WEEK 2: DNA AND CELL DIVISION Flashcards
What is The Cell Cycle?
A cell cycle is a series of events that takes place in a cell as it grows and divides.
State the 4 main stages of the cell cycle.
- G1 phase:
- 1st stage in growth after cell division. Cellular contents
made - more cytoplasm & organelles. - During G1 the cell grows physically larger, copies organelles, and makes the molecular building blocks it will need in later steps.
- S phase: synthesis stage:
-DNA replication - G2 phase:
-2nd stage after DNA has been copied.
-The cell structures needed for division are made; organelles.
- Mitotic Phase:
-Mitosis + Cytokinesis
What happens in cytokinesis?
*In cytokinesis, the cytoplasm of the cell is split in two, making two new cells.
PROCESS
* First, a cleavage furrow appears
* A contractile ring of actin microfilaments in association
with myosin
* The contraction of the dividing cell’s ring of microfilaments is like the pulling of drawstrings:
The cell is pinched in two.
What are G1, G2 and S phase collectively known as?
What is M phase known as?
Interphase
Metaphase
What cells tend to spend most of their time on the M phase?
Cancer cells
What is G0?
The G0 phase is a cellular state outside of the replicative cell cycle. It is often referred to as the resting phase because cells in this phase are neither dividing nor preparing to divide.
What is a checkpoint?
- Checkpoint - a critical control point in the cell cycle were
stop and go-ahead signals can regulate the cell cycle.
– Animal cells have built-in stop signals that halt the cell
cycles and checkpoints until overridden by go-ahead.
signals.
State the 3 major checkpoints.
– Three Major checkpoints: found in G1, G2, and M phases
of the cell cycle.
What does each of the checkpoints monitor or check?
- G1 checkpoint ensures:
* cell is large enough to divide
* enough nutrients available
- Go-ahead or Exit signal - G2 checkpoint ensures:
* DNA replication in S-phase completed successfully. - M-phase checkpoint ensures:
* all chromosomes attached to the mitotic spindle.
What is meiosis?
How many chromosomes are found in meiotic products?
Meiosis is the type of cell division by which diploid gametic precursors produce haploid gametes.
*These meiotic products have 23 chromosomes
rather than the 46 chromosomes.
What is gametogenesis?
What is it called in males?
What is called in females?
- Gametogenesis is the formation of the ova or sperm.
- In males, the process is called spermatogenesis.
*In females, it is called oogenesis.
Describe Spermatogenesis.
Where does it takes place?
1.Start with a spermatogonium.
2.Undergoes Mitosis to form primary spermatocyte.
3.Primary spermatocyte undergoes meiosis to form 2 Secondary spermatocytes.
4.Secondary spermatocytes undergo meiosis II to form 4 haploid spermatid which mature to become sperm cells.
Seminiferous tubules
How long does spermatogenesis take?
75 days
Describe the process of oogenesis.
Division of germ cell precursors in
females is restricted to the first few
months after conception.
1. Oogonia produce primary oocytes, which initiate meiosis about 4 weeks before birth.
- The primary oocytes become arrested in prophase I in a stage called dictyotene before ovulation.
- After maturity, individual ovarian follicles mature, release primary oocytes from dictyotene as ovulation occurs.
- Meiosis I result in unequal division of the cytoplasm: secondary oocyte and, the first polar body.
5.Meiosis II is not complete until fertilization. Meiosis II results in fertilized ovum and a second polar body.
- In females, meiosis produces only one functional gamete
Describe what happens in Homologous Recombination.
At what stage of meiosis does homologous recombination occur?
- Genetic material from the homologous chromosomes is
randomly swapped - This creates four unique chromatids
- Since each chromatid is unique, the overall genetic
diversity of the gametes is greatly increased
