Genomes Flashcards
1
Q
what is a genome
A
complete haploid set of genetic material of an organism
2
Q
what is the size of the human genome
A
3.2 x 109 base pairs
3
Q
chromosome consist of?
A
- single, enormously long linear DNA molecule
- proteins involved in DNA packaging e.g. histones
4
Q
What is chromatin?
A
a complex of DNA + tightly bound proteins
5
Q
Define a gene
A
- Most genes: segment of DNA that codes for a particular protein (or a family of related proteins)
- some genes (RNA genes): codes for functionally significant RNA molecules as final product
6
Q
What are introns and exons?
A
- sections within genes
- introns are long streches of non-coding DNA that interuptes relatively short exons (coding DNA)
- introns spliced out after transcription in mRNA processing
7
Q
What is C-value
A
C-value is the amount, in picograms, of DNA contained within a haploid nucleus
8
Q
What is the C-value paradox?
A
- lack of relationship between the complexity of organism and genome size
- closely related species, with similar number of genes can differ hundredfold in genome size
- especially prominent in eukaryotes
- prokaryotes have concise genome
9
Q
What caused the C-value paradox?
A
- Large amount of “junk DNA” (non-coding DNA)
- Some non-coding DNA has regulatory functions
- important for multicellular organisms, they need to turn genes on and off throughout development
10
Q
How does junk DNA persist in the eukaryotic genome?
A
- most junk DNA has no clear function
- not under strong selection pressure
- not easily lost
- junk DNA enhances their own transmission by e.g. over-replication
- have histones to turn genes off
11
Q
Why do prokaryotes have concise genome?
A
- need for constant DNA replication => selcection pressure for efficiency/speed in replication process
- don’t have histones to switch genes off => more prone to deleterious effects of parasitic sequences => selection pressure against junk DNA
12
Q
What are LINEs and SINEs?
A
13
Q
Why does DNA need packaging
A
- 2m of DNA need to fit in 5-6µm nucleus
14
Q
Why is DNA packaging dynamic
A
- need to be unpackaged for the access of enzymes to carry out:
- gene expression
- DNA replication
- DNA repair
- require specialised proteins to package DNA
15
Q
How is DNA packaged?
A
- DNA is wrapped around histones to form nucleosomes
- converts a DNA molecule into a chromatin thread about one-third of its initial length
- 11nm in diameter
- nucleosomes further packaged, forming 30nm chromatin fibre
- fifth histone (H1) pulls the nucleosomes into a regular repeating array
- 30nm fibre undergoes more packaging by unknown processes
- end product is approx. condensed 10000 times
16
Q
structure of nucleosomes
A
- complex of 8 histone proteins assemble to form a protein core which DNA is wrapped around about 2 times
- histone proteins: two molecules each of histones H2A, H2B, H3, and H4
