2 daughter cells. Marks the end of cell division

G1

Growth

SGrowth and DNA

synthesis G2

Growth and finalpreparations for

divisionM

G2 checkpoint

G1 checkpoint(restriction point)