Each chromosome contains one molecule of DNA, which includes specific lengths of DNA called genes.
Holds the instructions for making new cells. Daughter cells contain a copy.
In humans there are 46 chromosomes
1 of 19
What is the structure of chromosomes?
In a homologous pair of chromosomes, one copy comes from the mother and one the farther.
Each member of the pair contains genes for the same characteristics.
2 of 19
what is an alleles?
An alternative form of a gene which arises from mutations. Are found on the same place of a chromosome.
3 of 19
Why do cells divide?
To produce new cells:
-for growth,
-for replacement.
To reproduce:
-asexual reproduction,
-to produce gametes for sexual reproduction
Periods of growth and normal working.
Cells spend most their time in this stage.
6 of 19
What happens at each stage of interphase?
G1- first growth stage- proteins made, organelles replicate. call increases in size.
S (synthesis stage)- Synthesis of DNA (replication of chromosomes)
G2 (second growth stage)- cell increases further in size. energy stores increased and duplicated, DN
7 of 19
What happens in the G1 phase?
~First growth stage,
~Cells grown and increase in size,
~Transcription of genes to make RNA,
~Organelles duplicate,
~Biosynthesis,
~tumour suppression helps to control this phase.
8 of 19
What happens in Synthesis (S) phase?
Cells which enter this stage are committed to completing the cycle.
DNA replicates in the nucleus,
Rapid to reduce chance of spontaneous mutations.
9 of 19
what happens in G2 phase?
~Second growth stage,
~Cell continues to increase in size.
~Energy stores are increased,
~Duplicated DNA checked for errors.
10 of 19
What is G0?
G0 is the name given to the phase when the cell leaves the cell cycle- either temporarily due to the G1 check point or permanently
Apoptosis- programmed cell death.
11 of 19
How is the cell cycle regulated?
Checkpoints.
12 of 19
What are the cell cycle checkpoints?
The checkpoints are the control mechanisms of the cell.
G1/S checkpoint
G2/M checkpoint
M checkpoint (half way)
G1 checkpoint
13 of 19
What happens at the G1 checkpoint?
~End of the G1 phase, before entry into the S phase.
~checks chemicals needed for replication are present.
~checks for damage to the DNA before S phase.
~If the cell satisfies the requirements replication will begin, if not the cell enters resting state (
14 of 19
What happens at G2 checkpoint?
~At the end of G2, before the M phase.
~Cell has to check a number of factors.
~Checks whether DNA replicated without any damage.
~If checkpoint is passed the cell initiates mitosis through cell signalling.
15 of 19
What happens at M checkpoint?
~Also called spindle assembly checkpoint.
~Checks that all chromosomes are attached to the spindle.
~mitosis cannot processed until this is passed.
16 of 19
What is the purpose of the cell checkpoints?
~Prevent uncontrolled cell division that would lead to tumours.
~ Detect and repair damage to DNA.
17 of 19
Why does the cell cycle have to be in a specific sequence?
to ensure that:
~the cycle cannot be reversed,
~The DNA is only duplicated once during each cell cycle.
18 of 19
What is Tumour Protein p53?
~Located on short arm of chromosome 17.
~Gene triggers two checkpoints.
~Known as the tumour suppressor gene.
19 of 19
Other cards in this set
Card 2
Front
What is the structure of chromosomes?
Back
In a homologous pair of chromosomes, one copy comes from the mother and one the farther.
Each member of the pair contains genes for the same characteristics.
Comments
No comments have yet been made