Cell division and its control Flashcards
What is mitosis? Where does it occur?
daughter cell has the same number of genetically identical chromosomes as the parent cell.
Most cells
What is meiosis?Where does it occur?
daughter cell has half the number of chromosomes as its parent.
Germ line cells- in ovaries and testies
What holds single double helix of DNA
Chromatids
Describe the 3 broad stages of cell division?
- Interphase- DNA replication
- mitotic (M phase)-Nucleus divides
- Cytokenisis- Cytoplasm divides
Describe the 3 main stages of inter phase and what happens at each stage
- G1- Cell synthesis RNA, enzymes and proteins. No DNA synthesis.
Check point at the end- determines if cell divides or enters G0 - Synthesis- chromosomes are duplicated (short)
- G2- Cell prepares for division. Increase in tubulin to make micro tubules to make mitotic spindles. Cell continues to grow
What type of Cell enter G0?
Stem cells awaiting single to to re-enter the cell cyle
Post-mitotic cells no longer capable of mitosis
List the 6 stages of mitosis in order
prophase, prometaphase, metaphase, anaphase, telophase, and cytokinesis.
What occurs in prophase?
Nuclear chromatin condenses into chromosomes each consisting of two identical chromatids linked by centromer.
Mitotic spindle beings to form between centrioles
What occurs in Prometaphase?
Chromosomes attach to microtubules by the kinetochore in the centromere. The centrioles move apart (in pairs) towards opposite ends forming microtubule organising centres.
What occurs in Metaphase?
chromosomes become aligned in the centre of the mitotic spindle.
What occurs in Anaphase?
chromatids seperate (opposite poles) to form the chromosomes of the daughter cells. The poles of the mitotic spindle move further apart.
What occurs in Telophase?
separated chromosomes reach the poles of the mitotic spindle, which begins to disappear. A new nuclear membrane is formed around each daughter set of chromosomes and mitosis proper is complete.
What occurs in Cytokinesis?
Cytoplasm of daughter cells divide.
A Contractile ring formed from actin and myosin pinches the cell until it splits (cleaves) into 2 daughter cells
What is the consequence of errors during meiosis?
aneuploidy (abnormal number of chromosomes)
What occurs in Meiosis- Prophase I?
Cell goes through an interphase period in which it grows, replicates its chromosomes.
Homologous pairs of chromosomes align and crossing over of chromosomal segments occurs.
Spindles form from microtubules.
What causes Genetic Variation in Meiosis?
Recombination (homologous chromosomes) and independent assortment.
The chiasmata is the point of contact, between two chromatids of homologous chromosomes. At a chiasma, an exchange of genetic material occurs between both chromatids, - chromosomal crossover, does not occur in mitosis.
What occurs in Meiosis – Metaphase I
Nuclear envelop dissolves
Pairs of chromosomes move to the equator of the cell. The homolougs chromosome facing each spindle pole (male or female) is random.
What occurs in Meiosis – anaphase I?
Homologous chromosomes move to the opposite pole of each cell. Sister chromatids remain joined.
What happens at Telophase I and Cytokinesis I ?
. Each daughter cell now has half the number of chromosomes but each chromosome consists of a pair of chromatids
Telophase 1- Spindle microtubles disappear. Nuclear membrane surrounds haploid set.
chromosomes uncoil back into chromatin. Sister chromatids remain attached.
Cytokensis occurs - completeing daughter cell creation
Cells may enter a period of rest known as interkinesis or interphase II. No DNA replication occurs during this stage.
What happens at Meiosis II?
Cell division resembles a normal mitotic cell division in that the nuclear envelope reforms around each group of chromosomes. It differs in that it occurs without further DNA replication and the daughter cells have half the number of chromosomes of the parent.
Use of cohesin in chromatid separation. What happens when it goes wrong?
Cohesin is a protein complex that regulates the separation of sister chromatids during cell division, either mitosis or meiosis. Cohesins hold sister chromatids together after DNA replication until anaphase when removal of cohesin leads to separation of sister chromatids.
Warsaw-Breakage Syndrome
(Cohesionpathy) develops
List where all the cell cycle check point occure
- G1-S
- G2-M
- Exit M
What is assessed in the check point G1-S
The DNA of the cell is undamaged, cell organelles have been replicated and that the cell has sufficient organelles to divide
What is assessed in the check point G2-M?
The DNA has been completely replicated correctly before the start of mitosis
What is assessed in the check M
Have chromosomes attached to the mitotic spindle
What triggers the Cell to move from one phase of the cell cycle to the other? State another function of this agent?
Cyclin which binds to cyclin-dependent protein kinases- phosphorylates proteins
Acts at check points to interrupt progression
Which tumour suppressor proteins detect DNA damage?
p53, p21
p53 blocks progression of cell cycle and Sythesizes P21 which inhibits CDK2
State which cyclin regulates which part of the cell cycle
G1 phase-Cyclin D and CDK4 or
S phase- Cyclin E-CDK2
Cyclin A-CDK2 activates DNA replication
G2- Cyclin A-CDK1
Cyclin B-CDK1 takes cells into mitosis
What is the function of the Retinoblastoma (Rb) protein? Describe how it does this
Prevents cells from from entering S.
When stimulated Cdk2 inactivates Rb thus releasing the E2F protein which activates S-phase entry
Which cell activates S phase entery?
E2F
Name 2 anti-microtuble agents and there mode of action
Vinca alkaloids -prevent the formation of the microtubules
Taxanes- prevent microtubule disassembly
what is the function of Anti-mitotics - Anti-microtubule agents
They prevent the cancer cells from completing mitosis. Cell cycle arrest occurs, which induces programmed cell death (apoptosis)
Name 3 types of chemotherapy drugs and what they target
Anti-mitotic drugs- ant dividing cell
Biologics- monoclonal antibodies
Anti-hormonal drugs- block receptors on hormonal driven tumours
