Topic 3 The Cell Cycle Flashcards
Describe the stages of the cell cycle.
The cell cycle is made up of two phases: the interphase and mitotic phase.
The interphase consists of three stages: the gap 1(G1) stage, the synthetic(S) stage, the gap 2(G2).
The mitotic phase consists of two stages: mitosis and cytokinesis.
The interphase lasts much longer than mitotic phase.
Describe what occurs in the G1 stage of the cell cycle.
In G1, the cell has just finished dividing.
The seller replicate its organelles, increases in size, and synthesise is many proteins.
Describe the S phase of the cell cycle.
DNA is synthesis and the chromosomes are replicated which produces two identical chromatids joined at the centromere.
Describe what occurs in the G2 phase of the cell cycle
The solar replaces its energy stores, repairs any damaged chromosomes, synthesise proteins, and increases in size.
Name the different phases of mitosis.
Prophase, metaphase, anaphase, and telophase.
Describe the prophase of mitosis.
The chromosomes coil up and can be stained to become visible.
The nuclear envelope and nucleolus break down.
The centrioles moved to opposite poles of the cell and begin to pull apart to form the spindle.
Describe the metaphase of mitosis.
The spindle apparatus made of microtubules is fully formed between the two centrioles and connect to the centromere of each chromosome.
The spindle fibres then move each chromosome to line them up on the metaphase plate of the cell.
Describe the anaphase of mitosis.
The centromeres split so that identical linked chromatids become separate.
They are now called chromosomes again.
Each chromatid from the pair is pulled to opposite poles of the cell by the microtubule spindle apparatus.
At the end of anaphase, the two sets of chromatids have been separated to opposite ends of the cell.
Describe the telophase of mitosis.
The spindle apparatus breaks down and nuclear envelopes form around the two sets of chromosomes.
The centrioles and nucleolus reform.
The chromosomes coil back up and become difficult to see.
The result two genetically identical nuclei.
Describe cytokinesis in both animal and plant cells.
In animal cells, a ring of contractile fibres tightens around the centre of the cell. They continue to contract until the two cells have been separated.
In plant cells, a cellulose cell wall builds up from the inside of the cell outwards.
Describe the importance of mitosis.
It is used to create new genetically identical cells to grow and replace old cells.
It is used as a method of asexual reproduction in some organisms.
This is advantageous because it does not rely on finding a maid and can give rise to a large number of offspring very quickly.
The disadvantage is that all the offspring are genetically identical and can rapidly die out from a disease.
Define the mitotic index.
It is the ratio between the number of cells in a tissue sample that are in mitosis to the total number of cells in the sample.
Mitotic index = (No. of cells in mitosis) / ( Total No. of cells)
Name the stages of meiosis.
It’s is divided into stages of nuclear divisions: meiosis 1 and meiosis 2
Meiosis 1 is made up of prophase 1, metaphase 1, anaphase 1, and telophase 1.
Meiosis 2 is made up of prophase 2, metaphase 2, anaphase 2, and telophase 2.
Describe the prophase 1 of meiosis.
The chromosomes condense and can be stained.
The nucleolus and nuclear envelope breakdown.
The centrioles move to opposite poles of the cell and spindle fibres start to form.
Homologous pairs of chromosomes can exchange alleles.
The chromatids cross over each other and these points are called chiasma.
The chromatids break and recombine forming recombinant chromatids.
Crossing over is a great source of genetic diversity during meiosis.
Describe the metaphase 1 of meiosis.
The spindle apparatus is fully formed and the pairs of chromosomes line up on the metaphase plate.
The maternal and paternal chromosomes line up randomly along the metaphase plate and this leads to genetic diversity during the anaphase 1.
This is because the maternal/paternal chromosome can either remain together or be mixed and separated.
This is called independent assortment.
Describes the anaphase 1 of meiosis
The centromeres do not divide.
Instead, each chromosome from a homologous pair moves to each pool of the cell.
As a result that chromosome number in each daughter nucleus is halfed.
Describe the telophase 1 of meiosis
The nuclear membrane reforms and the cell undergoes cytokinesis.
There may be a period of interphase after this, but no DNA replication will take place.
Describe the prophase 2 of meiosis.
The nuclear envelope breaks down a new spindle fibres are formed.
Describe the metaphase 2 of meiosis
The chromosomes which are still made up of Sister chromatic lineup on the metaphase plate.
Describe the anaphase 2 of meiosis
The centromeres divide on the chromatics move to opposite poles of the cell
Describe the telophase 2 of meiosis
The nuclear envelope preforms and cytokinesis occurs.
The result is four genetically different haploid cells.
Explain the importance of meiosis in producing genetic diversity.
- Crossing over: This occurs in prophase 1. The paternal and maternal chromosomes can exchange alleles to form recombinat chromosomes.
The exchange of genetic material leads to genetic diversity, but also, errors in this process lead to mutations which can create new alleles. - Independent assortment: the maternal and paternal chromosomes are distrubuted into the gametes completely at random. This occurs when the chromosomes line up along the metaphase plate in metaphase 1.
