Sections 14.1-14.4 & 14.7-14.11

The genetic code is _________, meaning that an amino acid may be coded by more than one codon.

unambiguous degenerate commaless universal nonoverlapping

The genetic code is _________, meaning that an amino acid may be coded by more than one codon.

Answer:2. degenerate

Explanation:Degeneracy is a term for redundancy in the genetic code; 61 codons code for 20 amino acids.

The wobble hypothesis predicts that codons coding for the same amino acid

may differ at the first position.may differ at the second position.may differ at the third position.may differ at the first two positions.may differ at all three positions.

The wobble hypothesis predicts that codons coding for the same amino acid

Answer:3. may differ at the third position.

Explanation:The wobble hypothesis suggests that pairing may be less stringent at the third codon position. This allows the same tRNA molecule to pair with two or more codons that are identical at the first two codon positions.

A nonsense suppressor mutation is a mutation

that alters the reading frame.that changes the amino acid sequence of the

gene product. that creates a termination codon.in a tRNA gene that allows it to recognize a

termination codon. that allows a ribosome to bypass termination

codons.

A nonsense suppressor mutation is a mutation

Answer:4. in a tRNA gene that allows it to recognize a termination codon.

Explanation:A nonsense mutation changes an amino acid coding codon to a termination codon. A second suppressor mutation in a tRNA gene restores the function of the nonsense mutation by allowing an amino acid to be added to the polypeptide.

The sigma subunit of bacterial RNA polymerase

binds to a bacterial gene’s promoter. is composed of both polypeptide and RNA

molecules.is required for RNA polymerization. is required for termination of transcription. is required for ribosomal binding.

The sigma subunit of bacterial RNA polymerase

Answer:1. binds to a bacterial gene’s promoter.

Explanation:Sigma is a polypeptide subunit of RNA polymerase that binds to the Pribnow and TATA boxes of the promoter, putting the catalytic center of the enzyme in contact with the transcription initiation site of the gene.

The poly(A) tail of mRNAsis added to the 3 end of mRNAs.is found on most mature eukaryotic mRNAs.is found on some prokaryotic mRNAs.helps prevent degradation of eukaryotic

mRNAs.All of the above.

The poly(A) tail of mRNAsAnswer:5. All of the above.

Explanation:A string of many adenine residues is added posttranscriptionally to the 3 end of most eukaryotic mRNAs. The primary function is to stabilize mRNAs against degradation by exonucleases.

TRANSLATIONCharging tRNA

A. 20 Aminoacyl tRNA synthetases {aminoacylation}

B. Energy from ATP links (cov) 5-phosphate group of ATP to carboxyl end of the amino acid and loses two phosphates

TRANSLATIONC. Aminoacyl tRNA synthetase transfers amino acid onto tRNAD. AMP is lost from the charged amino acid

and the amino acid is attached to the tRNA via the 3’-OH or 2’OH group of the ribose of the adenine of the tRNA

Characteristics of the Genetic CodeTriplet codeContinuousNonoverlappingUniversal (almost)DegenerateStart and StopWobble

Initiation of TranslationInitiation (prokaryotes)

A. Formylmethionine (fMet)- brought to small ribosome by tRNA with codon 5’-CAU-3’B. Shine-Dalgarno Sequence – 5’-AGGAGG-3’ binds to 16S rRNA of small ribosome (5’CCUCCU3’)C. IF1, IF2, & IF3 (bound to ribosome)D. GTP & Mg (bound to ribosome)

Initiation of TranslationE. When fMet binds 30S-mRNA complex, IF3

leavesF. 50S binds, GTP hydrolysis, and IF1 and IF2

leavesG. 70S Initiation Complex formedH. fMet resides in the P site and A site is

vacant

Differences between Prokaryotic and Eukaryotic Translation1. No fMet in Eukaryotes2. No Shine-Dalgarno3. Cap-binding protein finds the end of mRNA

in Eukaryotes4. AUG embedded in the Kozak sequence5. Poly A tail associates with the eIF-4f protein

TRANSLATIONElongation

A. Two sites A and P – initiator tRNA goes directly to P siteB. Peptidyl transferase – peptide bond between amino acidsC. E site – uncharged tRNAD. EF’s

TRANSLATIONTermination

A. Termination triplets UAG, UGA, UAAB. GTP-dependent release factors – cleave polypeptide chainC. Polyribosome

TRANSLATIONProkaryotes vs. Eukaryotes

1. F-met vs. 5-cap2. Euk. larger ribosomes3. Euk. longer lived RNA4. Kozak Sequence – “ACCAUGG”

Posttranslational Modification1. N-terminus/C-terminus amino acids

removed (f-met) or acetylated2. Amino acids within peptide chain modified3. Carbohydrates attached4. Trimmed5. Signal peptides removed6. Cofactors (metals)

Amino Acid Structure1. Carboxyl group, amino group, R-group2. R-group may be a) nonpolar, b) polar, c)

negatively charged, and d) positively charged

3. N-terminus, C-terminus

Protein Structure1. Primary Structure – amino acid sequence2. Secondary Structure – helix, sheets3. Tertiary Structure – 3-D structure4. Quaternary Structure – assembling more

than one polypeptide chain

One Gene : One Protein1. Sickle Cell Anemia2. HbA, HbS, HbA HbS

3. Hemoglobin composed of 4 chains4. Glutamic acid (negative charge, polar)

changed to valine (uncharged, nonpolar)

tRNAshave double-stranded regions.contain unusual nucleotides coded by genes

with nonstandard bases.can be recognized by several aminoacyl-tRNA

synthetases.can carry more than one type of amino acid

per molecule.consist of two subunits.

A tRNAsAnswer:1. have double-stranded regions.

Explanation:Regions of tRNA molecules fold back and base pair with other regions of the same molecules, creating secondary structures that are double stranded.

Peptidyl transferaseis a polypeptide subunit of the small

ribosomal subunit.is not found in eukaryotes. is a function of an rRNA in the large

ribosomal subunit.catalyzes the reaction that joins a tRNA to its

amino acid. is active during initiation of translation.

Peptidyl transferaseAnswer:3. is a function of an rRNA in the large ribosomal subunit.

Explanation:Though once believed to be a protein enzyme, peptidyl transferase is a ribozyme (an RNA molecule with catalytic activity). In bacterial ribosomes, this function is assigned to the 23S rRNA. It catalyzes the formation of peptide bonds between amino acids during elongation of translation.

The phrase “one-gene:one-polypeptide” is more accurate than “one-gene:one-enzyme” because

most genes code for nontranslated RNAs.most proteins are not enzymes.not all enzymes are encoded by genes.most enzymes have multiple subunits coded

by different genes.not all enzymes are composed of

polypeptides.

The phrase “one-gene:one-polypeptide” is more accurate than “one-gene:one-enzyme” because

Answer:4. most enzymes have multiple subunits coded by different genes.

Explanation:Although most proteins coded by genes are enzymes, individual genes often code for polypeptides that are folded to become subunits of functional enzymes.