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VT 105
Comparative Anatomy and Physiology
Cell Anatomy and Physiology
Cell – basic structural and functional unit of life; undergoes basic life processes;
maintains homeostasis
Cytology – study of cell structure (anatomy)
3 BASIC CELLULAR COMPONENTS – cell membrane, cytoplasm, nucleus
1) Cell membrane – composed of a lipid bilayer (phospholipids and cholesterol)
containing many membrane proteins
flexible yet sturdy barrier enclosing cell contents
maintains internal environment and communicates with the external
environment
2) Cytoplasm – everything between the cell membrane and nucleus
Cytosol – intracellular fluid
mostly water with dissolved ions, amino acids, glucose, and
enzymes
content regulated by the cell membrane
Cytoskeleton – network of protein filaments; act as structural
framework and aid in cellular movements
microtubules – thick hollow tubes made of tubulin
tracks for movement of organelles
can be assembled or disassembled as needed
centrioles – pairs of microtubule structures
direct formation of mitotic spindle
cilia – hair-like projections on cell surface
sweep fluid on cell surface or move cell
flagella – similar to cilia but single and long
move entire cell (sperm)
intermediate filaments – strong, woven fibers
form an internal framework giving the cell strength and
structure
microfilaments – thinnest filaments made of actin
move cell membrane during cell division, amoeboid
locomotion, endocytosis or exocytosis
associated with motor proteins called myosin, which bind
to actin to cause movements
(thick filaments – special myosin filaments in muscle cells)
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Organelles (little organs) – membrane bound structures with characteristic
shapes and functions
contain specific enzymes for each organelle’s function
numbers vary depending on cell type and function
Mitochondria – “powerhouses” of cell
site of aerobic respiration – nutrients catabolized using
oxygen; produces energy stored in ATP molecules
number of mitochondria depends on activity level of cell
structure of mitochondrion
outer membrane
inner membrane
cristae – folds in inner membrane with
enzymes for ATP production
matrix – central fluid-filled cavity
mitochondria self-replicate during increased energy
demand or cell division
have own DNA and ribosomes
Ribosomes – made of rRNA and 50+ proteins
sites of protein synthesis
free ribosomes – scattered in cytosol
fixed ribosomes – attached to rough ER
Endoplasmic Reticulum – membrane network attached to nuclear
envelope (membrane)
Rough ER – covered with ribosomes; modifies proteins
and packs them for transport (transport vesicles)
Smooth ER – synthesizes lipids and glycogen,
breaks down drugs and toxins, stores calcium ions
Golgi Apparatus – 3-20 flattened sacs (cisternae) which modify
products of the ER and pack into vesicles with specific
destinations
cisternae contain enzymes to modify contents
secretory vesicles – contents released outside cell
membrane vesicles – fuse with cell membrane
lysosomes – remain in cytoplasm
Lysosomes – vesicles containing digestive enzymes
digest nutrients, old organelles, bacteria, debris
autolysis – lysosomes digest the cell when it dies
(suicide packets involved in programmed cell death)
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Peroxisomes – vesicles containing oxidizing enzymes which break
down toxins (eg. alcohol) and free radicals (damaging
by-products of metabolism)
peroxidase – converts free radicals to hydrogen peroxide
catalase – converts hydrogen peroxide to water
3) Nucleus – usually most prominent cell structure; contains cell’s genetic
material (DNA), which determines cell structure and function
nuclear envelope – double membrane with nuclear pores which control
movement of molecules between cytoplasm and nucleus
nucleolus (pl. nucleoli) – cluster of protein, DNA and RNA; site of
ribosome synthesis
chromatin – long strands of DNA coiled with protein molecules (histones)
seen whenever cell is not dividing
chromosomes – visible, tightly-coiled DNA molecules (seen only during
cell division)
chromatids – 2 identical copies of DNA formed by DNA
replication
centromere – junction where chromatids are joined
GENETIC CODE – DNA codes for synthesis of structural and functional proteins
DNA (deoxyribonucleic acid) – 2 huge chains of nucleotides held together by
hydrogen bonds between their nitrogenous bases (forms a double-helix)
nucleotide – deoxyribose (5-C sugar) + phosphate + nitrogenous base
4 types of nitrogenous bases in DNA and nucleotides take their name
from their base
adenine(A) always pairs with thymine(T); they are complementary
guanine(G) always pairs with cytosine(C); they are complementary
DNA strands are complementary – knowing the base sequence on one
you can predict the sequence on the other
genes – segments of DNA which determine inherited traits and cellular
activities by coding for synthesis of structural and functional proteins
(an average gene is around 3000 nucleotides long)
gene expression – activation of a gene results in production of a protein, which
alters the structure or function of the body in some way
cell differentiation – genes can be turned on or turned off; different cells
look and function differently due to expression of different genes
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2 PROCESSES INVOLVED IN GENE EXPRESSION – transcription & translation
1) Transcription – a DNA template (gene) forms a complementary strand of RNA
RNA (ribonucleic acid) – ribose (5-C sugar) + phosphate + nitrogenous base
4 bases – A, G, C, and uracil(U) instead of T
G is complementary to C
A is complementary to T
U is complementary to A
RNA is single-stranded
DNA transcriptions can form 3 kinds of RNA;
messenger RNA(mRNA) – template for protein synthesis (translation)
ribosomal RNA(rRNA) – forms ribosomes (assemble proteins)
transfer RNA(tRNA) – binds a specific amino acid and carries it to a
specific site during protein synthesis
RNA polymerase – enzyme that catalyzes transcription
unwinds and separates DNA helix
template strand – only one DNA strand is transcribed
RNA bases pair with their complementary DNA bases on template strand
DNA template
C
G
T
A
RNA
G
C
A
U
editing enzymes – cut out regions of the RNA strand and splice together the
remainder to produce the final mRNA template used for translation
2) Translation (protein synthesis)– mRNA template codes for a specific chain of
amino acids
codon – 3 adjacent nucleotides on mRNA
each codon specifies a particular amino acid during translation
ribosome – catalyzes translation
binds molecules involved (mRNA and 2 tRNA carrying amino acids)
orients them properly to react
tRNA – anticodon (3 nucleotides complementary to codon) binds to codon on
mRNA; each tRNA carries only 1 specific amino acid
(20 different amino acids – more than 20 types of tRNA)
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tRNA anticodon binds to mRNA codon and ribosome catalyzes formation of a
peptide bond between the amino acids tRNA is carrying
the ribosome travels down the mRNA forming a polypeptide chain
the polypeptide is modified in ER and Golgi apparatus to form the final protein
CELL DIVISION – division of a somatic (body) cell into 2 identical daughter cells
allows growth and repair of tissues
Cell Cycle – cycle of cell growth, replication, and division (2 main phases)
1) Interphase (rest phase) – phase of growth and replication
G1 (growth) –growth, replication of cytoplasm and organelles
S (synthesis) – DNA replication (forms 2 identical strands of DNA)
DNA helix unwinds and unzips
DNA polymerase – enzyme that catalyzes replication
semi-conservative replication – each strand binds
complimentary bases forming 2 double helixes
(chromatids)with 1 old strand and 1 new strand
G2 (growth) – growth, protein synthesis
2) Mitotic phase (Mitosis) – phase of cell division
4 Stages of Mitosis:
1) Prophase – chromatin coils into visible chromosomes
identical chromatids are paired at centromeres
centrioles form mitotic spindle from microtubules
spindle fibers attach to chromosomes at centromeres
nucleoli and nuclear envelope disappear
2) Metaphase – chromosomes align at central metaphase plate
3) Anaphase – centromeres split & identical chromatids migrate
to opposite poles of cell (now called chromosomes)
4) Telophase – daughter chromosomes uncoil, nuclear envelope
and nucleoli reappear, spindle disappears
Cytokinesis – cytoplasm divides at cleavage furrow
begins in anaphase, completed in telophase
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Cell Homeostasis – proliferation of cells vs cell death
cell destinies
function without dividing (G0) – eg. neurons, skeletal muscle
grow and divide constanly – eg. stem cells of skin
apotosis (programmed cell death)
cancer(neoplasia) – uncontrolled cell growth
Genetic mutation – errors in DNA replication leading to altered gene content of cells
CELL MEMBRANE PHYSIOLOGY
Fluid-Mosaic Model
amphipathic molecules – have charged and uncharged regions
polar end attracted to water – faces ICF or ECF
non-polar end repelled by water – faces interior of membrane
phospholipids – polar head, non-polar tail
cholesterol – weakly amphipathic
membrane proteins – amphipathic proteins
may cross through entire membrane or float surface
self-sealing if punctured
glycocalyx – sugar coat on outer surface formed by glycoproteins and
glycolipids
(involved in cell adhesion and recognition)
Functions of membrane proteins
channels – pores for passage of small solutes or water
carrier proteins – bind solutes and transport them across cell membrane
receptor proteins – bind specific chemical ligands and produce a change in
cell activity
enzymes – catalyze reactions inside or outside cell
recognition proteins – labels on cell surface recognized by immune cells
Selective Permeability – some solutes pass through more easily than others
determined by size of particle, charge, and presence of membrane protein
channels or carriers
permeable – smaller, uncharged (nonpolar covalent) molecules (02, lipids)
impermeable – larger, charged (polar covalent, ions) molecules (glucose,
amino acids, Na+)
special protein channels or carrier proteins (if present) allow permeability
of specific molecules that would otherwise be impermeable
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PERMEABILITY MECHANISMS – how substances cross the cell membrane
Passive Mechanisms – no energy input required
random movement of particles due to kinetic energy
particles move from areas of high concentration to low concentration until
reaching equilibrium (“down” concentration gradient)
Diffusion – solutes move down their concentration gradient
through the lipid bilayer – uncharged particles (O2, lipids)
through protein channels – small, charged particles (ions)
diffusion rate depends on:
concentration gradient – larger gradient = faster
temperature – higher temperature = faster
molecule size – smaller molecule = faster
diffusion distance – shorter distance = faster
electrical gradient – opposite charges attract, like charges
repel
simple diffusion – diffuse directly through lipid bilayer
channel-mediated diffusion – diffusion through protein channels
ion channels – K+, Cl-, Na+, Ca2+
aquaporins – water
“gated”channels – channels that open and close
Facilitated diffusion – solutes move down their concentration gradient
using membrane carrier proteins
proteins bind specific solutes and change shape to carry them
through the membrane
larger, charged particles (amino acids, glucose)
saturation – rate of diffusion is limited by number of carrier
proteins in the cell membrane
Osmosis – net movement of solvent (water) through a selectively
permeable membrane
(membrane must be permeable to water, but not to some solute)
water moves down its concentration gradient – moves from area of
low solute concentration to area of high solute concentration
hydrostatic pressure – increasing volume of water creates pressure
forcing water to move back against its concentration
gradient; equilibrium is reached when water movement due
to hydrostatic pressure equals movement due to osmosis
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osmotic pressure – pressure needed to stop water from moving
down its concentration gradient
depends on the concentration of impermeable solutes
tonicity – measure of a solution’s tendency to change cell volume
due to osmosis
isotonic solution
same solute concentration as cytosol = no osmosis
cell maintains normal size and is happy
hypotonic solution
lower impermeable solute concentration than cytosol
water enters cell; cell swells and may burst (lysis)
hypertonic solution
higher impermeable solute concentration than cytosol
water leaves cell; cell shrinks (crenation)
Active Mechanisms – require energy from ATP
solutes move from low concentration to high concentration (up gradient)
saturation - rate of solute transport is limited by number of carrier proteins
Primary Active Transport –energy from ATP used to change shape of
a carrier protein so solutes can move from low concentration to
high concentration (up concentration gradient)
exhibits saturation
sodium-potassium pump (pumps 3 Na+ out of cell & 2 K+ in)
uses 1 ATP molecule
produces concentration gradient
high sodium in ECF, high potassium in ICF
Secondary Active Transport – energy from a concentration gradient
used to transport solutes up their concentration gradient
Na+ has energy due to its high concentration gradient outside cell
symporter – special carrier protein allows another molecule
to cross in with Na+
antiporter – special carrier protein allows another moleucle
to cross out as Na+ crosses in
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Vesicular Transport – energy from ATP used to pinch off cell membrane
endocytosis – particles moved into the cell in vesicles
receptor-mediated endocytosis
receptors bind specific ligands and bring into cell
(eg. some hormones)
pinocytosis – brings in a droplet of extracellular fluid
phagocytosis – phagocytes (macrophages & neutrophils)
engulf debris or foreign objects (eg. bacteria)
vesicle formed fuses with a lysosome for digestion
exocytosis – particles moved out of cell by fusion of vesicles
with the cell membrane
excretion – release of wastes from cell
secretion – release of products produced by the cell
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