1. The Cell Cycle & Mitosis Flashcards
What is the Cell Cycle
The process that all body cells in multicellular organisms use to grow & divide.
Start & end of Cell Cycle
The Cell Cycle starts when a cell has been produced by cell division & ends with the cell dividing to produce 2 genetically identical cells
What does the Cell Cycle consist of
- The Cell Cycle consists of a period of cell growth & DNA replication, called Interphase, & a period of cell division called M phase.
- The mitotic phase (M phase) involves mitosis (nuclear division) & cytokinesis (cytoplasmic division).
- Interphase (cell growth) is subdivided into 3 separate growth stages: G1, S and G2.
How is the Cell Cycle regulated
The Cell Cycle is regulated by checkpoints - occur at key points to control the cycle, making sure the process is ready to continue
What is mitosis needed for
- The growth of multicellular organisms & for repairing damaged tissues.
- Its also a method of asexual reproduction for some plants, animals & fungi.
What is mitosis
- Mitosis is one continuous process, but is described as a series of division stages - prophase, metaphase, anaphase, telophase (PMAT).
- Interphase comes BEFORE mitosis in the cell cycle.
What is Interphase
- The cell carries out normal functions, but also prepares to divide.
- The cell’s DNA is unravelled & replicated, to double its genetic content.
- The organelles are also replicated so it has spare ones, & its ATP content is increased (ATP provides energy needed for cell division).
Stages of mitosis
- Prophase
- Metaphase
- Anaphase
- Telophase
What happens in Prophase
- The chromosomes condense or supercoil.
- The original chromosome & its copy are called chromatids. They are joined to their copy at a centromere. (there are 2 strands bc each chromosome has already made an identical copy of itself during interphase).
- The centrioles migrate to opposite poles of cells.
- Microtubules develop from each centriole, some spanning the cell from pole to pole (spindle fibres).
- The membrane of the nucleus breaks down.
What happens in Metaphase
- The chromosomes lines up at the equator & attach to certain spindle fibres at their centromeres.
- There is no association between the homologous pairs in terms of the way they line up at the equator.
- At the metaphase checkpoint, the cell checks that all the chromosomes are attached to the spindle before mitosis can continue.
What happens in Anaphase
- The centromeres divide, separating each pair of sister chromatids. The spindle fibres contract, pulling chromatids to opposite poles.
What happens in Telophase
- The chromatids reach the opposite poles on the spindle. They uncoil & become indistinct again.
- The spindle fibres break down & a new nuclear envelope forms around each group of chromatids. So there are now 2 nuclei.
What happens in Cytokinesis (after mitosis)
- The cytoplasm divides.
- A cleavage furrow forms to divide the cell membrane. The cell continues to constrict inwards from its middle until the cell physically splits into 2 cells.
- There are now 2 genetically identical daughter cells.
- Cytokinesis usually begins in anaphase & ends in telophase. It’s a separate process to mitosis.
Stages of Interphase
- G1
(G1 checkpoint) - S
- G2
(G2 checkpoint)
What happens in G1
- 1st growth stage: proteins from which organelles are synthesised are produced & organelles replicate.
- The cell increases in size.
- Cellular contents APART from chromosomes are duplicated.
What happens at the G1 checkpoint
The cell checks that the chemicals needed for replication are present & for any damage to the DNA before entering S-phase.
What happens in S
- Synthesis phase: Chromosomes (DNA) is replicated in the nucleus.
What happens in G2
- 2nd growth phase: Cell continues to increase in size.
- Energy stores are increased & proteins needed for cell division are made.
What happens at the G2 checkpoint
The cell checks whether all the DNA has been replicated w/o any damage.
If it has, the cell can enter mitosis.
How can you observe the Cell cycle & Mitosis
- You can stain chromosomes to see them under a microscope. This means you can watch what happens to them during mitosis.
(MUST be able to recognise, draw & label each stage from a microscope image)
pg61 practice
How can we make it easier to see the chromosomes in microscopes
- Plant root cells can be viewed on a ‘squash’ microscope slide. In other words, they’ve been deliberately squashed beneath the cover slip.
- This makes it easier to see the chromosomes.
use Cell cycle circle diagram, Stages of mitosis diagrams & pg60
