1.3 - Mitosis and Meiosis

Question 1

state of most cells in developed multicellular organisms

Answer 1

G0

Question 2

prophase (2)

Answer 2

1. replicated chromosomes condense
2. outside nucleus, mitotic spindle assembled between the 2 centrosomes which have begun to move apart

Question 3

prometaphase (2)

Answer 3

1. breakdown of nuclear envelope
2. chromosomes can attach o spindle microtubules via kinetochore and undergo active movement

Question 4

metaphase (2)

Answer 4

1. chromosomes aligned at equator of spindle midway between spindle poles
2. paired kinetochore microtubules on each chromosome attach to opposite poles of spindle

Question 5

anaphase (2)

Answer 5

1. sister chromatids synchronously seperate and each pulled towards spindle pole
2. kinetochore microtubules get shorter and spindle poles move apart
   (both contribute to chromosome segregation)

Question 6

telophase (3)

Answer 6

1. Chromosomes arrive at poles of the spindle and start to decondense
2. nuclear envelope reassembles following loss of mitotic cyclins
3. M-CDK signal absent so molecular signals that establish mitotic state lost, leading to reversion to G1 status
   (marks end of mitosis)

Question 7

cytokenesis

Answer 7

cytoplasm divided by contractile ring of actin and myosin filaments which pinches cell creating 2 daughter cells each with 1 nucleus

Question 8

condensin (2)

Answer 8

1. condensin complexes bind to chromosomes at beginning of mitosis, fold them into consecutive cis-loops until highly compacted and condensed
2. activity upregulated by mitotic CDK kinase

Question 9

SMC complexes

Answer 9

use the power of ATP binding and hydrolyses and manipulate DNA

Question 10

SMC complex action

Answer 10

Can bring together 2 different regions of DNA to either form DNA loop or cohese them together

Question 11

SMC complex cohesin and condensin in eukaryotes (2)

Answer 11

1. SMC complex cohesin cohese sister chromatids together from S phase to anaphase
2. SMC complex condensin folds chromosomes by looping into their mitotic condensed form

Question 12

breakdown of nuclear envelope (2)

Answer 12

1. phosphorylation of nuclear lamins which coat inner membrane of nucleus inhibits interaction with each other
2. causes breakup of nuclear lamina and attached nuclear membrane while mitotic CDK complexes are active

Question 13

when does nuclear envelope reform

Answer 13

when mitotic CDK complexes are inactivated ay the end of mitosis

Question 14

what is the mitotic spindle composed of?

Answer 14

microtubules that originate from one of 2 spindle poles at opposite ends of mitotic cell

Question 15

where do microtubules from spindle pole attach to chromosomes

Answer 15

specialised protein structure (kinetochore)

Question 16

SMC cohesin complex

Answer 16

enforces sister chromatid cohesion around the kinetochore to keep sister chromatids cohesed until anaphase

Question 17

how do microtubules find kinetochore?

Answer 17

microtubules from spindle pole grow and shrink across cell until they make contact with kinetochore

Question 18

when does chromosome segregation take place (kinetochores)

Answer 18

when all kinetochores have 2 kinetochore-microtubule attachments (one connected to each spindle pole)

Question 19

what monitors connection of kinetochores to microtubules?

Answer 19

spindle checkpoint

Question 20

metaphase to anaphase transition (2)

Answer 20

1. when all chromosomes bi-oriented in metaphase, kinetochore microtubules are actively trying to pull chromatids to opposite sides of cell
2. chromosome cohesion provided by cohesin prevents this

Question 21

what does APC promote?

Answer 21

destruction of cyclins allowing telophase to start (and mitotic exit)

Question 22

cytokineses in plants

Answer 22

plants form new cell wall through fusion of golgi vesicles during cytokineses as well as cell membrane

Question 23

difference in chromosome condensation in meiosis

Answer 23

chromosomes condense as during mitosis but homologous pairs also synapse (for crossing over)

Question 24

difference in metaphase 1 in meiosis

Answer 24

synapsed homologous pairs of chromosomes line up at metaphase plate

Question 25

producing genetic diversity in meiosis: crossing over during prophase 1 (2)

Answer 25

1. homologous chromosomes become synapsed with corresponding genes initially lined up along their entire length 2. double strand breaks introduced into chromosomes, repaired between homologous chromosomes to produce crossovers (observed as chiasmata) producing recombinant chromosomes

Question 26

sister chromatids

Answer 26

two identical copies of a single chromosome formed during DNA replication

Question 27

homologous chromosomes

Answer 27

pair of chromosomes (one from the mother and one from the father) that have the same genes at the same loci but may carry different alleles

Question 28

producing genetic diversity in meiosis: mixing of chromosomes in metaphase 1 (2)

Answer 28

1. chromosome pairs randomly oriented across centre of cell 2. leads to random sorting of homologous paternal/maternal chromosomes with other chromosomes

Question 29

what can non-disjunction errors errors during meiosis 1/2 lead to?

Answer 29

both chromatids being segregates into the same gamete -> leads to trisomy in fertilised embryo

Question 30

aneuploidy

Answer 30

too many or too few chromosomes in a cell