Unit 1: Key Area 5 - Protein control of cell division Flashcards
What is the function of cytoskeleton within a cell
The cytoskeleton gives mechanical support and shape to cells
Describe the structure of cytoskeleton
It consists of different protein structures including microtubules, which are found in all eukaryotic cells
Describe the structure of microtubules and where they radiate from
Microtubules are hollow cylinders composed of the protein tubulin. They radiate from the microtubule organising centre (MTOC) or centrosome.
What is the function of microtubules
Microtubules control the movement of membrane-bound organelles and chromosomes
What does cell division require
Cell division requires remodelling of the cytoskeleton
What does the formation and breakdown of microtubules require
Formation and breakdown of microtubules involves polymerisation and depolymerisation of tubulin
What do microtubules form during cell division
Microtubules form the spindle fibres that are active during cell division
What does the cell cycle consist of
The cell cycle consists of interphase and mitotic (M) phase
Describe interphase
Interphase involves growth and DNA synthesis including G1, a growth phase; S phase, during which the DNA is replicated; and G2, a further growth phase
What does mitotic phase include
Mitotic phase involves mitosis and cytokinesis
Describe what happens during mitosis and cytokinesis
In mitosis the chromosomal material is separated by the spindle microtubules. This is followed by cytokinesis, in which the cytoplasm is separated into two daughter cells.
What does mitosis consist of
Mitosis consists of prophase, metaphase, anaphase and telophase
Describe prophase
Prophase — DNA condenses into chromosomes each consisting of two sister chromatids. Nuclear membrane breaks down; spindle microtubules extend from the MTOC by polymerisation and attach to chromosomes via their kinetochores in the centromere region
Describe Metaphase
Metaphase- chromosomes are aligned at the metaphase plate (equator of the spindle).
Describe Anaphase
Anaphase — as spindle microtubules shorten by depolymerisation, sister chromatids are separated, and the chromosomes are pulled to opposite poles.
Describe Telophase
Telophase — the chromosomes decondense and nuclear membranes are formed around them.
How is progression through the cell cycle controlled
Progression through the cell cycle is controlled by checkpoints
Describe what checkpoints are
Checkpoints 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 do cyclin proteins do
Cyclin proteins that accumulate during cell growth are involved in regulating the cell cycle
Cyclins combine with and activate cyclindependent kinases (CDKs). Active cyclinCDK complexes phosphorylate proteins that regulate progression through the cycle. If sufficient phosphorylation is reached, progression occurs.
Describe what happens at the G1 checkpoint
- What does Phosphorylation by G1 cyclin-CDK do and what is the result of this
At the G1 checkpoint, retinoblastoma protein (Rb) acts as a tumour suppressor by inhibiting the transcription of genes that code for proteins needed for DNA replication
Phosphorylation by G1 cyclin-CDK inhibits the retinoblastoma protein (Rb)
This allows transcription of the genes that code for proteins needed for DNA replication. Cells progress from G1 to S phase.
Describe the metaphase checkpoint
A metaphase checkpoint controls progression from metaphase to anaphase
At the metaphase checkpoint, progression is halted until the chromosomes are aligned correctly on the metaphase plate and attached to the spindle microtubules.
What may an uncontrolled reduction in the rate of the cell cycle result in
An uncontrolled reduction in the rate of the cell cycle may result in degenerative disease
What may an uncontrolled increase in the rate of the cell cycle result in
An uncontrolled increase in the rate of the cell cycle may result in tumour formation
What is a proto-oncogene and what is it usually involved in
A proto-oncogene is a normal gene, usually involved in the control of cell growth or division, which can mutate to form a tumour-promoting oncogene
What triggers apoptosis
Apoptosis is triggered by cell death signals that can be external or internal
Give an example of external death signal
The production of death signal molecules from lymphocytes is an example of an external death signal.
Give an example of internal death signal
DNA damage is an example of an internal death signal.
Describe an external death signal
External death signal molecules bind to a surface receptor protein and trigger a protein cascade within the cytoplasm
Describe an internal death signal
An internal death signal resulting from DNA damage causes activation of p53 tumour-suppressor protein
Describe what happens as a result of both external and internal death signal
Both types of death signal result in the activation of caspases (types of protease enzyme) that cause the destruction of the cell
When is apoptossis essential and why
Apoptosis is essential during development of an organism to remove cells no longer required as development progresses or during metamorphosis
When may cells initiate apoptosis
Cells may initiate apoptosis in the absence of growth factors
