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8/25 Protein Synthesis
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Biology
Graduate
08/25/2011

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Term
Eukarayotic v. Prokaryotic
Definition
Eukaryotic mRNA is spliced then capped and and adenylated,whereas Prokaryotic mRNA is not spliced and can also by polycistronic
Term
Ribosome
Definition
- Made of 50 differnet proteins and several RNAs
- Eukary ribos can add 2 AA/sec and prokary add 20/sec
- Activity mostly conducted by rRNA
- 1 large and 1 small subunit fit together, mass of several mill daltons
- Subunits combine together on mRNA, otherwise seperate
Term
Ribosome has X binding sites
Definition
4; 1 for mRNA and 3 for tRNA E (exiting tRNA),
Term
The peptide bond is forms between _____ and ______ by the aid of ______ from ______
Definition
Incoming aminoacy-tRNA at the A-site and the peptidyl-tRNA in the P site by the aid of peptidyl transferase in the large subunit
Term
Steps of Initiating Protein Synthesis
Definition
1) Binding of initiater tRNA to small ribo subunit
2) Binding of 5' end of mRNA to the small ribosomal subunit
3. Identificaton of the initiation codon
4. Association of the large ribosomal subinit
5. Formation of the first peptide bond
Term
Initiator tRNA
Definition
1) Always carries methionine
2) Has a unique nucleotide sequence that allows it to be distinguished
- Loaded onto ribos subunit complexed with eIF2 and IF2
Term
the ____ subunit binds at the ____ end of mRNA. The 5' end is recongized by presence of ____ and _____
Definition
small subunit binds at the 5' end...
by presence of eIF4F and eIF4G
Term
eIF4E
Definition
Binds to 5' cap, needed to load mRNA
Term
eIF4G
Definition
Couples 5' end of mRNA with the 3' poly A tail; key for initiation and rate of translation
Term
The recognition step
Definition
- Subunit scans mRNA looking for first AUG
- Movement is aided by ATP-powered IF helicases that deal with secondary mRNA structure
- If the fist AUG does not have the Kozak sequence between ACC and G then small subunit moves on.
Term
Prokaryotic initiation sequwnce
Definition
Shine-Dalgarno sequence
Term
Eukaryotic initiation sequence
Definition
Kozak sequence
Term
Initiator tRNAs
Definition
Term
The association step
Definition
- Once AUG is recognized, TFs are released and large subunit binds
- tRNA is bound at P-site and A-site is vacant and the ribosome is ready to initiate protein synthesis
Term
eIF2-GTP
Definition
complexs with charged initiator tRNA and binds to the small subunit
Term
eIFB
Definition
swaps GTP in for used GDP on the eIF2 so it will be availible for next cycle
Term
eIF4
Definition
complex that binds to the 5' cap and helps the preinition complex, part of protein helps to unwind mRNA and part forms link between 5' end and polyA
Term
Elongation Steps
Definition
1)tRNA binding
2) Peptide ond formation
3) Large subunit translocation
4) Small subunit translocation
Term
E-Tu-GTP
Definition
E-Tu-GTP binds to A-tRNA to forma complex which moves into A-site until there is an appropriate match
Term
Bent-coformation
Definition
Complex of EF-Tu-GTP and aminoacyl tRNA is bent to allow codon/anti-codon interaction but no pep bond formation
Term
EF-G-GTP
Definition
Baceterial EF, catalyzes transolcation by hydrolizing GTP
Term
EF-2-GTP
Definition
Eukaryotic EF that catalyzes translocation via hydrolysis of GTP
Term
Termination Release Factors
Definition
Proteins that recognize stop codons, bind to the A site, forcing peptidyl transferase to catalyze addition of water instead of AA to peptidyl-tRNA

Additional release factors catalyze dissociation of ribo subunits
Term
Polysomes
Definition
Large assemblies of many ribosomes spaced as close as 80 nucleotides apart on mRNA
Term
Translation Regulation Mechanisms
Definition
MicroRNA's
TF Activity
RNA-binding proteins
Term
Regulation of IF Activity
Definition
1) GF Stim; triggers phosphorylation of eIF-$E increasing binding to 5'cap and increasing translation rate
2. GF deprivation phosphorylates eIF-2 which tightens its hold on GDP preventing recycling
Term
Aconitase as example of RNA binding protein and translation
Definition
- Iron Starvation; binds to 5' ferritin and blocks translation also binds to 3' of tranferrin recpetor transcript, increasing transferrin receptor transcript stability
Excel iron; iron binds to aconitase and changes conformation. Cant bind to ferritin transcript so ferriten is made, cant bind to tranferrin receptor transcript so transferrin receptor transcript is unstable and it is not made
Term
Ferritin
Definition
Binds iron and stores it in the cytoplasm
Term
Transferrin and Transferrin Receptor
Definition
Binds iron outside the cell and functions in iron transport, the receptor binds to transferring and transferrin-iron complexes and brings them into the cell
Term
miRNA's
Definition
short non coding, base-pair with specific mRNAs and regulate stability or translation
Term
IRES
Definition
- Internal Ribosome entry site, cap independant initiation of translation in Eukaryotes and many viral RNA
- Allows the translation of selected mRNA's at high rate when translation of cap-dependant mRNA is down
- Many viruses will block cap-dependant translation, effectively taking over
- Mitotic and cell death products rely on IRES
Term
Antibiotics
Definition
Inhibit bacterial protein synthesis
Term
Tetracycline
Definition
Blocks A-site
Term
Streptomycin
Definition
Prevents transition from initiating complex to chain elongating ribo
Term
Erythromycin
Definition
Blocks translocation
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