Cell Division, Cell Diversity and Cell Differentiation Flashcards
What is cytokinesis?
Cytoplasmic division following nuclear division, resulting in two new daughter cells.
These daughter cells are genetically identical to each other and their parents.
Once mitosis is complete, the cell splits into two, so that each new cell contains a nucleus.
In animal cells, the plasma membrane folds inwards and ‘nips in’ the cytoplasm.
In plant cells, an end plate forms where the equator of the spindle was, and new plasma membrane and cellulose cell-wall materials are laid down on either side along this end plate.
What is interphase?
Phase of cell cycle where the cell is not dividing, it is subdivided into growth and synthesis phases.
What is Mitosis?
A type of nuclear division that produces daughter cells genetically identical to each other and to the parent cell. They are also genetically identical to each other.
What are the purpose of cell-cycle checkpoints?
To prevent uncontrolled division that would lead to tumors (e.g. cancer).
To detect and repair damage to their DNA ( for example damage cause by UV light)
They ensure that the cell cycle cannot be reversed.
The DNA is only duplicated once during each cell cycle.
Stages of the Eukaryotic Cell Cycle:
M phase G0 (gap 0) phase G1 (gap 1) phase- the growth phase S (synthesis) phase of interphase G2 (gap 2) phase of interphase
M Phase:
A checkpoint chemical triggers condensation of chromatin. Halfway through the cycle, the metaphase checkpoint ensures that the cell is ready to complete mitosis.
Cell growth stops. Nuclear division (mitosis) consisting of stages: prophase, metaphase, anaphase and telophase.
Cytokinesis (cytoplasmic division).
G0 Phase:
A resting phase triggered during early G1 at the restriction point, by a checkpoint chemical. Some cells e.g. epithelial cells lining the gut, do not have this phase.
In this phase, cells may undergo apoptosis (programmed cell death), differentiation or senescence.
Some types of cells (e.g. neurone) remain in this phase for a very long time or indefinitely.
G1 Phase:
A G1 checkpoint control mechanism ensures that the cell is ready to enter the S phase and begin DNA synthesis.
Cells grow and increase in size.
Transcription of genes to make RNA occurs.
Organelles duplicate
Biosynthesis e.g. protein synthesis, including making the enzymes needed for DNA replication in the S phase.
The p53 (tumor suppressor) gene helps to control this phase
S Phase of interphase:
Because of the chromosomes are unwound and the DNA is diffuse, every molecule of DNA is replicated. There is a specific sequence to the replication of genes: housekeeping genes- those which are active in all types of cells, are duplicated first. Genes that are normally inactive in specific types of cells are replicated last.
Once the cell has entered this phase, it is committed to completing the cell cycle.
DNA replicates
When all chromosomes have been duplicated, each one consists of a pair of identical sister chromatids.
This phase is rapid, and because the exposed DNA base pairs are more susceptible to mutagenic agents, this reduces the chances of spontaneous mutations happening.
G2 Phase of interphase:
Special chemicals ensure that the cell is ready for mitosis by stimulating proteins that will be involved in making chromosomes condense and in formation of the spindle.
Cells grow
What are chromatids?
Replicates of chromosomes
What is Prophase?
The chromosomes that have replicated during the S phase of interphase and consists of two identical sister chromatids, now shorten and thicken as the DNA supercoils. The nuclear envelope breaks down. The centriole in animal cells divides and the two new daughter centrioles move to opposite poles of the cell. Cytoskeleton protein (tubulin) threads form a spindle between these centrioles. The spindle has a 3D structure and is rather like lines of longitude on a virtual globe. In plant cells, the tubulin threads are formed from the cytoplasm.
What is Metaphase?
The pairs of chromatids attach to the spindle threads at the equator region.
They attach by their centromeres.
What is Anaphase?
The centromere of each pair of chromatids splits.
Motor proteins, walking along the tubulin threads, pull each sister chromatid of a pair, in opposite directions, towards opposite poles.
Because their centromere goes first, the chromatids now called chromosomes, assume a V shape.
What is Telophase?
The separated chromosomes reach the poles.
A new nuclear envelope forms around each set of chromosomes.
The cell now contains two nuclei each genetically identical to each other and to the parent cell from which they arose.
What is Meiosis?
Sexual Reproduction
A type of nuclear division that results in the formation of cells containing half the number of chromosomes of the parent cell.
What are homologous chromosomes?
Matching chromosomes, containing the same genes at the same places (loci). They may contain different alleles for some of the genes.
There are 46 chromosomes in the human body cells. 23 from each parent.
Why is Meiosis significant in the life cycle?
Sexual Reproduction increases genetic variation because it involves the combining of genetic material from two unrelated individuals of the same species, by the process of fertilization.
Genetic Variation within a population increases its chances for survival when the environment changes.
What are the stages of Meiosis?
Prophase 1 Metaphase 1 Anaphase 1 Telophase 1 Prophase 2 Metaphase 2 Anaphase 2 Telophase 2
Prophase 1:
The chromatin condenses and each chromosome supercoils. In this state, they can take up stains and can be seen with a light microscope.
The nuclear envelope breaks down, and spindle threads of tubulin protein form from the centriole in animal cells.
The chromosomes come together in animal cells.
Each member of the pair consists of two chromatids.
Crossing over occurs where non-sister chromatids wrap around each other and may swap section so that alleles are shuffled.
Metaphase 1:
The pairs of homologous chromosomes, still in their crossed over state, attach along the equator of the spindle.
Each attaches to a spindle thread by its centromere.
The homologous airs are arranged randomly, with the members of each pair facing opposite poles of the cell. This arrangement is independent assortment.
The way that they line up in metaphase determines how they will segregates independently when pulled apart during anaphase.
Anaphase 1:
The members of each pair of homologous chromosomes are pulled apart by motor proteins that drag them along the tubulin threads of the spindle.
The centromeres do not divide, and each chromosomes consists of two chromatids.
The crossed-over areas separate from each other, resulting in swapped areas of chromosomes and allele shuffling.
