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many genes specify traits by encoding ______
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who was the first person to suggest the existence of a relation between genotype and proteins?
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Genetics Chapter 11
from DNA to proteins: Translation
| Term | Definition |
|---|---|
| many genes specify traits by encoding ______ | proteins |
| who was the first person to suggest the existence of a relation between genotype and proteins? | Garrod (in 1908) |
| the one-gene, one-enzyme hypothesis proposed what? | that each gene encodes a separate enzyme |
| This hypothesis was later modified to the one-gene, one-_________ hypothesis | polypeptide |
| all proteins are composed of ______ _____ | amino acids |
| twenty common amino acids are found in proteins. These amino acids are similar in structure. each consists of a central C atom bonded to what groups? | an amino group (NH3+), a H atom, a carboxyl group (COO-), and an R (radical) group that differs for each amino acid |
| the amino acids in proteins are joined together by _______ bonds to form polypeptide chains | peptide |
| like nucleic acids, polypeptides have p______ | polarity |
| explain the polarity of polypeptides | one end has a free amino group (NH3+) and the other end has a free carboxyl group (COO-) |
| like that of nucleic acids, the molecular structure of proteins has several levels or organization. Explain the primary structure | the sequence of amino acids |
| explain the secondary structure of a protein | the amino acid sequence (polypeptide chain) folds and twists into the secondary structure |
| two common secondary structures are the ____ pleated sheets and the ____ helix | beta, alpha |
| explain the tertiary structure of a protein | the secondary structure can further fold into the tertiary structure (overall 3D shape of the protein) |
| two or more polypeptide chains can associate to create a _________ structure | quaternary |
| in summary, what determines the secondary and tertiary structures of a protein? | the amino acid sequence of the protein |
| the set of nucleotides that encodes a single amino acid is called a _______ | codon |
| the genetic code is a ______ code requiring ____ nucleotides per codon to encode all 2o amino acids | triplet, three |
| a codon is therefor... | three nucleotides that encode an amino acid |
| the next step was to determine which groups of three nucleotides specify which amino acids. the first clues to the genetic code came from the work of what two people? | Nirenberg and Mathaei |
| Nirenberg and Mathaei created synthetic RNAs (homopolymers) and added them to a test tube containing a cell-free translation system, 1 radioactively labeled amino acid, and 19 unlabeled amino acids. What was the conclusion of their experiment? | (the tube in which the protein was radioactively labeled contained newly synthesized protein with the amino acid speciied by the homopolymer.) In this case... UUU specified the amino acid phenylalanin. |
| one amino acid is encoded by three consecutive nucleotides in mRNA, and each nucleotide can have one of four possible bases (A, G, C, and U) at each nucleotide position. How many possible codons can be made? | 4^3 = 64 codons |
| 3 of these codons are ____ codons, specifying the end of translation | stop |
| the other 61 codons are called _____ codons and encode amino acids | sense |
| explain the degenerate code | because there are 61 sense codons and only 20 different amino acids commonly found in proteins (only 60 codons needed), the code contains more info than is needed to specify the amino acids |
| what does the degeneracy of the genetic code means what? | that amino acids may be specified by more than one codon |
| codons that specify the SAME amino acid are said to be __________ | synonymous |
| tRNAs serve as adaptor molecules. What do they do? | they bind particular amino acids and deliver them to a ribosome, where the amino acids are then assembled into polypeptide chains |
| what are tRNAs that accept the same amino acid but have different anticodons called? | isoaccepting tRNAs |
| Francis Crick developed the wobble hypothesis which proposed what? | that there could be some nonstandard pairings of bases at the third position of a codon (G can pair with C AND with U) |
| wobble at the third position of the codon allows what? | allows different codons to specify the SAME amino acid |
| concept check: through wobble, a single _______ can pair with more than one ______ | tRNA, amino acid |
| the code is generally __________ meaning each nucleotide in an mRNA sequence belongs to a single reading frame | nonoverlapping |
| each different way of reading the sequence is called a _________ ______ | reading frame |
| any sequence of nucleotides has _#_ potential reading frames | 3 |
| the 3 reading frames have completely different sets of codons and will specify proteins with entirely different amino acid sequences. Thus, it is important for the translational machine to use the correct reading frame. How is the correct one established? | the reading frame is set by the INITATION CODON |
| initiation codon | the first codon of the mRNA to specify an amino acid |
| what is usually the initiation codon? | AUG |
| when a reading frame has been set, codons are read as what? | successive groups of three nucleotides |
| three codons do not encode amino acids but signal the end of the protein. What are these codons called? | stop codons, termination codons, or nonsense codons |
| what are the three termination codons? | UAA, UAG, and UGA |
| with a few exceptions, all organisms use the same genetic code. the cod is said to be almost _________ | universal |
| amino acids are assembled into a protein through the mechanism of __________ | translation |
| the translation of an mRNA molecule takes place on a _________ | ribosome |
| a ribosome attaches near the _' end of an mRNA strand and moves toward the _' end, translating the codons as it goes | 5', 3' |
| synthesis begins at the ______ end of the protein, and the protein is elongated by the addition of new amino acids to the ________ end | amino, carboxyl |
| protein synthesis can be divided into 4 stages: | tRNA charging, initiation, elongation, and termination |
| protein synthesis: tRNA charging | the binding of amino acids to the tRNAs |
| protein synthesis: initiation | the components necessary for translation are assembled at the ribosome |
| protein synthesis: elongation | amino acids are joined, on at a time, to the growing polypeptide chain |
| protein synthesis: termination | protein synthesis halts at the termination codon and the translation components are released from the ribosome |
| tRNA charging: although there may be several different tRNAs for a particular amino acid, each tRNA is specific for only one amino acid. The key to specificity between an amino acid and its tRNA is what? | a set of enzymes called aminoacyl-tRNA synthetases |
| tRNA charging: a cell has _#_ differenr aminoacyl-tRNA synthetases, one for each of the amino acids | 20 |
| tRNA charging: each synthetases _______ a particular amino acid and all the tRNAs that accept that amino acid | recognizes |
| tRNA charging: the attachment of a tRNA to its appropriate amino acid require energy. What is the energy supplied by? | ATP (adenosine triphosphate_ |
| concept check: amino acids bind to which part of the tRNA? | the 5' end |
| initiation comprises of three major steps: first, mRNA binds to what? | to the small subunit of the ribosome |
| initiation comprises of three major steps: second, initiator _____ binds to the _____ through base pairing between the codon and the anticodon | tRNA, mRNA |
| anticodon | sequence of 3 nucleotides in tRNA that pairs with the corresponding codon in mRNA in translation |
| initiation comprises of three major steps: third, the large ______ joins the initiation complex | ribosome |
| initiation in bacteria: the functional ribosome of bacteria exists as two subunits: | the small 30S and the large 50S |
| initiation in bacteria: when not actively translating, these two subunits are ______ | joined |
| initiation in bacteria: an mRNA molecules can bind to the small ribosome subunit only when the subunits are separate. What allow initiation factor is responsible for keeping the two subunits from joining? | initiation factor 3 (IF-3) |
| initiation in bacteria: What does the IF-3 do? | it binds to the small ribosomal subunit and prevents the large subunit from binding to it |
| initiation in bacteria: now that the two subunits are separate from eachother, what can happen? | the small ribosomal subunit may now bind to mRNA |
| initiation in bacteria: which other initiation factor enhances the disassociation of the large and small ribosomal subunits? | IF-1 |
| initiation in bacteria: next, what attaches to the initiation codon? | initiator tRNA |
| initiation in bacteria: the binding of initiator tRNA to the initiation codon requires which initiation factor? | IF-2 |
| initiation in bacteria: in this step, the initiator tRNA forms a complex with IF-2 and ___ | GTP |
| initiation in bacteria: the small subunit of ribosome, the mRNA, the initiator tRNA with its amindo acid, the one molecule of GTP, and the several IFs are collectively known as what? | 30S intiation complex |
| initiation in bacteria: what is the final step of initation? | the initation factors disassociate from the small subunit, allowing the large subunit of the ribosome to join the initiation complex |
| initiation in bacteria: when the large subunit has joined the initiation complex, what is the complex called? | 70S initiation complex |
| initiation in eukaryotes: in bacterial cells, sequences in 16S rRNA of the small subunit of the ribosome bind to the ______-_______ sequence in mRNA. no analogous consensus sequence exists in eukaryotic mRNA | Shine-Dalgarno |
| initiation in eukaryotes: instead, the _' end of the eukaryotic mRNA plays a critical role in the intiation of translation | 5' end |
| initiation in eukaryotes: the small subunit of the eukaryotic ribosome, initiation factors, and the initiator tRNA with its amino acid forms an initiation complex that does what? | recognizes and binds to the cap |
| initiation in eukaryotes: the initiation complex then does what? | scans the mRNA until it locates the first AUG codon (start codon) |
| initiation in eukaryotes: the identification of the start codon is facilitated by the presence of a consensus sequence called the ________ sequence that surrounds the start codon | Kozak: 5'-ACC AUG G-3' |
| initiation in eukaryotes: the poly(__) tail at the _' end of eukaryotic mRNA also plays a role in the initiation of translation | A, 3' end |
| initiation in eukaryotes: during initiation, proteins that attach to the poly(A) tail interact with proteins that bind to the _' cap | 5' cap |
| initiation in eukaryotes: what does this binding do? | it enhances the binding of the small subunit of ribosome to the 5' end of the mRNA |
| initiation in eukaryotes: This interaction idicates that the 3' end of the mRNA bends over and associates with the 5' cap during the intiation of translation, forming what? | a closed loop structure |
| elongation: a ribosome has three sites that can be occupied by tRNAs: | aminoacyl (A) site, peptidyl (P) site, and exit (E) site |
| elongation: the initiator tRNA immediately occupies the _ site, but all other tRNAs first enter the _ site | P, A |
| elongation: after initiation, the ribosome is attached to the mRNA, and the tRNA is positioned where? | over the AUG start codon in the P site |
| elongation: after initiation, the _ site is unoccupied | A |
| elongation takes place in three steps: first, a charged _____ binds to the A site | tRNA |
| elongation: this binding takes place when a three-part complex. What is this three-part complex composed of? | elongation factor Tu (EF-Tu) joins with GTP and then with a charged tRNA |
| elongation: after the charged tRNA is in the A site, GTP is cleaved to ___ and the EF-Tu- ___ complex is released | GDP |
| elongation: elongation factor Ts (EF-T) regenerates EF-Tu-___ to EF-Tu-___ | GDP to GTP |
| elongation takes place in three steps: second, the formation of a ______ bond between the amino acids that are attached to tRNAs in the P and A sites. | peptide |
| elongation: the formation of this peptide bond does what? | releases the amino acid in the P site from its tRNA |
| elongation takes place in three steps: third step is ___________, the movement of the ribosome down the mRNA in the 5'->3' direction | translocation |
| elongation: this translocation step positions the ribosome over the next codon and requires what two things? | elongation factor G (EF-G) and the hydrolysis of GTP to GDP |
| elongation: why do the tRNAs in the P and A sites do not move with the ribosome as it translocates? | because the tRNAs in the P and A sites are still attached to the mRNA through codon-anticodon pairing |
| elongation: this means that the ribosome shifts so that the tRNA that previously occupied the P site now occupies the _ site | E |
| elongation: after the tRNA is occupying the E site, then what? | it moves into the cytoplasm where it can be recharged with another amino acid |
| elongation: Translocation also causes the tRNA that occupied the A site to be in the _ site, leaving the A site open | P site |
| elongation: because the A site is now open, it is free to do what? | receive another tRNA |
| elongation: Summary of the progress of each tRNA through the ribosome in the course of elongation: ______ -> _ site -> _ site -> _ site -> ______ | cytoplasm -> A site -> P site -> E site -> cytoplasm |
| concept check: in elongation, the creation of peptide bonds between amino acids is catalyzed by what? | rRNA |
| termination: When does protein synthesis terminate? | when the ribosome translocates to a termination codon |
| termination: there are no tRNAs with anti-codons complementary to the termination codons which means what? | no tRNA enters the A site of the ribosome when a termination codon is encountered. |
| termination: instead, proteins called ______ factors bind to the ribosome (the termination codon) | release factors |
| termination: escherichia coli has three release factors (RF1, RF2, RF3) what termination codons does RF1 bind to? | UAA and UAG |
| termination: escherichia coli has three release factors (RF1, RF2, RF3) what termination codons does RF2 bind to? | UGA and UAA |
| termination: the binding of RF1 or RF2 to the A site of the ribosome promotes what? | cleavage of the tRNA in the P site from the polypeptide chain and the release of the polypeptide |
| termination: RF3 binds to the ribosome and forms a complex with ___ | GTP |
| termination: What does this complex do? | releases RF1 or RF2 from the A site and cases the tRNA in the P site to move to the E site (GTP is hydrolyzed to GDP) |
| termination: the tRNA is released from the _ site and the mRNA is release from the ________, and the ribosome disassociates | P site, ribosome |
| additional properties: each mRNA may be simultaneously translated by several ribosomes, producing a structure called a _________ | polyribosome |
| additional properties: (polyribosomes) each ribosome successively attaches to the ribosome-binding site at the _' end of the mRNA and moves toward the _' end. the polypeptide associated with each ribosome becomes progressively longer | 5' end to 3' end |
| concept check: in a polyribosome, the polypeptides associated with which ribosomes will be the longest? | those at the 3' end |
| additional properties: many proteins undergo ____________ modifications after their synthesis | posttranslational |
| additional properties: posttranslational modification can include what? (3) | cleavage from a larger precursor protein, the removal of amino acids, and the attachment of other molecules to the protein |
| functions of many proteins critically depend on the proper folding of the polypeptide chain. some fold into correct shapes, but other may initially require the participation of other molecules called what? | molecular chaperones |
| anitibiotics are drugs that kill __________ | microorganisms |
| translation is frequently the target of antibiotics because why? | translation differs significantly between bacterial and eukaryotic cells (ie: kill the bacteria, without harming the host) |
Created by:
cmccartney2