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101 Cards in this Set
- Front
- Back
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What is the 5' UTR?
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The 5' Untranslated region is the region between the 5' end and the start codon on mRNA
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What is the 3' UTR?
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The 3' Untranslated region is the region between the stop codon and the 3' end on mRNA.
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What does the 5' UTR contain?
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It contains sequences that help initiate translation.
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What does the 3' UTR contain?
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It contains sequences associated with transcription termination.
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Ribosomes in bacteria and eukaryotes perform what 3 essential tasks?
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1. Bind mRNA and identify start codon
2. Facilitate complementary base pairing of mRNA and tRNA 3. Catalyze peptide bond formation between amino acids |
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The small subunit of bacterial ribosomes has what Svedberg value?
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30S
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The large subunit of bacterial ribosomes has what Svedberg value?
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50S
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What comprises the small ribosomal subunit?
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21 proteins and a SINGLE 16S rRNA
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What comprises the large ribosomal subunit?
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31 proteins, a 5S rRNA, and a 23S rRNA
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When fully assembled, the intact bacterial ribosome has what Svedberg value?
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70S
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What is the P site?
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The Peptidyl site holds a tRNA to which the nascent polypeptide is attached
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What is the A site?
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The Aminoacyl site binds a new tRNA molecule carrying the next amino acid to be added to the polypeptide.
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What is the E site?
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The Exit site provides a way for tRNAs to leave the ribosome after their amino acid has been added to the peptide chain.
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In eukaryotes, what Svedberg value do the small ribosomal subunits have?
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40S
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In eukaryotes, what Svedberg value do the large ribosomal subunits have?
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60S
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When fully assembled, what Svedberg value do eukaryotic ribosomes have?
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80S
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Translation initiation in bacteria and eukaryotes begins when what happens?
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When the SMALL ribosomal subunit binds near the 5' end of mRNA and identifies the start codon sequence.
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After the small ribosomal subunit binds near the 5' end of mRNA, what is the next step in translation initiation?
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Initiator tRNA carrying the first amino acid of the polypeptide binds to the start codon.
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What is the final stage of initiation?
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The large ribosomal subunit joins the small subunit to form the intact ribosome and translation begins!
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During translation initiation, what help control ribosome formation and binding of the initiator tRNA?
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Initiation factor proteins!
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During translation initiation, what provides energy to the stages?
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GTP
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What is a Charged tRNA?
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Charged tRNA carry a specific amino acid
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What is an Uncharged tRNA?
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Uncharged tRNA are tRNA without an amino acid.
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What are the 6 critical translational initiation components in bacteria?
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1. mRNA
2. the small ribosomal subunit 3. large ribosomal subunit 4. the initiator tRNA 5. 3 essential initiation factor proteins 6. GTP |
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What is IF3?
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Initiation Factor 3 prevents the 30S subunit from binding the 50S subunit in bacteria
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When is the preinitiation complex formed?
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It is formed when the start codon sequence is identified by base pairing between the 16S rRNA in the 30S ribosome (small subunit).
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What is the Shine-Dalgarno sequence?
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It is a small purine-rich sequence of 6 nucleotides UPSTREAM of the Start codon that forms the preinitiation complex between the 16S rRNA in the small subunit.
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Where is the complementary pyrimidine-rich sequence of the Shine-Dalgarno sequence located? What's its purpose?
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It is found near the 3' end of 16S rRNA and it pairs with the Shine-Dalgarno sequence to position the mRNA on the 30S subunit.
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The Shine-Dalgarno sequence is another example of what kind of sequence?
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Consensus sequence!
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What are the 3 steps to Bacterial Translational Initiation?
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1. Formation of preinitiation complex
2. Formation of 30S initiation complex 3. Ribosome assembly |
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In bacteria, the amino acid on the initiator tRNA is what?
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A modified methionine - N-formylmethionine (fMet).
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The dissociation of what accompanies the joining of the subunits in bacterial translation?
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Initiation factors 1, 2, and 3.
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What is the Kozak sequence?
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A specific consensus sequence of eukaryotic mRNA that contains the AUG sequence.
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What are the 4 steps to Eukaryotic Translational Initiation?
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1. Formation of preinitiation complex (eIF3 and eIF1A with 40S subunit)
2. Formation of initiation complex (eIF4) 3. Scanning 4. Ribosome assembly |
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What is Scanning in eukaryotic translational initiation?
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Scanning is a process where ATP hydrolysis moves the small subunit through the 5' UTR to find the start codon.
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In eukaryotic translational initation, locating the start codon leads to what occurring?
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Leads to the recruitment of the 60S subunit to the complex using energy from GTP hydrolysis
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Elongation factors facilitate what 3 steps of polypeptide synthesis?
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1. Recruitment of charged tRNAs to A site
2. Formation of peptide bonds between amino acids 3. Translocation of the ribosome in the 3' direction along mRNA |
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What provides the energy for each step of elongation in bacteria and eukaryotes?
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GTP!
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Bacteria add how many amino acids per second to a polypeptide chain?
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20
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Eukaryotes add how many amino acids per second to a polypeptide chain?
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15
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What starts elongation in the second phase of translation?
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Recruitment of elongation factors!
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What is the error rate thought to be in polypeptide elongation in bacteria?
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1 amino acid in each 10,000 added to polypeptides
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What enzyme catalyzes the peptide bond formation between the amino acid at the P site with the newly recruited amino acid at the A site?
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Peptidyl transferase
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What is Peptidyl Transferase?
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It is an enzyme that catalyzes the peptide bond formation between the amino acid at the P site with the newly recruited amino acid at the A site.
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What is the end codon on ALL tRNA at the 3' end?
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CCA Terminus!
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In what direction does rRNA read the mRNA?
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5' to 3'
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What is the main difference between Eukaryotes and Prokaryotes?
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Eukaryotes have the Kozak sequence
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TRUE OR FALSE: Translation is done in the 5' to 3' direction of amino terminus to carboxy terminus.
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TRUE
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What are the three stop codons?
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UAG, UAA, and UGA
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Are there tRNAs with anticodons complementary to the stop codons?
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NO!
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Both bacteria and eukaryotes use what to bind a stop codon in the A site?
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Release Factors!
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In bacteria, what release factors recognize UAG and UAA?
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RF1
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In bacteria, what release factors recognize UAA and UGA?
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RF2
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Eukaryotic translation is terminated by the action of what?
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A single release factor called eRF
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What are Polyribosomes?
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Groups of ribosomes that all actively translate the same mRNA independently.
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Bacterial polyribosomes have a maximum density of about what?
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One ribosome per 80 nucleotides
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Do the ribosomes near the 5' end of the mRNA synthesize the longest length or the shortest length of polypeptide?
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Ribosomes near the 5' end synthesize the SHORTEST length of polypeptide.
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Do the ribosomes near the 3' end of the mRNA synthesize the longest length or the shortest length of polypeptide?
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Ribosomes near the 3' end synthesize the LONGEST length of polypeptide.
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In Eukaryotes, where does transcription take place?
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In the nucleus, where pre-mRNA is processed to form mature mRNA.
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In Eukaryotes, where does translation take place?
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In the cytoplasm after the release of mature mRNA!
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Can translation occur at the same as transcription in bacteria? In Eukaryotes?
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In bacteria, YUP! But in eukaryotes, translation and transcription are two uncoupled, distinct events.
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What is Monocistronic mRNA?
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mRNA that directs the synthesis of a single kind of polypeptide
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What is Polycistronic mRNA?
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mRNA containing the transcripts of two or more genes.
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The genetic code contains how many amino acids?
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64
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What are Synonymous Codons?
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Codons that specify for the same amino acid are synonymous codons.
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What are isoaccepting tRNAs?
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tRNA molecules with different anticodon sequences for the same amino acid
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What is the Third-Base Wobble?
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The mechanism that relaxes the requirement for complementary base pairing between the THIRD base of a codon and the corresponding nucleotide of its anticodon (1st base, technically).
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The 5' Nucleotide of the ANTICODON I can pair with what 3' nucleotide of the CODON?
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U, C, or A
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What is Inosine?
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Nucleotide structurally similar to G but lacks the amino group attached to G's 2 carbon, and thus can pair with both purines or pyrimidines.
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What enzyme catalyzes and thus charges tRNAs?
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Aminoacyl-tRNA synthetase (tRNA synthetase)
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How does Aminoacyl-tRNA synthetase charge tRNA?
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It catalyzes a two-step reaction that forms a bond between the carboxyl group of the amino acid and the 3' hydroxyl group of A in CAA.
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What are mistakes called in charging tRNAs? Their rate?
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Mischarging occurs 1 in 50,000 to 1 in 100,000 charged tRNAs.
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Is there overlap in the genetic code?
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NO
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If the genetic code were overlapping, what would happen if a single base was changed in mRNA?
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A single base change in mRNA would alter THREE CONSECUTIVE CODONS.
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If the genetic code were nonoverlapping, what would happen if a single base was changed in mRNA?
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A single base change in mRNA would alter a SINGLE CODON.
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What does Reading Frame refer to?
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Refers to the specific codon sequence as determined by the point at which the grouping of nucleotides into triplets begins.
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What is a Frameshift Mutation?
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The addition or deletion of nucleotides which then changes the reading frame.
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How can Frameshift Mutations be reversed?
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If a second mutation in a different location within the same gene restores the reading frame.
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What is the second mutation (the one that would reverse Frameshift Mutations) called?
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Reversion Mutation!
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What are the two categories of posttranslational events?
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1. Posttranslational polypeptide processing
2. Protein Sorting |
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What is Posttranslationang Polypeptide Processing?
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Modifies polypeptides into functional proteins through the removal or chemical alteration of amino acids after translation is completed.
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What is Protein Sorting?
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Separate, genetically controlled process that uses signal sequences to sort proteins and direct them to their cellular destinations.
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What are Signal Sequences?
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AKA Leader Sequences are short sequences of amino acids at the N-terminal end of a polypeptide.
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Why is protein sorting needed in bacteria?
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There are many proteins specifically destined for the cell membrane.
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In the ER, misfolded proteins are identified and bound by molecules called what?
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Chaperones
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What are Chaperones?
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They affiliate with proteins during the folding process and dissociate when the correctly folded structure is attained.
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What happens if the correct folding of protein does not occur?
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Attached chaperones ramain irreversibly bound resulting in their sequestration in the ER (then destroyed.)
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The attachment of a free amino acid to a specific RNA molecule is a key step in what?
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Charging of tRNA!
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Where are cytoplasmic proteins synthesized?
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On free ribosomes!
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Where are secreted proteins synthesized?
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Secreted proteins are synthesized on ribosomes bound to the rough ER.
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What normally binds to an open A-site on the ribosome?
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A tRNA that carries the next amino acid to be added to the polypeptide chain
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In the process of translational initiation in bacteria, where does the initiator tRNA first bind to the ribosome?
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To the partial P-site on the small ribosomal subunit
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Where does the formation of ribosomal subunits take place?
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In the nucleolus in the nucleus!
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Where does transcription and RNA processing occur?
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In the nucleus but OUTSIDE the nucleolus.
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What three RNAs are used in Transcription/RNA processing?
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1. snRNA
2. mRNA 3. pre-mRNA |
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What 2 RNAs are used in Translation?
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1. rRNA
2. tRNA |
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What elongation factor binds GTP and brings aminoacyl-rRNA to the A site?
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EF-Tu
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What elongation factor generates active EF-Tu?
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EF-Ts
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What elongation factor stimulates translocation? Is it GTP independent or dependent?
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EF-G and it is GTP dependent
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Where are their exceptions to the universal Genetic code?
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Mitochondrial DNA and some protozoans
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What are 6 Posttranslational Modifications of proteins?
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1. N-terminus amino acid removed or modified
2. Individual amino acids modified 3. Carbohydrates attached 4. Polypeptide chain trimmed 5. Signal sequences removed 6. Complexed with metal |
