Genetics Chapter 15 Translation

translation
Click the card to flip 👆
1 / 45
Terms in this set (45)
translation
the process in which the sequence of codons within the mRNA provides the information to synthesize the sequence of amino acids that constitute a polypeptide
Image: translation
messenger RNA
the RNA transcribed from protein-encoding genes
Archibald Garrod
-proposed a relationship between genes and protein production
-studied alkaptonuria
-patient's bodies accumulate abnormal levels of homogentisic acid
-proposed it was due to a missing enzyme, homogentisic acid oxidase
inborn error of metabolism
-the first suggestion that a connection exists between the function of genes and the production of enzymes
Beadle and Tatum's Experiments
- interested in the relationship among genes, enzymes and traits
-model is Neurospora crassa
Neurospora crassa
the model of Beadle and Tatum's experiments
-wild-type cells grew on minimal media (prototrophs)
-mutants could not grow on minimal media alone (Auxotrophs)
protorophs
wild type cells grew on minimal media
auxotrophs
mutants that could not grow on minimal media alone
Beadle and Tatum's Neurospora experiment
- they wanted to understand how enzymes are controlled by genes
- they concluded based on their findings that a single gene controlled the synthesis of a single enzyme
Image: Beadle and Tatum's Neurospora experiment
one-gene/one-enzyme hypothesis
1. enzymes are only one category of proteins and all proteins are encoded by genes, and many of them do not function as enzymes

2. some proteins are composed of 22 or more different polypeptides

3. one gene can encode 2 or more polypeptides due to alternative splicing or RNA editing

4. as of now, we know that many genes do not encode polypeptides (many genes encode functional RNAs)
An inborn error of metabolism is caused by a. a mutation in a gene that causes an enzyme to be inactive. b. a mutation in a gene that occurs in somatic cells. c. the consumption of foods that disrupt metabolic processes. d. any of the above.d. any of the aboveThe reason why Beadle and Tatum observed four different categories of mutants that could not grow on media without methionine is a. the enzyme involved in methionine biosynthesis is composed of four different subunits. b. the enzyme involved in methionine biosynthesis is present in four copies in the Neurospora genome. c. four different enzymes are involved in a pathway for methionine biosynthesis. d. a lack of methionine biosynthesis can inhibit Neurospora growth in four different ways.c. four different enzymes are involved in a pathway for methionine biosynthesisgenetic codethe sequence of bases within an mRNA molecule provides coded information that is read in groups of 3 nucleotides (codons) - nucleotide language of mRNA is translated into the amino acid language of proteinscodons3 nucleotide bases long -within mRNAsense codonsthe sequence of 3 bases in most codons specifies a particular amino acid EX: the codon AGC specifies the amino acid serinestart codonusually the first codon that begins a polypeptide sequence - AUG (methionine) is used as thisstop codons, termination codons, nonsense codons3 codons -UAA, UAG, and UGA- are used to end the process of translation5'-untranslated region and 3'-untranslatedprecede the start codon and follow the stop codon -they do not encode a polypeptideanticodons-in tRNA -recognizes the codons in mRNA - 3 nucleotide sequences that are complementary to codons in mRNAtRNAcarries the amino acids that correspond to the codons in the mRNAdegeneracy-more than one codon can specify the same amino acid Ex: the codons GGU, GGC, GGA, and GGG all specify the amino acid glycine - the 3rd base is usually thissynonymous codonsdifferent codons that specify the same amino acidwobble basethird base in a codonreading framea sequence of codons determined by reading bases in groups of 3, beginning with the start codon as a frame of reference - the start codon (AUG)peptide bondformed between the carboxyl groups in the last amino acid of the polypeptide and the amino group in the amino acid being added -occurs when a water molecule is released -the newest amino acid added to the growing polypeptide always has a free carboxyl groupamino-terminal end (N-terminus)the first amino acid of the of the polypeptide - an amino group (NH3+) is found here -refers to the presence of a nitrogen atom at this end -the first amino acid is specified by a codon that is near the 5' end of the mRNAcarboxyl- terminal end (C-terminus)- the last amino acid in a completed polypeptide -a carboxyl group (COO-) -the last amino acid is specified by a codon that is closer to the 3' end of the mRNAWhat is the genetic code? a. The relationship between a three-base codon sequence and an amino acid or the end of translation b. The entire base sequence of an mRNA molecule c. The entire sequence from the promoter to the terminator of a gene d. The binding of tRNA to mRNAa. The relationship between a three-base codon sequence and an amino acid or the end of translationThe reading frame begins with a _____________ and is read ____________________. a. promoter, one base at a time b. promoter, in groups of three bases c. start codon, one base at a time d. start codon, in groups of three basesd. start codon, in groups of three basesThe fourth codon in an mRNA is GGG, which specifies glycine. If we assume that no amino acids are removed from the polypeptide, which of the following statements is correct? a. The third amino acid from the N-terminus is glycine. b. The fourth amino acid from the N-terminus is glycine. c. The third amino acid from the C-terminus is glycine. d. The fourth amino acid from the C-terminus is glycine.c. The third amino acid from the C-terminus is glycine.recognition between tRNAs and mRNAs- the anticodon in a tRNA molecule binds to a codon in mRNA due to their complementary sequences -the codon/anticodon binding occurs in an antiparallel shape -carries the amino acid that is specific for that codontRNA structure- exhibits a cloverleaf pattern with 3 stem-loops and a few variable sites -has an acceptor stem with a 3' single-stranded region (this is where the amino acid becomes attached) - a numbering system for the nucleotides within a tRNA molecule begins at the 5' end and proceeds toward the 3' ( in blue) -the anticodon is located at the second loop region -commonly contain modified nucleotidesaminoacyl-tRNA synthetases-catalyze the attachment of amino acids to tRNA molecules -involves 3 different molecules: an amino acid, a tRNA molecule, and ATP -only reacts with specific amino acidsaminoacyl-tRNA synthetase steps1. a synthetase recognizes a specific amino acid as well as ATP 2. ATP is hydrolyzed, which results in attachment of AMP to the amino acid and the release of pyrophosphate 3. the correct tRNA then binds to the synthetase and the amino acid becomes covalently attached to the 3' end of the tRNA molecule at the acceptor stem and AMP is released 4. the tRNA is released along with its attached amino acid from the enzymecharged tRNAin this charged molecule, the amino acid is attached to the 3' end of the tRNA by a covalent bondwobble rulesthe first 2 positions pair strictly according the the AU/GC rule -the 3rd position can tolerate certain types of mismatches because the 3rd position in the codon does not have to hydrogen bond as precisely with the corresponding base in the anticodonthe function of aminoacyl-tRNA synthetases is to a. make tRNAs b. make amino acids c. attach specific amino acids to specific tRNAs d. allow wobble base pairingc. attach specific amino acids to specific tRNAsIf a tRNA has an anticodon with the sequence 5′-CAG-3′, which amino acid does it carry? a. Aspartic acid b. Leucine c. Valine d. Glutamined. GlutamineAn enzyme known as ____________ attaches an amino acid to the __________ of a tRNA, thereby producing __________. a. aminoacyl-tRNA synthetase, anticodon, a charged tRNA b. aminoacyl-tRNA synthetase, 3′ single-stranded region of the acceptor stem, a charged tRNA c. polynucleotide phosphorylase, anticodon, a charged tRNA d. polynucleotide phosphorylase, anticodon, an aminoacyl tRNAa. aminoacyl-tRNA synthetase, anticodon, a charged tRNAribosomewhere translation takes place - bacterial cells have one type in their cytoplasm -eukaryotes have 2 typesrRNAtype of RNA that combines with proteins to form ribosomesnucleolusa region of the nucleus specialized for the assembly of rRNAs and ribosomal proteins to make the 40S and 60S subunitspolyribosomeused to describe an mRNA transcript that has many ribosomes in the act of translationLabel the following image1. polypeptide 2. tRNA 3. A site (aminoacyl site) 4. mRNA 5. E site 6. P site (peptidyl site)