| How are mitosis and meiosis clinically significant | Mitosis
- regeneration of tissues
- manipulation of stem cells
Meiosis
- Consequences of faulty meiosis
- e.g.) infertility, retardation |
| Difference between RNA and DNA | RNA - Single stranded, ribose sugar, uracil
DNA- Double stranded, 2-deoxyribose sugar, thymine |
| Describe the formation of visible chromosomes (under light microscopes) from the double helix structure | In the nucleus
- double helix structure of DNA is wrapped around histones to form nucleosomes, which form 'beads on a string DNA'
- Nucleosomes tightly packs into solenoid structure, forming 30nm fibres
- Fibres are compacted into several hierarchical loops to create highly condensed structure which is visible |
| Describe what happens in each stages of cell cycle | G1
- Cell content replication
- lysosomes, mitochondria etc. doubled
- APART from chromosomes
S
- DNA replication
- each of 46 chromosomes are doubled
G2
- Cell division preparation
- double check of duplicated chromosomes and repair
Mitosis
- cell division
Cytokinesis
- division of cytoplasm
- parent cell becomes 2 daughter cells with identical genetic information |
| Describe the stages of mitosis
Prophase, prometaphase, metaphase, anaphase, telophase | Prophase
- breakdown of nuclear membranes
- chromosomes condense
Prometaphase
- Spindle fibres attach to chromosomes
Metaphase
- chromosomes align at the middle
Anaphase
- chromosomes divide and sister chromatids move to opposite poles
Telophase
- Nuclear membranes form
- chromosome decondense
- spindle fibre disappears |
| Give out the purpose of checkpoint 1 and 2 in the cell cycle
Also, indicate where they are in the cell cycle | Checkpoint 1
- in between G1 and S
- checking process before entering S phase
- signifies cells to enter S phase
Checkpoint 2
- in between G2 and mitosis
- waits for signal to enter mitosis
- Checks if everything has been replicated, and if DNA and chromosomes are fully intact |
| Name the catalyst used in DNA replication and how it catalyzes | DNA polymerase
- utilises deoxyribonucleoside triphosphate (dNTP) and joins new nucleotides onto template strand
- while the helicase unwind the DNA helicase and primase is removed |
| What does DNA ligase do | Joins okazaki fragments together on the opposite site of the double helix during elongation
- this is because the the helix runs in opposite directions (3' to 5')
*note that DNA polymerase acts on a normally running strand (5' to 3') on the oppposite side |
| Name drugs which may inhibit DNA replication | Cisplatin and BCNU
- treat cancer and leukaemia
- elongation inhibited
Arac and 6-MP
- treat acute leukaemia
- termination inhibited |
| How does genetic diversity arise from meiosis | Independent assortment of chromosomes
- meiosis I
Crossing over |
| At which stage does crossing over happen?
Also describe what happens in that stage in order for crossing over to happen | Prophase I
- disintegration of nuclear envelope
- formation of tetrad from pair of chromosomes |
| Difference between meiosis I and meiosis II | Meiosis I
- homologous chromosome pair divided
Meiosis II
- chromatids of each chromosome divided |
| As gametes are haploid, genetic information must be halved during
spermatogenesis and oogenesis.
Describe the process of each | Spermatogenesis
- spermatogonium->primary spermatocyte-> spermatids-> mature sperm
- 48 days
Oogenesis
- Oogonium, primary oocyte-> polar bodies -> mature ovum
- age 12 to 50 |
| How are mitosis and meiosis clinically significant | Mitosis
- regeneration of tissues
- manipulation of stem cells
Meiosis
- Consequences of faulty meiosis
- e.g.) infertility, retardation |
| Define genotype and phenotype | Genotype
- genetic composition of individual
Phenotype
- physical appearance of the gene |
