IMMS revised Flashcards
What is the structure of DNA? (coiling)
double helix
coils around nucleosomes and coils again into supercoils
then into chromosomes
What are the 4 DNA bases and their pairing?
Adenine binds to thymine (2 H bonds)
Guanine binds to cytosine (3 H bonds)
How many chromosomes are there?
46
22 pairs then sex chromosomes
Structure of chromosomes
Long arm (q)
Short arm (p)
Centromere controls movement at division
Telomere seals tip
Each chromosome contains hundreds of genes
What stains can be used to see chromosomes?
Giemsa: G banding
Quinacrine: Q banding
What does mitosis do?
Producing two daughter cells genetically identical to parent cell
Growth
Replace dead cells
What are the stages of the cell cycle?
G1
S phase
G2
Mitosis
Are mitotically inactive cells in the cell cycle?
No
They are in G0
What happens in interphase?
Cell grows
Replication of cytoplasmic organelles and DNA
When in the cell cycle does DNA replication occur?
S phase
What happens in prophase?
Chromatin condenses into chromosomes
Centrosomes nucleate microtubles and move to opposite poles of nucleus
What happens in prometaphase?
Nuclear membrane breaks down
Microtubules invade nuclear space
Chromatids attach to microtubules
What happens in metaphase?
Chromosomes line up along equatorial plane (metaphase plate)
What happens in anaphase?
Sister chromatids separate and are pushed to opposite poles of the cell
What happens in telophase?
Nuclear membranes reform
Chromosomes unfold into chromatin
Cytokinesis begins
Why is mitosis clinically relevant?
Categorising tumours as benign or malignant
Detecting chromosomal abnormalities
Grading malignant tumours
What does meiosis produce?
4 genetically different daughter cells
2 divisions
Where can mitosis and meiosis occur?
Mitosis can occur in all cells
Meiosis can only happen in gametes
How are sperm produced?
Primordial germ cells undergo mitoses to produce spermatogonia
Meiotic divisions commence at puberty
cytoplasm divides evenly
After meiosis II four equal gametes
Millions of mature sperm continuously produced
How long does sperm production take?
60-65 days
How are ova produced?
Primordial germ cell undergoes mitosis in utero to produce oogonia
First meiotic division in utero
Process suspended until ovulation in future
Second meiotic division only at fertilisation
Does the cytoplasm divide equally in ova?
No
1 egg and 3 polar bodies that apoptose
What is non-dysjunction?
Failure of chromosome pairs to separate in Meiosis I or sister chromatids to separate properly in meiosis II
What is trisomy 21?
Downs syndrome