Cell Division Flashcards
The CELL CYCLE is divided into 2 main parts:
M (MITOTIC) PHASE :
- mitosis takes place
- the cell divides into two
- relatively short period
INTERPHASE:
- longer period
- the cell is carrying out the functions of that particular cell type
FIRST STAGE of interphase
G1 PHASE:
The cell replicates organelles ~ requires proteins so a high level of transcription & translation take place.
The size of the cell increases ~ ensures when the cell divides the two daughter cells are the correct size.
SECOND STAGE of interphase
S (SYNTHESIS) PHASE:
- All of the chromosomes are replicated
- The cell synthesises a great deal of DNA
THIRD STAGE of interphase
G2 PHASE:
- Cell replaces the energy stores used during the S phase.
- Cell continues to carry out transcription & translation.
- Any damaged chromosomes are REPAIRED.
- Cell continues to grow
M (mitotic) phase
MITOSIS:
- Refers to the DIVISION of the NUCLEUS.
- The chromosomes are separated into two nuclei.
CYTOKINESIS:
- Refers to the DIVISION of the CELL.
- Cell divides into two
G0 phase
Sometimes cells can EXIT the cell, either permanently or temporarily.
FULLY DIFFERENTIATED CELLS:
- Permanent
- e.g adult neurones
SENESCENT CELLS:
- Permanent
- e.g damaged DNA , cell can no longer divide
CELLS IN G0 TEMPORARILY:
- e.g B memory cells
- These can be triggered to re-enter the cell cycle during infection.
CHECKPOINTS in the cell cycle
- The cell cycle is very TIGHTLY REGULATED
- These checkpoint are important and if failed, the cell leaves the cell cycle.
G1 CHECKPOINT:
- Cell has grown to the correct size
- Any DNA damage
- cell enters S phase
G2 CHECKPOINT:
- Cell has grown to the correct size
- Ay DNA damage
- cell enters mitotic phase
METAPHASE/SPINDLE CHECKPOINT:
- Checks chromosomes are assembled correctly on the mitotic spindle.
- Cell completes mitosis and proceeds through CYTOKINESIS.
DURATION of cell cycle
- The whole cell cycle can take a long time
- Most Mammalian cells ~ 24 hours
- Other cells can take much longer ,e.g moths
MITOSIS
- Start with ONE DIPLOID cell and end up with TWO IDENTICAL DIPLOID CELLS.
DIPLOID CELL ~ when cells contain chromosomes in PAIRS.
- Takes place when we want TWO identical copies of a cell.
USES:
- Growth & repair
- Asexual reproduction
- Part of a larger process called the CELL CYCLE.
CHROMATIN
- During INTERPHASE, we cannot see chromosomes in the nucleus.
- They are still there , but NOT VISIBLE as distinct structures.
- Instead we see DARK MATERIAL called CHROMATIN.
- CHROMATIN ~ chromosomes have a loose, open structure so DNA is accessible for transcription and replication
CHROMOSOME REPLICATION during:
Interphase
- A chromosome undergoes DNA replication to give TWO IDENTICAL molecules of DNA.
- These are called SISTER CHROMATIDS and are joined at a point called the CENTROMERE.
- This process happens for EVERY chromosome ~ in humans that means for 23 pairs.
- After interphase, the nucleus divides into two by mitosis.
Mitosis & the FIVE stages
A type of CELL DIVISION that forms TWO IDENTICAL diploid cells from ONE diploid cell.
5 Stages:
- Prophase
- Metaphase
- Anaphase
- Telophase
- Cytokinesis
PROPHASE
- The chromosomes CONDENSE and become VISIBLE.
- Each chromosome consists of TWO SISTER CHROMATIDS joined at the CENTROMERE.
- The NUCLEOULUS DISAPPEARS
- NUCLEAR MEMBRANE begins to BREAK DOWN.
- A pair of CENTRIOLES move to either POLE of the cell.
- PROTEINS begin to form SPINDLE FIBRES which attach to the CENTROMERE.
- This causes the chromosomes to move to the CENTRE of the cell.
METAPHASE
- The SPINDLE FIBRES completely form.
- Chromosomes are LINED UP along the EQUATOR of the cell.
ANAPHASE
- The CENTROMERES DIVIDE into TWO.
- SPINDLE FIBRES begin to SHORTEN
- This PULLS the SISTER CHROMATIDS to OPPOSITE POLES of the cell.
