1. The general mechanisms by which vaccines protect against diseases.
• Vaccines protect against disease by priming the immune system. They
introduce a harmless version of the disease into the body that allows
the immune system to gain “memory” of the invader for the next time
it encounters the disease
• Later, due to priming by the vaccine, the immune system is able to
respond faster and with more intensity with antibodies to the real,
damaging form of the disease
2. Why developing a vaccine against HIV is relatively challenging, compared to
• HIV has a high mutation rate so it changes the markers on its surface
too often to develop an effective vaccine. Each time the markers
change, the vaccine is useless and the immune system can’t recognize
3. Why people are encouraged to get a flu vaccine each year (as opposed to
one time only).
• Every year, the flu virus mutates so the previous year’s vaccine is
rendered useless by the mutation of the virus
Lecture 2 lecture
1. General global distribution of HIV infection
• HIV is felt globally (a pandemic)
• Every inhabited continent has been stricken with HIV.
• In Canada, in the US, and in Europe, HIV is less common
• In Sub-Saharan Africa, Aids and HIV are an incredibly prevalent disease
• Sub-Saharan Africa accounts for about 60% of all people infected with
the disease and 90% of children living with the disease
2. General temporal trends in HIV infection rates
• Over the last 20 years, HIV infection rates have increased but may be
reaching a plateau
• Deaths due to AIDS have been on the decline
3. Factors that explain why no cure or universal vaccine has been developed for
• The virus mutates and changes over time • Our immune defenses are crippled by HIV
4. Reasons why viruses are not considered “alive”.
• Viruses can’t self reproduce, they need a host (obligate parasites)
• No metabolic processes, not made up of cells
• Viruses are not cellular
5. Reasons why anti-viral drug therapies often have serious side effects.
• Viruses need a host cell to reproduce and use host cell mechanisms for
• Severe side effects because viruses are using the host cell almost
every step of the way so there is no way to target the virus without
targeting the host cell
• Anti-viral drugs can kill the virus, but there will be a lot of collateral
damage as well
6. Major steps in life cycle of HIV.
• The glycoproteins on the surface of HIV mediates attachment to the
protein receptors on the host cell and fuses with it
• The viruses injects RNA and reverse transcriptase into the host cell
which splices its genetic code into the host cell’s DNA with the help of
• Transcription of the viral DNA results in the production of RNA which
can serve as the genome for new viruses and can be translated to
produce viral proteins
• Complete HIV particles are assembled and in macrophages, HIV buds
out without rupturing the cell while in T cells, HIV exits by rupturing
and killing the cell
7. Specific role of integrase and reverse transcriptase in retroviral life cycle.
• Integrase splices viral DNA into host DNA
• Reverse transcriptase reverse transcribes the viral RNA into double
stranded viral DNA. It is highly error prone (no proofreading enzymes)
so it causes a lot of mutations
8. Mechanism of action of AZT. • Anti-retroviral therapies inhibit virus-specific enzymes0
• AZT mimics thymidine and inhibits reverse transcriptase
9. Reasons why effectiveness of AZT decreases over time.
• AZT resistance began to emerge as the virus evolved
• In a population of viruses, some will be more resistant to AZT than
• The presence of AZT selects for individuals with resistance so over
time, the population of the viruses becomes primarily populated by
resistant individuals as they reproduce successfully in the presence of
AZT while the other do not
• Evolution and natural selection in action
10.Rationale for multi-drug (drug cocktail) approach to treating viral infections.
• If multiple points of HIV action are targeted, it is much harder for
resistance to evolve
11.Principles of evolution of HIV: variation, heritability, differential reproduction,
change in genotype of population.
• Variation: in a large population of HIV particles, some virions will have
different mutations than others, with mutations occurring at a high
frequency. This creates a large variability in the genotypes of the HIV
• Heritability: mother virions produce daughter virions that are similar so
the mutations in a population are passed on from one generation to
the next (heritability)
• Differential reproduction: selection pressure favours reproduction of some
virions over other
• Change in genotype of population: eventually, the susceptible virions
die off. Only the resistant virions are able to reproduce. The population
thus changes over time
12.Role of CCR5-Δ32 mutation in human resistance to HIV infection.
• Some people will not catch HIV regardless of repeated exposure to HIV
or, if they do, the disease progresses very slowly. These people have a
deletion in one of the alleles that code for proteins on an immune cell
receptor 13.Global distribution of CCR5-Δ32 allele.
• The allele is not spread evenly over the population
• It is uncommon in African countries and more common in Scandinavia
and North Eastern Europe as well as among Ashkenazi Jews
14.Likely explanations of modern distribution of CCR5-Δ32 allele.
• Perhaps this allele was selectively favoured in Northern Europe during
historical epidemics like the plague and smallpox
• Perhaps it’s just chance and history
1. Characteristics shared by all life.
• All life displays order, harnesses and utilizes energy, reproduces,
responds to stimuli, exhibits homeostasis, grows and develops, and
2. In what way properties of life are "emergent".
• The characteristics of life come about, or emerge, from many simpler
interactions that in themselves do not have the properties found at
• Not only is the functional or structural complexity of living systems
more than the sum of the parts, it is fundamentally different
3. Characteristics of the "habitable zone" of a solar system.
• The region of space around a star where the heat from it allows for
surface temperatures to be within a range that allows water to exist in
a liquid state
4. Conditions of a primitive Earth.
• The atmosphere contained an abundance of water vapour as well as
large quantities of hydrogen (H )2 carbon dioxide (CO ), 2mmonia
(NH 3, and methane (CH ). 4
• There was almost a complete absence of oxygen (O ) 2
• According to Oparin and Haldane, the atmosphere was a reducing
atmosphere because of the presence of such molecules (eg. ammonia,
hydrogen, methane) • These molecules contain an abundance of electrons and hydrogen and
would have entered into reactions with one another that would have
yielded larger and more complex organic molecules
• Today, in our oxidizing atmosphere, high levels of oxygen prevent such
molecules from being formed because oxygen would itself accept the
electrons from organic molecules and be reduced to water
• The lack of oxygen also meant there was no ozone layer
• Without the ozone layer, energetic ultraviolet light was able to reach the
lower atmosphere to provide energy needed to drive the formation of key
5. Types of molecules that were, and were not, synthesized by the Millar-Urey
• Urea, amino acids, and lactic, formic, and acetic acids were formed
• When cyanide and formaldehyde were added to the simulated
primitive atmosphere, amino acids, fatty acids, the purine and
pyrimidine components of nucleic acids, sugars such as
glyceraldehyde, ribose, glucose, and fructose, and phospholipids were
• Debate has developed over whether or not Earth’s primitive
atmosphere contained enough methane and ammonia to be
• Polymers were not produced but clay catalysts may have helped
6. Importance of liposomes in evolution of first cells.
• A critical step along the path of life is the formation of a membrane-
• Such a compartment would allow metabolic reactions to take place in
an environment distinctly different than the external surroundings, the
concentration of key molecules could be higher, and greater
complexity could be maintained in a closed space
• A probiont is the term given to a group of abiotically produced organic
molecules that are surrounded by a membranelike structure
• An early type of probiont could have been similar to a liposome (lipid
bilayer cell) • Liposomes are selectively permeable and can swell and contract
depending on the osmotic conditions of their environment
7. Characteristics of mimivirus that suggest it should be considered to be alive.
• It can get sick, it has a large number of coding genes, it is really big
8. Characteristics of virophage.
• A virophage infects a virus that infects another cell and hijacks its
machinery to replicate itself. It is much smaller than its host virus
• The satellite virus can perform horizontal gene transfer between
Lecture 3 lecture
1. Age of the Earth.
• 4.6 billion years ago, Earth formed
2. Age of start of life on Earth.
• Based on geological evidence, 3.6 billion years ago cyanobacteria were
• But they weren’t the first form of life. Maybe 4 billion years ago life
3. Domains of life.
• Bacteria, archaea, eukaryotes. LUCA is common to all forms of life
4. Characteristics of LUCA
• Last Universal Common Ancestor: all life is derived from this single
form of life
• Embodied many key characteristics now seen in all forms of life (see
5. Characteristics shared by all domains of life.
• All use DNA, RNA, and protein (Central Dogma), DNA for genetic
system, DNA to RNA to protein transfer of information, cells made of
lipids, common system of protein assembly, ATP and glucose and
glycolysis for energy
6. Reason why the term “prokaryote” is inappropriate.
• Prokaryotes don’t exist. Archaea and bacteria used to be lumped
together and called prokaryotes but archaea are far more similar to
eukaryotes than bacteria. They share no common ancestor except
LUCA. Nothing in common
• No single group of organisms can be lumped into “prokaryotes” • “Pro” means anteriority, but there is no evidence prokaryotes came
7. Reductive evolution explanation for rise of bacteria and archaea.
• Evolutionary does not always move from simple to complex
• LUCA may have been a proto-eukaryote but by reductive evolution,
bacteria and archaea got rid of the eukaryote attributes
• Streamlined themselves
8. Advantages of evolutionary simplification (streamlining).
• To survive in harsh environments, to reproduce faster, to conserve
9. Relationship between homochirality and life
• Chirality means handedness
• You cannot superimpose one chiral partner on the other
• Two enantomers (optical isomers) have the same groups but differ in
the orders they are attached. Have identical chemical and physical
properties but have vastly different biological properties (thalidomide
can be an antiemetic or a teratogen through chirality)
• Life is homochiral. We only use one form of the chiral pair
• This is essential to the evolution of life (L amino acids, D sugars)
• But Miller-Urey could not explain this because the products were
• The cost to the cell to use both chiral partners would be huge (cell
would have to make two of everything)
• We don’t know where this homochirality came from
10.Reasons why we think RNA was the first of the three molecules of the Central
Dogma to evolve.
• Central Dogma: DNA to RNA to protein. Enzymes are needed to drive
this synthesis and enzymes are proteins. We need the product to
catalyze the intermediary steps
• But RNA could function as an enzyme catalyst (ribozymes) and carry
information so it was likely the first form of information transfer in
• After RNA was formed, protein probably came along, followed last by
11.Force that drives RNA folding.
• RNA is three dimensional and can fold into a very specific shape
• Watson-Cricks base pair interactions hold the molecule in its specific
12.Characteristics of a ribozyme.
• A ribozyme is an RNA molecule that can catalyze a reaction
• It plays a role in precursor tRNA processing, introns excision, mRNA
processing, etc. 13.Mechanism whereby a ribozyme cleaves RNA.
• A ribozyme catalyzes a reaction by forcing the substrate into a
conformation so it strains that substrate into a shape that favours
• The ribozyme cleaves RNA by removing a proton from oxygen which
becomes very reactive and forms a bond with the phosphodiester
group which cleaves it from the RNA
14.Characteristics of amino transferase activity.
• Ribosomes catalyze peptidyl transferase activity (formations of peptide bonds
in the translation process of protein biosynthesis). Ribosomes are 2/3 RNA, 1/3 protein
15.Reasons why a ribosome is considered a ribozyme.
• A ribosome catalyses the formation of protein chains
16.Advantage that protein has over RNA as a catalyst.
• More variability in sequence (20 amino acids vs. 4 base pairs)
• Enzymes have higher rates of catalysis and are more diverse in
structure and function
17.Advantage that DNA has over RNA as a repository for genetic information.
• Thymine replaces uracil because a cytosine to uracil mutation is
common. Now DNA polymerase can see that the uracil is a mutation
(increases the fidelity of the process)
18.Chemical basis for the advantage that DNA has over RNA as a repository for
• DNA is far more stable than RNA because of the difference on the
2prime group on the 5 carbon. RNA has a hydroxyl group, DNA doesn’t.
RNA degrades very quickly because of the hydroxyl group but we can
isolate DNA from millions of years ago
• As well, this change also alters the shape of the molecule just enough
to make it much more likely that two DNA strands will interact to form
the classic double helix
• Complementary strands allow you to rely on the other copy as a back-
1. The approximate times by which the first cells, and the first eukaryotic cells,
• The first organisms may have been single-celled methane producing
bacteria that existed more than 3.5 billion years ago
• The first eukaryotic cells appeared 2.5 to 2.8 Bya
2. The two-kingdom, five-kingdom and three-kingdom (three domain) systems
for classifying living things. • Until about 50 years ago, all organisms were classified into plants or
• Life was then classified into prokaryotes and eukaryotes using cellular
• Then, the five kingdom scheme came into being. Organisms were
divided into five groups: one for prokaryotes, four for eukaryotes
(protists, fungi, plants, and animals)
• About 30 years ago, life was reclassified using molecular evidence into
three kingdoms: Eubacteria, Archaea, and Eukarya
3. Main characteristics distinguishing members of the Eubacteria, Archaea,
Eukarya domains of life.
• Eubacteria includes the major form of bacteria and cyanobacteria
• Archaea are unicells with cell walls made of different molecules than
those found in Eubacteria. Archaea tend to live under harsher
• Eukarya includes some unicellular organisms (slime moulds, ciliates,
etc.) and the three groups of multicellular organisms (fungi, plants, and
• The Archaea have histones, and their genome is far different from
Eubacteria. They are more closely related to Eukarya than Eubacteria
4. Meaning of horizontal gene transfer and why this makes it challenging to
recreate the universal tree of life.
• Horizontal gene transfer is the transfer and incorporation of one
organism’s or species’ DNA into the DNA of a different organism or
• Horizontal gene transfer has occurred between prokaryotes and from
prokaryotes to eukaryotes
• HGT between individuals contrasts dramatically with the vertical
transmission of genes from generation to generation
• HGT obscures phylogenetic relationships when otherwise distantly
related organisms share a gene or sequence obtained through HGT
rather than through common ancestry • As much as one third of the genome of some prokaryotes was acquired
5. Monophyletic vs. polyphyletic groupings of organisms.
• Monophyletic means one origin. It is used for lineages that share a single
• Polyphyletic means many origins. It is used for groups that have more
than one (multiple) independent origins
Lecture 4 lecture
1. Most recent common ancestor (MRCA) for a given group(s), given a
• MRCA of all humans: 3,000 years ago
• MRCAs are the place where the phylogenetic tree branches off the
2. Why the idea that “humans are descended from chimps” is inaccurate.
• Humans did not evolve directly from chimpanzees, we simply share a
common ancestor with chimps. The lineages diverged and one formed
hominids and the other formed chimps and bonobos
• Our MRCA was not a chimp, it was intermediate between a chimp and
3. Order of main branching events in tree of life (dates not testable).
• Rendezvous 1: Chimps and bonobos, 5-6 million years ago
• Rendezvous 2: Gorillas, 7 millions years ago
• Rendezvous 3: Orangutans, MRCA of all great apes
• Rendezvous 4: Gibbons, MRCA of all apes
• Rendezvous 5, 6: Old and New World monkeys
• Rendezvous 7: Tarsiers, 58 million years ago
• Rendezvous 8: Lemurs and lorises, MRCA of all primates
• Rendezvous 9: mass extinction event, end of dinosaurs
• Rendezvous 10: Rodents and rabbits
• Rendezvous 11: Laurasiatheres (evolved in the north in Laurasia)
• Rendezvous 14 and 15: Marsupials and monotremes (MRCA of all
• Rendezvous 16: Reptiles and Rendezvous 17: Amphibians, MRCA of all
• Rendezvous 18 to 22: Lungfish, Coelacanths, Ray-finned fish, Sharks,
Jawless fish. MRCA of all vertebrates, 530 mya
• Rendezvous 26: Protostomes and Rendezvous 34, 35, 36: Fungi,
Amoebozoans, Plants • Rendezvous 38: Archaea, MRCA of all eukaryotes and Rendezvous 39:
4. Cause of global catastrophe associated with mass extinction 65 mya.
• End-Cretaceous mass extinction thought to be caused by a meteor
hitting the Earth and kicking up a giant dust cloud. Changed the
temperature and the availability of light
• Half the species on Earth went extinct. Global catastrophe. End of the
age of the dinosaurs, beginning of the age of the mammals
5. Relative proportion of protostome vs. deuterostome species.
• Deuterostomes are dwarfed in terms of species diversity compared to
• So many more protostomes, because they include insects, mollusks,
6. Information provided by genetic relatedness vs. traditional groupings of organisms
• When we look at their phylogeny and their patterns of descent and
relatedness, birds are actually just a type of reptile. Things like snakes
and lizards are more closely related to birds with a more recent
common ancestor than they do with turtles
• “Fish” can be no more closely related to each other than to us (ex.
Lungfish and Sharks)
7. Distribution of multi-cellularity in tree of life.
• Multi-cellularity has evolved in only three groups: plants, animals, and
• Plants can be unicellular or multicellular. Amoebozoans like slime
moulds can live as a unicellular organism or group to form multicellular
8. Why estimating numbers of species is uncertain.
• There are more species undiscovered than there are discovered
• Most of the species on Earth have not been described
• Many species live in environments that are hard to reach (ocean
depths, lizard lungs)
9. Role of similarities due to common descent (DNA genome) vs. convergence
(eyes) in constructing a phylogenetic tree.
• There are some things that are found in every living creature (DNA,
glycolysis, ATP, etc.)
• We have these traits in common because we descended form a single
• But some similarities reflect shared ancestry while other traits are
similar due to convergence (eyes have evolved multiple times, like
• If evolution were to rerun, would the outcomes be the same? Lecture 5
1. Meaning of "C-value".
• The amount of DNA contained within a haploid nucleus (1n)
2. "Paradox" or "enigma" associated with C values
• The puzzle surrounding the extensive nuclear genome size among
• Genome size does not correlate with organismal complexity (C-value
• The C-value enigma refers to the issue of variation in the amount of
non-coding DNA found within the genomes of different eukaryotes
3. Meaning of haploid (n) and diploid (2n)
• Haploid means the organism has only one of each chromosome, diploid
means the organism has two copies of each chromosome as a pair of
• The number of chromosome sets is called the ploidy of an organism
4. Relationship between C and n as measures of genome size
• In bacteria and archaea, larger genomes tend to reflect increased gene
• Members of the Eukarya domain vary widely in both C, gene number,
• There are no rules relating organism complexity and genome size or
• When DNA is being replicated in mitosis, C doubles, but n does not
5. Proportion of the human genome that codes for protein.
• Most is non-coding, only 2% of the human genome codes for protein
• Introns occupy about 24% of the genome
• The rest of the DNA occupies the space between the genes with more
than 50% having no known function
Lecture 5 lecture 1. Non-nuclear genomes in typical plant and animal cells.
• Animals have mitochondrial DNA, plants have mitochondrial and
2. Trend in C value from prokaryotic vs. eukaryotic cells.
• The amount of DNA is one genome is called C. Genome size is quite
• In general, genome size goes up among eukaryotes compared to
prokaryotes but within a taxonomic group, C-value has a very wide
3. Relationship between C value and organismal complexity
• There seems to be no relationship between C-value and organismal
• This is the C-value enigma
4. Relationship between C value and ploidy
• One C value is distributed over one set of chromosomes
• Two sets of chromosomes (2n) is equal to 2C. The organism is diploid.
Ploidy refers to the number of sets of chromosomes
• In trying to understand genomes, the number of chromosomes is not
5. Distribution of linear vs. circular chromosomes in the various domains of life.
• Linear chromosomes are characteristics of Eukarya
• Archaea and bacteria (prokaryotes) have circular chromosomes
• Mitochondria and chloroplasts also have circular genomes
6. Role of nucleosomes in DNA packaging in chromosomes
• A chromosome is packaged chromatin: DNA plus protein
• The DNA is wound around nucleosomes (made up of histone proteins)
to condense it
7. General trends in costs of DNA sequencing
• The cost of DNA sequencing is dropping quickly • From three million dollars to 10 thousand now
8. Relative distribution of various component of genome sequence ("junk" vs.
• 10% is essential DNA, with about 2% coding for proteins. 10% is intron
• 25% is unknown but more than 50% of DNA is thought to be “junk”
1. Purine and pyrimidine base-pairing in DNA/RNA
• DNA contains four different nucleotides with each containing the five-
carbon sugar deoxyribose, a phosphate group, and either adenine,
guanine, thymine and cytosine
• Two of the bases (adenine and guanine) are purines and the other two
(thymine and cytosine) are pyrimidines
• Purines bond with pyrimidines (A and T, C and G). These relationships
are Chargaff’s rules
• In RNA, thymine is replaced with uracil. The base pairing remains the
same (A with U)
• This is complementary base pairing. The purine and pyrimidine pair is
stabilized by hydrogen bonds and is just the right size to fit between the DNA
2. Outcome of the classic Meselson and Stahl experiment
• Meselson and Stahl tagged the DNA with non-radioactive, heavy nitrogen 15
isotopes (which has one more neutron than normal nitrogen 14) by growing E. coli
in a culture medium containing nitrogen 15. The DNA incorporates the denser
nitrogen into its structure
• Then they transferred the bacteria to a culture containing the nitrogen
14 so all the newly replicated DNA would incorporate it and be tagged
with the lighter nitrogen 14
• Just before the transfer to the nitrogen 14 medium and after each
round of replication following the transfer, they extracted DNA from
• DNA formed one density band when centrifuged after one replication,
two after two replication. The first density band contained equal amounts of N 14 and N ; the second two had an N 14and N 14 band and an
N N band. This matched the predicted results using the semi-
conservative replication model, supporting the hypothesis
3. Direction of movement of DNA polymerase on the template strand
• The deoxyribose sugars are linked by the breaking of phosphate
groups. This means DNA polymerase can only add molecules at the 3 I
end (on the hydroxyl group)
• Each phosphate group is a bridge between the 3 carbon of one sugar
and the 5 carbon of the other sugar
• Because of the anti-parallel nature of DNA, the template strand is read
in the 3 to 5 end. In one replication fork, DNA polymerase moves in
two different directions, always from the 3 end to the 5 end of the
4. Meaning of semi-conservative, semi-discontinuous, leading and lagging
• Semi-conservative replication: both original DNA molecules serve as
template strands and pair with the new strands to form an exact copy
of the original DNA molecules composed of one new and one old strand
• Semi-discontinuous replication: because the two strands of DNA are
anti-parallel, only one strand can be synthesized continuously in the 3
to 5 direction towards the replication fork. The other must be
replicated in short strands called Okazaki fragments away from the
• Leading strand: the new strand of DNA synthesized in the direction of
• Lagging strand: the new strand of DNA synthesized in the direction
5. General action of proteins in Fig. 12.15.
• DNA helicase unwinds the DNA
• Primase synthesizes RNA primers in the 5 to 3 direction (in the
direction of unwinding in the leading strand and in the opposite
direction in the lagging strand)
• Topoisomerase prevents twisting ahead of the replication fork as DNA
unwinds • DNA polymerase III adds DNA nucleotides to the RNA primer (3 to 5) I I
• DNA polymerase I removes the RNA primers and replaces then with
• A break in the backbone remains after DNA polymerase is done, DNA
ligase seals it
Lecture 6 lecture
1. Basic structure of double-stranded DNA
• DNA is a double helix composed of two DNA molecules running
antiparallel (conferring polarity) and stabilized by hydrogen bonds
between the base pairs
• This antiparallel arrangement is highly significant for the process of
• 3 has hydroxyl group, 5 has phosphate
2. Components necessary for DNA synthesis
• DNA synthesis requires a phosphate group to break and supply energy
to the replication process (at the 5 end)I
3. Direction of elongation of a given DNA strand
I I I
• Bases always added on the 3 end to the free 3’OH, 5 to 3
4. Structure of a replication bubble
• Two replication forks stuck together is one replication bubble
• Two forks at one origin, so at one origin, there are two leading strands,
and two lagging strands basically diagonal to each other
• There are multiple origins all across your genome
5. Relationship between replicated DNA and metaphase chromosomes
• Chromatids are identical DNA molecules attached at the centromere
• You have the same number of chromosomes whether they are
replicated or not, replication increases the amount of DNA (C), not the
number of actual chromosomes (n) • DNA replicates in S-phase, in G2, your genome is composed of two
DNA helixes, and in mitosis, the DNA condenses into chromatids and
separates into daughter cells
• Note: most cells are in G1 or G0, not in mitosis. Even if they are
cancerous, even if they are repairing a wound, even actively cycling
cells are mostly in interphase
6. Why chromosomes shorten at each replication
• An RNA primer is removed at the 3 end of the template and cannot be
replacedbecause DNA polymerase can only add new bases on the 3
end and at the 3 end of the template strand, the 5 end of the new
strand is exposed and so cannot be extended
7. Mechanism by which telomerase adds telomeres to chromosomes
• Telomerase extends the ends of the DNA by extending the 3 end through I
an RNA template.
• The DNA added is a telomere (it is a repeated stretch of DNA at the ends
• RNA primer is then added to the new telomere as usual and the 5 end I
extended as usual, from 3 to 5 end. Afterwards the primer is removed
1. Stages and main characteristics of the stages of mitosis.
• Prophase: DNA condenses into sister chromatids, translation and
• Prometaphase: nuclear envelope disappears, microtubules attach to
• Metaphase: chromatids line up at the spindle midpoint/metaphase
• Anaphase: cohesion dissolves and sister chromatids (now called
chromosomes) are pulled by motor proteins in kinetochore along
spindles to opposite poles of the cell
• Telophase: The spindle disassembles, the nuclear membrane
reappears and the chromosomes decondense. Cleavage furrow forms.
End stage of mitosis 2. Stage of cell division, given a micrograph of a dividing cell.
3. Role and mechanism of the mitotic spindle.
• The mitotic spindle does not actually pull the chromatids. Motor
proteins as part of the kinetochore walk their way along the
microtubules attached to the centromere
• The region where sister chromatids are closest to each other is called
• A microtubule attaches at the kinetochore protein complex which is
located at the centromere due to protein attraction. Spindle from opposite poles
have to attach to chromosomal kinetochores for anaphase to proceed
4. Role of cell cycle check points.
• Ensures one stage has completed properly before the cell proceeds to