Cell Division (Lecture 1) Flashcards
What is cell division?
The process by which cells make more cells
Why does cell division occur?
– Growth – Cell replacement – Healing – Reproduction
Cell division occurs by…
- Mitosis (eg, hair stem cells) 2. Meiosis (germ or sex cells)
If a stem cell divides once a day for 75 years how many times would it have divided without making a mistake?
Over 27,000
What are the main stages of the cell cycle?
- G1 phase 2. S phase 3. G2 phase 4. M phase 5. G0 phase
What happens in the G1 phase (gap 1)?
Growth, cellular metabolism
What happens in S phase (Synthesis)?
DNA replication (chromosome duplication)
What happens in G2 phase (Gap 2)?
Preparation for mitosis
What happens in M Phase (mitosis)?
Chromosomal separation and cytokinesis
Which parts of the cell cycle are involved in interphase?
- G1 phase 2. S phase 3. G2 phase 4. G0 phase
Interphase is the time between…
Successive mitoses G1 + S + G2
Cells exit the cell cycle from G1 and enter a state called… and why?
G0, Cells that are not actively cycling may exit
Cells that enter the G0 state are said to be…
Quiescent
What would be considered quiescent with respect to the cell cycle?
A neutron with its axon and dendrites would be quiescent with respect to the cell cycle. It will not re-enter the cell cycle
What are homologous chromosomes?
Homologous chromosomes are two pieces of DNA within a diploid organism which carry the same genes, one from each parental source
What is a centromere?
The centromere is the specialized DNA sequence of a chromosome that links a pair of sister chromatids
After two homologous chromosomes undergo S phase what happens?
Each chromosome duplicates creating sister chromatids attached to one centromere
What are sister chromatids?
A sister chromatid refers to the identical copies (chromatids) formed by the DNA replication of a chromosome, with both copies joined together by a common centromere
What events occur in Prophase?
Chromosomes condense. Centrosomes radiate microtubules and migrate to opposite poles
What are chromatin fibres?
Chromatin is composed of DNA and histones that are packaged into thin, stringy fibers
What is a nuclear envelope?
The double-layered membrane enclosing the nucleus of a eukaryotic cell. The nuclear envelope has pores that allow the passage of materials into and out of the nucleus. Also called nuclear membrane.
What events occur in Prometaphase?
Microtubules of the mitotic spindle attach to chromosomes, nuclear envelope starts to break down
What are kinetochores?
A complex of proteins associated with the centromere of a chromosome during cell division, to which the microtubules of the spindle attach
What events occur in Metaphase?
Chromosomes align in center of cell
What events occur in Anaphase?
Sister chromatids (which become individual chromosomes when the centromere splits) separate and travel to opposite poles
What events occur in Telophase?
Nuclear envelope re-forms and chromosomes decondense
What are ploidy levels?
The number of complete sets of chromosomes in a cell
What is a cell with a complete set of chromosomes?
Haploid
Sperm cell or an egg cell would be an example of what cell?
Haploid cell
What would a diploid cell have?
A diploid cell would have two complete sets of chromosomes. One copy from the mother and one copy from the father
What are examples of diploid cells?
Example of a diploid cell would be a somatic cell, such as a leaf cell or a skin cell or a stem cell in your colon
Explain haploid (n) vs diploid (2n)
When one unique chromosome from Dad’s germ cell (haploid cell (n)) comes together with 1 unique chromosome from Mom’s germ cell (haploid (n)) it creates one homolog (homologous chromosomes) which are now diploid cells (2n). 2 unique chromosomes (2n).
What happens to diploid somatic cells after s phase?
Still considered a diploid cell, even though there are 4 complete sets of chromosomes. This is a short and transient phase. Note that the amount of DNA has doubled.
What events occur in cytokinesis (animal)?
Cytokinesis divides the cytoplasm of a parental cell into two genetically identical daughter cells
What types of cells does Mitosis occur in?
Stem cells
Amount of ______ changes, but NOT the ________ level in Mitosis
Amount of DNA changes, but NOT the ploidy level in Mitosis
