Lecture 10: CSF Cell Division Flashcards
Do all cells in one human have the same DNA?
Yes
How are cells different even though they contain the same DNA?
Different parts of DNA (genes) are expressed
What are the 3 possible outcomes for a cell?
Live and function without dividing
Grow and divide
Die
What are somatic cells?
Body cells (all cells excluding gametes) - diploid (2n)
Why do somatic cells need to divide?
Tissue replacement
Growth
What is mitosis?
The division of a diploid cell to form two identical diploid daughter cells
What is meiosis?
The division of a diploid cell to form four haploid sex cells with different genetical information to parent cell
What are the steps of the eukaryotic cell cycle?
Mitotic phase -> G1 phase -> S phase -> G2 phase -> mitotic phase
What is interphase?
G1 phase S phase and G2 phase
Most cells of the body are performing there functions in interphase.
What occurs in the G1 phase?
Most cellular activities - the duration varies from cell to cell
What occurs in the S phase?
DNA replication - 23 sets of chromosomes before exist as single chromatids, they become 23 sets of chromosomes which are formed from two sister chromatids pairing up
What occurs in the G2 phase?
Checks for correct DNA synthesis
Preparation for mitosis (synthesis of proteins and enzymes, gathering of reactants)
Replication of centrosomes (made up of centrioles which organise microtubules)
What are the steps of the mitotic phase?
Prophase (early and late) Metaphase Anaphase Telophase Cytokinesis
What occurs in prophase of mitosis?
DNA condenses (existing as two identical chromatids per chromosome - sister chromatids) Mitotic spindle begins forming Nuclear envelope breaks down
What occurs in metaphase of mitosis?
Condensed chromosomes align at the equator via their centromeres
What occurs in the anaphase of mitosis?
The microtubules contract pulling apart sister chromatids to each end of the cell
What occurs in the telophase of mitosis?
Nuclear envelope reforms
Cleavage furrow
What are diploid cells?
Cells with 2 sets of chromosomes
What are haploid cells?
Cells with only 1 set of chromosomes (sex cells)
At what points do checkpoints exist for the mitotic cycle?
At the end of G1 phase (G1 checkpoint)
At the end of G2 phase (G2 checkpoint)
At the end of metaphase during mitosis (M checkpoint)
What is the G1 checkpoint?
Checkpoint near the end of G1 phase that checks for:
- Is the DNA undamaged?
- Is cell size and nutrition ok?
- Appropriate signals present?
What happens if a cell does not pass the G1 checkpoint?
Enters G0
What is the M checkpoint
Checkpoint at the end of metaphase to check whether all chromosomes have been attached to the equator of the spindle
Where does meiosis occur?
In the gonads (testes and ovaries)
What are the two stages of meiosis?
Meiosis I: Prophase I Metaphase I Anaphase I Telophase I
Meiosis II: Prophase II Metaphase II Anaphase II Telophase II
What occurs in meiosis I?
Separation of homologous chromosomes (diploid to haploid)
A diploid parent cell divides forming two haploid daughter cells with non-identical genetic information
What are homologous chromosomes
Homologous chromosomes are chromosomes that share the same structure and gene loci - one from female and one from male in human
What is synapsis?
When two sister chromatids of each pair of homologous chromosomes pair up
= two chromosomes, each with two sister chromatids paired up, that have the same structure and gene loci, pair up
A 4 chromatid structure called a tetrad is formed
What is a tetrad?
A 4 chromatid structure formed from synapsis in which homologous chromosomes each with 2 sister chromatids paired up pair up.
What occurs in prophase I of meiosis?
Homologous chromosomes pair up
Nuclear envelope breaks down
Spindle begins forming
Crossing over occurs - non-sister chromatids (chromatids from different chromosomes) pair up forming chiasmata and exchange genetic information
What is chiasmata?
Overlap of non-sister chromatids in a homologous pair of chromosomes
What is crossing over?
Exchange of genetic information between non-sister chromatids in a homologous pair of chromosomes during prophase I.
What occurs in metaphase I of meiosis?
The kinetochore (at centromere) of homologous chromosomes line up at the equator of the spindle
Independent assortment - the random splitting of homologous chromosomes at the equator during metaphase I
What occurs during anaphase I of meiosis?
The homologous chromosomes separate
Sister chromatids remain attached
What occurs during telophase I of meiosis?
Cleavage furrows
What occurs during meiosis II?
Each of the 2 daughter haploid cells divide in a process identical to mitosis forming 4 daughter haploid cells
What are the 3 sources of genetic variation and at what points do they occur?
Crossing over - prophase I
Independent assortment - metaphase I
Fertilisation - fusion between two gametes
