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CHAPTER 5

CELL STRUCTURE AND FUNCTION

Why are cells small? (surface to volume ratio)

LUCA is not the name of a famous scientist in the

field; it is shorthand for Last Universal Common

Ancestor, a single cell that lived perhaps 3 or 4

billion years ago, and from which all life has since

evolved.

The

genetic

code is

universal for all

life.

That the genetic code is universal

to all life tells us that everything is related. All life regenerates itself

by producing offspring, and over

time small changes in the offspring

result in small changes to the

protein recipes. But because the recipes are written in the same

language (the genetic code), it is

possible to compare these recipes

(and other genes) to build the

equivalent of a family tree

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I THE THREE DOMAIN SYSTEM OF CLASSIFICATION

Was first proposed by Carl Woese . He based this on

differences in the sequences of cell’s ribosomal RNA

( rRNA) as well as the membrane lipid structure and

sensitivity to antibiotics.

The system proposes that a common ancestor cell gave rise to

three different cell types each represented by a different

domain.

i. Archaea: archaebacteria ( Extremophiles)

Characteristics

a. Prokaryotic cells

b. Membranes composed of branched hydrocarbon

chains

c. Many times antibiotic resistant

d. Cell walls made of polysaccharides **

e. Live in extreme environments

i. Halophiles , hyperthermophiles

ii. Volcanic vents, midatlantic rift, Yellowstone

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ii. Bacteria: eubacteria

a. Prokaryotic cells

b. Plasma membranes have unbranched fatty acids (

same as eukaryotes)

c. Cell walls contain peptidoglycan ( murein

a type of sugar )**

d. rRNA is unique to bacteria only

e. ex. Cyanobacteria, gram- gram+ bacteria

f. Classified by shape: bacillus- rod :

coccus- sphere: spirilla- spiral

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g. EuBacteria are Classified as gram (-)

or gram (+) as to whether their cell wall will stain

with crystal violet ( gram stain)

iii. Eukarya : eukaryotes

a. 4 kingdoms

i. Protista

ii. Fungi

iii. Plantae

iv. Animalia

b. Eukaryotic cells

i. Cell walls of

1. plants made of cellulose ,

2. fungi made of chitin

ii. Membranes of all have unbranched fatty acid

chains

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L.U.C.A.

Cladogram:

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I TWO BASIC CELL TYPES (prokaryotic , eukaryotic)

A. Prokaryotic cells

(Pro: Before) ( Karyon: Nucleus)

1. Lack a discrete Nucleus

2. Usually small than Eukaryotic cells

3. Unicellular

4. Have rigid Cell Wall

5. Ex. Bacteria, cyano-bacteria , Archaebacteria

B. Eukaryotic cells

( Eu: good) ( Karyon: Nucleus)

1. Complete membrane bound nucleus

2. Specialized organelles( plastids, mitochondria,

vacuoles etc)

3. All organisms other than bacteria and

archaebacteria

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4. Unicellular- Protists

5. Multicellular- plants, fungi, animals

PROKARYOTES

1. Cyclic DNA

2. Ribosomes: smaller than eukaryotic

Ribosomes are not membrane bound

3. Mesosome : membrane that appears to be continuous

with the P.M.

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4. Thick cell wall:

a. Cell wall of Archaea made of polysaccharides

b. Cell wall of eubacteria made of Peptidoglycan

sugar

( also known as murein an amino-sugar comp.)

Some cell wall substances are toxic + cause diseases.

Antibiotics : such as Penicillin interfere w/ the

construction of the cell wall “amino-sugar” formation

therefore inhibiting bacterial growth.

5. Capsule:

- Polysaccharide or poly peptide chain found on the

outside of the cell wall . It is a feltlike capsule

enabling bacteria to stick to surfaces.

- Ex. Soil particles, rocks, animal cells, teeth ,

armpits.( Streptococcus mutans: uses sucrose to

make capsule to stick to teeth causing tooth

decay)

The surface of Bacillus anthracis. From Mesnage, et al. Journal of

Bacteriology (1998) 180, 52-58. The bacterial membrane is evident as the innermost layer surrounding the cytoplasm. P

denotes the peptidoglycan cell wall. S refers to the S-layer which consists of two proteins including the major antigen. C

denotes the poly-D-glutamic acid capsule that is exterior to and completely covers the S-layer proteins.

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6. Pili: Hundreds of hollow strands of proteins used for

attachment ( Pg78 read + know caption)

7. Flagella: movement of bacteria using long thin spiral

flagellum

8. Gram - appear red or pink

9. Gram + appear blue or purple

EUKARYOTIC CELLS OF HIGHER ORGANISMS

1. Much larger than prokaryotic cells.

2. Many membrane Bound Organelles

a. ( table 5-2) know all of these .

b. Plastids: found only in plants

c. Cell wall: in plants ( Cellulose)

In fungi ( Chitin)

d. Mitochondria

e. Lysosomes

f. Vacuoles ( Contractile Vacuoles : regulate

water in plants)

3. CYTOSOL: The soluble portion of the cytoplasm.

Contains:

a. Ions, molecules , molecular aggregates

b. ½ the cells volume is composed of cytosol

Cytosol= 20% protein

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COMPONENTS OF EUKARYOTIC CELLS

A. NUCLEUS:

a. Very complex in plants and animals

b. Genetic material (DNA) arranged into

Chromosomes

c. Chromosomes: Long DNA molecule + RNA proteins

d. Chromosomes coil up into short threadlike

structures before and during cell division

e. Most of time nucleus is not not dividing. During this

time chromosome s are uncoiled in loose indistinct

tangle called CHROMATIN.

Chromatin determines what RNA is mad in the

nucleus

f. RNA made in the nucleus travels to the Cytoplasm

to ribosomes where it directs protein synthesis

Note: there are substances in the cytop. That

enter nucleus and influence DNA

g. NUCLEOLI: ( sing. Nucleolus)

Area in the nucleus where ribonsomes are

made.( Disappears during cell division)

h. NUCLEAR ENVELOPE: ( nuclear membrane)

Double membrane surrounding the nucleus

Perforated w/ pores ( disappears during cell

division) ( double membrane)

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g. RIBOSOMES: ( not membrane bound)

Function : Sites of protein synthesis

Eukaryotes: madein nucleolus area- travel to the

cytoplasm through nuclear pores

Up to 500,000 in a cell - some attached to

membranes of the endoplasmic reticulum

Ribosomes:

1. Free Ribosomes: found in cytosol

a. Make proteins that act and stay in

cytosol

2. Bound Ribosomes : on the surface of RER

a. Make proteins that are destined for

outside of cell or other organelle

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h. ENDOPLASMIC RETICULUM

( know Fig. 5-8 pg 85)

1. Is a system of membranous tunnels and sacs

found in eukaryotes .

2. Usually lies just outside the nucleus

3. Appears as piles of sacs

4. Lumen: of er provides the cell w/ a

compartment to contain substances that must

be kept separate from the cytosol.

1. Rough Endoplasmic :

Ribosomes Attached to the outer surface give it a

bumpy appearance.

RER: Are predominant in cells that make proteins

that are secreted from the cell.

(Ex. Pancreas: makes insulin)

PROTEIN

Transport ERLumen Sacs called Vesicles Golgi Exocytosis

Out of cell

NOTE: Most of the cells new membrane is produced in the ER.

2. Smooth Endoplasmic

Not much found in most cells

A lot found in cells involved in lipid metabolism and

production of cholesterol and steroids.

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i. GOLGI COMPLEX : Pg 86

A stack of flattened Membranous sacs.

Around the edges of the stack, swarms of small,

round transport vesicles carry molecules to or

from.

Golgi lies near nucleus

Cells may have one large or hundreds of small

ones

Overall role: Modify, sort and package the cell

From the golgi …..

Molecules exocytosis

New proteins + lipids for P. Mem.

Production of new proteins

Ribo RER Golgi complex Final location

Proteins modified by enzymes

Further modified for transport w/ a transport marker

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j. Lysosomes: Pg 87

Membrane bound sac

Contains hydrolytic enzymes that were made in

ER.

Function: Digest: food , Disease causing viruses,

damaged organelles, entire cells,

Junk like old clothes and toys

( occurs when another vesicle fuses w/ lysosome)

K. Peroxisomes:

Small sacs containing enzymes that break down

amino acids, fatty acids, and hydrogen peroxide

H2O2 ---- H2O + O2

( many found in liver and kidney cells)

G. MITOCHONDRIA: (Power House) Pg 87

1. Produce almost all of the ATP for cell

2. Make adenosine tri-phosphate from cell

Respiration ( series of rxns that use O2 to

break down glucose into CO2 + H2O + ATP

3. High energy cells have many mito.

Ex. Heart cells, growing root tips, liver

4. ( know structure) has 2 membranes

Outer, and inner ( highly folded)

5. ** Contains own

a. **DNA b. RNA c. Ribosomes

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b. **Makes some of its own proteins +

membranes

c. **Also reproduces itself.

ENDOSYMBIONT THEORY: Many scientists believe that

Mitoch. Evolved from prokaryotic cells that came to live

inside of a larger cell. Thus becoming an organelle.

Plastids also are believed to have arisen this way from

cyanobacteria that invaded plant cells.

H. PLASTIDS:

** 1. Found only in plants

2. 3 unique structures in plants.

a. plastids

b. cellulose cell wall

c. large vacuole

3. plastids contain:

DNA, RNA, Ribosomes,

4.Can reproduce themselves

5. Endosymbiont theory

6. three types:

a. Chloroplasts: Green

Photosynthesis Contain green pigment

Chlorophyll

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b.Chromoplasts: Make + store yellow +

orange pigments: (Xanthophylls, Carotenoids

) ( flowers, fruits, roots)

c. Amyloplasts

Store starch

Lots found in tubers, roots,

I. CELL WALL :

Found outside of the plasma

membrane

Cellulose in plants, Chitin in Fungi

Porous enough to allow H20 through

Structural support

J. VACUOLES:

- Sac of fluid surrounded by a

Membrane

- occur in many cells but mostly plant

cells and some protists

- Function: to hold stored food , water

and pigments.

- Also store some toxic materials

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K. CYTOSKELETON:

- a network of assorted protein filaments

attached to the plasma membrane and to

various organelles : made up of three

types of fibers.

1. Microtubules: biggest

2. Intermediate filaments : intermediate in size

3. Microfilaments: ( actin) itty bitty lil guys

Without the cytoskeleton, the cell would have no

shape

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1. MICROTUBULES: ( LARGEST

a. Give general shape to cell

b. Help track organelles movement

c. Framework of cilia and flagella

d. Involved in the spindle during cell

Division

e. Composed of tubulin: globular protein

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2 INTERMEDIATE FILAMENTS

a. Main role is mechanical strength and shape of

cell

3.MICROFILAMENTS ( Actin filaments)

a. Responsible for movement in the cell.

( Intracellular: within)

b.Cell gliding contraction and cytokinesis

c. Associated with Myosin protein

d. Muscle contraction

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MICROTUBULES FUNCTIONS

1. Movement of organelles w/in the cell

2. Skeletal framework of cell

3. Largest fiber

4. Role in cell division ( spindle fiber)

5. Cilia and Flagella: Threadlike organelles present

on the surface of many eukaryotes

6. Cilia short and more numerous than flagella

7. Both function in locomotion

Ex sperm, paramecium covered w/ cilia

Cilia move mucous and debris out of air

passages in humans.

Structure: Nine pairs of microtubules in a circle

w/ 2 in the middle (9pairs 2 singles covered

by extension of plasma membrane)

Basal Body

A cilium or flagellum grows

From this : it has

1. 9 microtubule triplets

2. No 2 in the middle

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Movement of cilia and flagellum

1. Moves by action of arms of the protein

DYNEIN that extend from one microtubule

of each pair.

Centrioles : ( found only in animals)

1. Eukaryotic cells except higher plants

2. There are 2 centrioles

3. Same arrangement as microtubules basal

body: ( that is 9 triplets)

4. Before cell division they move apart

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INTERMEDIATE FILAMENTS:

1. These are protein fibers intermediate in

thickness. Between MT and MF

2. Ropelike polypeptides

3. Function : give cell mechanical strength

MICROFILAMENTS:

1. Thinnest filaments

2. Also called Actin filaments because made of

the protein actin ( found as contractile protein

in muscle cells)

3. Most abundant protein in the cytoplasm

4. FUNCTION

a. Movement of organelles

b. Structure + strength

c. Muscle contraction

d. Cytokinesis

e. Endocytosis/ exocytosis

5. Myosin: Protein associated w/ microF. : it

interacts w/ actin in muscle cell contraction

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TISSUES AND ORGANS:

Tissue:

A group of cells of one or a few types that

perform a specific job. Ex. Connective tissue,

bone tissue, cardiac tissue, epithelial tissue

Organ : Made up of a group of tissues

Functional unit of the body

Ex. Eyes, kidneys, heart, lungs, brain

System: ?

A group of organs working together to

perform a group of similar functions.

Ex. Nervous system, digestive system,

immune system, circulatory system

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MAIN ANIMAL TISSUES:

1. Epithelial tissue:

a. Form coverings and linings

b. Line lungs, digestive tract , mouth ,

Outside of body,

2. Connective tissue: ( mostly protein collagen)

Most abundant tissue :

Adipose(fat) , cartilage, bone, fibrous cells

3. Nervous tissue:

a. Consists of nerve cells that conduct

electric currents ( transmit messages)

b. Not contractile

4. Muscle tissue

a. Cells that can both conduct an electric

impulse and contract (* Unique trait)

PLANT TISSUES: FOUR MAIN TYPES

1. Epidermis :

Covers the outside of leaves and stems

2. Vascular tissues:

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Transports water , food, hormones through

the plant (Xylem ) H20 + minerals, nutrients

(Phloem ) Transports glucose from leaves

elsewhere in the plant

3. Ground tissues:

Fills in spaces between epidermis and

vascular tissues (Parenchyma cells loosely

packed cells)

4. Meristems :

Cells that are ready to divide and

develop Ex. Buds, root tips

CLADOGRAMS:

We can diagram a tree-like relationship called a

cladogram. The cladogram graphically represents a

hypothetical evolutionary process. Cladograms are

subject to change as new data becomes available.

The terms evolutionary tree, and sometimes

phylogenetic tree are often used synonymously with

cladogram,

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