MITOSIS AND MEIOSIS

Question 1

what is growth and cell division ?

Answer 1

cells duplicate its contents

parent cell divide into two daughter cells

Question 2

why cells divide ?

Answer 2

unicellular : reproduction

multicellular : growth and repair of tisuus

Question 3

key events for cell division

Answer 3

reproductive signal : initiate cell division
replication : DNA is duplicated
Segregation : distribution of DNA into two new cells
Cytokinesis : separation of two new cells

Question 4

what are reproductive signals ?

Answer 4

growth factors : external chemical factors that stimulate these cells to divide
e.g : platelet derived growth factor that initiate blood clotting, stimulate skin cells to divide and heal wounds

Question 5

what are important reproductive signal ?

Answer 5

nutrients conc. and environmental conditions

Question 6

what is the special thing about meiosis ?

Answer 6

provides diversity among us individual organisms

Question 7

what are somatic cells?

Answer 7

body cells that are not specialised for reproduction , contains homologous pairs of chromosomes (diploid)

Question 8

what are gamete cells?

Answer 8

cells that only contain one set of chromosomes (haploid)

Question 9

what are the three stages of interphase and what Is the key point

Answer 9

G1, S Phase, G2

DNA has replicated but x form condense structure of chromosome - remain as loosely coiled chromatin

Question 10

what happens in G1

Answer 10

decision to divide/not to divide
doubling of organelles
accumulation of materials for DNA synthesis

Question 11

what happens in the S phase

Answer 11

DNA replication occurs

-each chromosome being composed of two sister chromatids

Question 12

what happens in G2

Answer 12

synthesis of proteins needed for cell division

Question 13

what is centrosomes

Answer 13

microtubules organizing center of the cell which is replicated in the S phase
-composed of two centrioles surrounded by pericentriolar material

Question 14

what are two ways a cell can die ?

Answer 14

NECROSIS : accidental death - inflammation, loss of ATP

APOPTOSIS : programmed cell death - renewing RBC every other month

Question 15

what signals control cell death ?

Answer 15

• lack of mitotic signal (growth factor)
• recognition of damaged DNA
• external signals cause membrane proteins to change shape and activate enzymes called CASPASES which hydrolyze proteins of membranes

Question 16

what is G1 checkpoint ?

Answer 16

main checkpoint (restriction point)
determines whether all conditions are favourable for cell division to proceed
check for growth factors and damaged DNA
check the integrity of DNA

Question 17

what is G2 checkpoint ?

Answer 17

mitosis checkpoint
verifying of DNA replication - chromosomes must be duplicated
mitosis will occur only if DNA has been replicated correctly
check for damaged DNA and unreplicated DNA

Question 18

what is M checkpoint ?

Answer 18

spindle assembly checkpoint
occurs between metaphase and anaphase
ensure the chromosomes are properly attached to the spindle so it can be distributed accurately to the daughter cells
spindle checkpoint - kinetochore attachment
mitosis will not occur if chromosomes are not properly aligned

Question 19

what is cell maintenance ?

Answer 19

cell division > cell death = growth
cell division < cell death = atrophy - wasting away part of a body
cell division&raquo_space;> cell death = cancer - lose control over cell division, evade apoptosis, can migrate to other parts of body (METASTASIS)

Question 20

whar happens during mitosis ?

Answer 20

cell duplicates all of its contents including its chromosomes & split to form 2 identical daughter cells

Question 21

why does mitosis occurs ?

Answer 21

• Asexual reproduction to replace & repair body cells
• increase in the no. of cells during growth
• must be regulated correctly or cancer will occur

Question 22

name all the stages and phases

Answer 22

6 stages and 4 phase
Interphase
Prophase 
Metaphase
Telophase
Cytokinesis

Question 23

what happens during interphase

Answer 23

• DNA replication
• go through all the chekpoints
• two centrosomes are already present (key to cell division)

Question 24

what happens during prophase

Answer 24

• DNA molecules are shortened and condense by coiling to form chromosomes (sister chromatids)
• one pair of centrioles (1 chromosome) have migrated to the opp pole
• nuclear membrane and nucleolus starts to break down
• mitotic spindle is formed and attaches itself to the kinetochore of sister chromatidss

Question 25

what happens during metaphase

Answer 25

- chromosomes are moved to the central/metaphase plate by the mitotic spindle - sister chromatids line up in the middle of the cell - each chromatid is attached to one spindle fibre which comes from opp poles

Question 26

what happens during anaphase

Answer 26

microtubules attached to kinetochores of each sister chromatids shortens, hence sister chromatids are split and move to opp end of poles the unattached microtubules elongates to stretch the cells

Question 27

what happens during telophase

Answer 27

begins when chromosomes arrive at the poles of the cell chromosomes become indsitinct chromatin again spindle disappears and nuclear envelope reforms

Question 28

what happens during telophase in plant cells

Answer 28

- a cell plate forms across the cell in the location of the old metaphase plate where chromatids line up - vesicles from the Golgi apparatus migrate to the plane of the metaphase plate and fuse to form a new plasma membrane

Question 29

what happens during cytokinesis

Answer 29

- cleavage furrow passes around the circumference of the cell - actin filaments form a contractile ring which will cause the cleavage furrow to be pinched in half when the ring becomes smaller

Question 30

what happens during meiosis

Answer 30

2 nuclear divisions but DNA is replicated once only during the interphase

Question 31

name all the stages and phases

Answer 31

``` interphase prophase I metaphase I anaphase I telophase I Cytokinesis I prophase II metaphase II anaphase II telophase II Cytokinesis II ```

Question 32

what happens in meiosis I

Answer 32

reduction division - reduces the no. of chromosomes in half making haploid daughter cells

Question 33

when does genetic recombination occur in meiosis

Answer 33

- synapsis and crossing over happen during prophase I | - crossing over occurs as chromosomes condense

Question 34

what happens to the kinetochores of sister chromatids in Meiosis I

Answer 34

it fuses and functions as one so microtubules can attach to only one side of each centromere

Question 35

where are homologous pairs of chromosomes held at

Answer 35

chiasmata