L2 Mitosis Flashcards
How does DNA normally exist in cells
decondensed, spread out
What are the two forms of decondensed DNA
heterochromatin and euchromatin
What is a chromosome
linear DNA molecule
What is the centromere
region where the spindle attaches
What are homologous chromosomes
same genes arranged in same order
How are homologous chromosomes inherited
one from mother, one from father
What are chromatids
newly copied DNA strands joined to each other by a centromere
What is pulled apart
chromatids
Describe prophase
condensation of sister chromatids
Describe metaphase
attachment of mitotic spindle to kinetochore by microtubules
Describe anaphase
separation of sister chromatids to opposite poles
Describe telophase
nuclear envelope reassembly, start of cytokinesis
Why is prophase important
gets chromosomes into the right form for mitosis
During what phase can chromosomes get tangled
anaphase
What checks chromosome tangling
decatenation check point
What can chromosome tangling lead to
aneuploidy and chromosome rearrangements in daughter cells
What is a genetic model for the cell cycle
yeast
What are the advantages of yeast as a genetic model
rapid division, cell cycle control genes highly conserved, haploid or diploid
What is a use of haploid and diploid yeast
diploids are used to maintain lethal mutations - then studied in haploids
Why is yeast more flexible than mammalian cells
temperature sensitive mutations - allows growth at permissive temperature
What is used as a biochemical model for the cell cycle
xenopus
What are the advantages of xenopus as a biochemical model
easy to collect eggs, large size, rapid division, manipulated by injection
What complex is degraded quickly part way through M phase
Cyclin B complex
What drives the cell through M phase
M-Cdk
What must M-Cdk trigger
mitotic spindle assembly, chromosome condensation, breakdown of nuclear envelope
What is the effect of the inhibitory phosphate on the M-Cdk complex
keeps the protein complex inactive
What removes the inhibitory phosphate from the M-Cdk complex
phosphatase Cdc25
What activates phosphatase Cdc25
S-Cdk complexes
What is the effect of removing the inhibitory phosphate from M-Cdk complex
activates the M-Cdk
What is the effect of an active M-Cdk complex
positive feedback - build up of active M-Cdk complexes
What is the effect of active M-Cdk complexes
rapid activation of mitosis
What does APC stand for
anaphase promoting complex
What is progression through metaphase/anaphase transition driven by
protein destruction
What is loss of heterozygosity
cross chromosomal event that results in loss of the entire gene
Name the three ways that loss of heterozygosity can be induced
non-disjunction, mitotic recombination, gene conversion
Describe non-disjunction
wrong number of chromosomes
What can cause non-disjunction
lagging chromosomes
When can non-disjunction occur
anaphase
What is central to separation of chromosomes
spindle
What is the function of kinetochore microtubules
attach to chromosomes at the kinetochore
What is the function of astral microtubules
position the spindle
How does the cell detect incorrectly lined up kinetochores
low tension
True or false - properly lined up kinetochores are unstable
false - stable - therefore higher tension
What is the function of separase
destroy bridges between chromatids
What is a problem if a cell is hemizygous
if the allele is mutant there is no normal copy of the gene
What are the downstream consequences of no normal gene copy
no active proteins are made
Describe mitotic recombination
DNA swaps between chromatin arms
What can some mitotic recombinations cause
two mutant alleles on one set of chromatids
What enzyme causes gene conversion
DNA polymerase
Describe gene conversion
DNA polymerase jumps between 2 DNA molecules, replicates another allele
