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AP Review
• AP Review Part 2:
– Mitosis and Meiosis
– Molecular Genetics
• DNA Structure, DNA Replication, DNA  Protein
– Animal Structure and Function
• Nerve impulse transmission
• Muscle cell contraction
AP Biology Review
• 4. Cell Division
– Cell division has two
phases
• Nuclear division (either
mitosis or meiosis) and
cytokinesis
– Mitosis
» One cell  two
identical diploid
daughter cells
– Meiosis (reduction
division)
» One cell  4 non
identical haploid
cells
AP Biology Review
• Mitosis
– Series of events that divides
up replicated DNA into two
identical (genetically)
daughter cells.
Mitosis in a plant cell
AP Biology Review
• Stages of Mitosis (nuclear division)
–
–
–
–
Prophase
Metaphase
Anaphase
Telophase
Cell at end of
interphase, before
prophase starts.
AP Biology Review
• Prophase (longest phase)
–
–
–
–
–
–
duplicated chromosomes condense to form chromosomes
centrioles (animals only)move to opposite sides (poles) of cell
spindle fibers associate with centromeres on chromosomes
nucleolus and nuclear envelope disappear
mitotic spindle forms
Chromosomes start to move towards equator
Centromere connects
sister chromatids
Asters
AP Biology Review
Prophase
Animal cell
Plant cell
AP Biology Review
• Metaphase
– chromosomes align at equator “metaphase plate”
– microtubules attached to centromeres (at kinetochore) align
chromatids, start to pull apart
AP Biology Review
Metaphase
AP Biology Review
• Anaphase
– centromeres separate
– chromatids get pulled to opposite sides (poles)of cell
with help of spindle fibers
– cell elongates
– shortest phase, lasts a few minutes
– cytokinesis begins; cleavage furrow animals, cell plate
plants
AP Biology Review
Anaphase
AP Biology Review
• Telophase
–
–
–
–
–
–
chromosomes get to centrioles
spindle fibers and asters disappear
chromosomes start to unwind  chromatin
nuclear envelope re-forms
nucleoli re-form
cytokinesis continues
AP Biology Review
Cell Plate
Telophase
AP Biology Review
• Cell Cycle Clock
– Activation of kinases
by cyclins at two
critcal checkpoints
• End of G1 stage  S
stage
• End of G2 stage  M
stage
– Cause cell to continue
cycle
G1 checkpoint
Feedback from the cell determines
whether the cell cycle will proceed to
the S phase, pause, or withdraw into G0
AP Biology Review
AP Biology Review
• Signals to induce cell division
– Surface to volume ratio
– Genome (nuclear material) to volume ratio
AP Biology Review
• Replication Errors
– Some mutations are caused by an
error in DNA replication.
– Mismatched nucleotide happens
about once per 100,000 base
pairs.
– Cell is able to “proofread” DNA
and remove these errors.
– After proofreading, rate of error is
only about 1/billion base pairs.
AP Biology Review
• Meiosis
AP Biology Review
• Mitosis vs Meiosis
Mitosis
Meiosis
Growth and asexual
reproduction
Production of gametes or
spores
Homologous chromosomes not
paired
Homologous chromosomes
paired. Can have crossing over
One cell division
two identical daughter cells
Two cell divisions
four non identical haploid
daughter cells
Maintains chromosome number
Halves chromosome number
Diploid cell (2n) with 4
chromosomes (2 pairs)
Duplicated chromosome #1
from mother pairing with
duplicated chromosome #1
from father
Sister chromatids still attached
Two haploid cells (n)with 2
chromosomes, no pairs
• Meiosis 1
Prophase
mitosis
1-different than
–chromosomes appear, shorten
and thicken
Dyad
–nuclear membrane disappears
–spindles form
–homologous chromosomes
attracted to each other and
move towards equator
synapsis
= coming together
of homologous chromosomes
to form tetrads
crossing
over can occur
–longest phase
Tetrad
Meiosis Review
Animals – end of meiosis have
gametes. Gamete + gamete =
zygote (diploid)
AP Biology Review
• Genetic variability
– Crossing over
– Random alignment of tetrads in metaphase 1
– Random selection of gamete
AP Biology Review
• 5. Molecular Genetics
– DNA structure and replication
– Protein synthesis
AP Biology Review
• The Watson and Crick Model
AP Biology Review
• Replication of DNA
– Old strands acts as
templates.
– Each new DNA
molecule has one old
strand and one new
strand =
semiconseravative
replication.
AP Biology Review
• Replication of DNA
– Unwinding
• Parent DNA molecule
unwinds (breaks at
weak hydrogen bonds)
with the help of an
enzyme called
helicase. Forms
replication fork.
• Single stranded binding
proteins keep single
strands from rejoining
• Topoisomerases keep
strands from getting
knotted
AP Biology Review
Can only add
new
nucleotide
here
• DNA can only be synthesized from the 5’ to 3’ direction.
Reads the template in the 3’ to 5’ direction (as you would
read from 3-5, ie 1,2,3,4,5)).
• Leading strand is made in the 5’ to 3’ direction, from the 3’-5’
template strand of DNA
• Lagging strand is made from 5’-3’ strand, made in Okazaki fragments
AP Biology Review
• Replication of DNA
RNA Primase lays down a short piece
of RNA nucleotides called RNA primer.
DNA polymerase needs this primer to
start DNA replication and to elongate
the forming complementary strand.
3’  5’ template
5’ to 3’ template
DNA ligase binds Okazaki fragments together
after DNA polymerase removes RNA primers.
AP Biology Review
• DNA replication animation with enzymes
– ..\Biology Clipart and sounds\Biology movies and
animations\dna replication animation.dir
AP Biology Review
• Eukaryotic Replication
• Begins at numerous
locations along the strand –
called replication bubbles –
spreads in both directions.
• Replication forks
• Replication of diploid amount
of DNA (in humans that’s
over 6 billion base pairs!) in
eukaryotes takes a few
hours.
AP Biology Review
• DNA  Protein
– Transcription (initiation, elongation,
termination)
– RNA Processing
– Translation
– One gene, one polypeptide hypothesis
AP Biology Review
• From DNA to RNA to
Protein
– Gene = a sequence of
DNA nucleotide bases
that codes for a product
– DNA is in nucleus, protein
is made in cytoplasm,
RNA allows this to
happen.
AP Biology Review
• Types of RNA
– mRNA
• Takes message
from DNA in nucleus
to the ribosomes in
the cytoplasm.
– tRNA
• Transfers amino
acids to the
ribosomes.
– rRNA
• Along with protein,
makes up the
ribosomes.
AP Biology Review
• Transcription – the First Step
– RNA polymerase (of which there are
many
versions)
Many mRNAs can be synthesizing at the
same
time. Increases the
promotor
regionfrom
of DNA
speed at which the protein can be made• –Attaches
vs. justtomaking
protein
(Non transcribed region of gene
the DNA sequence.
upstream from the gene- that does
not code for anything. Has many TA
bonds – called TATA box)
• Starts to unzip the appropriate
section of DNA.
– Synthesizes mRNA from 5’ to 3’ by
attaching complementary bases.
– Stops at terminator (section of DNA
that tells mRNA to terminate
synthesis-different than stop codons
– often AAAAAA) releases mRNA
(now called RNA transcript or premRNA)
AP Biology Review
• mRNA is Processed
– mRNA transcript is modified before
it leaves the nucleus
• Cap is put on 5’ end
– Modified guanine (GTP) that tells
ribosome where to attach
• Poly A tail is put on 3’ end
– 150-200 adenines that help
facilitate mRNA transport out of
nucleus
• Introns cut out (intervening
sections)
• Exons – sections that express a
code for a polypeptide,are spliced
together
• Before modification (removing
introns)it is called heterogenous
nuclear RNA
– End result = mature mRNA exits
nucleus
AP Biology Review
• Translation
– Mature mRNA brings message out into the cytoplasm.
– mRNA code is read to form a specific protein.
– Ribosomes (rRNA + proteins) and tRNA read the mRNA to
synthesize the protein.
AP Biology Review
• tRNA
– Single strand of RNA (about
70-90 base pairs long)that
loops back on itself, forming a
cloverleaf shape.
– 3’ end holds the amino acid
– 5’ end carries the anticodon (3
base sequence that will match
up with complementary bases
on mRNA – called codon).
– At least one tRNA for each of
the 20 amino acids.
– tRNA synthetase assures
correct amino acid binds to the
tRNA.
AP Biology Review
• Ribosome
– Formed off a DNA template in the nucleolus of the nucleus.
– Made of rRNA and protein.
– Two subunits: small and large – leave nucleus separately – join
together for protein synthesis.
– Can be free in cytoplasm or attached to rough ER.
– Together with mRNA, allows protein to be synthesized.
AP Biology Review
• Translation Basics
– Ribosome attaches to mRNA
– at cap end
– tRNA brings appropriate
amino acids to ribosome.
– Amino acids form peptide
bonds between each other.
Polyribosome
– Protein and mRNA released
Several ribosomes can attach to the same
from ribosome.
mRNA at the same time. Once the first
ribosome moves out of the way, a second
one can bind etc.
AP Biology Review
• Translation – 3 phases (same phases as
transcription)
– Initiation
– Elongation
– Termination
AP Biology Review
• Translation - Initiation
– The small ribosomal
subunit binds to the mRNA
near the start codon
(AUG).
– tRNA brings the UAC
anticodon to the mRNA
and binds temporarily.
– Once the first (initiator)
tRNA binds, the large
ribosomal subunit joins the
small one.
The large ribosomal subunit has two binding sites:
– Click for Initiation
P (for peptide) and A (for amino acid). Initial tRNA
animation
binds to the P site and then the next tRNA occupies
the A site.
AP Biology Review
• Translation - Elongation
– tRNA brings next amino acid to A
(for amino acid) site.
– Amino acids bound together with
aid of ribozyme, an enzyme
contained in the large subunit
– As ribosome moves in the 3’
direction, tRNA from P(for
polypeptide) site released, tRNA
from A site transferred to the P
site.Called translocation.
– New tRNA enters the A site.
– Amino acids added one at a time in
this fashion.
– Click for Elongation animation
AP Biology Review
• Translation - Termination
– mRNA reaches a stop codon
(UAA, UAG, UGA).
– Polypeptide cleaved from
tRNA by a release factor.
– tRNA and polypeptide free in
cytoplasm.
– Ribosomal subunits
disassociate.
– Click for Termination
animation
AP Biology Review
Once final protein released,
interactions between the amino acid
give it its secondary and tertiary
structure. The ER and Golgi can make
final modifications.
AP Biology Review
• 6. Animal structure and function
– Nerve impulse propagation
– Muscle contraction
AP Biology Review
• Transmission of a Nerve
Impulse
– Resting potential
• Normally about –65mV (65mV
more negative inside cell than
outside cell
• Conditions that cause this resting
potential:
– More K ions inside than out
– More Na ions outside than in
– Membrane more permeable to K
diffusion than Na diffusion
– Na:K pump moves 2 K ions in
for every 3 Na ions out
– Large negatively charged
anions inside cell can”t fit
through membrane
– Na and K gated membrane
channels are closed
Polarized cell – at rest (-70mv)
AP Biology •Review
– K diffuses out
• Gets pumped back in (2)
– Na diffuses in more slowly
• Gets pumped out (3)
Inside of neuron
AP Biology Review
Transmission of a Nerve Impulse
Resting Potential animation
• ..\Biology Clipart and sounds\Biology movies and
animations\nerve_impulse.swf
AP Biology Review
• Transmission of a
Nerve Impulse
– Action Potential
• If nerve stimulated
enough, the membrane
will depolarize
• Must meet minimum
threshold of polarity
change for this to occur (40mV)
• Once axon reaches
threshold, “all or none”
response
AP Biology Review
• Transmission of a Nerve Impulse
– Events occurring in depolarization
• Threshold reached – action potential begins:
– Gated Na channels open  Na rushes in
– Charge inside cell becomes less negative/more positive (will
eventually reach about +30mV to +40mV)
– Positive charge stimulates more Na channels to open (positive
feedback), more Na comes into cell
– Once reach about +30mV to +40mV inside cell, Na channels
close
– K channels open, K goes out of cell reducing the + charge
inside
– K channels close
– Na:K pump helps regenerate resting potential
AP Biology Review
AP Biology Review
Impulse conduction animation:
..\Biology Clipart and sounds\Biology movies and animations\nerve impulse ion
chanels.swf
AP Biology Review
• Transmission of a Nerve Impulse
– Propagation
• If unmyelinated, action potential at one location stimulates the
one next to it
– About 1m/sec
• If myelinated, depolarizes at next node of Ranvier
– Saltatory conduction
– More than 100m/sec!
• Once impulse has passed a specific point, that point can not
depolarize again right away = refractory period (1-2 millisec)
Saltatory conduction
– Ensuresanimation:
one way impulse transmission
..\Biology Clipart and sounds\Biology movies and animations\nerve impulse
propagation.swf
AP Biology Review
• Transmission of a Nerve
Impulse
– Transmission across a synapse
• Axon bulb lies near another cell’s
dendrites or cell body (or muscle
cell)
• Synapse = space between the pre
and post synaptic neuron
• When impulse reaches axon bulb,
causes Ca channels to open  Ca
comes into cell causing
neurotransmitter vesicles to fuse
with membrane and release their
contents into the synaptic cleft
• Can be excitatory or inhibitory to
the post synaptic neuron
AP Biology Review
AP Biology Review
• Transmission of a Nerve Impulse
– Neurotransmitters
• At least 25 have been identified
• Acetylcholine(Ach) and Norepinephrine (NE)
most common
• Neurotransmitters need to be degraded or taken
back into vesicles quickly
– Acetylcholinesterase
• Many drugs act by interfering with this process
AP Biology Review
• Skeletal Muscle
– Microscopic
Anatomy
• Muscle fiber =
muscle cell
– Fibers made of
myofibrils, which are
made of
myofilaments (actin
and myosin)
» Thick – myosin
» Thin – actin
• Sliding filament
theory
Whole muscle
Several muscle
cells(fibers)
(cells)
AP Biology Review
AP Biology Review
AP Biology Review
• Sliding Filament Theory
– Actin and myosin make
crosslinks
– Muscle shortens as crosslinks
“pull”
– Needs a lot of ATP
AP Biology Review
• Neuromuscular Junction
AP Biology Review
• Neuromuscular Junction