Topic 1:7a - control of the cell cycle Flashcards
state the three phases of interphase and their corresponding lengths
G1 (10 hours)
S (9 hours)
G2 (4 hours)
describe the G1 phase of interphase
The cell grows and carries out metabolic reactions including protein synthesis.
The cell accumulates DNA nucleotides and ATP in preparation for DNA replication in S phase.
describe the S phase of interphase
Replication of DNA. Every chromosome in the nucleus is replicated and the copies, the sister chromatids, are joined by a centromere. They are not yet visible.
describe the G2 phase of interphase
Some organelles are replicated. ATP is replenished, the cytoskeleton is dismantled in preparation for mitosis, and protein synthesis continues.
describe the reason for the G1 checkpoint in the cell cycle
The chromosomes are checked for mutations and other forms of damage.
The availability of nutrients, DNA nucleotides, DNA polymerase enzymes and ATP is assessed.
The cell is prevented from entering the S phase if one or more conditions are unfavourable for DNA replication.
describe the reason for the G2 checkpoint in the cell cycle
The genome is checked to ensure that all chromosomes have been replicated and that each chromosome is free from mutations and damage before the cell enters mitosis.
describe the reason for the G2 checkpoint in the cell cycle
The sister chromatids are checked to ensure that the centromere is attached to spindle fibres before the chromatids are separated in anaphase.
How does the cell cycle move from the G1 phase to the S phase (through the G1 checkpoint)
Binding of growth factors initiates a metabolic pathway that enables the cell cycle to move from the G1 phase to the S phase and DNA replication occurs.
Growth factors, e.g. hormones, bind to specific receptors, usually imbedded in the membrane of the cell. However, lipid soluble growth factors diffuse through the lipid bilayer and bind to receptors inside the cell.
how are the G2 and M checkpoints regulated?
through the concentration of a complex called MPF
What two proteins are involved in the G2 and M checkpoints in interphase?
cyclin: a protein that is synthesised during the cell cycle and its concentration changes throughout the cycle.
cdk-1: an enzyme that remains at a constant concentration throughout the cell cycle
How does MPF regulate the G2 and M checkpoints?
As it accumulates, cyclin binds to Cdk to form a complex called MPF.
An increase in MPF at the G2 checkpoint triggers mitosis to start. It also triggers mitosis to stop at before anaphase.
As mitosis occurs, cyclin degrades, causing a decrease in concentration of MPF. A decrease in MPF at the M checkpoint (before anaphase) triggers mitosis to continue past metaphase to completion.
3 Internal factors controlling the cell cycle
Internal factors are located within a cell.
- Formation of mitosis promoting factor (MPF).
- Cyclin and other proteins that control the cell cycle are encoded by proto-oncogenes and tumour suppressing genes.
- Large cells have a low SA:V and this acts to stimulate cell division to give two smaller cells each with a higher SA:V.
describe briefly what external factors that control the cell cycle are
External factors act from outside the cell, can be both physical and chemical, can trigger internal factors and may initiate or inhibit cell division
list 4 External factors controlling the cell cycle
- nutrient dependence
- anchorage dependence
- density dependence
- growth factors and hormones
external factors: briefly describe nutrient dependence
Nutrient dependence: cells need particular nutrients in the extracellular fluid to divide.
external factors: briefly describe anchorage dependence
- physical factor
-many cells will only divide if they are attached to a substrate or surface.
external factors: briefly describe density dependence
- physical factor
-cells require space to divide into. If there is no space, then cells will not divide (Note: cancer cells are different.)
