Cytology

Cell Structure and Function

Overview of Animal Cell

Structure

A. Plasma Membrane

B. Cytoplasm

C. Major Organelles

1. nucleus

2. ribosomes

3. endoplasmic reticulum (ER)

4. Golgi complex (apparatus)

5. mitochondria

6. lysosomes

7. peroxisomes

D. Cytoskeleton, Cilia, Flagella

E. Inclusions

F. Extracellular Matrix

The Plasma Membrane

A. Chemical Composition

1. 80% phospholipids

a. "head" region of

molecule is hydrophilic

b. "tail" region of

molecule is hydrophobic

2. 10% proteins - peripheral

and integral

3. 10% cholesterol, glycolipids,

carbohydrates

B. Structure

1. phospholipid bilayer - two layers

of phospholipids with "head"

regions pointing inward and

outward while "tail" regions

intermingle in the middle of the

sandwich.

• Fluid motion of these molecules

is described as a “fluid mosaic”.

Here you can see the lipid bilayer with both integral

and peripheral proteins embedded in the

membrane.

2. integral membrane proteins

a. float in or completely across

lipid bilayer

b. act as selective channels for

transport

c. act as receptor sites for

messengers(hormones)

3. peripheral membrane proteins

a. lie on inner/outer surface of

lipid bilayer

b. many have enzymatic role

c. structural function in tissue

organization

C. Primary Functions

1. selective transport of materials

in and out of cell.

2. maintain cell structure and

intracellular climate.

Cytoplasm

A. Composition and Structure

1. 90% water, 10% protein,

carbohydrate, lipid, salts

2. colloids - collections of

organic molecules

3. jelly-like fluid surrounding

the nucleus

4. criss-crossed by

cytoskeleton that holds

cell shape

B. Function

1. site of many enzyme

controlled reactions

2. site of both synthesis and

degradation reactions

3. intermediate area for storage

and cell transport

Nucleus

A. Structure and Composition

1. nuclear membrane - double

lipid bilayer

2. perinuclear cisterna

3. nuclear pores

4. nucleoplasm (karyolymph)

5. Deoxyribose Nucleic Acids(DNA)

a. chromatin - dispersed

DNA, invisible

b. chromosomes - condensed

DNA, only when dividing

6. nucleolus - site of ribosome

synthesis

B. Primary Functions

1. house and protect hereditary

material (DNA)

2. copy DNA to RNA so proteins can

be manufactured

3. produce ribosomal RNA (rRNA) to

make ribosomes

Ribosomes

A. Composition and Structure

1. rRNA (made in nucleus) and

associated proteins

2. two subunits forming a 3-D

granule

B. Primary Functions

1. only site of protein synthesis

2. "read" the messenger RNA sent

out from nucleus

3. free ribosomes - scattered

throughout cytoplasm

4. attached ribosomes - found on

endoplasmic reticulum

Endoplasmic Reticulum (ER)

A. Structure

1. cisternae - double membranous sacs

2. extend directly from the nuclear

membrane

3. granular (rough) ER - have ribosomes

attached

4. agranular (smooth) ER - no ribosomes

B. Primary Functions

1. transport, storage, packaging of materials

2. surface area for cellular reactions

3. granular ER

a. synthesis of proteins bound for

secretion

b. passes proteins to Golgi for processing

4. agranular ER

a. storage area for Ca++ (muscle cells)

b. lipid synthesis inactivation

c. detoxification of harmful

compounds(liver)

Golgi Complex (Apparatus)

A. Structure

1. cisternae - lined up in

stacks next to nucleus

2. cis, medial, and trans parts

(Cis face receives material from the ER.

The trans face forms transport vesicles

that send material to the cell membrane

for secretion)

B. Primary Function

1. process, sort, package, deliver

proteins (UPS)

2. cis - closest to ER, receives new

proteins

3. medial - alters protein to functional

form

4. trans - forms secretory granules for

protein release:

a. digestive enzymes

b. antibodies

c. secretory glands

d. extracellular matrix material

Mitochondria

A. Structure

1. two-membrane structure

a. outer mitochondrial

membrane

b. inner mitochondrial membrane

(cristae)

2. matrix - within the inner

membrane

B. Primary Functions

1. powerhouse of the cell

2. foodstuffs (glucose) broken down in

cytoplasm converted to useable energy

"currency" called ATP

3. inner membrane contains

"respiratory" enzymes

C. Varied Distribution

1. low energy required - fewer

mitochondria

2. high energy required - more

mitochondria

a. muscle cells

b. liver cells

c. kidney tubule cells

Lysosomes

A. Structure

1. single membrane enclosed

spheres

2. primary lysosome - bud-off from

Golgi complex

3. secondary lysosome - when

fused with a vacuole

B. Primary Functions

1. breakdown (digestion) of compounds and

old parts

2. autophagy - "self eating" reuse old

organelles

3. autolysis - "self destruction" of entire cell

4. release digestive enzymes to outside

a. sperm entering egg during

fertilization

b. during repair of bodily injury

c. osteoclasts - during bone growth

Peroxisomes

A. Structure

1. small, single membrane enclosed

spheres

B. Primary Function

1. breakdown hydrogen peroxide (toxic

to cells)

2. catalase - enzyme that catalyzes

breakdown

Cytoskeleton

A. Microfilaments

1. 6 nanometers in diameter

2. made up of subunits called actin

3. support and cell shape

4. movement

a. muscle contraction

b. white blood cells (phagocytes)

B. Microtubules

1. ~24 nanometers in diameter

2. made up of subunits called tubulin

3. involved in intracellular transport

a. move organelles around like a

highway

4. involved in amoeboid motion of cells

(phagocytes)

5. chief components of cilia and flagella

C. Cilia and Flagella

1. both consist of microtubules (9+2

arrangement)

2. flagella very large for cell locomotion

(sperm)

3. cilia very small, fingerlike projections

a. epithelium of respiratory tract

b. lining of digestive tract (intestinal villi)

Cell Inclusions

A. Structure

1. conglomeration of molecules of

same type

2. melanin - pigment in skin, hair,

eyes

3. glycogen - glucose storage - liver

and muscles

4. lipids - stored in fat cells

(longterm energy)

Extracellular Materials

A. Different Types

1. interstitial (extracellular) fluid

2. plasma - liquid portion of blood

3. secretory material (mucus, saliva,

sweat)

4. extracellular matrix (binding cells into

tissue)

B. Fibrous Extracellular Components

(thread-like)

1. collagen - primary subunit of fibrous

components

2. collagenous fibers - bone, cartilage,

tendon, ligaments.

3. reticular fibers - fat, muscle, nerve, vessels

4. elastic fibers - (elastin) skin and blood

vessels