Proteins Flashcards
Define transcription
The synthesis of messenger RNA using DNA as a template which may then serve as a template for protein synthesis
Define translation
The synthesis of a polypeptide chain using mRNA as a template, which can go on to make a protein
What are the steps in producing immature mRNA from DNA?
Initiation
Elongation
Termination
What is an example of a promotor element in eukaryotes?
The TATA box (because they form the lowest energy base pairs so are the easiest to unwind)
What happens in the initiation stage of transcription?
RNA polymerase binds to the DNA upstream of the desired gene at a promotor region
What happens in the elongation stage of transcription?
The DNA helix unwinds and RNA polymerase reads the template strand adding nucleotides to the 3’ end of the growing chain (5’-3’ direction)
What happens in the termination stage of transcription?
RNA polymerase reaches the terminator sequence, transcription is stopped using a termination factor
The two strands come back together and reform the double helix
What is splicing?
Removal of introns from the pre-mRNA
How does splicing work?
Two reactions
1. Free 2’ hydroxy group
2. 3’ hydroxy group links to the splice site
The bit that is spliced out is called the lariat product
Why is splicing important?
Essential role in generating protein diversity
Regulates gene and protein content
Helps process of evolution of new and improved proteins
Key to cancer pathology where it regulates proliferation, metastasis and apoptosis
What are the steps of translation?
Initiation
Elongation
Termination
What happens in the initiation stage of translation?
Complex forms on mRNA
Three initiation factor proteins bind to the small subunit of the ribosome
The complex and a methionine-carrying tRNA then bind to the mRNA near the AUG start codon
What happens in the elongation stage of translation?
Ribosome moves along mRNA from 5’-3’ direction which requires the elongation factor G
TRNA starts out in the middle slot of ribosome called P site
Guanosine triphosphate acts as an energy source
Peptide bonds form between the adjacent first and second amino acids through peptides transferase activity
What happens in the termination stage of translation?
When the ribosome reaches a stop it is recognised by release factors which fit into the p site
Ribosome dissociates and protein is released
What is the systolic and secretory pathway for protein trafficking?
Systolic - Proteins synthesised on free ribosomes remain in the cytosol
Secretory - Proteins made of the RER get transported out of the cell
