Topic 3: Cell cycle and mitosis Flashcards
The ____ ______ and ______ are involved in the process of a fertilised egg (zygote) developing into a multicellular organism.
cell cycle
mitosis
What is the cell cycle? (1 point)
- the series of events that take place in acell involving growth, replication of DNA, nuclear division (mitosis) and cell division (cytokinesis) to produce daughtercells
What are the two main stages of the cell cycle?
The cell cycle is divided into TWO main stages:
- Interphase (G1, S and G2)
- Division (mitosis and cytokinesis)
NOTE: Then each new cell produced starts going through its own cell cycle
Describe what happens in G1
3 points
G1: (Gap 1 phase)
- Cell grows bigger
- New organelles can be made (eg. mitochondria)
- Protein synthesis to make enzymes for replication
Describe what happens in S
1 point
S: (DNA Synthesis phase)
- DNA REPLICATION doubles the {quantity of DNA/number of chromatids}
Describe what happens in G2
4 points
G2: (Gap 2 phase)
- Cell grows even bigger
- New organelles are made
- Protein synthesis to make proteins (eg. to form the spindle)
- Cell starts to prepare DNA for mitosis – supercoiling of DNA to form chromosomes
Describe what happens during Mitosis
1 point
Mitosis (nuclear division):
- Cell nucleus divides into two daughter nuclei, each GENETICALLY to parent cell nucleus and to each other
Describe what happens during Cytokinesis
1 point
Cytokinesis:
- The cytoplasm divides into two, forming 2 new cells
Key Summary: What is the {role/importance} of the cell cycle OR mitosis
(4 points)
- To produce NEW GENETICALLY IDENTICAL CELLS
- To INCREASE CELL NUMBERS FOR GROWTH
- And to REPLACE DAMAGED OR DEAD CELLS TO REPAIR DAMAGED TISSUE
- Asexual reproduction (in SOME organisms – read the Q)
What are the four stages of Mitosis?
Four stages (PMAT):
- Prophase (preparation)
- Metaphase (middle)
- Anaphase (apart)
- Telophase (termination/two)
NOTE: Cytokinesis is NOT PART OF MITOSIS, cytokinesis happens after mitosis
What happens during Prophase?
5 steps
Prophase (prepare):
- chromosomes CONDENSE (become shorter and thicker) and become VISIBLE
- NUCLEAR ENVELOPE BREAKS DOWN
- nucleolus breaks down
- CENTRIOLES move to opposite POLES
- SPINDLE FIBRES BEGIN TO FORM BETWEEN CENTRIOLES
- chromosomes and spindle {become/are} visible
- nucleolus and nuclear envelope become invisible
Note: there are NO CENTRIOLES in plant cells but the spindle fibres do form
What happens during Metaphase?
2 steps
Metaphase (middle):
- the chromosomes (made of 2 chromatids) ATTACH TO THE SPINDLE BY THEIR CENTROMERES
- chromosomes line up at the EQUATOR OF THE CELL
What happens during Anaphase?
3 steps
Anaphase (apart):
- CENTROMERES SPLIT, separating the two sister chromatids of each chromosome
2 (this point is important). spindle fibres CONTRACT PULLING THE CHROMATIDS BY THEIR CENTROMERES
- chromatids separate and MOVE TO OPPOSITE POLES (ends) of the cell
What happens during Telophase?
4 steps
Telophase (termination/two):
- CHROMOSOMES UNCOIL so decondense (become long, thin chromatin again)
- NUCLEAR ENVELOPE REFORMS around each group of chromosomes (forming 2 separate nuclei)
- NUCLEOLI REFORM in each nucleus
- Spindle breaks down
- 2 nuclei in one cell
- chromosomes and spindle become less visible
- nuclear envelopes and nucleoli become visible
Note: opposite of prophase
What is cytokinesis? (1 point)
How does it happen in animal cells? (1 point)
How does it happen in plant cells? (1 point)
- Division of the cytoplasm
- In animal cells, the cell surface membrane CONSTRICTS AROUND THE CENTRE OF THE CELL - a ring of protein filaments on the inside of the cell surface membrane are thought to contract
- Plants cells synthesise a new CELL PLATE between the two new cells
