biology - 1.5 Flashcards
What does the cytoskeleton 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?
Hollow cylinders composed of the protein tubulin.
Where do microtubules radiate from?
The microtubule organising centre (MTOC) or centrosome.
What do microtubules do?
They control the movement of membrane-bound organelles and chromosomes.
What does cell division require?
Remodelling of the cytoskeleton.
What does 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 (M) phase.
What does interphase involve?
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 involve?
Mitosis and cytokinesis.
In mitosis, how is the chromosomal material separated?
By the spindle microtubules.
What happens in cytokinesis, which follows mitosis?
The cytoplasm is separated into two daughter cells.
What does mitosis contain?
Prophase, metaphase, anaphase and telophase.
What happens in 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.
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.
How is the progression through the cell cycle controlled?
By checkpoints.
What are checkpoints?
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 are involved in regulating the cell cycle?
Cyclin proteins that accumulate during cell growth.
What do cyclins do?
They combine with and activate cyclin- dependent kinases (CDKs).
What do active cyclin-CDK complexes phosphorylate?
Proteins that regulate progression through the cycle. If sufficient phosphorylation is reached, progression occurs.
At the G1 checkpoint, what happens?
Retinoblastoma protein (Rb) acts as a tumour suppressor by inhibiting the transcription of genes that code for proteins needed for DNA replication.
What does phosphorylation by G1 cyclin-CDK do?
Inhibits the retinoblastoma protein (Rb).
What does inhibition of the retinoblastoma protein allow?
Transcription of the genes that code for proteins needed for DNA replication. Cells progress from G1 to S phase.
At the G2 checkpoint, what is assessed?
The success of DNA replication and any damage to DNA.
What does DNA damage trigger?
The activation of several proteins including p53.
What can p53 do?
It can stimulate DNA repair, arrest the cell cycle or cause cell death.
What does a metaphase checkpoint control?
Progression from metaphase to anaphase.
At the metaphase checkpoint, what happens?
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?
Degenerative disease.
What may an uncontrolled increase in the rate of the cell cycle result in?
Tumour formation.
What is a photo-oncogene?
A normal gene, 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 that can be external or internal.
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 do external death signal molecules bind to?
A surface receptor protein and trigger a protein cascade within the cytoplasm.
What does an internal death signal resulting from DNA damage cause?
Activation of p53 tumour-suppressor protein.
What do both types of death signal result in?
The activation of caspases (types of protease enzyme) that cause the destruction of the cell.
What does apoptosis do during the development of an organism?
It is essential as it removes cells which are no longer required as development progresses or during metamorphosis.
When may cells initiate apoptosis?
In the absence of growth factors.
