Cell Cycle Flashcards
what are two major forms of cell division in eukaryotic cells?
Mitosis and Meiosis
Break down the differences between Mitosis and Meiosis
Mitosis:
One parental cell produces two genetically identical daughter cells
one round of DNA replication and one round of nuclear division
Replacement of dead or damaged cells
growth and development
occurs in somatic cells
some organisms use mitosis to reproduce asexually
meiosis:
One parental cell produces four genetically different daughter cells
one round of DNA replication and two rounds of nuclear division
Formation of sex cells/ gametes that are required for sexual reproduction
Gametes contain half the DNA of parental cell
occurs in germ cells
In sexual reproduction male and female gametes combine to form zygote
provide an overview of the cell cycle
G1 and G2 are ‘gap phases’
S-phase (DNA synthesis phase)
M-phase - mitosis - cell divides into 2
Interphase = G1+S+G2
Cells can also enter G0 (exit G1)
Complex regulatory mechanisms!
Explain the G1 phase
Period of growth and synthesis
No DNA replication
For progression to S-phase. DNA must be undamaged and cells must have appropriate nutrients/ extracellular growth signals
Once cell passes restriction point, cell is commited to entering S-phase
it lasts 10-12 hours
Explain the G0-Phase
Some cells exit the cell cycle and enter G0- phase, where there is no cell division
G0 can be transient- quiescent cells caused by nutrient deprivation
Quiescent cells can re enter the cell cycle with appropriate stimuli
Important for tissue repair
Explain what the S-Phase is
Each chromosome is accurately replicated
Protein synthesis - histones needed for packaging of newly synthesised DNA
Lasts 8-10 hours and only one round of DNA replication will occur
Cells will only enter G2 once DNA replication is fully completed
Explain the G2 Phase
Relatively short, 2-4 hours in duration
Cytoplasmic growth and protein synthesis continues
centrosomes duplicated in nucleus
Two centrosomes organise microtubules from opposite poles of the cell during mitosis
Centrosomes consist of two centrioles - barrel- shaped clusters of microtubules
M-phase
Cells can be grown in a cell culture dish and DNA labelled with a fluorescent molecule
A fluorescence microscope can then be used to visualise M-phase
Cane be useful for research
what are the 5 steps of Mitosis
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Describe Prophase
Chromosome condensation
Centrosomes begin to move to opposite poled of cell
Microtubules begin to form at centrosomes
Nuclear envelope remains intact
Describe Prometaphase
Chromosomes become more condensed
Breakdown of nuclear envelope
Formation of kinetochore-microtubule attachment, allowing active movement of chromosomes
what is a centromere
Sequence of DNA where the sister chromatids are most closely associated- centromeric DNA
What is the Kinetochore
The protein complex assembles on the centromere of each sister chromatid
Describe Metaphase
Chromosomes align at the equator of the spindle, midway between the spindle poles- the ‘metaphase plate’
Equal and opposing forces on each chromosome cause them to align
Cells remain at this phase until all chromosomes are properly attached to the microtubules and aligned
Describe Anaphase
Once all chromosomes are properly attached to kinetochore microtubules, anaphase can begin
centromeres separate and sister chromatids are pulled to opposite poles of the cell
Activation of the anaphase promoting complex/cyclosome
Kinetochore microtubules shorten to pull separated daughter chromosomes to opposite poles of the cell
Requires activation of separase
