TRANSCRIPTION AND TRANSLATION
True or False? A codon is a group of three bases that can specify more than one amino acid.
False
Stop Codon
UAA, UAG, or UGA; signal end of translation when protein complete
The RNA that has an amino acid attached to it, and that binds to the codon on the mRNA, is called a _______.
tRNA
type of RNA that plays a role in translation
tRNA, rRNA
Translation is _____.
the coding from mRNA to proteins
process of translation: elongation
1. new amino acid-tRNA molecule binds in A site (where all new tRNA begin) 2. peptide bond forms between amino acids in P and A site- catalyzed by rRNA; causes tRNA in P site to release its amino acid 3. ribosome moves along mRNA (translocation) and the 1st tRNA moves from P to E site so it can exit *these steps repeated dozens to thousands of times until complete protein has been made*
characteristics of transcription initiation in bacteria
1. separate double strand of DNA by breaking H-bonds 2. DNA reforms double strand as it exits 3. RNA exits 5' end first 4. start of gene is upstream, end of gene is downstream 5. promoters of gene: upstream of gene
process of translation: initiation
1. small subunit binds mRNA- recognizes binding site and lines up ribosome with start site 2. tRNA binds- uses initiation factor 3. large subunit binds- releases initiation factor *first tRNA starts in the P site*
steps of RNA splicing
1. snRNPs (snRNA+protein) bind to mRNA 2. snRNPs assemble into spliceosome 3. intron is cut and forms a loop 4. intron is released, and exons join together
At which site do new aminoacyl tRNAs enter the ribosome during elongation?
A-site
Consider the following two mRNA molecules: Original RNA sequence: 5' AUGACGUGUACC 3' New RNA sequence: 5' AUGACGUUGUACC 3' The difference between the two molecules would most likely result in which type of change in the resulting protein molecule?
A frameshift mutation resulting in a change in the amino acid sequence
Which of the following is a correct description of a knockout allele?
A gene altered so that it no longer produces the intended proteins
Start Codon
AUG
RNA polymerase
Catalyzes synthesis of RNA from ribonucleotides using a DNA template
List steps linking a change in base sequence of gene to a change in phenotype of organism
Change in DNA sequence → change in sequence of transcribed mRNA → change in amino acid sequence of protein → altered protein function → change in phenotype.
Proteins are made up of 20 different amino acids. How many fewer amino acids would have to be used in order to have the genetic code be made up of two-letter words?
Four
In a eukaryotic cell, the DNA is enclosed in the nucleus, whereas ribosomes that make proteins are located in the cytoplasm. How does the information in DNA that specifies the amino acid sequence of a particular protein get to the cytoplasmic protein-manufacturing centers?
Messenger RNA molecules act as the link between genes and the protein-manufacturing centers
What feature of the genetic code makes it possible for a single protein to be encoded by more than one mRNA sequence? See Section 16.3
More than one codon can specify the same amino acid
are introns ever part of an mRNA transcript?
NO! they are always removed, only exons remain in the mRNA transcript (but some of those can be removed too if needed)
Which type of mutation causes a premature termination of protein synthesis?
Nonsense
A point mutation that results in an early stop codon within a protein is a ______. See Section 16.4
Nonsense Mutation
The initiator tRNA attaches at the ribosome's ______ site.
P
A frameshift mutation that occurs very early in a protein sequence would have what effect on the protein's structure?
Primary, secondary, and tertiary structures would be altered.
not used in protein synthesis
RNA primers
The discovery of retroviruses and their mechanism of replication required scientists to rethink the central dogma of molecular biology. Based on this information, which of the following statements would represent an appropriate adjustment to the central dogma?
RNA → DNA → RNA → protein
Which enzyme allows RNA to be coded into DNA?
Reverse transcriptase
Which of the following is an exception to the central dogma of molecular biology?
Single-stranded RNA from a virus is used as a template for producing DNA that inserts into the host genome.
If a researcher added a polymer of synthetic DNA that contained only adenine (A) residues to a reaction containing RNA polymerase and ribonucleotide monomers, what would be the composition of the RNA polymer produced?
The RNA polymer would contain only uracil
Why is it possible for a point mutation to have no effect on an individual's fitness?
The encoded protein may be unchanged due to the redundancy of the genetic code
Which of the following is true about the evolution of the genetic code?
The existing genetic code is structured in a way that efficiently minimizes the phenotypic effects of small changes in DNA and errors during translation.
What change in the nature of the genetic code could be possible if, instead of two sets of base pairs (A-T, G-C), there were three sets of base pairs (A-T, G-C, and X-Y)?
The extra base pair would make it possible to have codons two bases in length rather than three.
A metabolic pathway synthesizes a product through a series of steps, with each step having an intermediate compound. What conclusion should be drawn when a genetic mutation in the DNA results in the production of only the first few intermediates?
The gene that codes for the enzyme required to produce the next intermediate in the pathway is knocked out.
Genetic code
The set of all codons and their meaning
The number of bases that specify an amino acid is ____.
Three
What is the function of mRNA?
To carry information from DNA out of the nucleus to the site of protein synthesis
How many amino acids are represented in the genetic code by just one codon?
Two
What is the most common number of codons that specifies a single amino acid?
Two
Spliceosomes are composed of ________. a) snRNPs and other proteins b) polymerases and ligases c) introns and exons d) the RNA transcript and protein e) snRNPs and snurps
a) snRNPs and other proteins
5' cap
a modified form of guanine nucleotide added onto the 5' end of a pre-mRNA molecule
Which of these is currently considered the best definition of a gene? a) A gene codes for either a polypeptide or an RNA molecule. b) A gene codes for a single protein. c) A gene codes for a particular ribozyme. d) A gene codes for a single polypeptide. e) A gene codes for a single enzyme.
a) A gene codes for either a polypeptide or an RNA molecule.
Transcription begins at a promoter. What is a promoter? a) A site in DNA that recruits the RNA Polymerase b) Part of the RNA molecule itself c) A site found on the RNA polymerase d) The same as a start codon
a) A site in DNA that recruits the RNA Polymerase
Which of the following terms best describes the relationship between the newly synthesized RNA molecule and the DNA template strand? a) Complementary b) Covalently bound c) Permanently base-paired d) Identical
a) Complementary
Which of the following mutations would likely be most dangerous to a cell? a) Deletion of one nucleotide b) Deletion of three nucleotides c) Substitution of one nucleotide for another
a) Deletion of one nucleotide
What name is given to the process in which pre-mRNA is edited into mRNA? a) RNA processing b) gene expression c) polypeptide formation d) transcription e) translation
a) RNA processing
What is meant by translocation? a) The ribosome slides one codon down the mRNA b) completed polypeptide is released from the ribosome c) two ribosomal subunits are joined in a complex d) polypeptide chain grows by one amino acid
a) The ribosome slides one codon down the mRNA
What does a mutagen cause? a) a change in the sequence of DNA b) problems with mitosis c) a reduction in the number of tRNA molecules available for protein synthesis d) decreased enzyme activity throughout the cell e) decreased permeability of the nuclear envelope
a) a change in the sequence of DNA
What enzyme catalyzes the attachment of an amino acid to tRNA? a) aminoacyl-tRNA-synthetase b) rubisco c) dextrinase d) argininosuccinate lyase e) nuclease
a) aminoacyl-tRNA-synthetase
If a mutated DNA sequence produces a protein that differs in one central amino acid from the normal protein, which of the following kinds of mutations could have occurred?a) An addition mutation and a deletion mutation b) A deletion mutation c) none d) An addition mutation
a) an addition mutation and a deletion mutation
The anticodon of a particular tRNA molecule is a) complementary to the corresponding mRNA codon. b) catalytic, making the tRNA a ribozyme. c) complementary to the corresponding triplet in rRNA d) the part of tRNA that bonds to a specific amino acid e) changeable, depending on the amino acid that attaches to the tRNA
a) complementary to the corresponding mRNA codon.
After transcription begins, several steps must be completed before the fully processed mRNA is ready to be used as a template for protein synthesis on the ribosomes. Which three statements correctly describe the processing that takes place before a mature mRNA exits the nucleus? a) Noncoding sequences called introns are spliced out by molecular complexes called spliceosomes. b) Coding sequences called exons are spliced out by ribosomes. c) A cap consisting of a modified guanine nucleotide is added to the 5' end of the pre-mRNA d) A translation stop codon is added at the 3' end of the pre-mRNA. e) A poly-A tail is added to the 3' end of the pre-mRNA.
a, c, e
ribozyme
an RNA molecule that functions as an enzyme, such as an intron that catalyzes its own removal during RNA splicing
linking amino acids and tRNA molecules
an aminoacyl tRNA synthetase molecule forms a covalent bond between tRNA and it's matching amino acid before translation can occur
The direction of synthesis of an RNA transcript is _____. a) 1'→5' b) 5'→3' c) 1'→3' d) 3'→5' e) 2'→4'
b) 5'→3'
Which of the following statements about mutations is false? a) Addition and deletion mutations disrupt the primary structure of proteins. b) A knock-out mutation results in a total absence of the mutated protein. c) An addition mutation results in an added base in the DNA sequence. d) A deletion mutation results in the loss of a base in the DNA sequence.
b) A knock-out mutation results in a total absence of the mutated protein.
During RNA processing a(n) ____ is added to the 3' end of the RNA. a) 3' untranslated region b) a long string of adenine nucleotides c) 5' untranslated region d) coding segment e) modified guanine nucleotide
b) a long string of adenine nucleotides
After an RNA molecule is transcribed from a eukaryotic gene, what are removed and what are spliced together to produce an mRNA molecule with a continuous coding sequence? a) operators...promoters b) introns...exons c) exons...introns d) promoters...operators e) silencers...enhancers
b) introns...exons
The average length of a transcription unti along a eukaryotic DNA molecule is about 27,000 nucleotide pairs, whereas an averaged-sized protein is about 400 amino acids long. What is the best explanation for this fact? a) Each amino acid in a protein is encoded by a triplet of nucleotides b) most eukaryotic genes and their RNA transcripts have long noncoding stretches of nucleotides that are not translated c) many genes are subject to alternative RNA splicing
b) most eukaryotic genes and their RNA transcripts have long noncoding stretches of nucleotides that are not translated
In eukaryotic cells, transcription cannot begin until a) DNA nucleases have isolated the transcription unit. b) several transcription factors have bound to the promoter. c) the two DNA strands have completely separated and exposed the promoter d) the DNA introns are removed from the template. e) the 5' caps are removed from the mRNA
b) several transcription factors have bound to the promoter.
During transcription in eukaryotes, a type of RNA polymerase called RNA polymerase II moves along the template strand of DNA in the 3'→5' direction. However, for any given gene, either strand of the double-stranded DNA may function as the template strand. For any given gene, what ultimately determines which DNA strand serves as the template strand? a) the location along the chromosome where the double-stranded DNA unwinds b) the base sequence of the gene's promoter c) which of the two strands of DNA carries the RNA primer d) the location of specific proteins (transcription factors) that bind to the DNA
b) the base sequence of the gene's promoter
prokaryotes: transcription and translation coupled
both occur at the same time- RNA polymerase and ribosomes bind at the same time and the ribosome "chases" the RNA polymerase
If a DNA sequence is altered from TAGCTGA to TAGTGA, what kind of mutation has occurred? a) Both addition and deletion b) Addition c) Deletion d) None
c) Deletion
Generally speaking, which of the following mutations would most severely affect the protein coded for by a gene? a) a base substitution at the beginning of the gene b) a base substitution at the end of the gene c) a frameshift deletion at the beginning of the gene d) a frameshift deletion at the end of the gene
c) a frameshift deletion at the beginning of the gene
Which of the following mutations would be most likely to have a harmful effect on an organism? a) a deletion of three nucleotides near the middle of a gene b) a single nucleotide deletion in the middle of an intron c) a single nucleotide insertion downstream of, and close to, the start of the coding sequence. d) a nucleotide-pair substitution e) a single nucleotide deletion near the end of the coding sequence
c) a single nucleotide insertion downstream of, and close to, the start of the coding sequence.
Which mutation(s) would not change the remainder of the reading frame of a gene sequence that follows the mutation(s)? a) One deletion mutation. b) One addition and two deletion mutations. c) One addition and one deletion mutation. d) One addition mutation.
c) one addition and one deletion mutation
If the sequence ATGCATGTCAATTGA were mutated such that a base were inserted after the first G and the third T were deleted, how many amino acids would be changed in the mutant protein? a) One b) none c) two d) three
c) two
In eukaryotic cells, translation occurs in the ________
cytoplasm, after leaving the nucleus
What determines which base is to be added to an RNA strand during transcription? a) The previous base b) The order of the chemical groups in the backbone of the RNA molecule. c) Base pairing between the two DNA strands. d) Base pairings between the DNA template strand and the RNA nucleotides
d) Base pairings between the DNA template strand and the RNA nucleotides
The tRNA anticodon, GAC, is complementary to the mRNA codon with the sequence _____. a) CAG b) CTG c) GAC d) CUG e) TCG
d) CUG
Which component is not directly involved in translation? a) mRNA b) ribosomes c) GTP d) DNA e) tRNA
d) DNA
Which of the following is not true of RNA processing? a) a primary transcript is often much longer than the final RNA molecule that leaves the nucleus. b) Ribozymes may function in RNA splicing c) nucleotides may be added at both ends of the RNA d) Exons are cut out before mRNA leaves the nucleus e) RNA splicing can be catalyzed by spliceosomes
d) Exons are cut out before mRNA leaves the nucleus
Which of the following is not true of a codon? a) It never codes for more than one amino acid. b) It consists of three nucleotides. c) It is the basic unit of the genetic code. d) It extends from one end of a tRNA molecule. e) It may code for the same amino acid as another codon.
d) It extends from one end of a tRNA molecule.
What happens to RNA polymerase II after it has completed transcription of a gene? a) It begins transcribing the next gene on the chromosome. b) It joins with another RNA polymerase to carry out transcription. c) It is degraded. d) It is free to bind to another promoter and begin transcription.
d) It is free to bind to another promoter and begin transcription.
What is the function of RNA polymerase? a) It adds nucleotides to the 5' end of the growing mRNA molecule b) It relies on other enzymes to unwind the double helix. c) It proceeds slowly along the DNA strand, requiring about a minute to add two nucleotides to the growing mRNA molecule. d) It unwinds the double helix and adds nucleotides to a growing strand of RNA. e) All of the above.
d) It unwinds the double helix and adds nucleotides to a growing strand of RNA.
Which of the following steps occurs last in the initiation phase of translation? a) an aminoacyl tRNA binds to the start codon b) peptide bond is formed between two adjacent amino acids c) small subunit of the ribosome binds to the 5' cap on the mRNA d) large ribosomal subunit joins the complex
d) large ribosomal subunit joins the complex
RNA processing converts the RNA transcript into _____. a) a protein b) DNA c) a eukaryotic cell d) mRNA e) a polypetide
d) mRNA
How is translation initiated? a) small ribosomal subunit binds to the mRNA b) tRNA bearing methionine binds to the start codon c) the large ribosomal subunit binds to the small one d) the start codon signals the start of translation e) all of the above
e) all of the above
Polypeptides are assembled from ______. a) hexoses b) glycerol c) nucleotides d) proteins e) amino acids
e) amino acids
During RNA processing a(n) _____ is added to the 5' end of the RNA. a) 3' untranslated region b) a long string of adenine nucleotides c) 5' untranslated region d) coding segment e) modified guanine nucleotide
e) modified guanine nucleotide
Which one of the following is true of tRNAs? a) there are four types of tRNA b) Each tRNA binds a particular codon c) tRNAs are double-stranded d) tRNAs carry special sequences known as codons e) all of the above f) none of the above
f) none of the above
True or false. A tRNA with an anticodon complementary to the stop codon catalyzes the reaction by which translation is terminated
false
comparison of gene and mRNA
gene is longer than the transcribed mRNA when both are single stranded and this is because of introns that are in the gene but are spliced out before the mRNA moves on because they're unnecessary for the gene
multiple ribosomes on a single mRNA
helps with efficiency, and occurs in prokaryotes and eukaryotes
how are codons read?
hypothesis 1: there is a direct interaction between the amino acid and the mRNA (FALSE) hypothesis 2: adapter molecules assist, called tRNA (TRUE)
basics of RNA synthesis
incoming NTP no primer needed not all DNA transcribed
transcription termination in bacteria
loop forms in mRNA between complementary bases when the RNA polymerase transcribes the transcription termination signal this causes the active site to release the created mRNA DNA also disconnects from polymerase
Which nucleic acid is translated to make a protein?
mRNA
tRNA: the adapter molecule
mRNA transcript contains codons, which match the anticodons held on a tRNA molecule each anticodon is associated with a certain amino acid, which the tRNA molecule carries
ribosomes
made of rRNA and protein consist of two subunits, one small and one large
Duplication of a segment of a chromosome would result in _______.
more copies of the genes present in the duplicated portion of the chromosome. This type of error can provide an opportunity for evolution to occur.
translation: gene synthesis
normally occurs in cytosol or RER ribosomes help create peptide bonds but do not synthesize amino acids proteins form N terminus to C terminus, with peptide bond between C of one amino acid and N of the next
process of translation: termination
occurs because of a STOP codon, which puts a release factor (made of protein) in the A site this breaks the bond between P site tRNA and its amino acid so the protein can be released then the mRNA leaves ribosome as the subunits fall off
Proteins code for
phenotypical traits, such as proteins produced in melanin
gene expression
process by which information encoded in DNA directs the synthesis of proteins or, in some cases, RNA that are not translated into proteins and instead function as RNAs
transcription initiation in bacteria
promoter is found just before start of gene- the +1 site sigma protein: helps RNA polymerase find the right spot to bind, and recognizes the -35 box and -10 box sequences when the sigma protein binds it changes shape and hooks DNA into active site of RNA polymerase, allowing transcription to start at +1 site
Where does translation take place?
ribosome
advantage of splicing: alternative splicing
seen in the tropomyosin gene: it has 14 exons and the final mRNA transcript differs whether made in skeletal muscle or smooth muscle -- they are different lengths and contain different exons, allowing the organism to use one gene to create multiple related but different proteins
Reading Frame
series of adjacent non-overlapping three-base-long sequences (potential codons) in DNA or RNA. i.e normal rading frame "The fat cat ate the rat" would change into "The atc ata tet her at" if f was removed, shifting the sequence, creating a gibberish protein in result. Also possible to remove some, to "The cat ate the rat" can still produce functional protein, but missing information
type of RNA that plays a role in transcription
snRNA, pre-mRNA, mRNA
The function of RNA polymerase is to __________.
transcribe DNA to RNA
transcription in eukaryotes
transcription factors form a binding site for RNA polymerase at the TATA box, which is a 25-35 base pair sequence upstream of the gene
