mitosis

Question 1

what is the series of events in which a cell is formed and divides into daughter cells called

Answer 1

the cell cycle

Question 2

what are the 3 phases of the cell cycle

Answer 2

interphase - the longest
nuclear division - mitosis
cell divisison- cytokinesis

Question 3

what is interphase

Answer 3

90% of cell cycle
cell is metabolically active

Question 4

what is G1

Answer 4

intensive growth and activity
organelles - mitochondira golgi etc are produed
rRNA,mRNA,tRNA IS PRODUCED

Question 5

What is the point at the end of G1 called

Answer 5

the restriction point

Question 6

what is the role of the restriction point

Answer 6

cells that pass are committed to completing the cell cycle many cells do not pass this point and remain in g1

Question 7

what is S

Answer 7

synthesis
DNA is replicated by the semi-conservative method
chromosomes now consist of two identical molecules called chromatids- joined at the centromere

Question 8

what is G2

Answer 8

period of cell synthesis -histones synthesised and spindle proteins are produced
DNA checking occurs

Question 9

What is m phase

Answer 9

mitosis

Question 10

what is cytokinesis

Answer 10

cell organelles + cytoplasm separated equally and cell divides into 2 daughter cells

Question 11

description of mass graph

Answer 11

mass doubles (from given units in question) in 12 hours (or given hrs in q)
then mass havles from ‘’’ at ‘’ hrs

Question 12

explanation of mass graph

Answer 12

from ‘’’ hrs cell undergoes growth,synthesis, DNA replication and nuclear divison
at ‘’ hrs the cell cycle is completed as the cell undergoes cytokinesis , forming 2 new daughter cellls

Question 13

DNA graph D + E

Answer 13

d = FROM ‘’ HRS dna mass remains constant at ‘’ units
E= the cell is in G1 which is a period of cell growth and cell activity
d= the DNA mass doubles from ‘’-‘’ units in ‘’-‘’ hours
E= DNA is replicated by the semi-conservative method during the S phase, so at the end of the S phase each chromosome is now 2 chromatids
d= from ‘’-‘’ hrs DNA mass remains constant at ‘’ units
e= as the cell completes G2 and mitosis
d= DNA mass havles at ‘’ hrs from ‘’-‘’ units=
e= as the cells complete cytokinesis

Question 14

what are the four stages of mitosis

Answer 14

prophase
metaphase
anaphase
telophase

Question 15

what is the process of mitosis

Answer 15

it is a continuous process

Question 16

what is prophase

Answer 16

-chromosomes condense - get fatter + shorter
this is bc the condense around histone proteins
-individual chromosomes are now seen as chromatids joined at the centromere
-the nucleolus disappears
-the centriole migrate to the opposite ends of the cell
-spindle forms
-nuclear membrane breaks down and disappears

Question 17

what is metaphase

Answer 17

-chromatids become attached to the equator of the spindle by their centromeres

Question 18

what is anaphase

Answer 18

-the centromeres split and the chromatids split
-this is bc spindle fibres begin to pull apart
-each pair of sister chromatids separate and are pulled to opposite poles of the spindle

Question 19

what is telophase

Answer 19

-chromosomes at each end of the spindle decondense
-spindle fibres breakdown
-nuclear membrane forms around each of daughter nuclei
-nucleolus reappears

Question 20

what is cytokinesis in animal and plant cells

Answer 20

cell organelles are equally distributed bwt 2 ends of the cell
-animal - cell membrane invaginate at the equator of the cell - the cell then splits in 2
-plant-fibres bulge outwards to form barrel shaped called phragmoplast
-organelles gather and golgi produce many vesicles fuse and form a cell plate
new double membrane forms and the cell wall material deposited bwt membrane layers - cell in 2

Question 21

what is the significance of mitosis

Answer 21

-genetic stabilty- clone produced as the cells hab=ve same no. of chromosomes
-growth- cell tissue needs to be identical to the existing cels so they carry the same function
-repair- must replace damaged cells with exact copies of the original cell for the tissue to function produces
-asexual reproduction- produces offspring that is genetically identical to parent

Question 22

what does the mitotic index show

Answer 22

how much a tissue is actively dividing

Question 23

what is the mitotic index

Answer 23

no. of cells in mitosis/ total no. cells counted

Question 24

mitotic index example

Answer 24

cell cycle = 22 hrs
and mitotic index = 0.18
so mitosis takes 22 x 60 x 0.18 = 237.6 min

Question 25

what is cancer

Answer 25

uncontrolled cell division
form a tumour (an irregular mass of cells)

Question 26

how are cancers formed

Answer 26

Cancers start when changes occur in the genes that control cell division. A change in any gene is known as a mutation. If the mutated gene is one that causes cancer it is referred to as an oncogene

Question 27

how are cancers not developed more often

Answer 27

Mutations are common events and don’t lead to cancer most of the time
Most mutations either result in early cell death or result in the cell being destroyed by the body’s immune system
As most cells can be easily replaced, these events usually have no harmful effect on the body

Question 28

how do the mutations cause cancer

Answer 28

the mutations that result in the generation of cancerous cells do not result in early cell death or in the cell being destroyed by the body’s immune system
This means that the harmful mutation occurring in the original cell can be passed on to all that cell’s descendants
A typical tumour contains around a thousand million cancerous cells by the time it is detected

Question 29

what are carcinogens

Answer 29

Carcinogens are any agents that may cause cancer (eg. UV light, tar in tobacco smoke and X-rays). If the agent causes cancer it is described as carcinogenic

Question 30

what are the genes involved in controlled cell division

Answer 30

proto-oncogenes = stimulate cell division
tumor suppressor genes = inhibit cell division

Question 31

when does uncontrolled cell division occur

Answer 31

when the TS genes are off and the POG genes are on all the time

Question 32

how do prokaryotes divide

Answer 32

binary fission

Question 33

what is the process of binary fission

Answer 33

-dna in singular circle chromosomes copies by semi-conservative method
-each copy becomes attached to the CSM and the cell elongates
-the two copies separate - so each daughter cell receives one
-cell membrane invaginates and new cell wall material is laid down
-cross wall completed and two new daughter cells become separated
-2 daughter cells are genetically identical clones of each other and the original parent cell

Question 34

how do viruses replicate

Answer 34

-infect a host cell
-use host cell machinery to produce copies of the viral nucleic acid and proteins
-released from the host cell either by causing the host cell to burst or by budding from the host cell membrane

Question 35

how do bacteriophages replicate

Answer 35

-virus attaches to the bacterial host cell and injects the DNA into the cell
-the viral cell DNA is copied to make copies of the DNA and it is also transcribed and translated making new viral proteins
-new virus particles are then assembled and the host cell burst releasing new viral proteins

Question 36

how does HIV replicate

Answer 36

-virus attaches to specific receptor protein in the T-helper cells and the protein of the capsid of the virus fuses with the host cell membrane
-viral RNA and reverse transcriptase released into host cell
-reverse transcriptase makes a DNA copy of viral RNA
-DNA copy is integrated into t-helper cells own DNA
-DNA transcribed to RNA
-some of RNA is transcribed to viral proteins and forms new genetic material of the virus particle
-new virus particles assembled and bud off from CSM

Question 37

how does cytokinesis differ in plants and animals

Answer 37

animals-cell mem pulled inwards across the centre of the cell
-seperates the cytoplasm into two havles - each containing a nucleus

plants- vesicles fuse to extned the cell membranes across the cytoplasm
-new cell wall develops between the cell membranes