Mitosis and cytokinesis

Question 1

What is chromosome condensation?

Answer 1

Chromosome condensation is the dramatic reorganisation of the long thin chromatin strands into compact short chromosomes that occurs in mitosis and meiosis.

Question 2

What is reorganised and broken down during chromosome condensation?

Answer 2

• Nuclear envelope break down.
• Endoplasmic reticulum and Golgi apparatus reorganise.
• Cell-cell and cell-matrix adhesion altered.

Question 3

What happens when a cytoskeleton is reorganised?

Answer 3

Cytoskeleton reorganised:
- Microtubule instability is 20 x greater
-Phosphorylation of MAPs enhances dynamic instability
-Catastrophins also enhance destabilisation of mts

Question 4

What are the different protein families (9 things)?

Answer 4

1) Enzymes - catalyses reactions (e.g. DNA polymerase)
2) Structural - outside cells (e.g. collagen); inside cells (e.g. tubulin)
3) Transport - haemoglobin, ion channels (e.g. calcium pump)
4) Motor - myosin in muscle
5) Storage - ferritin binds iron (found in liver)
6) Signalling - hormones (e.g. insulin)
7) receptors - rhodopsin in the retina detects light
8) Gene regulatory protein (e.g. Homeodomain protein acts in genetic switch)
9) Other (highly specialised) - green fluorescent protein in jellyfish

Question 5

In the cytoskeleton what 3 tissues uses interacting filaments to accomplish movements?

Answer 5

• 3 major cytoskeletal ‘elements’ commonly found in eukaryotic cells
  – actin filaments
  – microtubules
  – intermediate filaments

Question 6

Where is intermediate filaments found?

Answer 6

intermediate found between thick (myosin) and thin (actin) filaments

Question 7

What are microtubules polymers of?

Answer 7

Microtubules are polymers of tubulin

Question 8

What is microtubules approx diameter?

Answer 8

Microtubules are approximately 28 nm in diameter

Question 9

What are microtubules composed of and what is the sub-unit for microtubule?

Answer 9

• Composed of globular a and b tubulin (54 kDa)
• The sub-unit for microtubule assembly (the protomer) is a heterodimer of one molecule of a and b tubulin

Question 10

What does microtubes show?

Answer 10

Can show dynamic instability (growing and shrinking rapidly)

Question 11

What are microtubules integral in?

Answer 11

Microtubules are integral in separating sister chromatids during mitosis

Question 12

What are the 2 motor proteins involved with microtubles?

Answer 12

Acts as structures for cargoes to be transported on (by other proteins - kinesin and dynein)

Question 13

Where are g-tubulin found?

Answer 13

g-tubulin is found at the centrosome and can act as a site of ‘nucleation’for microtubule assembly

Question 14

What are the motor proteins for microtubles?

Answer 14

Acts as structures for cargoes to be transported on (by other proteins - kinesin and dynein)

Question 15

What is the microtubule’s role?

Answer 15

The microtubule network is recognized for its role in regulating cell growth and movement as well as key signalling events, which modulate fundamental cellular processes.

Question 16

What does the dynamic instability of microtubules allow for?

Answer 16

Dynamic instability of microtubules: allows the cell to rapidly reorganise the cytoskeleton when necessary

Question 17

In the cytoskeleton how does the organelles move?

Answer 17

Organelle movement: involving microtubules and actin filaments. Can move about cell with the help of the cytoskeleton

Question 18

What diseases coincides with the cytoskeleton?

Answer 18

Lamin mutation and Emery-Dreyfuss muscular dystrophy.

Question 19

What are the 6 stages of mitosis?

Answer 19

1) Interphase
2) Prometaphase
3) Metaphase
4) Anaphase
5) Telophase
6) Cytokinesis
Daughter cells physically separate

Question 20

What happens during the interphase stage of mitosis?

Answer 20

During interphase the cell increase in size. The DNA of the chromosome is replicated and the centrosome is duplicated.

Question 21

What happens during the prophase stage of mitosis?

Answer 21

At prophase, replicated chromosomes each consisting of 2 closely associated sister chromatids, condense. Outside the nucleus, the mitotic spindle assembles between the 2 centrosomes, which have replicated and moved apart. For simplicity only 3 chromosomes are shown, in diploid cells, there would be 2 copies of each chromosome present.

Question 22

What happens during the prometaphase stage of mitosis?

Answer 22

Prometaphase starts abruptly with the breakdown of the nuclear envelope. Chromosomes can now attach to spindle microtubules via their kinetochores and undergo active movement.

Question 23

What happens during the metaphase stage of mitosis?

Answer 23

• At metaphase the chromosomes are aligned at the equator of the spindle, midway between the spindle poles. The paired kinetochore microtubules on each chromosome attach to opposite pole of the spindle.
• Kinechores of all chromosomes aligned in a plane midway between two spindle poles.

Question 24

What happens during the anaphase stage of mitosis?

Answer 24

At anaphase, the paired chromatids synchronously separate to form 2 daughter chromosomes and each is pulled slowly toward the spindle pole it faces. The kinetochore microtubules gets shorter and the spindle poles also move apart, both contributing to chromosome separation.

Question 25

What happens during the telophase stage of mitosis?

Answer 25

During telophase, the 2 sets of daughter chromosomes arrive at the poles of the spindle. A new nuclear envelope reassembles around each set, completing the formation of 2 nuclei and marketing the end of mitosis. The division of the cytoplasm begins with the assembly of contractile ring.

Question 26

What happens when you stain DNA with the DNA binding dye DAPI?

Answer 26

DAPI associates with the minor groove of double-stranded DNA, with a preference for the adenine-thymine clusters. Cells must be permeabilized and/or fixed for DAPI to enter the cell and to bind DNA. Fluorescence increases approximately 20-fold when DAPI is bound to double-stranded DNA.

Question 27

What are the advantages of asexual reproduction (3 things)?

Answer 27

Advantages:
- Efficient
- Rapid multiplication
- Potentially a highly adapted genome can be passed on without modification

Question 28

What is the disadvantage of asexual reproduction?

Answer 28

Gathers more deleterious mutations as time goes on (Muller’s ratchet)

Question 29

What is the disadvantage of sexual reproduction?

Answer 29

males are expensive: do not themselves produce offspring

Question 30

What is the advantages of sexual reproduction?

Answer 30

• genomes are mixed
• Sexual reproduction allows for more variation in organisms
• combining beneficial mutations
• removing deleterious mutations and minimising the effect of recessive (harmful) genes.

Question 31

How are gametes formed trough meiosis?

Answer 31

Gametes are formed through meiosis (reduction division), in which a germ cell undergoes two fissions, resulting in the production of four gametes.

Question 32

What happens during fertilisation?

Answer 32

During fertilization, male and female gametes fuse, producing a diploid (i.e., containing paired chromosomes) zygote.

Question 33

What is gametogenesis?

Answer 33

Gametogenesis is the process by which diploid precursor cells undergo meiotic division to become haploid gametes (sex cells)

Question 34

In males what are gametogenesis called and what does it produce?

Answer 34

In males, this process is called spermatogenesis and produce spermatozoa (sperm)

Question 35

In females what are gametogenesis called and what does it produce?

Answer 35

In females, this process is called oogenesis and produce ova (eggs).

Question 36

What happens during the first phase - multiplication phase of gametogenesis?

Answer 36

1) Multiplication Phase - In this phase, the diploid germ cell divides by mitosis to form diploid oogonia in oogenesis & spermatogonia in spermatogenesis.

Question 37

What happens during the second phase - growth phase of gametogenesis?

Answer 37

2) Growth Phase - This phase involves only growth in size. It is the longest phase. It results in the formation of the primary oocyte in oogenesis and primary spermatocyte in spermatogenesis.

Question 38

What happens during the third phase - maturation phase I of gametogenesis?

Answer 38

3) Maturation Phase - This phase involves meiotic division and it is divided into two phases -

• Maturation - I - The diploid primary oocyte/ spermatocyte divides by meiosis-I to form two haploid secondary spermatocytes in spermatogenesis and in oogenesis one secondary oocyte & one polar body is formed.

Question 39

What happens during the third phase - maturation phase II of gametogenesis?

Answer 39

Maturation - II - In spermatogenesis, the two secondary spermatocytes divide by meiosis-II to form four haploid spermatids which finally convert into four haploid sperms. In oogenesis, the secondary oocyte divides by meiosis-II to form one haploid ootid and one haploid polar body-II.

Question 40

What happens during oocyte formation?

Answer 40

An oocyte is produced in a female fetus in the ovary during female gametogenesis. The female germ cells produce a primordial germ cell (PGC), which then undergoes mitosis, forming oogonia. During oogenesis, the oogonia become primary oocytes.

Question 41

What happens during spermatozoa?

Answer 41

• A spermatozoon is a male reproductive cell that is produced in testis by highly orchestrated processes called spermatogenesis and spermiogenesis. During spermatogenesis, undifferentiated spermatogonia (stem cells) transform into type Al spermatogonia (differentiated cells).

Question 42

What is the purpose of a sperm cell?

Answer 42

The purpose of a sperm cell is to be released during sexual intercourse and to eventually meet with an ovum (egg cell), which is produced by a biologically female body. Once united, the sperm will penetrate and fertilise the egg in order to create new genetic material.

Question 43

What can an egg do that other cells cant?

Answer 43

An egg is the only cell in a higher animal able to develop in a new individual