Translation Flashcards
Translation is the biochemical synthesis of proteins. How is this done?
The translation of sequences of nucleotide in mRNA into the sequence of amino acids in polypeptide
In translation the AAs are unable to bind directly to the codon so tRNA functions as an adaptor molecule between the two sequences. How does this work?
The anticodon of tRNA interacts with codon of mRNA
The Wobble hypothesis accounts for what phenomenon?
Why multiple codons code for one amino acid One tRNA can recognize more than one codon due to less precise base pairing –> Therefore fewer than 61 tRNAs are required for efficient translation
What are the 4 characteristics of genetic code?
Specificity => specific codon always codes for same AA Universality => specificity of genetic code has be conserved from very early stages of evolution (exception in mitochondria) Redundancy => given AA may have more than one triplet for it (Arg/Ser = 6 codons) Non-overlapping and commaless => Code is read from fixed starting point as continues sequence of bases three at a time
A point mutation occurs when 1 base is altered. List and descirbe the 6 point mutations:
Silent: changed codon may code for same AA (no consequences)
Missense: changed codon codes for different AA
Nonsense: Changed codon codes for STOP codon
Insertions, deletions, and frameshift mutations
What is a frameshift mutation?
Occurs when the number of inserted or deleted nucleotides is not a multiple of 3
Which type of mutation is known to cause Sickel Cell Anemia
Missense mutation
*in the sickle cell gene, GTG (Val) replaces the normal GAG (Glu)*
What are the 3 steps of Translation?
Initiaion- Recognition of mRNA by small ribosomal subunit and formation of initiation complex
Elongation- Repeated addition of AAs to a growing polypeptide
Termination- Stop codon leads to the release of complete polypeptide; dissociation of ribosome from mRNA
What type of template is used in Translation?
mRNA
prokaryotic mRNA is has several coding regions (polycistronic)
Eukaryotic mRNA only codes for one polypeptide chain (monocistronic)
How are ATP and GTP used in translation?
ATP: used to attach AA to tRNA
GTP: used for binding of aminoacyl-tRNA to A site and for translocation step
*additional ATP and GTP are used in initation and termination steps
What is the aminoacyl-tRNA responsible for?
specificity and proofreading and high fidelity translation
A ribosome has 3 sites where tRNA molecules bind or exit. List and define these sites:
A site: binds incoming aminoacyl-tRNA and specifies next AA to be added
P site: occupied by peptidyl-tRNA; this tRNA carries synthesized peptide
E site: occupied by empty tRNA as it is about to exit
In eukaryotes, 16S ribosomal RNA (rRNA) contains the sequence which is complementary to the shine-delgarno sequence in mRNA. What does binding of these 2 sequences do to the mRNA position?
Positions it on the 30S subunit
In eukaryotes the 40S subunit binds to the what of mRNA?
cap structure
What is the anitcodon to UCA?
UGA
During the iniation step of tranlsation the tRNA binds to which site?
P site
After initiation, the tRNA binds to which site for the duration of translation?
A site
Describe the translational-inhibitory effect of Streptomycin
Binds the 30S subunit and distorts its structure, interferring with initiation of protein synthesis
Describe the translational-inhibitory mechanism of Tetracyclines
Interact with small ribosomal subunits, blocking access of aminoacyl-tRNA to the mRNA-ribosome complex
What is the function of peptidyl transferase?
A component of the 50S ribosomal subunit, transfers the amino acid from the P-site onto the amino acid at the A-site, and catalyzes peptide bond formation
Describe the translational-inhibitory mechansim of Chloramphenicol
Inhibits prokaryotic peptidyl transferase; high levels may also inhibit mitochondrial protein synthesis
Describe the translational-inhibitory mechansim of antibiotics Clindamycin and Erythromycin
Bind irreversibly to a site on the 50S subunit of the bacterial ribosome, thus inhibiting translocation
Describe the translational-inhibitory mechanism of Diptheria toxin
Inactivates (ADP-ribosylates) the eukaryotic elongation factor, eEF-2, thus preventing translocation
Describe the translational-inhibitory mechanism of ricin
Inhibits eukaryotic trranslation by removing adenine from 28S rRNA
–> This modification inhibits ability of large ribosomal subunit to bind elongation factors
Elongation is signified by the movement of STOP codon to an “A” site triggering what series of events?
Release factors bind to “A” site of ribosome
Peptidyl transferase hydrolyzes bond between peptide and tRNA
Once the polypeptide is released from the ribosome, chaperones bind to the polypeptide in order to do what? What family of proteins do these chaperones belong to?
Prevent non-specific folding
Heat shock proteins
In addition to heat shock proteins, another important step in proper protein folding is formation of what bond? What enzyme is responsible for this?
Disulfide bond between cystein residues
Protein disulfide isomerase (PDI)
What is the process utilized in order to label misfolded proteins for degradation?
Polyubiquitination
What are the two ways in which protein misfolding materializes as a disease?
Loss of function mutations
Gain of function mechanisms => mutations that cause a toxic novel function, dominant negative mutations and amyloid accumulation (neurodegenerative)
Nuclear proteins have
Nuclear localization signal
Mitochondrial proteins have
Mitochondrial entry signal
What is the fate of proteins produced on the ER?
Lysosomes- peptides, nucleic acids, carbs, lipids
Secretory vesicles- gastric acid, digestive enzymes, lung surfactant, sebum
Extracellular vesicles- protein and nucleic acids (can be considered another type of cell signaling)
On the list of covalent modifications of polypeptides (either during or after their synthesis) is phosphorylation (or dephosphorylation). What are the three amino acids which are the only 3 that will bind a phosphate group?
Serine
Threonine
Tyrosine
Methylation of histones is inlvolved in the regulation of transcription (transcriptional activation). What are the two AAs that accept methyl groups?
Lysine
Arginine
In order to stabilize collagen there is the process of hydroxylation. What 2 AAs will accept a hydroxyl group?
Proline
Lysine
Carboxylation
Blood coagulation
Attachment of fatty acids
anchoring of protein to membrane
Glycosylation
Serine
Threonine
Asparagine
residues of membrane or secreted proteins
Biotinylation
Regulation of carboxylases via Lysine residue
What are 4 examples of activation via proteolytic cleavage?
zymogens (stomach–>pancrease) via enteropeptidase
Blood clotting cascade
Procollagen–>Collagen
Apoptosis => mediated by caspases (procaspases–>caspases)
Postranslational modifications increase
Proteomic diversity
