What is the difference between heterochromatin and Euchromatin?
Relatively few active genes
- Dark bands
- A + T rich
- replicate late in S phase
- 80% active genes
- Light bands
- G + C rich
- Replicate early in S phase
What is the difference between constitutive and regulated gene expression?
•Products made by all cells all the time -often called ‘housekeeping’ genes
•Expression is constant
•Time (developmental), place (cell type), amount, in response to signals
•Can be under very tight control
Illustrate the different products of gene expression
Discuss the role of the spliceosome in RNA splicing of protein-coding genes
The spiceosome is a large ribonucleoprotein complex that splices primary RNA transcripts to remove introns
Splicing occurs between a donor splice site and an acceptor splice site downstream. The intervening intronic region between the two genes is loooped and cleaved out of the mRNA transcript at the donor and acceptor splice sites. The two sites are then bound together to form an exonic mRNA
What processes can be modulated to alter gene expression?
How does chromatin remodelling affect gene expression?
Chromatin remodelling requires chemical modification (epigenetic markers) to histones and DNA
Acetylation promotes open euchromatin conformation
Methylation promotes heterochromatin conformation
DNA methylation suppresses gene expression at CpG islands which surround promotor regions of genes
What is required for transcriptional regulation?
Initiation of transcription requires RNA polymerase and other proteins (transcription factors) to bind at promoter regions (egTATA box) at the very minimum.
Is there a single promotor region to a gene?
Many genes have more than one promotor region that dictates the beginning of transcription
This introduces greater diversity into the genome
What post-transcriptional regulation of gene expression can occur?
Alternative splicingof different exonscan lead to different protein products -often tissue specific
Alternatively spliced transcripts can be identified for almost every human gene
Depending upon the splicing regulation; a sequence can be an intron or exon
What effects can long non-coding RNAs have of gene expression?
Long non-coding RNAs can regulate gene expression as:
- act as decoys that titrate away DNA-binding proteins such as transcription factors or RNA polymerase
- bring or more proteins together into a functional complex of spatial proximity
- recruit proteins to DNA
- Assists in looping the chromosome/DNA sequence and guiding proteins to the loop
How can siRNAs degrade mRNA
Short interfering RNA (siRNA) can bind a RNA-induced silencing complex (RISC) within the cytoplasm
Upon binding, the siRNA can bind a complementary sequence of mRNA where the RISC then cleaves at this site
This degrades mRNA
What are the effects of miRNAs?
Although the mechanism remains unclear, miRNA molecules can bind RNA-induced silencing complexes and caused repressed translation.
miRNAs direct the complex to complementary mRNA where its presence prevents further translation by ribosomes