2 - MZH - Cell cycle Flashcards
Define cell cycle
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The highly ordered sequence of events that takes place in a cell, resulting in division of the nucleus and the formation of 2 genetically identical daughter cells
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What are the 3 main stages of the cell cycle?
What happens in each stage?
Interphase - The cell grows and increases in size, new proteins are synthesised, new organelles made and DNA replicates.
Mitosis - When nuclear division takes place.
Cytokinesis - When the cytoplasm of the cell and its organelles divide more or less equally between 2 daughter cells.
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Why do cells of higher organisms generally only able to go through a limited number of cell cycles + exmaple?
What is the difference between the cells above and those that divide continuously + example?
What do other cells require in order to divide + exmaple?
They differentiate and specialise. They’re unable to divide any more e.g. Nerve cells
Some cells remain actively dividing all their lives, cell division replaces the entire lining of the mammalian small intestine every few days.
Some cells require a TRIGGER, e.g. liver cells will divide to repair damage
How is a tumour formed?
Cancer cells carry on dividing indefinitely which results in the formation of a tumour.
Name the 3 sections that make up interphase. State what happens during each section.
G1 (first growth period) - Cells prepare for DNA replication. It’s a period of intense protein synthesis to make both structural proteins and enzymes. New organelles are formed. Cell has a high metabolic rate, reflected by increased ATP production.
S (synthesis) - DNA replciation occurs
G2 (second growth period) - Spindle protein is formed, energy stores are increased and the replicated DNA is checked for errors.
What is checked at the checkpoints? (G1 + G2)
Adequate growth (whether it’s big enough)
Condition of the DNA (for mutations)
Chemical signals (presence of hormones)
Decribe how the amount of DNA within a cell changes as it goes through the cell cycle
G1 - Normal amount of DNA
S phase - Quantity of DNA is doubled. The increase is gradual as the cell’s DNA molecules gradually unwind and new DNA strands are formed.
End of mitosis - Halves almost instantly. This marks the point at which the cell undergoes cytokinesis becoming 2 daughter cells.
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What is G0 and what role does it play in the cell cycle?
G0 is the name given to the phase when a cell may leave the cell cycle either temporariy or permanently.
3 reasons:
Differentiation - Cell becomes specialised to carry out a particular function. No longer able to divide.
DNA of cell is damaged - Damaged cell can no longer divide and eventually becomes senescent (old)
Age + senescent cells + disease - As humans age, the number of cells in the body increases and an increasing proprtion of them are senescent. These large proportion of senescent cells are linked to many age-related diseases e.g. cancer and arthiritis.
Contidions of which a cell needs in order to divide and remain in the cell cycle
- Has grown to the right size
- Replcated DNA is error free or is repaired
- Chromosomes are in their correct positions during mitosis
What are checkpoints in the cell cycle?
Checkpoints are the control mechanisms of the cell cycle. They monitor and verify whether the porcess at each stage have been accurately completed before the cell progresses to the next phase
Where are the checkpoints of the cell cycle? What does each stage check?
G1 checkpoint - End of G1 phase, before entry into the S phase. checks cell size, nutrients, growth factors, DNA errors.
G2 checkpoint - End of G2 phase, before entry into the mitotic phase. Checks the same factors as G1 checkpoint does.
Spindle assembly checkpoint (metaphase checkpoint) - Occurs at the point in mitosis where all chromosomes should be attached to the specific fibres and correctly alligned. Occurs during metaphase and mitosis can’t procees if this checkpoint is not passed.
If conditions of G1 and G2 are not satisfied then the cell enters G0.
Chromosomes:
- What is the structure like in eukaryotic cells?
- What do they contain?
- Chromatin?
- What are they ike during cell division?
- What is the centromere?
- In eukaryotic cells - they’re thread like structures.
- They contain genetic material arranged in packages called genes.
- Chromatin = Uncondensed DNA in a complex with histones.
- Curing cell division they become shorter and thicker and can be identified as seperate structures. This process is called condensation.
- Part that joins the 2 chromatids together.
Number of:
- Chromosomes in a human body cell
- Pairs of homologous chromosomes in a human body cell
- 46
- 23
What is a pair of homologous chromosomes?
Properties?
What is the gene locus?
Matching pair of chromosomes, one inherited from each parent.
They will always have the same sequence of genes although individual alleles are not always identical.
Gene locus - each gene occupies a specific place on the chromosomes.
What are non-sex chromosomes called?
How many pairs do human body cells have?
What is the other pair made of?
Autosomes
22
There’s 1 pair of sex cells in the human body cell.