cell cycle Flashcards
List the stages of the cell cycle in order
G1 S G2 Mitosis Cytokinesis G0
Describe what happens during interphase.
- DNA is replicated
- protein synthesis occurs in the cytoplasm
- mitochondria grow and divide, increasing in number
- in plants, chloroplasts also grow and divide
- normal metabolic processes occur.
Describe what happens in G1 phase of interphase.
The first growth phase. Proteins from which organelles are synthesised are made and organelles replicate. The cell grows in size
Describe what happens in S phase of interphase.
DNA is replicated
Describe what happens in G2 phase of interphase
The second growth phase. The cell continues to increase in size. Energy stores are increased and the DNA is checked for any errors
What are the two parts of the mitotic phase? And what happens at each?
Mitosis - nucleus divides
Cytokinesis - cytoplasm divides
What is G0 phase?
When the cell leaves the cell cycle, either temporarily or permanently
Why would a cell go into G0 phase?
- when a cell differentiates and becomes specialised
- when there is damage to the DNA
- the number of cells in G0 increases with age
What is the role of checkpoints in the cell cycle?
They monitor whether each phase has been completed correctly. This stops faulty DNA from being replicated
Where the three checkpoints in the cell cycle?
At the end of G1
At the end of G2 phase
At the point in mitosis where the the spindle fibres attach.
What happens at each checkpoint in the cell cycle?
G1 - if the cell passes the DNA is allowed to replicate. Checks correct proteins being produced etc.
G2 - checks the DNA for errors.
Mitosis - checks that the spindle fibres are correctly attached to the Chromosomes.
Define the term mitosis.
The process of the cell dividing. First the nucleus, then cytoplasm to produce two genetically identical daughter cells.
Define the term chromosome
A condensed form of chromatin - a DNA molecule.
Define the term centromere
The region joining two chromatids
Define the term sister chromatids
Two identical DNA molecules - chromosomes joined together
Define the term homologous pair
Two chromosomes that contain the same genes in the same loci
Describe how DNA is packaged in a chromosome
The DNA double helix is coiled and wrapped in loops around cores of the protein histone.
List the stages of mitosis in order
Prophase
Metaphase
Anaphase
Telophase
describe what happens in prophase of mitosis.
- chromatin coils and condenses to form chromosomes. the nucleolus disappears and the nuclear membrane begins to break down.
- protein microtubules form spindles linking the poles of the cell
- two centrioles migrate to opposite poles of the cell
- the spindle fibres attach to specific areas on the centromere and start to move the chromosomes to the centre of the cell.
describe what happens in metaphase of mitosis.
the chromosomes are moved by the spindle fibres to form a plane in the centre of the cell, called the metaphase plate.
describe what happens in anaphase of mitosis.
- the centromeres holding sister chromatids together divide, the chromatids are pulled to opposite ends of the cell by the spindle fibres.
- the v shape of the chromatids is due to them being dragged through the cytosol.
describe what happens in telophase of mitosis.
- the chromatids have reached the poles and are now called chromatids
- the two new sets of chromosomes assemble at each pole and a new nuclear membrane begins to form around each one.
- the chromosomes start to uncoil and the nucleolus is formed.
describe the process of cytokinesis in animal cells
a cleavage furrow forms around the middle of the cell. the cell surface membrane is pulled inwards by the cytoskeleton until it is close enough to fuse in the middle creating two cells.
describe the process of cytokinesis in plant cells
vesicles from the golgi apparatus begin to assemble in the same area as the metaphase plate. the vesicles fuse with each other and the cell surface membrane dividing the cell into two. new sections of the cell wall then form along the cell membrane.
