D2.1 Cell and nuclear division

Question 1

Compare and contrast cytokinesis in animal and plant cells

Answer 1

Animal cells:
- a ring of contractile actin and myosin PINCH cell membrane to split
- forms a cleavage furrow

Plant cells:
- vesicles assemble sections of membrane and cell wall, forming a cell plate

Question 2

examples of unequal cytokinesis

Answer 2

Oogenesis: the formation of eggs in females. Involves unequal division of cells during meiosis to produce one large egg cell.

Budding: A form of asexual reproduction in yeast where a smaller daughter cell buds off from its parent cell by cytokinesis.

Question 3

prophase I

Answer 3

• homologous chromosomes pair up to form bivalents
• crossing over occurs (alleles switch between non-sister chromatids)
• nuclear envelope breaks down
• spindle fibres start to form
• centrioles move towards the poles

Question 4

metaphase I

Answer 4

• spindle fibres move the bivalents (homologous chromosomes) to the equator of the cell
• sister chromatids are attached to spindle fibres by the centromere
• maternal and paternal homologous chromosomes are randomly assorted as they are lined up along the equator

Question 5

anaphase I

Answer 5

• homologous chromosomes of the bivalents are separated and are pulled towards the poles by microtubule motors on the kinetochore

Question 6

telophase I

Answer 6

• sister chromatids arrive at the poles and uncoil
• nuclear membrane forms around sister chromatids at each pole, producing 2 haploid nuclei
• cytokinesis occurs, producing 2 haploid cells.

Question 7

prophase II

Answer 7

• chromosomes, as sister chromatids, supercoil and appear in both haploid cells
• centrioles move towards the poles, producing spindle fibre microtubules
• sister chromatids attach to spindle fibres at centromere

Question 8

metaphase II

Answer 8

• sister chromatids line up at the equator

Question 9

anaphase II

Answer 9

• sister chromatids pulled apart, producing single stranded chromosomes
• single stranded chromosomes moved towards the poles by microtubule motors on the kinetochore

Question 10

telophase II

Answer 10

• chromosomes reach the poles of the cell and uncoil
• nuclear membrane forms around each set of chromsomes
• cytokinesis occurs in both cells, forming 4 cells with haploid nuclei which are not identical

Question 11

Down syndrome

Answer 11

Extra chromosome results from non-disjunction, where the 21st chromosome pair does not separate during anaphase I

If non-disjunction happens in the ovary, the egg carries 2 chromosome 21’s instead of one. When fertilised by sperm, resulting in 3 chromosome 21’s.

Question 12

Why the need for genetic diversity? (crossing over and random orientation)

Answer 12

increase variety among offspring - increases the chances of survivability if one combination of alleles proves to be more favourable to survive than the others

Question 13

Describe crossing over

Answer 13

The exchange of genetic material between non-sister chromatids by breaking, twisting around the same point, and connecting to the other’s initial point.

occurs during prophase I

allows for DNA transfer between maternal and paternal chromosomes, forming recombinant chromatids

Question 14

Describe random orientation

Answer 14

occurs during metaphase 1 when the homologous pairs of chromosomes line up along the equator of the cell.

Which of the pairs end up at which poles is entirely up to chance = random oreintation`

Question 15

Proliferation of meristematic cells for plant growth examples

Answer 15

Meristematic cells have the ability to divide rapidly, facilitating plant growth
Apical meristematic tissue found in root tips and branches to help the plant lengthen

Lateral meristematic tissue found in stem tissue to widen stems.

Question 16

Cell proliferation, animal cells examples

Answer 16

Zygote - An undifferentiated cell that divides by mitosis to make thousands of cells. These cells organise into layers and a hollow sphere to form an embryo. The cells then. begin to differentiate to form other parts of the body.

Skin replacement, wound healing - The skin sheds dead cells, and the bottom layer produces new cells via mitosis.
If skin is broken or wounded, all damaged/lost cells are replaced by mitosis.

Question 17

Describe the 3 phases of interphase

Answer 17

G1 - the cell grows, accumulating materials such as proteins and nucleotides.
S - DNA replication to produce chromosomes with sister chromatids
G2 - Cell prepares for mitosis by growing and replicating organelles.
DNA condenses from chromatin to chromosomes, microtubules can begin to form

Question 18

How do cyclins control the cell cycle?

Answer 18

The concentration of cyclins increase and decrease throughout the cell cycle.

Each cyclin must reach a certain concentration/threshold level to pass each checkpoint in the cell cycle

Question 19

Proto-oncogene (mutation, role, consequences)

Answer 19

Proto-oncogenes play a role in regulating cell division. It mutates to become an oncogene.

Oncogenes modify cell apoptosis such that instead of dying and breaking down, the cell continues dividing by mitosis.

Oncogenes may be mutated due to an outside agent, or a mutagen, e.g. cigarette smoke

Question 20

Tumour Suppressing Genes (mutation, role, consequences)

Answer 20

Tumour Suppressing Genes regulate the cell cycle by controlling cell growth, apoptosis, and DNA repair.

Mutations in TSG lead to uncontrolled cell division or tumour formation

Question 21

4 types of tumours

Answer 21

Primary - The one that occurs at the original site of the cancer

Secondary - A metastasis, a cancerous tumour that has spread from the original location to another site of the organism

Benign - Cells forming a mass but not spreading to the other organs

Malignant - Cells that rupture the organ they are in and spread to the rest of the body

Question 22

what is metastasis

Answer 22

The spread of cancer cells away from their original organ.
e.g. if breast cancer spread to the lungs, the cancer cells are still breast cancer cells not lung cells.

Question 23

describe prophase

Answer 23

• chromatin fibres condense to form chromosomes
• nuclear envelope disintegrates and nucleoli appear
• mitotic spindle forms as centrosomes builds new microtubules
• kinetochores attach to spindle
• centromeres move to opposite poles of the cell

Question 24

Describe metaphase

Answer 24

• chromosomes move to the equator of the cell and align
• centromeres now at opposite poles

Question 25

describe anaphase

Answer 25

• chromatids move towards opposite poles of the cell
• ## they move as a result of motor proteins pushing microtubules in opposite directions

Question 26

describe telophase

Answer 26

• nuclear envelope reforms around each set of chromosomes
• chromsomes elongate
• nucleoli disappear.
• spindle fibres disintegrate
• cell elongates and is ready for cytokinesis

Question 27

Difference and role of mitosis and meiosis

Answer 27

Mitosis maintains the chromosome number and genome of cells, for all cells
Meiosis halves chromosome number and encourages genetic diversity, for gametes

Question 28

Describe the purpose and process of condensation of DNA

Answer 28

To prepare for DNA replication, and avoid tangling and misplacing DNA.

DNA is wrapped around histone proteins, being organised into coils, forming a structure called chromatin. Once supercoiling is complete, the chromosome takes its familiar shape.

Question 29

What are motor proteins and how do they work?

Answer 29

Motor proteins use microtubules as tracks to push and pull objects around the cell. They can also attach to 2 different microfibres and cause them to slide past each other.

Motor proteins use ATP to produce a conformational change that moves the microtubules.