How much of our genome is transcribed?
Very little of this actually codes for protein
Describe the mitochondrial genome?
13 protein-coding genes
24 RNA-coding genes
Describe the difference between heterochromatin and euchromatin?
Heterochromatin: dark bands on chromosome, A and T rich, few active genes, closed conformation
Euchromatin: light bands on chromosome, C and G rich, 80% active genes, open conformation
Describe the different types of primary transcripts that can result from gene transcription?
rRNAs and tRNAs > further processing
mRNAs > proteins
Other non-coding RNAs > further processing
Describe the RNA splicing of protein-coding genes?
snRNPs bind to splice and branch sites on RNA > spliceosome forms > cleavage > introns removed
Spliceosome: large ribonucleoprotein complex that splices primary trasncripts to remove introns
Describe how a single gene can produce a complex array of different protein products?
Each gene can have multiple start sites for transcription/promoter regions
At which points of gene expression can regulation occur?
Open conformation of chromatin
Protein targeting and transport
How can histone proteins be aletered, and what effect can this have on the DNA that they are associated with?
Can be chemically modified, e.g. acetylation, methylation
Can cause DNA to wind more or less tightly
How does chromatin remodelling occur?
Chemical modification to histones and DNA
Describe how chromatin is remodelled via DNA methylation?
A large proportion of cytosines are in CG adjacent pairs (CpG), and are methylated
This pattern is passed to daughter cells during replication
Where are CpG island usually found in genes?
Associated with 5' region
Often surround promoters of genes
Describe how methylation and acetylation differ between euchromatin and heterochromatin?
Euchromatin: active; hypomethylation, hyperacetylation
Heterochromatin: silent; hypermethylation, hypoacetylation
Describe the post-transcriptional regulation of gene expression?
Alternative splicing of exons > different combinations create different proteins
Describe how long non-coding RNAs can regulate gene expression?
Can acts as:
Scaffold (bring in other transcription factors)
Guide (guide transcription factors or RNA polymerase)
Enhancer (bring enhancer close to region)
Describe how siRNAs can regulate gene expression?
siRNAs produced in short double stranded format > interact with RISC > binds and degrades mRNA
Describe how miRNAs can regulate gene expression?
miRNAs bind RISC > bind mRNA > translation repressed (mechanism unclear)