Mitosis and Meiosis

Question 1

What are the stages of the cell cycle?

Answer 1

G phase 1
Synthesis
G phase 2
Mitosis

Question 2

What are the stages of mitosis?

Answer 2

Prophase
Prometaphase
Metaphase
Anaphase
Telophase

Question 3

What happens in prophase?

Answer 3

Replicated chromosomes condense

Mitotic spindle assembles between the two centrosomes which have been replicated and moved apart

Question 4

What happens in Prometaphase?

Answer 4

Starts abruptly with the breakdown of the nuclear envelope

Chromosomes attach to the spindle via the kinetochore

Question 5

What happens in Metaphase?

Answer 5

Chromosomes are aligned in the middle along the equator

The kinetochore microtubules attach sister chromatids to opposite ends of the cell

Question 6

What happens in Anaphase?

Answer 6

Sister chromatids are synchronously separated

They are pulles separate slowly as microtubules get shorter and spindle poles move apart

Question 7

What happens in Telophase?

Answer 7

Chromosomes decondense at the two poles of the spindle

New nuclear envelope reassembles forming two new nuclei

Question 8

What happens in cytokinesis?

Answer 8

The cytoplasm is divided into two by a contractile ring of actin and myosin filamets, creating two new daughter cells

Question 9

What are the two types of yeast cell division?

Answer 9

Fission yeast (Schizosaccharomyces pombe)
Budding yeast (Saccharomyces cerevisiae)

Question 10

What are the advantages of using yeast to study cell division?

Answer 10

Rapid division rate (<1 hour)
Cell cycle genes are highly conserved
Yeast can be grown as haploids or diploids

Question 11

How can you study which genes are essential for survival?

Answer 11

Genetic tricks allow us to identify lethal mutations:
Diploids can be used to maintain lethal mutations that are then studied in haploids
Temperature sensitive mutations allow growth only at a permissive temerature

Question 12

What are the genes called that control cell division?

Answer 12

Cell division cycle genes (cdc genes)

Question 13

What are the advantages of using the Xenopus as a model for the cell cycle?

Answer 13

Easy to collect eggs
Rapid division rate (30 mins)
Large size makes purification of proteins easier
Can be manipulated by injection of RNAs or chemicals into the oocyte

Question 14

What is cell free mitosis?

Answer 14

Gentle centrifugation is used to break open a large batch of frog eggs and separate the cytoplasm from other cell components
Sperm nuclei is added with ATP
The sperm nuclei condense and undergo repeated mitosis

Question 15

How long does a free mitotic spindle last?

Answer 15

40 to 60 minutes

Question 16

Where are there check points in the cell cycle?

Answer 16

G1
G2/M
Metaphase to Anaphase

Question 17

What is checked at the G1 checkpoint?

Answer 17

If enviroment is favourable for the cell to commit to the cell cycle and chromosome duplication

Question 18

What is checked at the G2/M checkpoint?

Answer 18

All DNA is replicated and the enviroment is favourable

Question 19

What is checked at the Metaphase to Anaphase checkpoint?

Answer 19

Checks that all chromosomes are attached to the spindle

Question 20

What are cyclins?

Answer 20

Proteins expressed at different levels in the cell cycle

They bind to and activate cdks

Question 21

What is the role of cdks?

Answer 21

They phosphorylate many proteins that are specific to a certain stage in the cell cycle

Question 22

What are the three classes of cyclins which bind to cdks in eukaryotes?

Answer 22

G1/S cyclins
S cyclins
M cyclins

Question 23

What is the role of G1/S cyclins?

Answer 23

Activate cdks in late G1 so help trigger progression through START = cell cycle commitment

Question 24

What is the role of S cyclins?

Answer 24

Binds to cdks after start and help stimulate chromosome duplication - levels are elavated until mitosis

Question 25

What is the role of M cyclins?

Answer 25

Activate cdks that stimulate entry into G2/M checkpoint

Mechansisms destroy them later on

Question 26

What can activate cdk-cyclin complex and how?

Answer 26

Wee1kinase

It phosphorylates the active sites

Question 27

Which enzyme inhibits the cdk-cyclin complex?

Answer 27

Cdc25 phosphatase

Question 28

What is APC?

Answer 28

Anaphase promoting complex - ubiquitin ligase

With E1 and E2 it transfers ubiquitin on to M cyclin for its degredation

Question 29

When is APC activated?

Answer 29

In mitosis by association with Cdc20

Question 30

What happens in meiosis 1?

Answer 30

Crossing -over and segregation

Question 31

What happens in meiotic prophase 1?

Answer 31

Homologues pair up

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

Question 32

What is the purpose of homologous recombination between two non sister chromatids?

Answer 32

It aligns the chromosomes up ready for anaphase and facilitates formation of the synaptomenal complex
It allows for genetic recombination between paternal and maternal DNA on the same chromosomes

Question 33

What percentage of mammalian eggs and sperm are aneuploid?

Answer 33

20%

4%

Question 34

What is meant by aneuploid?

Answer 34

Cell with an extra chromosome

Question 35

List four ways proliferation can be detected

Answer 35

1) DAPI is a dye that shows all nuclei
2) BrDU is a thymidine analogue which can detect fluorescent antibodies
3) Pulse treatment can tell you which cells were in S phases during the treatment
4) DNA dyes can be used to sort cells in suspension based upon the fluorescence