2C Flashcards
Translational regulation of gene expression brief overview
.mRNA-> polypeptide/protein
- Initiation
- Élongation
- Termination
Translation
Assembly of a.a. Into polypeptides
Amino acid components
Amino + carboxyl group (bonded to central carbon with hydrogen and R group)
R group? And role in a.a.
Its variable and determine unique character of a.a.
Bond between 2 a.a.?
Covalent peptide bond between amino and carboxyl in dehydration rxn (produce H2O by taking it out of a.a.)
Peptide bond
C-N
Polypeptide
Linear chain of a.a. Linked by peptide bond
Nonpolar a.a.
R group has -CH2 or -CH3
Uncharged polar a.a.
R group has -O or -OH
Charged a.a.
R group has acid or base that can ionize
Aromatic a.a.
R group has carbon. Ring with alternating single and double bond
Special fxnal a.a.
- Methionine: first a.a. In polypeptide
- Proline: kink in polypeptide chain
- Cysteine (S-S): disulfide bridge contributes to structure of polypeptide
Primary protein
A.a.sequence
Secondary structure
H-bonding in polypeptide backbone (alpha helix and beta sheet)
Tertiary structure
3-D structure of single polypeptide and made of interactions between a.a. Side chains
Quaternary structure
Interaction between more than 1 polypeptide=multisubunit protein like hemoglobin
What disrupts protein folding
Dénaturation (heat and chemicals/ mutations that change a.a. Sequence)
Chaperone??
Fxn: protect slow-folding/denatured protein and prevent aggregation
.tRNA
Adaptor between codon (mRNA) and a.a.
2D and 3D RNA from self complimentarity
Acceptor stem (a.a. Attaches here) has 5’-CCA-3’ at 3’ end of tRNA
Where is the anticodon in the 2D RNA cloverleaf for tRNA
Bottom loop of cloverleaf and has 3 nucleotide sequence and recognize codon by base pairing with mRNA
Aminoacyl-tRNA (charging)
Adding a.a. To tRNA
Aminoacyl tRNA synthase adds a.a. To acceptor stem of tRNA
Each a.a. Has a different and unique aminoacyltRNA synthétase
Charging rxn (aminoacylation)
A.a.+ tRNA+ ATP-> aminoacyl-tRNA+ AMP+ PPi
Genetic code
Multiple of the sense codons+ a.a.
Initiation/ start codon
AUG
Termination/stop codon
UAA/UAG/UGA… DO NOT code for a.a. (.tRNA doesn’t bind to these)
How are codons written
5’->3’ likemRNA
Rules of genetic code
1.codons of mRNA read in 5’->3”
2.codons non overlapping and no gaps
3. Message translating in fixed reading frame set by start codon (AUG)
Wobble in tRNA anticodon
Base of 5’ end of anticodon form H-bond with more than 1 type of base at 3’ end of codon
Pairing of other 2 nucleotides in anticodon… codon is precise (no wobble)
Pair combination with wobbling
If A (1,2,3,4,5-anticodon) then B (codon)
- G
- C
- A
- U
- INOSINE
- U/C
- G
- U
- A/G
5.A/U/C
Ribosome (prokaryote): protein synthesis machinery
2 subunits:
1. Large subunit (5OS): S+ S rRNA+ proteins that have peptides transféras E center for formation of peptide bonds
2.small subunit (3OS)L S rRNA+ protein+ decoding center where charged tRNA read and decode codon of mRNA
S???
Svedberg unit
Measure mass…each subunit exist separately in cytoplasm (small and large subunit) but join on mRNA
.tRNA binding sites of ribosomes
- P site (peptidyl): bind to tRNA attached to growing peptide chain
- A site (aminoacyl): bind to tRNA carrying next a.a. To be added
3.E site (exit): bind to tRNA where previous a.a. Was added
Translation initiation (eukaryotes)
Initiation complex (ribosome+mRNA+initiator tRNA bound to methionine)
- Initiator tRNA met brought to P-site of small ribosome subunit (need GTP)
2.complex of initiator tRNA met and small ribosomalunit added to capped 5’end (mRNA) and scan mRNA in 5->3 till 5-AUG-3 (start codon) - Complementary base pairing… between anticodon of initiator tRNA met and start codon of mRNA
- Large ribosomal subunit bind small subunit= intitiation complex… ready to accept first tRNA in A site
- GTP hydrolysée to GDP and translation begin
Translation elongation (growth of polypeptide)-eukaryote
1.aminoacyl tRNA added to A site (elongation factor GTP) (tRNA anticodon is complementary to mRNA codon in A-site)
2. Peptidyl transferase (large subunit)= peptide bond between carboxyl group of polypeptide and a. Group of a.a. In A site (tRNA in P site is uncharged)
3. Ribosome translocates (tRNA shift from A->P site and uncharged tRNA from P->E site then ejected)
4.next codon of mRNA is in A site and next aminoacyl tRNA loaded by EF-GTP
Termination (eukaryotes)- release completed polypeptide from ribosome
3 stop/termination codon at end of protein coding sequence in mRNA (UAA,UAG, UGA)… recognized by release factors
Ribosome reaches stop codon and release factorbinds the A-site and stimulates peptidyl transferase to leave polypeptide from P-site tRNA
Ribosome subunit separate and detach frommRNA and empty tRNA and release factor separate
Posttranslational regulation of gene brief overview
Mod. Of proteins with chemical groups for activity and degradation
- Phosphorylation: add phosphate to protein by kinase (activate or inhibit activity)
2.ubiquitination (add ubiquities molecule to protein target them for destruction by proteasome) - Proteolysis (specific cleavage of protein induce activity)
Postranslational regulation of proteins steps and example using spline les assembly
1.phosphorylation: CDK1 (cyclin dependent kinase)phosphorylates and activates MAP (microtubule associated protein) thus promote spindle assembly and mitotic entry
2. Ubiquination: cyclin (CycB) is destroyed at end of mitosis= inactivate CDK 1
3. Proteolysis (Proteolysis of viral envelope glycoprotein triggers maturation of HIV)
Epigenetics
Postranslational mod of histones affect transcription
Change in gene transcription affect DNA sequence??
W/o change in DNA sequence
What affects transcription of genes/histone code
Mod to lysine on histone tail
Histone acetyl transféras E (HATs) add acetyl group (CH3CO-) to histone tail= increase gene transcription and loosen DNA binding
Methylation of histone tail??
Posttranslational mod and activates and repress transcription of genes
DNA methylated @ CPG islands close to promoter repressing transcription
Chromatin remodeling complex??
Displace nucleosome from promoter region (ATP dependent) activating transcription
Is heterochromatin active or inactive
Inactive
Is euchromatin active or inactive
Active
Acetylation by histone acetyltransferase… ____->_____
Heterochromatin->euchromatin
Deacetylation by histone deacetylase… ____->_____
Euchromatin->heterochromatin
Translational regulation
Control protein synthesis (rate of translation intitiation/formation of initiation complex)
Postranslational regulation
Control protein abundance and activity (availability of fxnal protein)
Abundance of protein depend on…
Postranslational mod (phosphorylation)
Processing (cleavage)
Levels of eukaryotic gene regulation brief overview
- Epigenetics (chromatin remodelling)
- Transcriptional (mRNA synthesis)
- Post transcription (mRNA processing)
- Translation (protein synthesis)
- Post-translation. (Protein processing)
Epigenetics (chromatin remodelling
-Postranslational mod of histones
-DNA methylation
Transcriptional (mRNA synthesis)
-initiation elongation termination
-transcription factors promotes enhancers
Posttranscription (mRNA processing)
-5’capping
-3’ polyadenylation
-splicing
-mRNA degradation (exoribonucleases and siRNA)
Translation (protein synthesis)
-initiation
-elongation
-termination
-microRNA
Posttranslation (protein processing)
-Postranslational mod: phosphorylation,acetylation, methylation, ubiqutination
-protein degradation
What would happen if you made changes at a level of eukaryotic gene regulation
Potentially alter protein expression and cause variation in phenotype
