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Biology 231
Human Anatomy and Physiology
Chapter 3 Lecture Outline
Cell – basic structural and functional unit of life; undergoes basic life processes;
maintains homeostasis
Cytology – study of cell structure (anatomy); special structures compartmentalize
chemical reactions
3 BASIC CELLULAR COMPONENTS – membrane, cytoplasm, nucleus
1) Cell membrane – lipid bilayer composed of phospholipids, cholesterol,
glycolipids and containing membrane proteins; flexible yet sturdy barrier
enclosing cell contents
functions in maintaining internal environment and communicating with
external environment
2) Cytoplasm – everything between cell membrane and nucleus
cytosol – intracellular fluid; mostly water; contains solutes, suspended
particles, and inclusions
content regulated by cell membrane
organelles (little organs) – have characteristic shapes and functions;
many are membrane bound and contain enzymes for specific
reactions; numbers vary depending on cell type and function
Cytoskeleton – network of protein filaments; act as structural
framework and aid in cellular movements
microfilaments – thinnest filaments
found peripherally, anchored to cell membrane
support microvilli, aid in movement during cell
division, migration, muscle contraction
intermediate filaments – several different proteins
strong internal framework
microtubules – thick hollow tubes
move organelles, chromosomes, cilia, flagella
centrioles – pair of microtubule structures at 90
degrees to each other
direct formation of mitotic spindle
cilia – hair-like projections; sweep fluid on cell
surface; move cell or debris
flagella – similar to cilia but single and long; move
entire cell (sperm)
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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
rough ER – covered with ribosomes; processes and packs
proteins for transport
smooth ER – synthesizes membrane lipids, triglycerides,
steroids, glycogen; detoxifies drugs; stores calcium
ions
Golgi Apparatus – 3-20 flattened sacs (cisternae)
contains enzymes to modify products of ER
packages modified products into vesicles
secretory vesicles – contents released outside cell
membrane vesicles – fuse with cell membrane
lysosomes – remain in cytoplasm
Lysosomes – vesicles containing digestive enzymes
digest old organelles (autophagy)
digest bacteria and foreign debris
autolysis – destroy own cell if enzymes are released
involved in programmed cell death
Peroxisomes – vesicles containing oxidases (oxidizing enzymes)
break down amino acids and fatty acids
hydrogen peroxide - toxic by-product of oxidation
catalase – enzyme that breaks down hydrogen peroxide
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 aerobic respiration
matrix – central fluid-filled cavity
mitochondria self-replicate during increased energy
demand or cell division
have own DNA and ribosomes
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3) Nucleus – usually most prominent cell structure; contains cell’s genetic
material (DNA)
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 in cells that are not dividing
chromosome – visible, tightly-coiled DNA molecules (seen only during
cell division)
chromatids – 2 identical strands 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 – pentose sugar(deoxyribose) + phosphate + nitrogenous 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 of one
strand, you can predict the sequence of the other
genes – segments of DNA which determine inherited traits and control cellular
activities by coding for synthesis of structural and functional proteins
gene expression – activation of a gene results in production of a protein, which
alters the structure or function of the body in some way
2 PROCESSES INVOLVED IN GENE EXPRESSION – transcription & translation
1) Transcription – DNA template forms a complementary strand of RNA
RNA (ribonucleic acid) – pentose(ribose) + phosphate + nitrogenous base
contains 4 bases – A, G, C, and uracil(U) (instead of T seen in DNA)
U is complementary to A
G is complementary to C
RNA is single-stranded
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DNA transcriptions can form 3 kinds of RNA;
messenger RNA(mRNA) – template for protein synthesis
ribosomal RNA(rRNA) – forms ribosomes (assemble proteins)
transfer RNA(tRNA) – binds specific amino acid and carries it to a
specific site during protein synthesis
RNA polymerase – enzyme that catalyzes transcription; DNA strands must
unwind and separate for RNA polymerase to bind
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
2) Translation – mRNA codes for a specific sequence of amino acids to form a
protein (protein synthesis)
ribosome – binds molecules involved (mRNA and tRNAs) and catalyzes the
reaction
codons (nucleotide sequences on mRNA) code for binding of
anticodons (complementary nucleotide sequences on tRNA)
each tRNA carries only 1 specific amino acid
(20 different amino acids – more than 20 types of tRNA)
ribosome catalyzes formation of a peptide bonds between amino acids
polypeptide formed is modified in ER and Golgi apparatus to form final protein
CELL DIVISION – division of a parent cell into 2 identical daughter cells
occurs in somatic (body) cells for growth and repair
Cell Cycle – cycle of cell growth, replication, and division (2 main phases)
1) Interphase – phase of growth and replication
G1 (growth) –growth, duplication of cytoplasm
S (synthesis) – DNA replication
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
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2) Mitotic phase (Mitosis) – phase of nuclear division
4 Stages of Mitosis:
1) Prophase – chromatin coils into visible chromosomes
centrioles form mitotic spindle from microtubules
spindle fibers attach to chromosomes at centromeres
nucleoli and nuclear envelope disappear
2) Metaphase – centromeres align at central metaphase plate
3) Anaphase – centromeres split & identical chromatids migrate
to opposite poles of cell
4) Telophase – daughter chromosomes uncoil, nuclear envelope
and nucleoli reappear, spindle disappears
Cytokinesis – cytoplasm divides at cleavage furrow
begins during anaphase, completed during telophase
Cell Homeostasis – proliferation of cells vs cell death
cell destinies
function without dividing – eg. neurons, skeletal muscle
grow and divide – eg. stem cells of skin
apotosis (programmed cell death)
aging – many cells stop dividing
cancer – uncontrolled cell growth
CELL MEMBRANE PERMEABILITY
Fluid-Mosaic Model
amphipathic molecules – have polar and non-polar parts
polar end attracted to water – faces ICF or ECF
non-polar end repelled by water – faces interior of membrane
phospholipids
cholesterol
membrane proteins
glycocalyx – sugar coat on outer surface formed by glycoproteins and
glycolipids
Selective Permeability – some solutes pass through lipid membrane, others don't
permeable – non-polar (uncharged) molecules will pass (02, CO2, lipids)
impermeable – ions or polar (charged) molecules (eg. water)
permeability also depends on presence of membrane proteins
Functions of membrane proteins
channels – pores for passage of small solutes or water
carrier proteins – bind large solutes and transport them across membrane
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MECHANISMS OF TRANSPORT – how substances cross the cell membrane
Passive Transport – no energy input required
diffusion – 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 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 – permeable solutes diffuse directly through lipid bilayer
channel-mediated diffusion – impermeable solutes diffuse through protein
channels
facilitated diffusion – solutes too large for channels bind to carrier proteins
carriers change shape to carry them through
saturation – rate of transport depends on number of carrier proteins
Active Transport – requires energy input
can move solutes from low concentration to high concentration
exhibits saturation
primary active transport – directly uses energy from ATP
sodium-potassium pumps – membrane carrier proteins that use
energy from ATP to pump Na+ out of cells and K+ into cells
produces a concentration gradient
high sodium in ECF, high potassium in ICF
secondary active transport – energy from Na+ concentration gradient
used to transport other solutes up their concentration gradient
symporter – a solute crosses in with Na+
antiporter – a solute crosses out as Na+ crosses in
vesicular transport – energy from ATP used to move solutes in or out of
cell in membrane-bound vesicles
endocytosis – particles moved into cell in vesicles
phagocytosis – specialized cells (phagocytes) engulf extracellular materials and bring them into cell to be digested
exocytosis – particles moved out of cell in vesicles
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Osmosis – net movement of solvent (water) through a selectively permeable membrane
(membrane must be permeable to water, but not to some solute particles)
water moves down its concentration gradient (passive transport)
(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
tonicity – measure of a solution’s tendency to change cell volume due to osmosis
isotonic solution – same impermeable solute concentration as cytosol
no osmosis occurs; 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)
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