Cell Cycle, Cell Division and its Control Flashcards
what happens when cells divide
- They produce 2 daughter cells that are diploid and cell have a full set of chromosomes – mitosis
- Or they produce 4 daughter cells that contain only one copy of each chromosome they are haploid – meiosis
what are the 4 main phases of the cell cycle
- G1
- S
- G2
- M
- GO – non dividing, fully differentiated or quiescent stem cells, or not going through the cell cycle
How long does each part of the cell cycle take
- 23 hours spent in interphase
- 1 hour spent in mitosis
what phase does cell growth occur in
cell growth occurs in interphase and not mitosis
what is interphase made up of
G1
GO
S
G2
what is mitosis made up of
Prophase
Metaphase
Anaphase
Telophase
describe what happens in G1 and G2
- Gap (growth) phases – need to grow so they can make two cells out of one cell
- Longest phases
- No synthesis of DNA
- Cell has checkpoints and the cell will not progress unless they are met
- Replication of organelles happen in G1 and production of proteins, cytoplasm and nucleotides
- G2 – cell double checks DNA has been copied properly and checks for errors, if they are unable to repair errors then the cell undergoes apoptosis
- G1 - Cell checks the environment both internally and externally – make sure that the external environment is correct around the cell so it can receive the daughter cell
what is the interphase phase the cell spends most of the time in
G1 and G2
what happens in S phase
- Synthesis phase
- DNA is duplicated
- 2n to 4n – sister chromatids, each chromosome replicates
- chromosome are held at the centromere, so they are not mixed up at this point
- need 4N for two of the daughter cells
- semi-conservative replication
- this is where mutations can occur
describe mitosis
- division of the cell into 2 identical cells
what is cytokinesis
actual separation of the parent cell into two daughter cells
what happens in prophase
- DNA condenses to form chromosomes that are joint at the centromere
- Nucleoli disappears
- Nuclear envelope breaks down – chromosomes need to go into the main part of the cell,
- Centromere is a specialisation of the histones, this is an attachment point onto the microtubules
- Centrioles are special hollow structure that organise the microtubule assembly, organise mitotic growth spindles
- Centrioles separate and move apart towards opposite poles and organise the production of microtubule filaments
- Mitotic spindles start to appear and grow towards the equator of the cell
- Microtubules form a radiating array
- Chromosomes are attached to the microtubules by kinetochore
describe the structure of the kinetochore
- Contains two regions – inner region binds to the centromere and is assembled from specialised nucleosomes which are present throughout the cell cycle
- Outer region interacts with microtubules are only assembled during cell division
whats the role of the kinetochore
- attaches to the sister chromatids and pull the chromosomes apart, attached to the microtubules as well
describe the process of metaphase
- Chromosomes are lined up in the metaphase plate
- Centrosomes are at polar ends
- Microtubules and centromeres bind together to form kinetochores
- Kinetochore/microtubules are used to pull chromosomes apart, one from each pair of sister chromatids pulled towards opposite ends
- Cohesion are now only present in centromere to hold sister chromatids together
Describe the process of anaphase
- When chromosome reaches centrosome, the poles separate further by elongation of the polar microtubules
- Cohesin is hydrolysed and it is not functional anymore this allows separation
- they are pulled to polar ends
what are cohesinopathies diseases
- Cohesinopathies can lead to missing or extra chromosome in daughter cells
- Roberts syndrome
- Cornelia de lange syndrome
- Non disjunction of chromosmes – down syndromes meiosis I or ii
what holds the chromatids together
- Cohesin a protein holds sister chromatids together as they condense down
- There are enzymes that break down the cohesins except at the centromere so they can be pulled apart
- centromere
How do you get aneuploidy
don’t break down the cohesin therefore when pulling the chromosome apart can cause the microtubules to break and both chromosomes at one end and one daughter cell does not have the chromosome
describe telophase work
- Uncoiling of chromosomes
- Reformation of nuclear envelope
- Contractile ring forms of actin and myosin pinches the cell until it splits into 2 daughter cells , cytoplasm is dividing and division is completed
what is meiosis for
- Specialised for division for reproduction
- Leads to development of gametes
what does meiosis produce
produces haploid cells with half the number of chromosome