Gene expression Flashcards
Does DNA exit the nucleus?
No, it stays in nucleus to be protected
What is mRNA and its features?
mRNA is a copy of one of the strands of DNA (shorter section)
- Has a cap and tail (via RNA processing)
- Relatively smaller than DNA
- Subsequently travels to a ribosome (for translation)
What are the stages of transcription?
Initiation
Elongation
Termination
What is involved in the initiation stage of transcription?
RNA polymerase binds onto the promoter region of the gene
- transcription factors can assist this process
DNA is unwound, hydrogen bonds are broken and bases are exposed
What is involved in the elongation stage of transcription?
RNA polymerase reads template strand in 3’-5’ direction while adding complementary nucleotides to the pre-mRNA strand in the 5’-3’ direction
- Replacing thymine with Uracil
What is involved in the termination stage of transcription?
RNA polymerase continues transcribing until it reaches the terminator region
RNA polymerase is removed (so now the pre-mRNA molecule is ready for processing)
What is RNA processing?
Introns removed and exons are spliced together
- resulting in shorter mRNA strand (than the DNA it originated from)
A methyl cap and a poly-A tail are added to protect mRNA
What are the processes involved in translation?
Initiation
Elongation
Termination
What is involved in the initiation stage of translation?
the 5’ end of mRNA molecule binds to a ribosome and is read from the start codon (ANA). A specific tRNA molecule binds to ribosome - the anticodon binds to the mRNA codon
What is involved in the elongation stage of translation?
The next codon is read and a tRNA with specific anticodon delivers a specific amino acid
Two amino acids are bonded together during condensation polymerisation forming a peptide bond
This repeats for every codon and polypeptide (type of covalent) chain is formed
What is involved in the termination stage of translation?
When ribosome reaches a STOP codon, it will terminate translation and polymerisation
The complete polypeptide chain will be released for folding
What is tRNA?
Transfer RNA - it transfers specific amino acids to the ribosome (each tRNA has an anti-codon)
What are ribosomes made of?
multiple proteins and rRNA
Where can ribosomes be found?
Rough ER - exit the cell
Free floating in cytosol - within cell
Chloroplasts - within cell
mitochondria - within cell
What is DNA polymerase?
enzymes that run along the template (non-coding) strand in a 3’ to 5’ direction, unwinding and unzipping the DNA, and building a complementary strand in the 5’ to 3’ direction
Which direction can you add nucleotides?
can only add nucleotides to the 3’ end of a nucleic acid
What is the difference between pre-mRNA and mRNA
pre-mRNA is the mRNA strand in the nucleus before RNA processing
mRNA has a poly A tail (3’), no introns, and a methyl cap (5’)
mature mRNA leaves the nucleus
Why is the template strand also known as the anti-sense strand?
It is used as a template to make mRNA and has anticodons to the coding strand, therefore will have the opposite sequence to the RNA (known as the negative sense)
Why is it called the coding strand?
Despite not being used in the process of transcription, the codons on the coding strand will have the same sequence as the RNA that will be copied from the DNA (positive sense)
What is the structure of RNA polymerase?
an enzyme made of a number of subunit proteins (quaternary structure) one of which has helicase activity - unwinds DNA
What happens after transcription?
coding strand will anneal to the template strand again, the RNA that is formed will contain a positive sense copy of the coding strand (it is pre-mRNA before RNA processing)
What happens after RNA processing?
mRNA leaves the nucleus and enters a ribosome, 5’ end first
Where does RNA processing occur?
within the nucleus
What is post translational modification?
Once a polypeptide has been synthesised it can still be modified
What are examples of post translational modification?
Adding compounds to the protein
May be cut by proteases
Can be folded by chaperone proteins
May be combined with other polypeptides into a functional protein with a quaternary structure
