cells (and other stuff)

CELLS (and other stuff)

• Life’s basic characteristic is a high degree of order.

– At the lowest level are atoms that are ordered into

complex biological molecules.

– Many molecules are arranged into minute structure

called organelles, which are the components of cells.

– New properties emerge at each higher level of org.

1. Each level of biological organization has

emergent properties

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 1.2(1) Fig. 1.2(2)

• The cell is the lowest level of structure that is capable of

performing all the activities of life (metabolism,

response, homeostasis, growth, reproduction, nutrition).

• Two big names in early cell discoveries:

• Robert Hooke

• Anton vanLeeuwenhoek

2. Cells are an organism’s basic

unit of structure and function


• In 1839, Matthais Schleiden and Theodor

Schwann extrapolated from their own

microscopic research and that of others to

propose the cell theory.

– 1. All living things consist of cells.

– 2. All cells come from other cells.

• This suggests a big idea, foreshadowing Darwin’s idea of

descent with modification. Pasteur’s famous experiment

contributed to this idea. Remember it?

-3.Cells are the smallest unit of life, capable of

carrying out all life functions. Everything we

do is a result of something our cells do.


• All cells are enclosed …

• At some point, all cells contain …

• Two major kinds of cells - prokaryotic cells and

eukaryotic cells - can be distinguished by their

structural organization.

– The cells of the microorganisms called bacteria and

archaea are prokaryotic.

– All other forms of life have the more complex

eukaryotic cells.


• All cells are surrounded by a plasma membrane.

– The term plasma is reserved for the outer membrane.

• The semifluid substance within the membrane is the

cytosol, containing the organelles.

• All cells at some point contain chromosomes which have

genes in the form of DNA.

• All cells also have ribosomes, tiny organelles that make

proteins using the instructions contained in genes.

1. Prokaryotic and eukaryotic cells

differ in size and complexity


• A major difference between prokaryotic and

eukaryotic cells is the location of chromosomes.

• In an eukaryotic cell, chromosomes are

contained in a …

• In a prokaryotic cell, the DNA is concentrated

in the nucleoid without a membrane separating

it from the rest of the cell.

• The –oid suffix means what?


Terms to keep straight:

• Cytoplasm:

• Nucleoplasm:


Fig. 7.4 The prokaryotic cell is much simpler in structure, lacking a nucleus and the other

membrane-enclosed organelles of the eukaryotic cell.

• Eukaryotic cells are generally 10 times bigger

than prokaryotic cells

• Here’s a size comparison, let’s practice some

math:

– Molecules – 1 nm (scientific notation?)

– Membrane thickness – 10 nm

– Viruses – 100 nm

– Bacteria – 1 um (how much bigger than a virus?)

– Organelles – 10 um

– Cells – up to 100 um

– See the pattern? 10 times bigger each.



Fig. 7.5

• Metabolic requirements also set an upper limit

to the size of a single cell.

• As a cell increases in size its volume increases

faster than its surface area.

– Smaller objects have a greater

ratio of surface area to volume.

• The volume of cytoplasm determines the need

for the exchange of nutrients and wastes across

the plasma membrane.

• Rates of chemical exchange may be inadequate

to maintain a cell with a very large cytoplasm.

• Why can’t a cell be as big as a left tackle for the

Seminoles?

• Larger organisms do not generally have larger

cells than smaller organisms - simply more

cells.

• How about some math practice?


Tips • Grid LEFT to right

• Use the formula sheet

• Don’t round until the end

• Look at HOW the answer should be given

“round to nearest…”

.123

The 1 is in the tenths place

The 2 is in the hundreds place

The 3 is in the thousandths place

Q2: Surface Area and Volume

• What is the SA/V for this cell? Round your

answer to the nearest hundredths.

Q2

SA= 4 r2

=4(3.14) 52

=314

Volume of a sphere= 4/3 r3

=4/3 (3.14)53

=523.33

SA/V=314/523.33

=.60

• A eukaryotic cell has extensive and elaborate internal

membranes, which partition the cell into compartments.

• These membranes also participate in metabolism by

providing a surface for reactions to occur on, as well as

enzymes to speed them up.

• What is the advantage of such partitioning???

2. Internal membranes compartmentalize the

functions of a eukaryotic cell


• The plasma membrane separates the living cell

from its nonliving surroundings.

• This thin barrier, 8 nm thick, controls traffic into

and out of the cell.

• Like other membranes, the plasma membrane is

selectively permeable, meaning what???

• Check this out:

http://www.johnkyrk.com/cellmembrane.html

Introduction


http://www.johnkyrk.com/cellmembrane.html

• The main macromolecules in membranes are

_____and _____ but include some ________.

• The most abundant lipids are _______.

• The phospholipids and proteins in membranes

create a unique physical environment, described

by the fluid ______ model.

– A membrane is a fluid structure with proteins

embedded or attached to a double layer of

phospholipids each of which has a polar “head” and

non-polar fatty acid “tails”.


• In 1972 (when I was your age), S.J. Singer and

G. Nicolson presented a model that proposed

that the membrane proteins are dispersed and

individually inserted into the phospholipid

bilayer.

– In this fluid mosaic

model, the hydrophilic

regions of proteins

and phospholipids are

in maximum contact

with water and the

hydrophobic regions

are in a nonaqueous

environment. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 8.2b

• Membrane molecules are held in place by

relatively weak hydrophobic interactions.

• Most of the lipids and some proteins can drift

laterally in the plane of the membrane, but rarely

flip-flop from one layer to the other.

1. Membranes are fluid


Fig. 8.4a

• The steroid cholesterol is wedged between

phospholipid molecules in the plasma membrane

of animal cells, (not other kinds).

• At warm temperatures, it restrains the movement

of phospholipids and reduces fluidity.

• At cool temperatures, it maintains fluidity by

preventing tight packing.


Fig. 8.4c

• A membrane is a collage of different proteins

embedded in the fluid matrix of the lipid bilayer.

3. Membranes are mosaics of

structure and function


Fig. 8.6

• Proteins determine most of the membrane’s

specific functions.

• The plasma membrane and the membranes of

the various organelles each have unique

collections of proteins.

• There are two populations of membrane

proteins.

– Peripheral proteins are not embedded in the lipid

bilayer at all.

– Instead, they are loosely bound to the surface of the

protein, often connected to the other population of

membrane proteins.


– Integral proteins penetrate the hydrophobic core of

the lipid bilayer, often completely spanning the

membrane. What level of organization do you see?


Fig. 8.7

• The proteins in the plasma membrane may

provide a variety of major cell functions.


Fig. 8.9

• The membrane plays the key role in cell-cell recognition and communication

– Cell-cell recognition is the ability of a cell to distinguish one type of neighboring cell from another.

– This attribute is important in cell sorting and organization as tissues and organs in development.

– It is also the basis for rejection of foreign cells by the immune system.

– Cells recognize other cells by keying on surface molecules, often carbohydrates, on the plasma membrane.

4. Membrane carbohydrates are

important for cell-cell recognition


• Membrane carbohydrates are usually branched with

fewer than 15 sugar units.

• They may be covalently bonded either to lipids,

forming glycolipids, or, more commonly, to proteins,

forming glycoproteins.

• They form what is called the cell coat in animal cells

and vary from species to species, individual to

individual, and even from cell type to cell type within

the same individual.

– This variation marks each cell type as distinct.

– Blood groups example???


Many things, like a girl’s car, can be

identified by their surface markings.


Fig. 7.7


Fig. 7.8

• The nucleus contains most of the genes in a eukaryotic cell. – Some genes, however, are located in _____ and

_______.

• The nucleus is separated from the cytoplasm by a double membrane.

• Where the double membranes are fused, a pore formed by 8 protein molecules in a ring allows large macromolecules and particles to pass through.

1. The nucleus contains a

eukaryotic cell’s genetic library



Fig. 7.9

• Within the nucleus, the DNA and associated proteins are organized into fibrous material, chromatin. Prokaryotic cells don’t have as much protein stuck to their DNA.

• In a normal cell they appear as a diffuse mass.

• However, What happens to chromatin when a cell is getting ready to divide????

• Each eukaryotic species has a characteristic number of chromosomes.

– A typical human cell has ___ chromosomes (but so do a plum’s), fruit flies have 8, pea plants have 14.


• In the nucleus is a region of densely stained

fibers and granules, the nucleolus.

– What happens in this region????

• The nucleus directs protein synthesis by

synthesizing messenger RNA (mRNA).

• Can a cell have more than one? Why? None?

Examples?


• Cell types that synthesize large quantities of

proteins (e.g., pancreatic cells) have large

numbers of ribosomes and prominent nuclei.

• Free vs. Bound ribosomes????


• The endoplasmic reticulum (ER) accounts for

half the membranes in a eukaryotic cell.

• The ER includes membranous tubules and

internal, fluid-filled spaces, the cisternae.

• The ER membrane is continuous with the nuclear

envelope and the cisternal space of the ER is

continuous with the space between the two

membranes of the nuclear envelope.

1. The endoplasmic reticulum manufacturers

membranes and performs many other

biosynthetic functions


• There are two, albeit

connected, regions of ER

that differ in structure

and function.

– Smooth ER looks smooth

because ________.

– Rough ER looks rough

because ______ including

the outside of the nuclear

envelope.

– Watch what they do:

http://www.johnkyrk.com/

golgiAlone.html


Fig. 7.11

http://www.johnkyrk.com/golgiAlone.html

http://www.johnkyrk.com/golgiAlone.html

http://www.johnkyrk.com/golgiAlone.htmlhttp:/vcell.ndsu.nodak.edu/animations/proteintrafficking/movie.htm

• The smooth ER is rich in enzymes and plays a

role in a variety of metabolic processes.

• Enzymes of smooth ER synthesize lipids,

including oils, phospholipids, and steroids.

– These includes the sex hormones of vertebrates and

adrenal steroids.

• The smooth ER also catalyzes a key step in the

mobilization of glucose from stored glycogen in

the liver. Smooth ER helps make everything

but protein.


• Other enzymes in the smooth ER of the liver

help detoxify drugs and poisons.

– These include alcohol and barbiturates.

– Frequent exposure leads to proliferation of smooth

ER, increasing tolerance to the drug.

– What do you think Michael Jackson’s liver cells

looked like?


• Rough ER is especially abundant in those cells that

secrete _______(like __________secreted from

pancreas cells).

– As a polypeptide is synthesized by the ribosome, it is

threaded into the cisternal space through a pore formed by a

protein in the ER membrane.

– Many of these polypeptides are glycoproteins, a polypeptide

to which an oligosaccharide is attached.

• These secretory proteins are packaged in transport

vesicles that carry them to their next stage.


• Rough ER is also a membrane factory.

– Membrane bound proteins are synthesized directly

into the membrane.

– Enzymes in the rough ER also synthesize

phospholipids from precursors in the cytosol.

– As the ER membrane expands, parts can be

transferred as transport vesicles to other

components of the endomembrane system.


• Many transport vesicles from the ER travel to the

Golgi apparatus for modification of their

contents.

• The Golgi is a center of manufacturing,

warehousing, sorting, and shipping.

• In what kind of cells would you expect to find a

lot of Golgi?

2. The Golgi apparatus finishes,

sorts, and ships cell products


• The Golgi apparatus consists of flattened

membranous sacs - cisternae - looking like a

piece of pita bread.

• Try this link

– http://vcell.ndsu.nodak.edu/animations/proteintraffi

cking/movie.htm

– One side of the Golgi, the cis side, receives material

by fusing with vesicles, while the other side, the

trans side, buds off vesicles that travel to other

sites, often the next cisternae in the Golgi.


../Animations/ProteinTrafficking.wmv

http://vcell.ndsu.nodak.edu/animations/proteintrafficking/movie.htm

http://vcell.ndsu.nodak.edu/animations/proteintrafficking/movie.htm

http://www.johnkyrk.com/golgiAlone.htmlhttp:/vcell.ndsu.nodak.edu/animations/proteintrafficking/movie.htm

• Products from the ER are modified as they pass

through.

• The Golgi can also manufacture its own

macromolecules, including pectin and other

noncellulose polysaccharides.

• Each cisterna has its own set of enzymes.

• Finally, the Golgi tags, sorts, and packages

materials into transport vesicles.


• The lysosome is a membrane-bound sac of

hydrolytic enzymes that digests macromolecules.

3. Lysosomes are digestive components


Fig. 7.13a

• The lysosomal enzymes and membrane are

synthesized by rough ER and then transferred to

the Golgi.

• Lysosomes

bud from

the trans

face of

the Golgi.


Fig. 7.14


• Lysosomes can fuse with food vacuoles.

• As the polymers are digested, their monomers

pass out to the cytosol to become nutrients for

the cell.

• Lysosomes can also

fuse with another

organelle or part

of the cytosol.

– This recycling, this process of autophagy, renews the cell.

Fig. 7.13b

• The lysosomes play a critical

role in apoptosis, or

programmed cell death.

–Tails of tadpoles?

–Webbing between fingers and toes?

–It’s a good thing this happens so

that we can do this….


• Vesicles and vacuoles – what’s the difference??

– Food vacuoles.

– Contractile vacuoles,

– Central vacuoles are found in many mature ______

cells, but none so big are ever found in ________

cells.

4. Vacuoles have diverse functions

in cell maintenance


http://www.linkpublishing.com/video-transport.htm

http://www.linkpublishing.com/video-transport.htm


Fig. 7.15

• Mitochondria are the sites of cellular ________, generating _____ from the catabolism of sugars, fats, and other fuels in the presence of ________.

• Chloroplasts, found in plants and eukaryotic algae, are the site of __________________.

– They convert solar energy to chemical energy and synthesize new organic compounds, mostly _______ from CO2 and _____.

1. Mitochondria and chloroplasts are the

main energy transformers of cells


• Mitochondria and chloroplasts are not part of

the endomembrane system.

• Their proteins come primarily from free

ribosomes in the cytosol and a few from their

own ribosomes.

• Both organelles have small quantities of

bacteria-like DNA that direct the synthesis of

the polypeptides produced by these internal

ribosomes.

• Mitochondria and chloroplasts grow and

reproduce as semiautonomous organelles.

• The Endosymbiont theory. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

http://www.sumanasinc.com/webcontent/animations/content/organelles.html




• Almost all eukaryotic cells have

mitochondria. Name one that doesn’t???

– There may be one very large

mitochondrion or hundreds to thousands

of individual mitochondria.

– The number of mitochondria is correlated

with aerobic metabolic activity; muscle

cells have a lot.

– A typical mitochondrion is 1-10 microns

long, similar to a _______________ cell.


• Two membranes, inner one is folded into____.

– This creates a fluid-filled space between them, the

intermembrane space.

– Classic S-F connection??????

• The inner membrane encloses the

mitochondrial ________, a fluid-filled space

with DNA, ribosomes, and enzymes.



Fig. 7.17

• The chloroplast is one of several members of a

generalized class of plant structures called plastids.

– Amyloplasts store starch in roots and tubers.

– Chromoplasts store pigments for fruits and flowers.

• The chloroplast produces sugar via photosynthesis.

– Chloroplasts gain their color from high levels of the

green pigment chlorophyll.

• Chloroplasts measure about 2 microns x 5 microns and

are found in leaves and other green structures of plants

and in eukaryotic algae.


• The processes in the chloroplast are separated

from the cytosol by two membranes.

• Inside the inner membrane is a fluid-filled

space, the stroma, in which float membranous

sacs, the thylakoids.

– The stroma contains DNA, ribosomes, and enzymes

for part of the photosynthetic reactions..

– The thylakoids, flattened sacs, are stacked into

grana and are critical for converting light to

chemical energy.



Fig. 7.18

Theme time…

• So let’s see how many

similarities and differences

we can list between

mitochondria and

chloroplasts.

• Peroxisomes contain enzymes that transfer hydrogen from various substrates to oxygen

– An intermediate product of this process is hydrogen peroxide (H2O2), a poison, but the peroxisome has another enzyme, catalase, that converts H2O2 to water.

– Other peroxisomes in liver cells detoxify alcohol and other harmful compounds.

– Specialized peroxisomes, glyoxysomes, convert the fatty acids in seeds to sugars, an easier energy and carbon source to transport.

Peroxisomes


• The cytoskeleton is a network of protein fibers

extending throughout the cytoplasm.

• The cytoskeleton

organizes the

structures and

activities of

the cell.

Introduction


Fig. 7.20

• The cytoskeleton provides mechanical support and maintains or helps change the shape of the cell.

• The cytoskeleton provides anchorage for many organelles and cytosolic enzymes.

• The cytoskeleton is dynamic, dismantling in one part and reassembling in another to change cell shape.

Cytoskeleton functions


• The cytoskeleton also plays a major role in cell

motility.

– This involves both changes in cell location and

limited movements of parts of the cell.

• The cytoskeleton interacts with motor proteins.

– In cilia and flagella motor proteins pull components

of the cytoskeleton past each other.

– This is also true

in muscle cells.


Fig. 7.21a

• Motor molecules also carry vesicles or

organelles to various destinations along

“monorails’ provided by the cytoskeleton.

• Interactions of motor proteins and the

cytoskeleton circulates materials within a cell -

called cell streaming or cyclosis.


Fig. 7.21b

• There are three main types of fibers in the

cytoskeleton: microtubules, microfilaments,

and intermediate filaments.


• Microtubules, the thickest fibers, are hollow

rods about 25 microns in diameter.

– Microtubule fibers are constructed of the globular

protein, tubulin, and they grow or shrink as more

tubulin molecules are added or removed. See here

• They move chromosomes during cell division.

• Another function is

as tracks that guide

motor proteins

carrying organelles

to their destination.


Fig. 7.21b

http://www.sinauer.com/cooper5e/animation1203.html


Fig. 7.22

• In animal cells, the centrosome has a pair of centrioles, each with nine triplets of microtubules arranged in a ring.

• During cell division the centrioles replicate.

• Microtubules are the central structural supports

in cilia and flagella.

– Both can move unicellular and small multicellular

organisms by propelling water past the organism.

– If these structures are anchored in a large structure,

they move fluid over a surface.

• For example, cilia sweep mucus carrying trapped debris

from the lungs.


Fig. 7.2

• In spite of their differences, both cilia and

flagella have the same ultrastructure.

– Both have a core of microtubules sheathed by the

plasma membrane.

– Nine doublets of microtubules are arranged around

a pair at the center, the “9 + 2” pattern.

– Flexible “wheels” of proteins connect outer

doublets to each other and to the core.

– The outer doublets are also connected by motor

proteins.

– The cilium or flagellum is anchored in the cell by a

basal body, whose structure is identical to a

centriole.



Fig. 7.24

• The bending of cilia and flagella is driven by the

arms of a motor protein, dynein.

– Dynein arms alternately

grab, move, and release

the outer microtubules.

– Protein cross-links limit

sliding and the force is

expressed as bending.

– Watch this cilia on cells

– In a clam’s gill


Fig. 7.25

http://www.linkpublishing.com/video-cell.htm

• Microfilaments, the thinnest class of

the cytoskeletal fibers, are solid rods of

the globular protein actin.

• Microfilaments are designed to resist

tension.

• With other proteins, they form a three-

dimensional network just inside the

plasma membrane.


• In plant cells (and others), actin-myosin

interactions drive cytoplasmic streaming.

– This creates a circular flow of cytoplasm in the cell.

Watch here

– This speeds the distribution of materials within the

cell.


Fig. 7.21c

http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artnov00/dwelodea.html

• Intermediate filaments, intermediate in size at 8 - 12 nanometers, are specialized for bearing tension.

– Intermediate filaments are built from a diverse class of subunits from a family of proteins called keratins.

• They reinforce cell shape and fix organelle location.

• Watch how structure is related to function. Link to Intermediate Filaments


Fig. 7.26

http://www.sumanasinc.com/webcontent/animations/content/intermediate_filaments.html

• The cell wall, also found in prokaryotes, fungi,

and some protists, has multiple functions.

• In plants, the cell wall protects the cell, maintains

its shape, and prevents excessive uptake of water.

• It also supports the plant against the force of

gravity.

• The thickness and chemical composition of cell

walls differs from species to species and among

cell types.

1. Plant cells are encased by cell walls


• The basic design consists of microfibrils of cellulose embedded in a matrix of proteins and other polysaccharides.

– This is like steel-reinforced concrete or fiberglass.

• A mature cell wall consists of a primary cell wall and layers of secondary cell wall.


Fig. 7.28

Cell wall structure

• Primary cell walls contain cellulose and pectin, and is thin and flexible.

• Secondary cell walls are thicker and also contain lignin, which further stiffens it. Cells of hard plant parts such as stems have one or more layers of secondary walls.

• A middle lamella of sticky pectin separates the cell walls of adjoining cells.

• Neighboring cells in tissues, organs, or organ

systems often adhere, interact, and communicate

through direct physical contact.

• Plant cells are perforated with plasmodesmata,

channels allowing cysotol to pass betells.

3. Intracellular junctions in plant cells


Fig. 7.28 inset

• Animal cells have 4 main types of intercellular

links: tight junctions, desmosomes, gap

junctions and the newly discovered tunnelling

nanotubes.

• In tight junctions, membranes of adjacent cells

are fused, forming continuous belts around

cells.

– This prevents leakage of extracellular fluid.


Fig. 7.30

• Desmosomes (or anchoring junctions) fasten cells

together into strong sheets, much like rivets.

– Intermediate filaments of keratin reinforce

desmosomes.

• Gap junctions (or communicating junctions) provide

cytoplasmic channels between adjacent cells.

– Special membrane proteins surround these pores.

– Salt ions, sugar, amino acids, and other small

molecules can pass.

– In embryos, gap junctions facilitate chemical

communication during development.


Practice time…

• List as many similarities and

differences as you can for:

– Prokaryotic vs. Eukaryotic cells

– Plant cells vs. animal cells

– http://multimedia.mcb.harvard.edu/a

nim_innerlife_hi.html

http://multimedia.mcb.harvard.edu/anim_innerlife_hi.html

http://multimedia.mcb.harvard.edu/anim_innerlife_hi.html

Tunnelling nanotubes

• Discovered in 2004, these narrow tubes can

form between all types of cells to allow

them to pass things such as protein

hormones and molecules that cause genes to

become active. Unfortunately, they also

can allow for viruses to pass from cell to

cell.

cells (and other stuff)

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