D2.1 - mitosis (3l)

Question 1

how are new cells generated using the process of mitosis?

Answer 1

• in all living organisms, a parent cell (a mother cell) divides to produce 2 daughter cells
• mitosis maintains the chromosome number and genome of cells, so the daughter cells are genetically identical to the parent cells
• mitosis is involved in asexual reproduction, and in the generation of new cells that are used for growth, or for repair of tissues

Question 2

what is cytokinesis?

Answer 2

the splitting of cytoplasm in a parent cell, between daughter cells

Question 3

how does cytokinesis occur in animal cells?

Answer 3

in an animal cell a ring of contractile actin and myosin proteins pinches a cell membrane together, forming a cleavage furrow, to split the cytoplasm

Question 4

how does cytokinesis occur in plant cells?

Answer 4

in a plant cell vesicles fuse together to assemble sections of membrane and cell wall to achieve splitting

Question 5

what is equal cytokinesis?

Answer 5

in equal cytokinesis each daughter cell receives approximately half of each component of the parent cell (eg, half of each type of organelle)

Question 6

what is unequal cytokinesis?

Answer 6

in unequal cytokinesis, each daughter cell receives different amounts of the cells’ components

Question 7

what is required for unequal cytokinesis?

Answer 7

for unequal cytokinesis to occur, it is still necessary for each daughter cell to receive at least one mitochondrion and one of any other organelle that can only be made by dividing a pre-exisiting structure

Question 8

what are some examples of unequal cytokinesis?

Answer 8

e.g) budding in yeast, following mitosis, and oogenesis in humans, following meiosis

Question 9

what is the role of mitosis in eukaryotes?

Answer 9

mitosis is a type of nuclear division
- it is essential before cell division to avoid the production of anucleate cells

Question 10

what are the characteristics of mitosis?

Answer 10

• mitosis maintains the chromosome number and genome of cells, so the daughter cells are genetically identical to the parent cells
• mitosis is involved in asexual reproduction
• mitosis is involved in the generation of new cells that are used for growth, or for repair of tissues

Question 11

why must nuclear division occur before cell division?

Answer 11

mitosis is essential before cell division to avoid the production of anucleate cells

Question 12

why is DNA replication a prerequisite for both mitosis and meiosis?

Answer 12

• after replication, each chromosome consists of two elongated DNA molecules held together at the centromere
• when these sister chromatids are separated at the anaphase, the chromosome number briefly doubles
• once telophase and cytokinesis have occured, the original number of chromosomes are restored

Question 13

why is DNA replication important?

Answer 13

DNA replication is important as the number of chromosomes does not change

Question 14

what is the role of histones in nuclear division?

Answer 14

histones are proteins that wrap DNA around themselves to supercoil the DNA and condense the chromosomes

Question 15

why does DNA need to be condensed?

Answer 15

in order for chromosomes to be able to move around the cell efficiently the DNA is condensed

Question 16

how are chromosomes moved around the cell using spindle fibres?

Answer 16

spindle fibres are long strands of microtubules that are produced by the centrosome, which can be lengthened or shortened by changing the number of microtubule subunits

Question 17

what are the 3 types of microtubules?

Answer 17

1. astral microtubules
2. overlap microtubules
3. kinetochore microtubules

Question 18

what is the function of astral microtubules?

Answer 18

astral microtubules contribute to separating the poles of the cell

Question 19

what is the function of overlap microtubules?

Answer 19

overlap microtubules are connected in pairs by microtubule motor proteins, and when the motor proteins become activated the two connected overlap microtubules are pushed apart, one towards each pole

Question 20

what is the function of kinetochore microtubules?

Answer 20

kinetochore microtubules bind to the centromere of chromosomes, with each chromatid attached to microtubules coming from opposite poles
- when the overlap microtubules move apart, kinetochore mictroubules pull each chromatid in the opposite direction to separate the chromatids and move them to each pole

Question 21

what is the process of mitosis?

Answer 21

1. prophase - chromosomes condense
2. metaphase - chromosomes align in the equator
3. anaphase - homologous chromosomes separate
4. telaphase - nucleus forms around chromosomes at each pole
5. a sister chromatide from each chromosome is then pulled away by spindle fibres shortening to the poles of the cell, and the nucleus divides

Question 22

what occurs during prophase?

Answer 22

• chromosomes supercoil
• centrosomes move away to the poles and form spindle fibres
• nuclear membrane breaks down

Question 23

what occurs during metaphase?

Answer 23

• spindle fibres grow and attach to centromeres on opposite sides
• chromosomes move to align on the equator

Question 24

what occurs during anaphase?

Answer 24

• spindle fibres contract and separate the cetromeres and sister chromatids, with the single-armed chromosomes moving to opposite poles

Question 25

what occurs during telophase?

Answer 25

- nuclear membrane reforms around chromosomes at each pole and form two new nuclei

Question 26

what is the order of the cell cycle?

Answer 26

1. interphase - growth and number of sub-cellular structures double 2. mitosis - cell division 3. cytokinesis - cytoplasm splits and moves apart