Lecture 9 - gene to protein Flashcards
3 main steps of gene expression
Transcription, where DNA is copied into pre-mRNA; Processing, where pre-mRNA is checked/fixed; Translation, where protein is made from mRNA instructions
Transcription process
1.) During Initiation, polymerase binds to promotor 2.) During Elongation, polymerase transcribes RNA moving downstream 3.)During Termination, detachment upon reaching terminator region.
RNA vs DNA
RNA single while DNA double stranded; RNA pairs Adenine/Uracil while DNA pairs Adenine/Thymine
Transcription Initiation Complex
RNA polymerase II and several associated Transcription factors (proteins)
Where do Transcription Factors bind on DNA
At the TATA box in the promotor region
How many nucleotides are exposed when DNA is unwound?
10-20 nucleotides
Elongation process transcription
Complementary nucleotides to the template strand of DNA are added to 3’ end of new pre-mRNA. Double helix reforms as polymerase II leaves. Phosphodiesterase bonds form between 3’OH and 5’ phosphate.
Termination process transcription
Once AAUAAA has been transcripted, pre-mRNA released from nuclear enzymes and
3 modifications in processing and purpose
Capping, Tailing, Splicing allows for stability, export, ribosome binding
Capping
1 modified Guanine is added to 5’ end
Tailing
50-250 Adenine nucleotides are added to 3’ end (polyA tail)
Splicing
Spliceosomes cut out introns and splice exons together with cap and tail
Exons vs Introns
Exons are kept in mRNA and between untranslated regions (UTR) while introns are cut out
Spliceosome components
large complex of proteins and small RNAs
A codon is a…
Set of 3 bases coding for a specific amino acid. Some examples: start = AUG, UAA or UAG or UGA = stop
Translation
tRNA brings amino acid to ribosome, if complementary to the next codon hydrogen bonding forms between mRNA and anti codon. Amino acid forms peptide bonds with polypeptide chain.
tRNA structure/function
anti codon corresponds to amino acid; physical link between mRNA and amino acid sequence
Ribosome structure translation
In large unit, A site for tRNA waiting line, P site for tRNA adding aa to polypeptide, E site for tRNA exit.
Small unit for binding of mRNA
Assemble of ribosome, mRNA, tRNA
Needs GTP. Initiator RNA (methionine/Met) ) added to small unit of ribosome, small uni scans for start codon and hydrogen bonds form mRNA/ini tRNA, large unit binds
4 control points of gene expression
Transcription factors need to be assembled, processing of pre-mRNA, export of mRNA thru nuclear pores reg by specific proteins, regulatory proteins can block translation/ mRNA life spans
Translocation in translation elongation
movement of tRNA thru A-P-E
what enzyme refills tRNA
aminoacyl-tRNA synthetase
GTP function in gene expression
Gtp for assembling of translation complex,2 GTP used to disassemble translation complex, increases efficiency and accuracy of codon recognition
Level of structures
Primary - protein sequence; secondary - alpha helixes/beta sheets; tertiary - 3D; quaternary - multiple proteins associate to form protein
Primary structure of protein
NH3 is N-terminus is 5’ end, COOH is C-terminus is 3’ end; amino acids bonded with relatively strong covalent bonds
Secondary structure of protein
Alpha helixes or beta sheets from weak hydrogen bonds
Tertiary and quaternary structure of protein
tert- 3D shape stabilised by side chain interactions; quat - not all proteins form quaternary
Signal peptides process
Protein synthesis starts until signal peptide at N-terminus reached –> Signal recognition particle (SRP) binds to signal peptide + signal receptor protein then leaves–> finish synthesis then enzyme cleaves protein from receptor protein –> protein folds
post translation modifications
may occur in golgi appartus or cytosol
- _____ylation = adding ____
- carbohydrate addition = adding carb (glycoprotein for cell recognition)
- cleavage
- ubiquitination = degradation
post translational- purpose/location
Allow for interaction with other molecules, activation, direct to particular locations
Signal receptor particles binds where?
At N terminus when there is a signal peptide of approximately 20 amino acids
Where do secretory proteins and membrane peptides go after translation
Golgi apparatus for further modification and maturation. Secretory proteins are solubilsed in RER lumen
