Transcript Chapter 3

Chapter 3
Cell Structure and Genetic Control
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Cell

Basic unit of structure and function of the
body.


Great diversity of function.
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Highly organized molecular factory.
Organ physiology derived from complex functions
of the cell.
3 principal parts:
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
Plasma membrane.
Cytoplasm and organelles.
Nucleus.
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Plasma Membrane
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
Is selectively permeable.
Composition:
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Double layer of phospholipids due to hydrophobic/hydrophilic
parts.
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Proteins span or partially span the membrane.

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Restrict passage of H20 and H20 soluble ions.
Provide structural support, transport molecules, serve as
receptors.
Negatively charged carbohydrates attach to the
outer surface.

Involved with regulatory molecules.
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Plasma Membrane
(continued)
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Cytoplasm, Organelles, Nucleoli
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Cytoplasm:
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Organelles:
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Aqueous content of the cell.
Sub-cellular structures within the cytoplasm.
Nucleus:
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Is a large spheroid body.
Largest of the organelles.
Contains the genetic material (DNA).
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Nucleoli:
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Centers for production of ribosomes.
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Cytoplasm, Organelles, Nucleoli
(continued)
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Bulk Transport

Phagocytosis:
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Phagocytic cells use pseudopods to surround and engulf particles.
Pseudopods join, fuse, and surround ingested particle (food
vacuole).
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Lysosomes digest food vacuole.
Protects from invading organisms.
Removes debris.
Endocytosis:
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Pinocytosis:
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Nonspecific process.
Plasma membrane invaginates, fuses, vesicle containing ECF pinches
off, and vesicle enters cell.
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Bulk Transport

Receptor-mediated endocytosis:
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(continued)
Interaction of molecules in ECF with specific membrane receptor
proteins.
Membrane invaginates, fuses, pinches off and forms vesicle.
Vesicle enters cell.
Exocytosis:
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Process by which cellular products are secreted into extracellular
environment.
Proteins and other molecules to be secreted are packaged in
vesicles by Golgi complex.
Vesicles fuse with plasma membrane and release contents into
extracellular environment.
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Cilia, Flagella, Microvilli
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Cilia:
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Tiny hair-like structures that project from the
surface of the cell.
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Stroke in unison.
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Flagella:
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Respiratory tract, uterine tube.
Simple whip-like structure that propels sperm
through its environment.
Microvilli:
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Numerous folds (finger-like projections) increase
surface area.

Aid absorption.
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Cytoplasm and Cytoskeleton

Cytoplasm:
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Jelly-like matrix within
the cell.
Includes organelles and
cytosol.
Highly organized
structure with
microtubules and
microfilaments that
function as cytoskeleton.
Cytoskeleton:


Actin and myosin
(microfilaments).
Spindle apparatus
(microtubules).
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Lysosomes
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Primary:
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Contain only digestive enzymes.
Secondary:
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Primary lysosome fuses with food vacuole or organelle.
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Residual body:
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Contain undigested wastes.
Autophagy:
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Contain partially digested remnants of other organelles and
organic material.
Process that destroys worn-out organelles, so that they can
be continuously replaced.
Apoptosis (programmed cell death):

Lysosomes release digestive enzymes into the cell.
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Peroxisomes
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Membrane-enclosed organelles.
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Contain specific enzymes that promote
oxidative reactions.
Oxidize molecules and form H202.
Catalase: converts H202
H20 + 02.
Oxidation of toxic molecules by
peroxisomes is an important function of
liver and kidney cells.
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Mitochondria
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Sites for energy
production of all cells; but
mature RBCs.
Contain own DNA, can
reproduce themselves.
Structure:
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Outer membrane: smooth.
Inner membrane: cristae.
Cristae and matrix
compartmentalize
mitochondrion space.

Have different roles in
energy generation.
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Ribosomes
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Protein factories:
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Proteins produced according to genetic information
contained in mRNA.
Located in cytoplasm and on the surface of
endoplasmic reticulum.
rRNA molecules serve as enzymes (ribozymes)
required for protein synthesis.

Contains 2 subunits composed of rRNA and
proteins.
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Endoplasmic Reticulum (ER)
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Granular (rough) ER:
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Bears ribosomes on
surface, in cells active in
protein synthesis.
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Proteins enter cisternae
are modified for
secretion.
Agranular (smooth) ER:
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Provides site for enzyme
reactions in steroid
hormone production and
inactivation.
Storage of Ca2+ in
striated muscle cells.
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Golgi Complex
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Stacks of hollow, flattened
sacks with cisternae.
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One side of sack faces site for
entry of vesicles from ER that
contain cellular products.
Other site faces towards
plasma membrane and
releases vesicles of
chemically modified products.
Modifies proteins, separates
according to destination, and
packages into vesicles.
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Cell Nucleus
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Most cells have single nucleus.
Enclosed by inner and outer membrane
(nuclear envelope).
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Outer membrane is continuous with ER.
Nuclear pore complexes fuse inner and outer
membranes together.
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Selective active transport of proteins and RNA.
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Regulation of gene expression.
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Transport of mRNA out of nucleus to ribosomes.
Nucleoli:
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DNA contains the genes that code for the
production of mRNA.
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Chromatin
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DNA within nucleus combines with protein (histones) to
form chromatin.
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Euchromatin:
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Thread-like material that makes up the chromosomes.
Histone proteins are positively charged and form spools around
which the negatively charged DNA strands wrap.
Active in genetic transcription.
Heterochromatin:

Contains genes that are permanently inactivated.
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Chromatin
(continued)
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RNA Synthesis
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One gene codes for one polypeptide chain.
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Each gene is several thousand nucleotide pairs
long (DNA).
Each gene contains the code for the
production of a particular type of mRNA.
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For the genetic code to be translated into
synthesis of a particular protein, the DNA code is
copied onto a strand of RNA (genetic
transcription).
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Genetic Transcription
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RNA-polymerase breaks weak
hydrogen bonds between paired
bases of DNA.
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Regulatory molecules act as
transcription factors by binding to
promoter region of gene,
activating the gene.
Double stranded DNA separates at
region to be translated.
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One freed strand of DNA serves as
guide.
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Freed bases pair with
complementary RNA nucleotide
bases.
RNA detaches.
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Types of RNA
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4 types of RNA produced within nucleus
by transcription.
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Precursor mRNA pre-mRNA):
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Messenger RNA (mRNA):
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Contains the code for synthesis of specific
proteins.
Transfer RNA (tRNA):
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Altered in nucleus to form mRNA.
Decodes genetic message contained in mRNA.
Ribosomal RNA (rRNA):
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Forms part of the ribosome structure.
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Pre-mRNA
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Contains excess bases
within the
pre-mRNA.
Introns:
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Exons:
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Regions of non-coding
DNA within a gene.
Coding regions.
Introns are removed
and the ends of exons
spliced by snRNPs to
produce mRNA.
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Protein Synthesis
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Each mRNA passes through ribosomes forming
a polyribosome.
Association of mRNA with ribosomes is needed
for genetic translation.
Translation:

Production of specific protein according to code
contained in mRNA base sequence.
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Protein Synthesis
(continued)
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Protein Synthesis

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(continued)
Each mRNA contains hundreds of
nucleotides arranged in sequence
determined by the complementary base
pairing with DNA.
Codon:
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Each 3 bases (triplet) is a code word for a
specific amino acid.
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Protein Synthesis
(continued)
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Transfer RNA
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Translation of the
codons accomplished by
tRNA and enzymes.
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tRNA bends on itself,
making an anticodon (3
nucleotides that are
complementary to codon
of mRNA).
Synthetase enzymes
join specific amino acids
to the ends of tRNA
within a given codon.
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Formation of a Polypeptide
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Anticodons of tRNA binds to mRNA codons.
Each tRNA carries a specific amino acid.
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tRNA bring amino acids close together.
Amino acid detaches from tRNA.
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Enzymatically this amino acid is transferred to the amino
acid on the next tRNA.
Polypeptide chain grows.
Interactions between amino acids cause chain
to twist and fold forming secondary and
tertiary structure.
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Translation of mRNA
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Functions of ER and Golgi
Complex

Proteins to be secreted by the cell are
synthesized by mRNA-ribosome complexes
located on granular ER.
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Proteins enter the cisternae, and are
modified.
Leader sequence of amino acids is attracted
to membranes of ER.
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Once proteins are in cisternae, the leader
sequence is removed.

Enzymatic removal of regions in protein, alter structure.
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Functions of ER and Golgi
Complex
(continued)

Secretory proteins are transported to Golgi complex.
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Further modified, packaged in vesicles, and secreted.
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DNA Replication
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DNA is the only molecule in the body capable of
replication.
DNA helicases break weak hydrogen bonds to produce 2
free strands of DNA.
Bases of each of the freed DNA strands can bind to
complementary bases.
Each copy is composed of one new strand and one strand
from the original DNA molecule.
Preserves the sequence of bases in DNA.
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DNA Replication
(continued)
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DNA
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Law of Complementary Base Pairings:
# of purine bases = # pyrimadine
bases.
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Adenine only pairs with thymine.
Guanine only pairs with cytosine.
DNA polymerases join the nucleotides
together to form a second polynucleotide
chain.
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Cell Cycle
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Interphase (non-dividing cell phases):
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G1:
 Produces mRNA and proteins.
S:
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If cell is going to divide, DNA replicated.
G2:
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Chromosome consists of 2 chromatids joined by
centromere.
Each chromatid contains a complete double-helix DNA
molecule. Each chromatid will become a separate
chromosome once mitotic division completed.
Completes interphase.
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Cyclins
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Cyclins promote different phases of the cell cycle.
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During G1 phase an increase in cyclin D proteins activates
enzymes to move the cell quickly through the G1 phase.
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Oncogenes:
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Overactivity of a gene that codes for cyclin D might cause
uncontrolled cell division (cancer).
Mutated forms of normal genes that contribute to cancer.
Tumor suppressor genes:
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Inhibit cancer development.
Suppressor gene p53 indirectly blocks the ability of cyclins to
stimulate cell division.
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Induces the expression of gene p21, which inactivates the
cyclin-dependent kinases.
Promotes cell differentiation.
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Mitosis (M Phase)
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Prophase:
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Chromosomes become visible distinct structures.
Metaphase:
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Chromosomes line up single file along equator.
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Anaphase:
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Centromeres split apart.
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Action of spindle fibers attached to kinetochore
Spindle fibers shorten, pulling the 2 chromatids in each
chromosome to opposite poles.
Telophase:

Division of cytoplasm, producing 2 daughter cells.
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Mitosis
(continued)
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Mitosis
(continued)
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Role of Centrosome

All animal cells have centrosome, located near nucleus in
non-dividing cell.
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At center are 2 centrioles.
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Each centriole composed of 9 bundles of microtubules.
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Microtubules grow out of pericentriolar material.
Centrosome replicates itself during interphase (if cell is going to
divide).
Identical centrosomes move away from each other during
prophase.
Take up opposite poles by metaphase.

Microtubules from both centrosomes form spindle fibers.

Spindle fibers pull chromosomes to opposite poles during anaphase.
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Telomeres and Cell Division
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Decreased ability of cells to divide is an indicator of
senescence (aging).
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May be related to the loss of DNA sequences at the ends of
chromosomes (regions called telomeres).
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Telomeres serve as caps on the ends of DNA.
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DNA polymerase does not fully copy the DNA at end-regions.
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Prevent enzymes from mistaking the normal ends for broken DNA.
Each time a chromosome replicates it loses 50-100 base pairs in its
telomeres.
Germinal cells can divide indefinitely due to an enzyme
telomerase.

Duplicates telomere DNA.
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Meiosis (Reduction Division)
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Cell division occurring in ovaries and
testes to produce gametes (ova and
sperm cells).
Has 2 divisional sequences:
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First division:
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Homologous chromosomes line up side by side
along equator of cell.
Spindle fibers pull 1 member of the
homologous pair to each pole.

Each of the daughter cells contains 23 different
chromosomes, consisting of 2 chromatids.
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Meiosis (Reduction Division)

(continued)
Second division:
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Each daughter cell divides, with duplicate
chromatids going to each new daughter cell.
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
Testes: produce 4 sperm cells.
Ovaries: produce one mature egg, polar bodies die.
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Cell Death

Pathologically:
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Apoptosis:
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Cells shrink, membranes become bubbled, nuclei
condense.
Capsases (“executioner enzymes”):
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
Cells deprived of blood supply swell, the membrane
ruptures, and the cell bursts (necrosis).
Mitochondria membranes become permeable to proteins
and other products.
Programmed cell death:

Physiological process responsible for remodeling of tissues
during embryonic development and tissue turnover in the
adult.