Gene Expression 1 Flashcards
What are housekeeping genes?
Cells often have some of the same proteins that keep it working such as histones, RNA polymerase. If these genes were taken away then the cell would die
Why are some genes not found in all cells still vitally important?
Specialised proteins not essential for cell viability but are for the organism
Therefore the cell will have the same housekeeping genes but some different genes for the main cells specialisations
How many genes do most cells express?
10 000-15 000
Housekeeping proteins are needed by all cells
What is the concept unequal gene expression
Not all genes are expressed at an equal rate. Some genes are abundant such as mRNAs where as other genes may be scarce in other cells.
What is the concept of constitutively or conditionally expressed genes?
Constitutively expressed genes - genes that are always on such as the housekeeping genes.
Conditionally expressed genes - inducible expression from external environmental signals telling the genes to be switched on.
How do cells regulate gene expression?
- Transcriptional control
- RNA processing control
- RNA transport and localisation control
- Translation control
- mRNA degradation control
- Protein activity control
What is transcriptional control?
mRNA population is regulated by:
which genes are transcribed (active vs repressed)
the rate at which they are transcribed
the transcriptional start site used.
What is mRNA processing control?
Splicing: Introns (intervening sequence) are removed and exons (expressed sequence) are kept in determining what kind of protein forms. Capping: Addition of 5' methyl cap place on Polyadenylation: Addition of a 3' poly A tail.
What is the idea of alternative splicing?
Determining on where the splicing occurs, different proteins can be made (eg. different forms of insulin) depending on where on the gene splicing occurs.
What is Pol II?
Acts as a transcription factory allowing RNA processing to be carried out co-transcriptionally.
Why is there variation in gene organisation?
Intron and exon size varies and the number of exons/introns present in a gene varies.
24-28% of the human genome are introns and only 1% of the human genome is exon.
Why do we have introns?
Exons often encode discrete protein functional domains.
Exon shuffling can only occur due to having introns.
This allows different proteins to be formed from the same gene (alternative splicing) (idea of multiple types of insulin)
what defines an intron?
Most introns contain STOP codons in all reading frames.
Have conserved sequences at the intron-exon boundaries (splice sites)
What are snRNPs?
They recognise intron-exon boundaries
They are structural RNAs due to RNA-RNA interaction.
U1 and U2 snRNPs bind to 5’ and 3’ splice sites to splice out the introns
What is the concept of alternative splicing?
The idea that the same gene can create related proteins that have similar but not the same functional properties
How does alternative splicing occur?
Alternative selection of promoters
Alternative selection of cleavage/polyadenylation sites
Intron retaining mode
Exon cassette mode
(different exons = different protein domains)
(additional exons = larger proteins with additional functionality)
What is the concept of tissue specific expression?
Different proteins are produced from the same gene but they occur in different locations of tissue
