Genome structure Flashcards
How does DNA exist in 3D?
- two antiparallel strands
- stacked bases
- two grooves (major and minor)
What is the order in which DNA is packed?
- DNA basic helix
- nucleosomes
- chromatin fibre
- extended section of chromosome
- loops of chromatin fibre
- chromosome
What are histones?
Basic proteins that bind DNA
Eight histones in total form the nucleosome unit, with histone one binding to the linker DNA
What is the relationship between DNA and genes?
The primary DNA sequence encodes all the gene products necessary for an organism, and also includes a large number of regulatory sequences
Much of the DNA sequence does not have an assigned function as of yet
What is a gene?
All of the DNA that is transcribed into RNA, plus all the cis-linked control regions required to ensure quantitatively appropriate tissue-specific expression of the final protein
- not just the bits that code for the final protein
How is the genome organised?
Genes cluster into families (e.g. globin clusters), whic allows for co-ordinate gene regulation and reflects evolutionary history
What are the intergenic regions of the genome?
Contain sequences of no known function, such as repetitive DNA, endogenous retroviruses, pseudogenes, etc.
How does RNA polymerase bind to the strand?
Promoters recruit RNA polymerase to a DNA template, which binds asymmetrically and moves 5’ to 3’
List the functions of the three RNA polymerases
RNA polymerase I: needed to transcribe rRNA genes
RNA polymerase II: needed to transcribe mRNA
RNA polymerase III: needed to transcribe tRNA and other small RNAs
Summarise the steps of transcription
1) RNA polymerase recruited
2) DNA helix locally unwound
3) RNA synthesis begins
4) Elongation
5) Termination
6) RNA polymerase dissociates
What are enhancers?
Short sequences that can be in the gene or many kb distant. They upregulate gene expression and are targets for transcription factors (activators)
What are silencers?
Downregulate gene expression. They are also position-independent and are also targets for transcription factors (repressors)
What are insulators?
Short sequences that act to prevent enhancers/silencers influencing other genes
How is eukaryotic mRNA modified after transcription?
- capped at the 5’ end
- polyadenylated at the 3’ end
- intervening sequences (introns) removed
What is alternative splicing?
Exons can be skipped or added, so variations of a protein (isoforms) can be produced from the same gene
