Molecular Genetics and Pathology Flashcards
What is less stable; RNA or DNA?
RNA is less stable.
-hydroxyl (OH) group on C2»_space; neutrophilic attack»_space; breaks chain
What direction are DNA and RNA synthesised in?
5’ to 3’ direction.
What strand is normally written in DNA shorthand?
The ‘sense’ strand.
-strand that ends up as mRNA
How many base pairs are present in a human haploid genome?
~3,000 Mbp.
chr 1 = 263, chr 22 = 39
What proportion of DNA is non-coding?
> 90%.
How many protein-coding genes are there?
~20,000.
What is the average size of a gene (kb)?
50-100 kb.
What are the classes of genome sequences? (2)
- Single copy sequences (non-repetitive)
- Repetitive sequences
What is transcription?
DNA»_space; mRNA.
- by RNA polymerase
- 1st step of gene expression
What is translation?
mRNA»_space; proteins.
-at ribosomes
What are regulatory sequences?
Components of genes.
- promoters
- enhancers
- locus control regions
What is the general process of gene production?
(NUCLEUS) >>transcription >>cleavage and polyadenation >>splicing >>(CYTOPLASM) >>translation >>postranslational modifications
What is alternative splicing?
Exon skipping.
-large variation; single gene can code for multiple proteins
What are pseudogenes?
DNA sequences that resemble protein-coding genes, but are non-functional due to mutations.
-cannot be translated
What are processed genes?
Intronless copies of other genes.
-occasionally remain functional (e.g. PGK2)
What causes processed genes?
Spliced RNA copy genes being reverse transcribed»_space; DNA and re-entering genome.
-e.g HIV
What are the main types of repetitive sequences?
- ‘Satellite’ DNA
- Interspersed repeat
What is satellite DNA?
Large repetitive DNA sequences at centromeres and heterochromatic chromosomal regions.
-various sizes (polymorphic)
What is alphoid DNA an example of?
Satellite DNA.
- 171 bp unit
- at centromeres, required for assembly
- particularly repetitive
How is alphoid DNA used to identify individual chromosomes?
It’s chromosome specific.
What are interspersed repeats?
Repeats scattered around the genome.
-may form part of gene structure
Give an example of an interspersed repeat (most widely distributed).
Alu repeat.
- 500,000 copies
- 5% of genome
- dispersed by retrotransposition
What problem can occur during meiosis 1 (crossing over)?
Misalignment of chromosomes due to interspersed repeats.
»unbalanced ‘hybrid’ chromosomes
-1 deletion, 1 duplication
What size deletion is most likely to remain functional?
3bp deletion.
-doesn’t cause a frameshift mutation