Lecture 3 - Mitosis & Meiosis

Question 1

what state do most developed multicellular cells exist in?

Answer 1

G0 state

Question 2

allows cells to enter the cell cycle:

Answer 2

signals from their environment allows cells to initiate the cell cycle

Question 3

cell division is not carried out correctly, causing daughter cells to not get enough genetic information:

Answer 3

the daughter cells will die

Question 4

prophase:

Answer 4

replicated chromosomes consisting of two closely associated sister chromatids will condense

outside the nucleus the mitotic spindles assemble between the two centrosomes, which have begun to move apart

Question 5

prometaphase:

Answer 5

starts abruptly with the nuclear envelope breakdown, chromosomes can now attach to spindle microtubules via their kinetochores and undergo active movement

Question 6

metaphase:

Answer 6

the chromosomes will be aligned in the equator of the spindle (mid way of the spindle)

the paired kinetochore microtubules on each chromosome attach to opposite poles of the spindle

Question 7

anaphase:

Answer 7

sister chromatids synchronously separate, and each is pulled slowly toward the spindle pole it is attached to

the kinetochore microtubules (ones attached to the chromosome) get shorter, and the spindle poles also move apart - both contributing to chromosomal separation

Question 8

telophase:

Answer 8

two sets of chromosomes arrive at the poles of the spindle

new nuclear envelope reassembles around the two new sets of chromosomes - completing the formation of two nuclei and marking the end of mitosis

cytoplasm division begins with the assembly of the contractile ring

Question 9

cytokinesis:

Answer 9

cytoplasm is divided in two by a contractile ring of actin and myosin filaments which pinches the cell to create two daughters each with their own nucleus

Question 10

how are chromosomes very tightly packed for mitosis?

Answer 10

condensing complexes bind to chromosomes at the beginning of mitosis and folds them into consecutive cis-loops until highly compacted and condensed

Question 11

what do SMC complexes use?

Answer 11

SMC complexes use the power of ATP binding and hydrolysis to manipulate DNA

Question 12

SMC complexes can bring together two different regions of DNA to either form:

Answer 12

a DNA loop or to cohese them together

Question 13

in eukaryotes, in what part of the cell cycle does SMC complex cohesin coheres sister chromatids together?

Answer 13

from S phase to anaphase

Question 14

how does the SMC complex condensing fold chromosomes?

Answer 14

by looping into their mitotic condensed form

Question 15

what inhibits the interaction between the nuclear lamins which coat the inner membrane of the nucleus?

Answer 15

phosphorylation of the nuclear lamins which coat the inner membrane of the nucleus inhibits their interaction with each other

Question 16

what does phosphorylation of the nuclear lamins which coat the inner membrane of the nucleus cause?

Answer 16

this causes a breakup of the nuclear lamina and attached nuclear membrane while mitotic CDK complexes are active

Question 17

what happens when mitotic CDK complexes are inactivated at the end of mitosis?

Answer 17

the nuclear envelope reforms

Question 18

mitotic spindles are designed to:

Answer 18

the mitotic spindle is designed to line up all the duplicated sister-chromatids in the middle of the cell in metaphase, before pulling one copy to opposite ends of the cell before cell division

Question 19

what attaches chromatids to microtubule s?

Answer 19

The microtubules emanating from the spindle pole become attached to a specialized protein structure on chromosomes called the kinetochore where they can become stably attached

Question 20

what do microtubules coming from the mitotic spindle do before they bond to the kinetochores?

Answer 20

grow and shrink across the cells until they make constant with the kinetochore

the contact is then stabilised to an end-on contact

Question 21

chromosome segregation does not take place until:

Answer 21

all kinetochores have two kinetochore –microtubule attachments, one connected to each spindle pole

Question 22

when all chromosomes are bi-orientated in metaphase the kinetochore microtubules…

Answer 22

are actively trying to pull the chromatids to opposite sides of the cell, the chromosome cohesion provided by cohesin prevents this

Question 23

___ promotes the destruction of cycling’s and mitotic exit

Answer 23

APC

Question 24

cytokinesis is different in animals and plants:

Answer 24

plants need to form a new cell wall through the fusion of golgi vesicles during cytokinesis as well as cell membrane

Question 25

meiosis:

Answer 25

meiosis is a specialised reductional form of cell division, a parental diploid cell divides to produce four haploid cells

Meiosis achieves this by undergoing one S (duplication) phase followed by two divisions of the duplicated chromosomes; meiosis I and meiosis II

Question 26

meiosis generates genetic diversity via two ways:

Answer 26

genetic recombination during prophase I & independent assortment during metaphase I

Question 27

producing genetic diversity via crossing over during prophase I:

Answer 27

Double strand breaks are introduced into the chromosomes and these are repaired between homologous chromosomes to produce crossovers, observed as chiasmata (sing. Chiasma).

Resolution of crossover produces recombinant chromosomes composed of parts of both maternal and paternal chromosomes

Question 28

producing genetic diversity through the mixing of chromosomes in metaphase I:

Answer 28

Chromosome pairs are orientated randomly across the centre of the cell in metaphase I. This leads to the random sorting of homologous paternal and maternal chromosomes with other chromosomes. In humans with 23 pairs of chromosomes this results in 223 = 8388608 possible combinations of paternal and maternal chromosomes.

Question 29

errors in meiosis:

Answer 29

Non-disjunction errors during meiosis I or II can lead to both chromatids being segregated into the same gamete which leads to trisomy in the fertilised embryo

Too many or too few chromosomes in a cell is known as aneuploidy. Too few and essential enzymes are not expressed. Too many and some processes don’t work properly leading to cell death or a failure in development.

Question 30

what is the only trisomy that can be handled in the human body?

Answer 30

trisomy of chromosome 21 - which leads to downs-syndrome

Question 31

how do cells initiate the metaphase to anaphase transition?

Answer 31

cells initiate the metaphase to anaphase transition by triggering the cleavage of cohesion by separase