L8 - Gene To Protein Flashcards
Genotype
Organism’s hereditary info
Phenotype
Actual observable/physiological traits
= genotype + interaction w/environ.
Control points of gene expression
- transcription
- processing of pre-mRNA
- transport
- translation
Importance of control points
Gene expression tightly regulated to achieve right thing at right time in the right place (temporal/spatial control)
DNA orientation
Upstream = promotor end = 3’ end of template strand = 5’ end of non-template strand
- has control elements that dictate things need to be assembled: when and how
Downstream = terminator end = 5’ end of template strand = 3’ end of non-template strand
Purines
Adenine, guanine
Pyrimidine
Thymine, cytosine
Transcription initiation
1) eukaryotic promotor (TATA box sequence ~25 nt upstream)
2) promotor assemble transcription factors (including TATA box binding protein, TBP) - allows RNA polymerase II to bind
3) transcription factors + RNA polymerase II (teardrop shaped enzyme) form transcription initiation complex
Transcription elongation
10-20 nucleotides exposed at a time when DNA unwound (H-bonds broken)
- H-bonds between RNA nucleotides and DNA bases
- phosphodiester bonds between RNA nucleotides
Transcription termination
1) polyadenylation signal (AAUAAAA)
2) pre-mRNA released, RNA polymerase dissociated
Fidelity (proofreading)
Less than for DNA replication
UTR
Untranslated regions at 5’ and 3’ ends
Steps of processing pre-mRNA transcript
Capping, tailing, splicing
Capping
Modified guanine added to 5’ end
Tailing
50-250 adenine nucleotides (polyA) added (strand is polyadenylated) to 3’ end to form poly-A-tail
Splicing location
Spliceosome
- large complex of proteins and small RNA
- in nucleus
Alternative splicing
- process by which different combos of exons are joined together
- results in production of multiple forms of mRNA from single pre-mRNA
- 1 gene to multiple gene products
Translation components
Ribosomes, tRNA
Ribosome sites
- mRNA binding site on small subunit
- tRNA binding sites on large subunit
tRNA binding sites
- A (aminoacyl-tRNA binding) site: holds next-in-line tRNA
- P (peptides-tRNA binding) site: holds tRNA carrying the growing polypeptide
- E (exit) site: tRNAs exit from here
Translation process
- codons translated into amino acids
- protein synthesis catalysed by ribosomes
Initiator tRNA
TRNA carrying methionine (Met)
Translation initiation
1) small ribosomal subunit with initiator tRNA + bind to 5’ cap end of mRNA
2) small ribosomal subunit scans downstream to find translation start site (AUG)
3) H-bond between anticodon/mRNA
4) large ribosomal subunit binds = initiation complex
GTP required
GTP
Guanosine triphosphate