the cell cycle

Question 1

what is the cell cycle

Answer 1

a highly ordered sequence of events that takes place in a cell, resulting in division of a cell and the formation of two genetically identical daughter cells

Question 2

what are the two main phases of the cell cycle

Answer 2

• interphase
• mitotic (division) phase

Question 3

is interphase a stage in cell division

Answer 3

no its the stage between the cell divisions. longest stage

Question 4

what are the two mitotic divisions

Answer 4

mitosis and cytokinesis

Question 5

do cells divide continuously

Answer 5

no they are long periods of growth and normal working separate divisions

Question 6

what is interphase

Answer 6

the periods where the cell spends most of its time

Question 7

why is interphase sometimes referred to as the “resting phase”

Answer 7

the cells arent dividing

Question 8

why is calling interphase the “resting phase” inaccurate

Answer 8

interphase is actually a very active phase - the cell carries out all of its major functions such as producing enzymes or hormones whilst also actively preparing for cell division

Question 9

what happens during interphase

Answer 9

• DNA is replicated and checked for errors in the nucleus
• protein synthesis occurs in the cytoplas
• mitochondria grow and divide, increasing in number in the cytoplasm
• chloroplasts grow and divide in plant and algal cell cytoplasm, increasing in number
• the normal metabolic processes of cells occur (some including cell respiration, also occur throughout cell division)

Question 10

what are the 3 stages of interphase

Answer 10

G1 - the first growth phase
S - synthesis phase
G2 - the second growth phase

Question 11

what happens in the first growth phase

Answer 11

the new cell grows and carries its normal life functions such as protein synthesis and respiration.
proteins from which organelles are synthesised and organelles replicate. the cell increases in size

Question 12

what happens in the synthesis phase

Answer 12

DNA is replicated in the nucleus. the cells DNA is replicated so that each chromosome is double stranded. energy is saved in the form of ATP ready for the process of cell division

Question 13

what happens in the 2nd growth phase

Answer 13

the cell continues to increase in size, energy stores are increased and the duplicated DNA is checked for errors and damage is repaired before proceeding to mitosis

Question 14

what is G0

Answer 14

the name given to the phase when the cell leaves the cycle either temporarily or permanently

Question 15

why might a cell enter G0

Answer 15

differentiation - a cell that is specialised to carry out a particular function is no longer able to divide. it will carry out this function indefinitely and not enter the cell cycle again
The DNA of a cell may be damaged so that it can no longer divide and then enters a period of permanent cell arrest. most cells will do this as they can only divide a set number of times before they become senescent

Question 16

what does senescent mean

Answer 16

a process by which cells age and permanently stops dividing but dont die

Question 17

when do the number of senescent cells increase in the body

Answer 17

as you age. growing numbers of senescent cells have been linked with many age related diseases such as cancer and arthritis

Question 18

which cells that enter G0 can be stimulated to go back into the cell cycle and start dividing again

Answer 18

lymphocytes in an immune response

Question 19

what is the mitotic phase

Answer 19

period of cell division

Question 20

what are the two stages of the mitotic phase

Answer 20

mitosis and cytokinesis

Question 21

what is mitosis

Answer 21

types of nuclear division that produces daughter cells genetically identical to eachother and the parent cell

Question 22

what is cytokinesis

Answer 22

cytoplasmic division following nuclear division resulting in two daughter cells

Question 23

how are all cells formed

Answer 23

by divisions of existing cells. they all follow the same sequence of events between mitotic divisions

Question 24

how can eukaryotic cells divide

Answer 24

either by mitosis or meiosis

Question 25

what is the difference between mitosis and meiosis

Answer 25

mitosis - division into two daughter cells that are genetically identical to eachother and the parent cell meiosis - division into four unique daughter cells with 1/2 the chromosomes of the parent cell

Question 26

what happens in mitosis

Answer 26

one strand of each chromosome in eahc daughter nucleus. each is now identical to the parent nucleus (as it was before DNA replication)

Question 27

what happens in cytokinesis

Answer 27

the cytoplasm is divided between the two daughter cells to finish the cycle. each new cell enters G1 and resumes its normal functions. cytoplasm and membranes divide and separate

Question 28

how do prokaryotic cells divide

Answer 28

by binary fission - the cell growis to its limit of size and then splits into two. DNA replicated before cell divides, two new loops of DNA are pulled to opposite ends of the cell and a cell wall forms separating the bacterial cell. each new cell also contains replicated plasmids and synthesised ribosomes.

Question 29

what also divides by binary fission

Answer 29

mitochondria and chloroplasts

Question 30

how can we ensure the fidelity of cell division (two identical daugher cells are produced from the same parent cell)

Answer 30

ensure the cell only divides when it has grown to the right size, the replicated DNA is error free (or is repaired) and the chromosomes are in their correct positions during mitosis

Question 31

what are checkpoints

Answer 31

the control mechanism of the cell cycle.

Question 32

what do checkpoints do

Answer 32

they monitor and verify whether the processes at each phase of the cell cycle have been accurately completed before the cell is allowed to progress to the next phase

Question 33

G1 checkpoint

Answer 33

happens at the end of the G1 phase before S phase checks for nutrients, growth factors, DNA damage if the cell satisfies the requirements of this checkpoint it is triggered to begin DNA replication. if not, it enters a resting phase

Question 34

metaphase checkpoint

Answer 34

at the point in mitosis where all the chromosomes should be attached to spindles and have aligned. mitosis can't proceed till this checkpoint has passes

Question 35

G2 checkpoint

Answer 35

end fo G2 phase before mitotic phase check for cell size, DNA replication errors if this checkpoint is passed the cell initiates the molecular processes that signal the beginning of mitosis

Question 36

what is the purpose of checkpoints

Answer 36

- to prevent uncontrolled division leading to tumours - detect and reapiar damage to DNA - ensure the cycle cannot be reversed - DNA is duplicated once during each cell cycle

Question 37

what brings about the passing of a cell cycle checkpoint

Answer 37

kinases

Question 38

what are kinases

Answer 38

a class of enzyme that catalyse the addition of a phosphate group to a protein (phosphorylation)

Question 39

what does phosphorylation do

Answer 39

changes the tertiary structure of a 3D protein activating them at certain points in the cell cycle

Question 40

what activates kinases that are involved in cell cycle regulation

Answer 40

cyclins

Question 41

what causes cyclin-dependant kinase complexes (CDK) to form

Answer 41

binding of the correct cyclin to the appropiate kinase forms CDK complexes. these complexes are activated by enzymes

Question 42

what do CDK complexes do

Answer 42

they catalyse the activation of key cell cycle proteins by phosphorylation. it ensures a cell progresses through the different phases of its cell at the appropiate times

Question 43

what happens if CDK complexes arent needed

Answer 43

they signal a cell to move to the next phase of the cell cycle

Question 44

what is cancer

Answer 44

a group of many different disease caused by the uncontrolled division of cells

Question 45

what is the name given to an abnormal mass of cells

Answer 45

a tumour

Question 46

what is benign tumour

Answer 46

they stop growing and do not travel to other locations in the body

Question 47

what is malignant tumour

Answer 47

if the tumour continues to grow unchecked and uncontrolled

Question 48

which tumours are the basis of cancer

Answer 48

malignant tumours

Question 49

what causes tumours

Answer 49

they are the result of damage or spontaneous mutation of the genes that encode the proteins that are involved in regulating the cell cycle, including the checkpoint proteins

Question 50

what would happen if mutations cause overexpression of a cyclin gene

Answer 50

the abnormally large quantity of cyclins produced would disrupt the regulation of the cell cylce, resulting in uncontrolled cell division, tumour formation and possibily leading to cancer.

Question 51

what can CDK complexes be used for

Answer 51

possible targets for chemical inhibitors in the treatment of cancer

Question 52

what can happen if the activity of CDKs can be reduced

Answer 52

it may reduce or stop cell division and therefore cancer formation