Lecture 8 Flashcards
What is the name of the complex that marks cyclins for degradation and how is this achieved
The E3-ubiquitin ligase, anaphase promoting complex (APC) marks cyclins for degradation by ubiquitination
Explain the enzymes involved in the regulation of Cdk activity
Wee1 kinases is responsible for the phosphorylation and inactivation of Cdk. Whereas Cdc25 phosphatase removes a phosphate group from the inactive Cdk hence activating it. The interplay between Wee1 kinase and Cdc25 phosphatase determines that activity of Cdks.
Cyclins are a class of protein involved in the regulation of the cell cycle, explain how they interacts with their targets
Cyclins bind to cyclin-dependant kinases (Cdks) to activate them
What is the main difference between meiosis and mitosis
Meiosis resembles mitosis except there are extra steps that segregate homologous chromosomes
How are the cells that arise from gametes that contain an extra chromosome or missing homologue referred to
Aneuploid
Explain how pairing of chromosomes is facilitated in meiotic prophase I
Pairing is facilitated by the synaptonemal complex as well as DNA base pairing between homologues
What is the name of the protein inhibits the activity of the cyclin-cdk complex
p27
During which phase of mitosis do the sister chromatids condense
Prophase
What happens during anaphase
Sister chromatids are separated
Telophase corresponds to cytokinesis, T or F
T
How often to mammalian cells divide on average
Every 24 hours
What are the advantages of using yeast to study the cell cycle
Rapid division rate <1hr, cell cycle control genes almost identical to human, can be grown as haploids or diploids
What is the restriction or start point
A point in the cell cycle after G1 phase that determines the commitment of the cell to S phase and the completion of the rest of the cycle to G1 again
During which stage of mitosis do the chromosomes attach to the mitotic spindle via their kinetochores and the microtubules
Metaphase
What is the purpose of the G2/M checkpoint
Checks to see is all DNA has replicated and if the environment is favourable before assembling the mitotic machinery
What are Cdks and how do they act
Cyclin dependant kinases (Cdks) are kinases that phosphorylate proteins involved in specific stages of the cell cycle
What are the advantages using Xenopus laevis as a biochemical model when looking at the cell cycle
Easy to collects its eggs, rapid division rate, large sized eggs makes protein purification easier and they can be manipulated by injection of RNA or chemicals into the oocytes
What is G0 phase
A quiescent, non-dividing phase
Pairing of homologues before segregation allows for crossing-over via homologous recombination, T or F
T
What are the stage of mitosis
Prophase, prometaphase, metaphase, anaphase and telophase
In meiosis I sister chromatids aren’t separated, what does happen during this stage
Homologous chromosomes pair up and crossing over takes place. These cells will be haploid with each homologue represented by two sister chromatids
What is cell-free mitosis
Technique that allows you to observe mitosis/nuclear division in a test tube outside of the cell membrane. This can be used to study changes i.e. in protein phosphorylation over time after cytoplasmic depletion using antibodies
What is meant by G1 phase and what is going on the cell during this phase
G1 or gap 1 phase is the phase in which most cells are in. The cell is growing and constantly checking its environment. This growth is required to maintain cell size with subsequent divisions.
Levels of Cdk remain constant throughout the cell cycle, T or F
T
What happens during G2 phase of the cell cycle
More growth of the cell and environmental checking. It has a shorter duration than G1 phase
How can the ability of yeast to be haploid or diploid be harnessed to study the cell cycle
If you want to study a gene involved in cell cycle, manipulation will have a very deleterious effect on that organism. If you have carriers of the deleterious gene in diploid state and then switch the yeast to haploid when you want. Thus, diploids can be used to maintain lethal mutations that are then studied as haploids
During DNA duplication, each chromosome pair (maternal and paternal) is duplicated to give rise to sister chromatids, T or F
T
Sex chromosomes don’t cross over, T or F
F – they behave like homologues during sperm formation due to small regions of homology
What are the two purposes of homologous recombination between non-sister chromatids
Aligns the chromosomes ready for anaphase and facilitates formation of the synaptonemal complex as well as allowing for genetic recombination between paternal and maternal DNA on the same chromosome
Mistakes during meiosis I result in gametes with an extra chromosome or lacking a homologue, what is the name given to this event
Nondisjunction
What percentage of mammalian sperm and eggs contain extra chromosomes or missing homologues
4% of sperm, 20% of eggs
What is the purpose of regulating the rate of division in cells and tissue
Enables you to maintain cell numbers in each tissue
What can be said about the genes that control the cell cycle
They are extremely conserved and almost identical across the species
What are the constituent parts of M phase
Nuclear division – mitosis and cytoplasmic division (cytokinesis)
Sister chromatids are then segregated between the two daughter cells, T or F
T
What is the role of the start checkpoint
Checkpoint at the end of G1 that checks to see if the environment is favourable before triggering the DNA replication machinery to replicate the DNA. It ensures that the cells have enough resources to go through the cell cycle to G1 again
How can you use temperature sensitive mutations in yeast to study the cell cycle
You can introduce mutations that only disrupt gene functions at particular temperatures into the yeast. Keeping the yeast at a low permissive temperature maintains gene function but switching to a restrictive (high) temperature enables you to study the genes function
How are Cdks further regulated other than the action of cyclins
Cdks are also regulated by their phosphorylation state. Active Cdk contains 1 phosphorylated serine residue whereas inactive Cdk has 2 phosphorylated serine residues. Unusually phosphorylation is an inhibitory signal in the case of Cds.
Cdks require cyclin to become active, T or F
T
Cyclins are expressed at constant levels during the cell cycle, T or F
F – cyclins are transiently expressed and are synthesised and degraded throughout the cell cycle
What are the two different types of yeast models
Fission yeast and budding yeast
What happens at the metaphase to anaphase transition
Cell checks that all the chromosomes are attached to the mitotic spindle before triggering anaphase and completing cell division
What happens during meiosis II
Chromosomes line up on the metaphase plate and sister chromatids are separated
Give examples of different cyclins and how they act with Cdks at different times in the cell cycle
M-cyclin is high during mitosis and the Cdk-M-cyclin complex leads to phosphorylation of protein involved in the assembly of the mitosis machinery. Whereas S-cyclin is high during S phase and the Cdk-S-cyclin complex phosphorylates proteins involved in the assembly of DNA replication machinery
