IMMS HK Flashcards
Med 1
Describe the structure of DNA?
•Double helix •Complementary base pairs Adenine A= T Thymine Cytosine C G Guanine (3 lines in the bond) -- Coils around nucleosomes -- Coils again into super coils. -- and again into chromosomes > found in -nucleus --> mitochondria.
Describe chromosomes?
•Human genome –> 46 chromosomes–> each contains continuous DNA duplex/double stranded (10⁷ base pairs) –> several 100 genes.
• Centro-mere has Long arm (q) and short arm (p)
• Characterisically stained for identification and analysis with dyes.
> Giemsa - G banding
G banding, or Giemsa banding is a
technique used in cytogenetics to produce a
visible karyotype by staining condensed
chromosomes.
> Quinacrine -Q banding
is the first chromosome banding pattern
reported. It is done by treating the chromosomes
with quinacrine dihydrochloride.
(each band -> 6-8 Mbp mega base pairs)
What is mitosis for?
- Producing 2 daughter cells –>genetically identical to parent cell.
- Growth
- Replace dead cells.
What is the cell cycle?
• Mitosis –> G1 growth phase –> synthesis phase (–>DNA/centrosome replication) –> G2 growth phase –> Mitosis
(Interphase
What is the clinical relevance and pharmacology of mitosis?
- Detecting chromosomal abnormalities.
- Categorising tumours as benign/malignant
- Grading malignant tumours.
• Mitotic spindle
--> Taxol
--> Vinca alkaloids --> vinblastine/vincristine
• Anaphase --> colchicine-like drugs
• Spindle poles --> Ispinesib
What are the steps of mitosis?
PMAT
1) Prophase:
> chromatin condenses to chromosomes > centrosomes nucleate microtubules & move to opposite side of pole.
2) Prometaphase:
> nuclear membrane breaks down
> microtubules invade nuclear space.
> chromatids attach to microtubules.
3) Metaphase:
>chromosomes line up along equatorial plane (metaphase plate).
4) Anaphase:
> sister chromatids separate and are pushed to opposite poles of cell.
5) Telophase:
> nuclear membrane reforms, chromosomes –> chromatin cytokinesis begins
Describe meiosis?
•Similar to mitosis but differences > only in gametes > recombination of genetic material > diversity. • 2 cell divisions • 4 haploid cells • cross over in prophase 1 > genes sort independently. • Meiotic division 1 and meiotic division 2.
What is non-disjunction and how does Downs syndrome arise form it?
•Non-disjunction: > failure of chromosome pairs to separate in meiosis I or sister chromatids to separate in meiosis II. •Downs syndrome 75% maternal meiosis I > 25% maternal meiosis II > 3-5% paternal non-disjunction.
What is gonadal mosaicism?
One cell line normal and one cell line mutated.
• Occurs when precursor germline cells to ova or spermatozoa are a mixture of 2 or more genetically different cell lines. (parent is healthy but fetus has genetic disease).
> incidence increase w/ paternal age.
• Most commonly autosomal dominant/x linked.
• Osteogenesis imprefecta/duchenne muscular dystrophy
What are the different causes of disease?
Genetic (individually rare, cumulatively enough to have regional genetic services). •Downs syndrome •Cystic fibrosis •Huntington disease. •Haemiphilia
Multifactorial (main cause of disease in developed countries).
> Combination of environmental and genetic factors.
•Spina bifida
• Cleft palate
• Diabetes
• Schizophrenia
Environmental (main cause in developing countries + A+E) • Poor diet • Drugs • Infection • Accidents
What is the difference between genotype and phenotype?
- Genotype > genetic constitution of an individual.
- Phenotype > appearance of an individual (physical, biochemcial, physiological) which results from interaction of environment and genotype.
What is an allele and polymorphism?
Allele
•One of the several alternative forms of a gene at a specific locus.
>Normal allele is wild type
>Disease allele is carrying a pathogenic variant.
Polymorphism
•Frequent hereditary variations at a locus.
What are the different ways to describe alleles?
- Homozygous - both alleles the same at a locus.
- Heterozygous - alleles at a locus are different.
- Hemizygous - only 1 allele refers to a locus on an x chromosome in a male.
What is imprinting?
•For some genes, only 1 out of 2 alleles is active (the other is inactive).
> For particular genes, it is always paternal or maternal allele.
How do you classify a disease?
•Chromosomal
•Mendelian
> autosomal dominant - manifest in heterozygous state.
> autosomal recessive - manifest in homozygous state
> X-linked - pathogenic variants in X chromosome.
•Non-traditional.
>mitochondrial
>imprinting
>mosaicism
