Lecture 3: Structure of the Cell
I. Overview of Animal Cell Structure
A. Plasma Membrane
B. Cytoplasm
C. Major Organelles
1.
2.
3.
4.
5.
6.
7.
nucleus
ribosomes
endoplasmic reticulum (ER)
Golgi complex (apparatus)
mitochondria
lysosomes
peroxisomes
D. Cytoskeleton, Cilia, Flagella
E. Inclusions
F. Extracellular Matrix
II. 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 (see below)
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.
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
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C. Primary Functions
1. selective transport of materials in and out of cell
2. maintain cell structure and intracellular climate
III. Cytoplasm
A. Composition and Structure
1.
2.
3.
4.
90% water 10% protein, carbohydrate, lipid, salts
colloids - collections of organic molecules
jelly-like fluid surrounding the nucleus
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
IV. Nucleus
A. Structure and Composition
1.
2.
3.
4.
5.
nuclear membrane - double lipid bilayer
perinuclear cisterna
nuclear pores
nucleoplasm (karyolymph)
Deoxyribose Nucleic Acids (DNA)
a. chromatin - dispersed DNA, invisible
b. chromosomes - condensed DNA, only when dividing
6. nucleolus - site of ribosome synthesis (see below)
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
V. 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.
2.
3.
4.
only site of protein synthesis
"read" the messenger RNA sent out from nucleus
free ribosomes - scattered throughout cytoplasm
attached ribosomes - found on endoplasmic reticulum
VI. Endoplasmic Reticulum (ER)
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A. Structure
1.
2.
3.
4.
cisternae - double membranous sacs
extend directly from the nuclear membrane
granular (rough) ER - have ribosomes attached
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)
VII. Golgi Complex (Apparatus)
A. Structure
1. cisternae - lined up in stacks next to nucleus
2. cis, medial, and trans parts
B. Primary Function
1.
2.
3.
4.
process, sort, package, deliver proteins
cis - closest to ER, receives new proteins
medial - alters protein to functional form
trans - forms secretory granules for protein release
a. digestive enzymes
b. antibodies
c. secretory glands
d. extracellular matrix material (see below)
VIII. 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
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1. low energy required - fewer mitochondria
2. high energy required - more mitochondria
a. muscle cells
b. liver cells
c. kidney tubule cells
IX. 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.
2.
3.
4.
breakdown (digestion) of compounds and old parts
autophagy - "self eating" reuse old organelles
autolysis - "self destruction" of entire cell
release digestive enzymes to outside
a. sperm entering egg during fertilization
b. during repair of bodily injury
c. osteoclasts - during bone growth
X. 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
XI. Cytoskeleton
A. Microfilaments
1.
2.
3.
4.
6 nanometers in diameter
made up of subunits called actin (myosin in muscle)
support and cell shape
movement
a. muscle contraction
b. white blood cells (phagocytes)
B. Intermediate Filaments
1.
2.
3.
4.
8-12 nanometers in diameter
support, shape, some intracellular movement
best studied: in nerve cells (neurons)
possible role in Alzheimers, other neuro disorders
C. Microtubules
1. ~24 nanometers in diameter
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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 (see below)
D. Microtrabecular Lattice
1. framework of all components working together
2. the skeleton that supports/organizes the cell
E. 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)
XII. Cell Inclusions
A. Structure
1.
2.
3.
4.
conglomeration of molecules of same type
melanin - pigment in skin, hair, eyes
glycogen - glucose storage - liver and muscles
lipids - stored in fat cells (longterm energy)
XIII. Extracellular Materials
A. Different Types
1.
2.
3.
4.
interstitial (extracellular) fluid
plasma - liquid portion of blood
secretory material (mucus, saliva, sweat)
extracellular matrix (binding cells into tissue)
B. Amorphous Extracellular Components (jelly-like)
1.
2.
3.
4.
hyaluronic acid - binding, lubrication, shape (eyes)
chondroiton sulfate - cartilage, bone, vessels
dermatin sulfate - skin, tendons, heart valves
keratin sulfate - bone and cornea
C. Fibrous Extracellular Components (thread-like)
1.
2.
3.
4.
collagen - primary subunit of fibrous components
collagenous fibers - bone, cartilage, tendon, ligs.
reticular fibers - fat, muscle, nerve, vessels
elastic fibers - (elastin) skin and blood vessels
----------------------------------------------------Lecture 3A: Cell Replication - Mitosis
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I. Overview of Mitosis
A. General Characteristics
1. cells duplicate all chromosomes
2. one cell divides evenly to form 2 daughter cells
3. organelles and cytoplasm divided equally
C. Interphase (normal part of cell life cycle)
1. centrioles (anchor microtubules) duplicated
2. DNA strands (chromatin) are duplicated
D. Prophase
1.
2.
3.
4.
5.
chromatin condense to form visible chromosomes
nuclear membrane slowly dissolves
nucleolus (ribosome factory) becomes disorganized
centrioles migrate to opposite "poles" of the cell
"spindle fibers" (microtubules) emerge from the
centrioles, growing toward centromere of chromosomes
E. Metaphase
1. spindle fibers attach to centromere of chromosomes
2. chromosomes pulled tight along cell "equator"
F. Anaphase
1. spindle fibers pull chromosomes apart at centromere
2. copies of each chromosome migrate to pole of cell
G. Telophase
1.
2.
3.
4.
5.
chromosomes uncoil and return to chromatin form
nuclear membrane reforms around the uncoiled DNA
nucleoli reform within the nucleus
spindle fibers disappear, each pole has 1 centriole
"cleavage furrow" forms, dividing cell into 2 cells
H. Cancer - uncontrolled mitosis of a particular cell
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