1. Key Area 5- Protein Control and Cell Division Flashcards
What is the purpose of the cytoskeleton?
To give mechanical support and shape to cells
What does the cytoskeleton consist of?
Different protein structures including microtubules which are found in all eukaryotic cells
What are microtubules composed of?
They are hollow cylinders composed of the protein tubulin. They radiate from the microtubule organising centre (MTOC) or centrosome
What is the function of microtubules?
Control the movement of membrane-bound organelles and chromosomes
What does cell division require?
The remodelling of the cytoskeleton
What does the formation and breakdown of microtubules involve?
Polymerisation and depolymerisation of tubulin
What do microtubules form?
The spindle fibres that are active during cell division
What does the cell cycle consist of?
Interphase and Mitotic phase
What does interphase involve?
The growth and DNA synthesis including G1: growth phase, S phase: during which the DNA is replicated, and G2: a further growth phase
What does the mitotic phase involve?
mitosis and cytokinesis
What occurs in mitosis?
the chromosomal material is separated by the spindle microtubules
When and what occurs in cytokinesis?
Following mitosis, the cytoplasm is separated into two daughter cells
What does mitosis consist of?
PMAT
prophase
metaphase
anaphase
telophase
What happens in prophase?
DNA condenses into chromosomes consisting of sister chromatids. Nuclear membrane breaks down, spindle microtubules extend from the MTOC (microtubule organising centre) by polymerisation and attach to chromosomes via their kinetochores in the centromere region
What happens in metaphase?
Chromosomes are aligned at the metaphase plate (equator of the spindle)
What happens in anaphase?
As spindle microtubules shorten by depolymerisation, sister chromatids are separated and the chromosomes are pulled to opposite poles
What happens in telophase?
The chromosomes decondense and nuclear membranes are formed around them
Define the mitotic index
A measure of the activity of a particular tissue. The number of cells in M/ total cells as a percentage
What is progression through the cell cycle controlled by?
Checkpoints
What are checkpoints?
They are mechanisms within the cell that assess the condition of the cell during the cell cycle and halt progression to the next phase until certain requirements are met
What accumulates during cell growth which is involved in regulating the cell cycle?
Cyclin proteins
What do cyclins combine with and activate?
cyclindependent kinases (CDKs)
What do active cyclindependent kinases complexes (CDKs) do?
They phosphorylate proteins that regulate progression through the cycle. If sufficient phosphorylation is reached, progression occurs
Where does the retinoblastoma protein (Rb) acts as a tumour suppressor?
At the G1 checkpoint
How does the retinoblastoma protein (Rb) act as a tumour suppressor?
By inhibiting transcription of genes that code for proteins needed for DNA replication
What inhibits the retinoblastoma (Rb) protein?
Phosphorylation by G1-cyclin-CDK
What is the order of the cell cycle?
G1 to S phase to G2 to M phase
What is assessed at the G2 checkpoint?
The success of DNA replication and any damage to DNA is assessed
What does DNA damage trigger at the G2 checkpoint?
DNA damage triggers the activation of several proteins including p53 that can stimulate DNA repair, arrest the cell cycle or cause cell death.
What is the function of the protein p53?
Stimulates DNA repaire, arrests the cell cycle or causes cell death
What controls the progression from metaphase to anaphase?
The metaphase checkpoint
What happens at the metaphase checkpoint?
Progression is halted until the chromosomes are aligned correctly on the metaphase plate and attached to the spindle microtubules
What does an uncontrolled reduction in the rate of the cell cycle result in?
Degenerative disease
What does an uncontrolled increase in the rate of the cell cycle result in?
Tumour formation
What is the function of a proto-oncogene?
It is a normal gene which is usually involved in the control of cell growth or division which can mutate to form a tumour-promoting oncogene
What is apoptosis triggered by?
Cell death signals which can be internal or external
Once external death signal molecules bind to a surface receptor protein, what do they trigger?
A protein cascade within the cytoplasm
What is an example of an external death signal?
The production of death signal molecules from lymphocytes
What is an example of an internal death signal?
DNA damage
What does an internal death signal resulting from DNA damage cause?
The activation of p53 tumour-suppressor protein
What does both types of death signal result in?
The activation of caspases (types of protease enzyme) that cause the destruction of the cell
Why is apoptosis essential during the development of an organism?
To remove cells no longer required as the development progresses or during metamorphosis
Even in the absence of growth factors, what may cells initiate?
Apoptosis
