book 5 (mitosis and meiosis)

Question 1

describe the process of interphase

Answer 1

1. G1 phase
   - cell increase in size
   - free deoxyribonucleotides synthesis
   - organelles synthesis
   - proteins and enzymes synthesis
   - G1 checkpoint to ensure that the cell is ready for DNA synthesis
2. S phase
   - semi-conservative replication of DNA whereby each chromatin replicates
   - each duplicated chromatin consists of 2 identical sister chromatids
   - the amount of DNA of the cell doubles during this phase
3. G2 phase
   - cell growth
   - ATP production from increased rate of cellular respiration
   - G2 checkpoint ensures that the cell is ready for mitosis and cytokinesis

Question 2

describe the process of prophase in mitosis

Answer 2

1. chromatin coils and thicken to form duplicated chromosome
2. each duplicated chromosome consists of two genetically identical sister chromatids held together by a centromere
3. centrioles move to opposite poles of the cell to determine the polarity of cells
4. nucleoli disappear
5. nuclear envelope fragments and disappear
6. the 2 centrosomes move apart as spindle microtubules grow out from them
7. the spindle forms - it consists of centrosomes and microtubules that extend from the centrosomes
8. kinetochore microtubules attach to the kinetochore protein at the centromere of duplicated chromosomes

Question 3

describe the process of metaphase in mitosis

Answer 3

1. the centrosomes are now at opposite poles of the cell
2. duplicated chromosomes are pulled up to line up in a single file along with the metaphase plate
3. the kinetochores on sister chromatids are attached to kinetochore microtubules coming from the opposite poles

Question 4

describe the process of anaphase in mitosis

Answer 4

1. centromeres divide
2. sister chromatids separate to form individual daughter chromosomes which are pulled apart by the shortening of kinetochore microtubules
3. the cell elongates as polar microtubules lengthen
4. at the end of anaphase, the 2 poles will have equivalent and complete sets of chromosomes

Question 5

describe the process of telophase in mitosis

Answer 5

1. chromosome reach the opposite poles of the cell, it uncoil and lengthen to form chromatin again
2. spindle fibres depolymerise and disintegrate
3. nuclear envelope re-forms around the chromosome at each-pole
4. nucleoli reappear

Question 6

describe the process of cytokinesis in animal cells

Answer 6

1. via the cleavage of cell surface membrane
2. cell surface membrane invaginates in the area that was previously preoccupied with the metaphase plate
3. cleavage furrow develops in the cell membrane
4. the furrow deepens until the 2 daughter cells pinch off and separate

Question 7

describe the process of cytokinesis in plant cells

Answer 7

1. via cell plate formation
2. small fluid-filled vesicle produced by golgi body apparatus move along the microtubules to the equator of the parent cell
3. vesicle fuse to form the cell plate
4. it enlarges across the equator
5. cell wall material carried in golgi vesicles contributes to the cell wall of the daughter cells while the membrane of the vesicles contributes to the cell surface membrane of the daughter cells
6. cell wall fuses with the parent cell wall and cell membrane, separating the 2 daughter cells

Question 8

describe the process of prophase I in meiosis I

Answer 8

1. the chromatin coil and condense to form duplicated chromosome
2. synapsis occurs – homologous chromosome pair up along their lengths, aligned gene by gene precisely, each pair is called bivalent
3. crossing over occurs at the chiasmata to exchange equivalent parts of the chromatid
4. nuclear envelope starts to fragment and disappear, nucleoli disappear
5. the 2 centrosomes, together with their accompanying pair of centrioles, move to the opposite poles of the cell
6. spindle fibres assemble

Question 9

describe the process of metaphase I in meiosis I

Answer 9

1. homologous chromosomes arranged in pairs along the metaphase plate
2. the 2 homologous of each pair orient themselves to face the opposite poles of the cell
3. kinetochore microtubules extending from one centrosome are attached to the centromere of one of the homologous chromosomes
4. the other homologous chromosome is attached to the kinetochore microtubules extending form the centrosome at opposite poles of the cell

Question 10

describe the process of anaphase I in meiosis I

Answer 10

1. homologous chromosomes separates and moves towards the opposite poles of the cell, guided by the shortening of the kinetochore microtubules
2. centromere does not divide, the 2 chromatids of 1 homologous chromosome moves together towards the same pole of the cell
3. by the end of anaphase I, each daughter cell has haploid set of chromosome s as it only receives one of the pair of homologous chromosomes
4. halving of chromosome number has occurred but the duplicated chromosomes are still composed of 2 chromatids

Question 11

describe the process of telophase I in meiosis I

Answer 11

1. in some species, chromosomes uncoil and lengthen to form chromatin fibres
2. in some species, nuclear envelope re-forms, nucleoli re-appear
3. spindle fibres depolymerise and disintegrates
4. cell surface membrane may begin to invaginate as the cell go into cytokinesis simultaneously resulting in 2 genetically non-identical haploid cell