Chapter 8: Gene Expression - The Flow of Information from DNA to RNA to Protein

Based on Yanofsky's comparison of DNA mutations and protein sequence, how many amino acids are affected by a single nucleotide mutation

1

When the ribosome synthesizes a 281-amino acid polypeptide, ______ rounds of elongation are required

280

The last amino acid in a polypeptide chain is encoded by a codon near the

3' end of the mRNA

Which anticodon would bind to a codon with the sequence 5'-CAG-3'?

3'-GUC-5'

When accounting of the pairing rules allowed for by wobble, which of the following mRNA codons could pair with he anticodon 3' UAG 5'

5' AUU 3' 5' AUC 3'

A frameshift mutation is caused by what?

A base deletion A base addition

Selenocysteine (Sec) is a rare amino acid that is only incorporated into about 25 proteins in humans, The standard genetic code direct the placement of the 20 common amino acids. Place the event required for Sec incorporation int he order that they occur

A special tRNA^Sec is charged with serine (Ser) by serine tRNA synthetase Serine (Ser) is enzymatically modified to selenocysteine (Sec) A tRNA^Sec interacts with an mRNA with a Sec insertion sequence (SECIS) Sec is incorporated into a protein at a UAG codon

What must bind to an aminoacyl-tRNA synthesis enzyme in order to charge a transfer RNA

A specific transfer RNA A specific amino acid ATP

What are the features of transcription in eukaryotes only?

Enhancer sequences can be distant from promoter Addition of 5' cap to mRNA Presence of multiple types of RNA polymerases Alternative splicing of transcripts can produce multiple types of polypeptides

A prokaryotic promoter differs from a eukaryotic promoter because

Eukaryotic promoters are bound by histone proteins that must be released Prokaryotic promoter sequences are closer to the transcription start site

T/F: Prokaryotic and eukaryotic cells use different genetic codes

False

In prokaryotic cells, formation of the initiation complex requires the binding of tRNA^fMet to the ______ site of the ribosome

P

What codons do not encode an amino acid?

UAA, UGA, UAG (stop codons)

The genetic code is described as universal, yet exceptions tot he rules exist. How widespread are these exceptions

a few codon difference exist, particularly within mitochondria

Two functions of transfer RNA are to

bind to a specific codon and carry the amino acid specified by that codon to the growing polypeptide chain

A transfer RNA that has an amino acid attached to its 3' end is called a(n)

charged tRNA

For protein-encoding genes, the RNA-like strand is also called the ______ strand

coding

The CUA codon specifies leucine in yeast cytoplasmic translation, but the same codon specifies threonine in yeast mitochondria. What is the explanation for this phenomenon

codons used in mitochondria show a few exceptions to the universal genetic code

When scientists were determining the genetic code, they hypothesized that genes are ______ with their encoded polypeptides. In other words, the order of bases in a gene corresponds to the order of amino acids in the encoded polypeptide

colinear

In prokaryotic cells, translation of an mRNA begins before its transcription has been completed. This phenomenon is called __________ of transcription and translation

coupling

Both eukaryotic and prokaryotic cells have ribosomes in the

cytoplasm

In which cellular location would ribosomes be found for both prokaryotic and eukaryotic cells?

cytosol

In response to either of the codons CUC or CUU, leucine would be placed at a particular location on a polypeptide chain. The existence of more than one codon for the same amino acid shows that the genetic code is

degenerate

Amino acids are added sequentially to a growing polypeptide chain during

elongation

proteins known as _____ factors help place the correct tRNA in the A site

elongation

The RNA-like strand of DNA is also called the coding strand because it

has the same polarity and sequence as the mRNA but with T's instead of U's

How was Yanofsky able to show that the sequence of a gene is collinear with the sequence of amino acids in the encoded protein

he generated multiple trpA mutants can compared the genetic map of mutants with positions of the substitutions of amino acids in mutant proteins

An mRNA is monocistronic if

it codes for a single polypeptide

From crystallization studies, it has been shown that the components located on the outer surface of a ribosome and on the periphery of the interface between the ribosomal subunits are the ribosomal

proteins

Studies of the crystal structure of the 50S ribosomal subunit showed that the catalytic component of peptide transferase is

rRNA

A codon region on a single DNA strand can be read in three different ways, depending on the position of the first codon. Thus, the first codon determines the region's

reading frame

At termination of translation, a stop codon is recognized by a(n)

release factor

A site

site of aminoactyl-tRNA binding

To decipher the genetic code, an in vitro translation system containing cellular extras with ribosomes, tRNA, enzymes and radioactive amino acids was used to

synthesize radioactively-tabled polypeptides from synthetic messenger RNAs

Initiation

A complex forms between the ribosomal subunits, one mRNA molecule and the first tRNA molecule

What features of transcription are only in prokaryotes

A single type of RNA polymerase A single mRNA Fontaine's multiple polypeptide start sites The promoter consists of a -35 and a -10 sequence

To begin each round of elongation during translation, a tRNA carrying the next amino acid to be added to the polypeptide binds to what

A site on the ribosome

What are possible post translational modifications

Addition of a carbohydrate Peptide cleavage Addition of a phosphate group

Common structural features of transfer RNA molecules

Amino acid acceptor stem with a 3' single-stranded region Anticodon sequence Cloverleaf shape formed by complementary base pairing 74-95 nucleotides in length

Elongation

Amino acids are linked together in the order designated bu the codons

In order to charge a tRNA, ATP, a specific transfer RNA and a specific amino acid all bind to which enzyme?

Aminoacyl-tRNA synthetase

When cells were exposed to radioactive amino acids, it was observed that protein synthesis occurred in the cytoplasm. What did researches conclude from this discovery?

An intermediate molecule transports sequence information from the nucleus to the cytoplasm

If a cell-free translation were carried out with synthetic mRNAs produced from a mixture of 25% G and 75% A, which amino acids would be incorporated into the resulting polypeptides

Arginine Glycine Glutamic acid Lysine

What are the functions of a transfer RNA (tRNA) molecule?

Carry a specific amino acid Recognize a three base codon in messenger RNA

What is used in prokaryotic translation but not in eukaryotic translation

Coupling of transcription and translation tRNA^f-Met as the initiator tRNA Shine-Dalgarno sequence to facilitate mRNA binding to the small ribosomal subunit

For some amino acid positions, Yanofsky identified multiple missense mutations that resulted in a change in the amino acid. For example, in tryptophan synthesis, the sequence GGA codes for a glycine at position 211. Mutation to AGA causes an argon at this position. Mutation to GAA results in a glutamic acid. Neither of these mutants is able to survive in the absence of tryptophan. Yanofsky found that he could recombine these mutations, resulting in

GGA recombinants that could survive int he absence of tryptophan

What provides the source of energy for movement of the ribosome along an mRNA

GTP

If a cell-free translation were carried out with synthetic mRNAs produced from a mixture of 25% A and 75% C, which amino acids would be incorporated into the resulting polypeptides

Histidine Asparagine Lysine Threonine Glutamine Proline

Possible functions of post translational modifications to proteins

Localization to a particular sub cellular compartment Proper protein folding Activation of enzyme function

From crystallization studies, it has been shown that the components making up most of the mass in the central part of the ribosome is the ribosomal

RNA

What evidence suggests that RNA could function as the intermediary between DNA and protein

Radioactive uracil was incorporated into molecules in the nucleus and the exported to the cytoplasm RNA can base pair with DNA

In bacteria, the ribosome-binding site is also called the ____ -______ box

Shine-Dalgarno

Crick and Brenner performed experiments using combinations of bacteriophage mutations. If a single nucleotide deletion (-) occurred, which additional mutations or combinations of mutations could suppress the mutant phenotype

Single nucleotide insertion (+) Two single nucleotide deletions (--)

What occurs in eukaryotic translation but not in prokaryotic translation?

Small ribosomal subunit interacts with 5' cap A single AUG for synthesis of one type of polypeptide per mRNA

Termination

The newly produced polypeptide is released from the ribosome

Yanofsky found that recombination between two mutations that altered the same amino acid could restore a wild-type phenotype. For example, in tryptophan syntheses, the sequence GGA codes for a glycine at position 211. Mutation the AGA causes an arginine at this position. Mutation to GAA results in a glutamic acid. Neither of these mutants can survive in the absence of tryptophan (trpA-). Recombination between these two mutants yields trpA+ (GGA) recombinants. What conclusion about the genetic code do these data support?

a codon is composed of more than one nucleotide

A polyribosome is

a messenger RNA transcript that has many bound ribosomes in the act of translation

If proflavin induces a single nucleotide insertion that alters the reading frame of a protein, how could a revertant of the mutation be obtained

a single nucleotide deletion that restores the reading frame

The single-stranded region at the 3' end of a transfer RNA is the location where a(n) ______ becomes attached

amino acid

A series of three nucleotides in transfer RNA that is complementary to a codon in messenger RNA is called a(n)

anticodon

The order in which amino acids are added to a polypeptide chain is determined by hydrogen bonding between each codon and the _______ of the tRNA carrying the amino acid

anticodon

To decipher the genetic code, scientists were able to synthesize radioactively-labled polypeptides from synthetic messenger RNAs in a(n)

in vitro translational system

An AUG codon, which specifies the amino acid methionine and is often the first codon that begins a polypeptide sequence, is called the ________ codon

initiation

The synthesis of a polypeptide from an mRNA template is called

translation

Codons UUC and UUU lead to the placement of phenylalanine at a specific position in the protein chain. These two codons can be recognized by the same tRNA. This type of mismatch in codon-anticodon binding that can occur at the third baes of the codon is called

wobble

The ability of a single tRNA to recognize more than one codon is called

wobble

What components are assembled into the subunits of a ribosome?

Ribosomal proteins Ribosomal RNA

During initiation of translation, which proteins have a transient role

initiation factors

What occurs relatively often because the genetic code is degenerate

intrageni suppression

__________ suppression occurs when the function of a mutated gene is restored by a second mutation within the same gene

intragenic

In some cases of intragenic suppression, the frame shifted part of a protein can be as long as 50 amino acids. This indicates that

most of the 64 codons code for an amino acid

A mutation that results in a premature termination of the synthesis of a polypeptide is called a(n) __________ mutation

nonsense

Provlavin is an intercalating mutagen that causes insertions or deletions in DNA. Crick and Brenner observed that mutagens that cause nucleotide substitutions never suppressed proflavin-induced mutations. What is the explanation for this result

nucleotide substitutions cannot restore the reading frame of a sequence

A nucleotide triplet, called a codon, specifies

one amino acid

During elongation, the enzyme that catalyzes the transfer of the polypeptide in the P site to the amino acid in the A site is

peptide transferase

What is the role of initiation factors

play a transient role in initiation of translation

A bacterial mRNA that contains multiple ribosome binding sites is

polycistronic

A large polypeptide that is cleaved into multiple polypeptides is called a

polyprotein

A cell-free translation system with synthetic mRNAs produced from a mixture of 40% C and 60% A nucleotides showed incorporation of the amino acids histidine, proline and threonine at 9.6%, 16% and 24% respectively. This suggested that the codon for histidine had two Cs and one A. In a separate mixture of synthetic mRNAs containing only C nucleotides, proline represented 100% of the amino acids incorporated into the resulting polypeptides. For an additional analysis, a polynucleotide with alternating A and C bases, ACACACAC(AC)n, produced a polypeptide with an alternating sequence of amino acids: threonine-histidine-threonine-histidine-(threonine-histidine)n. If the 5' end of the codon is designated as number 1, what is the position of the A in the histidine codon

position 2

An enzyme adds a phosphate group to the protein MAP kinase. This ______ modification allows MAP kinase to leave the cytoplasm and enter the nucleus

posttranslational

P site

site that contains a tRNA with an attached peptide

E site

site where an uncharged tRNA leaves the ribosome

In prokaryotic cells, a transfer RNA carrying N-formylmethionine recognizes the ________ and is the first tRNA to bind to the ribosomal subunits, so it is called the initiator tRNA

start codon

The signal for termination of translation is called a(n) ________ codon

stop

A codon specifies the correct amino acid by using ________ as an adaptor molecule

tRNA

Researchers could determine the codon that specified a particular amino acid in an experiment where a three-nucleotide RNA molecule caused a ribosome to bind the _______ carrying that amino acid

tRNA

The base sequence of the RNA transcript is complementary to the ________ strand of DNA

template

The strand of DNA that is used to produce the RNA transcript is called the ________ strand, while the opposite strand of DNA is called the _______ strand or non-template

template; coding

The stage of translation that occurs when a ribosome reaches a stop codon is called

termination

What aspect of the genetic code was revealed by using n vitro translational system with a three-nucleotide mRNA molecule to cause a ribosome to bind to a fabled tRNA

the codon that specified a particular amino acid

Yanofsky's observation that a single nucleotide mutation changed a single amino acid in a protein was evidence that

the genetic code in nonoverlapping

Yanofsky generated a large number of trpA- mutants and produced a recombination map of the mutations. By comparing the order of mutations in the map with the substitutions of amino acids in the mutants, he was able to show that

the order of mutations in DNA is collinear with he positions of amino acid substitutions in the mutant proteins

A mutation in the E. coli tryptophan synthase gene produces arginine (Arg) instead of glycine (Fly) at position 211 of the protein and the bacteria are unable to survive in the absence of tryptophan. A different mutation produces serine (Ser) at the same position and the bacteria can survive in the absence of tryptophan. What is the conclusion from this result

the tryptophan synthase enzyme can function with either Gly or Ser at position 211

How did Watson and Crick determine that there are 20 amino acids that are encoded by DNA

they looked at the available polypeptide sequences at the time and made a list of all the amino acids that are commonly found in them

In order to determine the number of amino acids encoded by DNA, Watson and Crick looked at the available polypeptide sequences. How did they produce their list of amino acids

they selected only amino acids that were commonly found in polypeptides

According to the wobble rules, which base of the codon can be mismatched with an anticodon base on the tRNA

third base of the codon