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BMS238 Molecular and Cell Biology > Lecture 8 > Flashcards

Lecture 8 Flashcards

1
Q

What is the name of the complex that marks cyclins for degradation and how is this achieved

A

The E3-ubiquitin ligase, anaphase promoting complex (APC) marks cyclins for degradation by ubiquitination

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2
Q

Explain the enzymes involved in the regulation of Cdk activity

A

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.

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3
Q

Cyclins are a class of protein involved in the regulation of the cell cycle, explain how they interacts with their targets

A

Cyclins bind to cyclin-dependant kinases (Cdks) to activate them

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4
Q

What is the main difference between meiosis and mitosis

A

Meiosis resembles mitosis except there are extra steps that segregate homologous chromosomes

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5
Q

How are the cells that arise from gametes that contain an extra chromosome or missing homologue referred to

A

Aneuploid

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6
Q

Explain how pairing of chromosomes is facilitated in meiotic prophase I

A

Pairing is facilitated by the synaptonemal complex as well as DNA base pairing between homologues

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7
Q

What is the name of the protein inhibits the activity of the cyclin-cdk complex

A

p27

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8
Q

During which phase of mitosis do the sister chromatids condense

A

Prophase

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9
Q

What happens during anaphase

A

Sister chromatids are separated

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10
Q

Telophase corresponds to cytokinesis, T or F

A

T

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11
Q

How often to mammalian cells divide on average

A

Every 24 hours

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12
Q

What are the advantages of using yeast to study the cell cycle

A

Rapid division rate <1hr, cell cycle control genes almost identical to human, can be grown as haploids or diploids

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13
Q

What is the restriction or start point

A

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

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14
Q

During which stage of mitosis do the chromosomes attach to the mitotic spindle via their kinetochores and the microtubules

A

Metaphase

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15
Q

What is the purpose of the G2/M checkpoint

A

Checks to see is all DNA has replicated and if the environment is favourable before assembling the mitotic machinery

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16
Q

What are Cdks and how do they act

A

Cyclin dependant kinases (Cdks) are kinases that phosphorylate proteins involved in specific stages of the cell cycle

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17
Q

What are the advantages using Xenopus laevis as a biochemical model when looking at the cell cycle

A

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

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18
Q

What is G0 phase

A

A quiescent, non-dividing phase

19
Q

Pairing of homologues before segregation allows for crossing-over via homologous recombination, T or F

A

T

20
Q

What are the stage of mitosis

A

Prophase, prometaphase, metaphase, anaphase and telophase

21
Q

In meiosis I sister chromatids aren’t separated, what does happen during this stage

A

Homologous chromosomes pair up and crossing over takes place. These cells will be haploid with each homologue represented by two sister chromatids

22
Q

What is cell-free mitosis

A

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

23
Q

What is meant by G­1 phase and what is going on the cell during this phase

A

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.

24
Q

Levels of Cdk remain constant throughout the cell cycle, T or F

A

T

25
Q

What happens during G2 phase of the cell cycle

A

More growth of the cell and environmental checking. It has a shorter duration than G1 phase

26
Q

How can the ability of yeast to be haploid or diploid be harnessed to study the cell cycle

A

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

27
Q

During DNA duplication, each chromosome pair (maternal and paternal) is duplicated to give rise to sister chromatids, T or F

A

T

28
Q

Sex chromosomes don’t cross over, T or F

A

F – they behave like homologues during sperm formation due to small regions of homology

29
Q

What are the two purposes of homologous recombination between non-sister chromatids

A

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

30
Q

Mistakes during meiosis I result in gametes with an extra chromosome or lacking a homologue, what is the name given to this event

A

Nondisjunction

31
Q

What percentage of mammalian sperm and eggs contain extra chromosomes or missing homologues

A

4% of sperm, 20% of eggs

32
Q

What is the purpose of regulating the rate of division in cells and tissue

A

Enables you to maintain cell numbers in each tissue

33
Q

What can be said about the genes that control the cell cycle

A

They are extremely conserved and almost identical across the species

34
Q

What are the constituent parts of M phase

A

Nuclear division – mitosis and cytoplasmic division (cytokinesis)

35
Q

Sister chromatids are then segregated between the two daughter cells, T or F

A

T

36
Q

What is the role of the start checkpoint

A

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

37
Q

How can you use temperature sensitive mutations in yeast to study the cell cycle

A

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

38
Q

How are Cdks further regulated other than the action of cyclins

A

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.

39
Q

Cdks require cyclin to become active, T or F

A

T

40
Q

Cyclins are expressed at constant levels during the cell cycle, T or F

A

F – cyclins are transiently expressed and are synthesised and degraded throughout the cell cycle

41
Q

What are the two different types of yeast models

A

Fission yeast and budding yeast

42
Q

What happens at the metaphase to anaphase transition

A

Cell checks that all the chromosomes are attached to the mitotic spindle before triggering anaphase and completing cell division

43
Q

What happens during meiosis II

A

Chromosomes line up on the metaphase plate and sister chromatids are separated

44
Q

Give examples of different cyclins and how they act with Cdks at different times in the cell cycle

A

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

BMS238 Molecular and Cell Biology (31 decks)

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