Chapter 15 Pt 2

A charged tRNA with the ______________ that is complementary to the codon in the A site enters and binds to the A site.

anticodon

DNA is used as a template to make a complementary strand of DNA

DNA replication

A hypothetical new organism contains genetic material consisting of a single-stranded nucleic acid with six different nitrogenous bases. Like other organisms that have been studied, segments of the nucleic acid contain the code for making proteins. Experiments indicate that a single deletion in the nucleotide chain almost always leads to loss of function in the coded protein. However, when you make two deletions very close together, the protein usually functions normally. Based on these results, you conclude that the genetic code in these organisms is read in groups of ______ nucleotides.

2

Translation is terminated when a stop codon is presented at the ________ site. A P E either A or P either A or E

A

The ribosome moves along the mRNA so that the tRNA that was in the __ site is now in the P site and the tRNA that was in the P site is now in the E site. The movement of the ribosome is called _______________

A translocation

What mutation in the ribosome would have the most detrimental effect on peptide bond formation? -A mutation in the A-site that allowed non-specific binding of t-RNA. -A mutation in the P-site causing a loss of function of peptidyl transferase. -A mutation in the E-site causing a delay in the release of tRNA molecules. -A mutation in the A-site preventing the binding of the release factor protein. -All of these would be equally detrimental to peptide bond formation.

A mutation in the A-site preventing the binding of the release factor protein.

Translation is terminated when a stop codon is presented at the A site. P site. E site. either the A or P site. either the A or E site.

A site

The tRNA in the __ site is ejected.

E

During translation elongation, amino acids are brought to the ribosome with the help of EF-T. EF-Tu. EF-Ts. EF-G. EF-Tz.

Ef-TU

T/F During initiation of translation, the small ribosomal subunit joins to the mRNA and initiator rRNA, followed by the large ribosomal subunit.

False

T/F Ribosomes are composed of tRNA and protein

False

The coding strand of a particular DNA molecule has the following sequence: ATCCCTGCA. Assuming that this sequence is part of an exon, and represents three codons, what sequence would be found on the tRNA anticodon loop used to translate the second codon? CCU CCT GGA CGU GCA

GGA

How is GTP used during elongation? -It aids in the binding of the incoming tRNA to the A site of the ribosome. -It provides energy for the formation of the peptide bond. -It aids in translocating the ribosome one codon down the mRNA. -It provides energy for the formation of the peptide bond AND it aids in translocating the ribosome one codon down the mRNA. -It aids in the binding of the incoming tRNA to the A site of the ribosome AND It aids in translocating the ribosome one codon down the mRNA.

It aids in the binding of the incoming tRNA to the A site of the ribosome AND It aids in translocating the ribosome one codon down the mRNA.

What is unusual about the initiator tRNA? -It carries a modified amino acid -It does not bind to the ribosome at the A site -Its anticodon is not complementary to the codon with which it associates -It carries a modified amino acid AND it does not bind to the ribosome at the A site -All of these are true

It carries a modified amino acid AND it does not bind to the ribosome at the A site

What is unusual about the initiator tRNA? -It carries a modified amino acid. -It does not bind to the ribosome at the A site. -Its anticodon is not complementary to the codon with which it associates. -It carries a modified amino acid AND it does not bind to the ribosome at the A site. -All of these are TRUE.

It carries a modified amino acid AND it does not bind to the ribosome at the A site.

Which of the following statements about peptidyl transferase is TRUE? -It catalyzes the formation of peptide bonds. -It is present in the 50S ribosomal subunits. -It is a protein. -It catalyzes the formation of peptide bonds and It is present in the 50S ribosomal subunits. -It catalyzes the formation of peptide bonds, It is present in the 50S ribosomal subunits, and It is a protein.

It catalyzes the formation of peptide bonds and It is present in the 50S ribosomal subunits.

Suppose a mutation changes the amino acid that an aminoacyl-tRNA synthetase enzyme recognizes without changing the tRNA molecule that it recognizes. How is this likely to affect the process of protein synthesis? Check all that apply. -It will alter the location of the start sites during transcription -It will alter the sequence of bases in the mature mRNAs -It will alter the location of splice sites in the pre-mRNAs -It will alter the location of the start codons during translation -It will alter the sequence of amino acids in the polypeptide chains -It will cause premature termination of translation, resulting in shortened polypeptide chains -It will affect the synthesis of only one or a few types of protein produced by the cell -It will affect the synthesis of most or all of the proteins produced by the cell

It will affect the synthesis of most or all of the proteins produced by the cell It will alter the sequence of amino acids in the polypeptide chains

Which of the following statements about termination is TRUE? -No tRNA can recognize a stop codon. It is recognized by a release factor protein. -Only a single release factor tRNA can recognize a stop codon. -There are three release factor tRNAs that can recognize a stop codon. -No tRNA can recognize a stop codon. After the ribosome stalls on the mRNA for a certain length of time, it falls off and termination occurs. -All tRNAs can recognize stop codons, and so the last amino acid of all newly formed proteins is random.

No tRNA can recognize a stop codon. It is recognized by a release factor protein.

How does the ribosome recognize the proper tRNA to bind? -An elongation factor recognizes the tRNA and aids its binding through GTP hydrolysis. -Only a tRNA with an anticodon that is complementary to the codon will bind in the A-site. -Only a tRNA carrying the amino acid that is complementary to the amino acid in the P-site will bind in the A-site. -The ribosome recognizes only the proper tRNA that needs to bind in the A-site through GTP-hydrolysis. -The enzyme peptidyl transferase allows only the appropriate tRNA to bind in the A-site.

Only a tRNA with an anticodon that is complementary to the codon will bind in the A-site.

A peptide bond forms between the amino acid attached to the tRNA in the A site and the growing polypeptide chain attached to the tRNA in the ___ site

P

The initiating transfer RNA, carrying formylmethionine, binds to which site? E site P site A site E, P, and A sites P and A sites

P site

Which of the following is not involved in the initiation of translation? mRNA ribosomal subunits initiator tRNA RNA polymerase all of these choices are involved

RNA polymerasem

Why is RNA synthesis called 'transcription' and protein synthesis called 'translation?' -RNA synthesis happens in the nucleus and protein synthesis happens in the cytoplsam. -RNA synthesis makes an exact copy of the DNA molecule and protein synthesis makes a complementary copy of the RNA. -RNA synthesis produces nucleic acid from nucleic acid and protein synthesis produces polypeptides from nucleic acid. -RNA synthesis makes a complementary copy of the entire DNA molecule and protein synthesis only uses a short piece of the RNA molecule. -Because that's one someone named them a long time ago.

RNA synthesis makes a complementary copy of the entire DNA molecule and protein synthesis only uses a short piece of the RNA molecule.

__________ combines with protein to form particles that help ribosomes attach to the endoplasmic reticulum in eukaryotes.

SRP RNA

A single point mutation has occurred a gene causing a stop codon to appear early in the translation of the protein. What effect will this have on the protein? -A single point mutation will have only a minimal effect on the protein. -The early stop codon will cause premature termination, and the protein will be abnormally short. -Proofreading by the ribosome will recognize the abnormal stop codon and a random tRNA will bind at the A-site rather than the release factor. This will likely result in a single amino acid substitution. -The protein will be produced in two pieces. One piece that occurs before the stop codon, and the second piece is the remainder of the protein after the stop codon. Chaperone proteins will then facilitate the proper assembly of the functional protein. This will require extra energy for the cell. -None of these are true

The early stop codon will cause premature termination, and the protein will be abnormally short.

A mutation occurred in the third codon position of a gene, but the protein still functions normally. How is this possible? -DNA polymerase's proofreading function fixed the mistake in the nucleus. -RNA polymerase detected the mutation and transcribed the gene with the proper nucleotide. -The ribosome recognized the mutated codon and bound the tRNA that carried the proper amino acid rather than the one specified after the mutation. -The genetic code is redundant, so that mutations in the third position of the codon often result in the same amino acid being specified. -Proteins still function normally if only one amino acid is substituted.

The genetic code is redundant, so that mutations in the third position of the codon often result in the same amino acid being specified.

If the Shine-Delgarno sequence was mutated, what might be a consequence? -The mRNA would not bind to the small ribosomal subunit in the proper location. -The initiator tRNA would not bind to the small ribosomal subunit in the P-site. -The initiation factors would not bind to the ribosome, and initiation would not occur. -The initiation factors would not be released from the ribosome, and elongation would not occur. -The initiation factors would not be able to hydrolyze GTP, and the mRNA, initiator tRNA, and the ribosome would not form a strong association.

The mRNA would not bind to the small ribosomal subunit in the proper location.

Specific amino acids are attached to tRNA molecules by -anticodons. -initiation factors. -deactivating enzymes. -hydrogen bonds. -aminoacyl-tRNA synthetases.

aminoacyl-tRNA synthetases.

Which of the following occurs as a result of translocation? -The tRNA that was in the A site moves into the E site. -The tRNA that was in the P site moves into the A site. -The tRNA that was in the E site moves into the P site. -The tRNA that was in the E site moves into the A site. -The tRNA that was in the P site moves into the E site.

The tRNA that was in the P site moves into the E site.

If an aminoacyl-tRNA synthetase added the wrong amino acid to a tRNA, what would happen? -The tRNA could not bind to the ribosome, and no amino acid would be added to the growing peptide -The tRNA would associate with the wrong codon, and the wrong amino acid would be incorporate into the growing peptide. -The tRNA would carry the wrong amino acid, and it would be incorporated into the growing protein -The ribosome would not be able to recognize the stop codon, and translation would continue to occur when it should have been terminated -The ribosome would not be able to recognize the start codon, and translation would not eb initiated.

The tRNA would carry the wrong amino acid, and it would be incorporated into the growing protein

Why are there fewer tRNA anticodons than the 61 needed to match each mRNA codon that codes for an amino acid? -There is some flexibility in pairing between the middle base of the codon and the middle base of the anticodon. -There is some flexibility in pairing between the 5' base of the codon and the 3' base of the anticodon. -There is some flexibility in pairing between the 3' base of the codon and the 5' base of the anticodon. -There is some flexibility in pairing between all 3 bases of the codon and all 3 bases of the anticodon

There is some flexibility in pairing between the 3' base of the codon and the 5' base of the anticodon.

You are studying a eukaryotic gene that codes for the alpha-subunit in hemoglobin. What is the most likely result if base substitutions occur in the first nucleotide at the 5' end of an intron and also in the last nucleotide at the 3' end? -There will be no change in the polypeptide coded by this gene because introns are not expressed. -A change in reading frame will alter all amino acids in the polypeptide past the point of the first substitution. -A change in reading frame will alter all amino acids in the polypeptide past the point of the second substitution. -This intron will not be removed during pre-mRNA splicing because the spliceosome will not recognize the intron-exon junctions. -Each base substitution is likely to alter only one amino acid in the final polypeptide chain.

This intron will not be removed during pre-mRNA splicing because the spliceosome will not recognize the intron-exon junctions.

T/F During translation in eukaryotes, some ribosomes remain free in the cytoplasm while others attach to protein channels embedded in the RER.

True

T/f Most amino acids are specified by more than one codon.

True

New amino acids (other than the initial f-Met) enter at which site? E P A Any of the choices

a

One or a few base pairs are gained.

addition

A bacterial cell has a nonsense mutation in the gene that codes for hexokinase, an enzyme used during glycolysis. This mutation is most likely to affect the expression of this gene by -preventing formation of the initiation complex during transcription. -causing early termination during the elongation cycle of translation. -causing early termination during the elongation cycle of transcription. -preventing formation of the initiation complex during translation. -preventing formation of the transcription terminator.

causing early termination during the elongation cycle of translation.

One or a few base pairs are lost.

deletion

Segments of a chromosome that are lost are called ______________.

deletions

Alteration of the nucleotide sequence in SRP RNA would most likely affect -of introns during pre-mRNA splicing. -docking of ribosomes to the RER. -wobble pairing during translation. -release of uncharged tRNAs from the E site of the ribosomes. -initiation of transcription in eukaryotes.

docking of ribosomes to the RER.

Segments of a chromosome that are repeated are called ________________

duplications

____________: the ribosome moves along the mRNA so that the tRNA that was in the A site is now in the P site and the tRNA that was in the P site is now in the E site

elongation

_____________: A peptide bond forms between the amino group of the amino acid attached to the A site tRNA and the carboxyl group of the growing polypeptide chain

elongation

_____________: a charged tRNA with a complementary anticodon to the codon in the A site enters and binds

elongation

______________: the tRNA in the E site is ejected

elongation

T/F When a ribosome first assembles on the mRNA, the initiator tRNA occupies the A site while the P and E sites are empty

false

T/f During translation, an amino acid attached to a tRNA in the A site is transferred to a growing polypeptide attached to a tRNA in the P site.

false

T/f All codons code for amino acids.

false

T/f During translation, a charged tRNA first binds to the ribosome if its anticodon matches the codon in the E site

false

T/f During translocation of the ribosome, tRNA molecules move from the P site, to the A site, to the E site, and are then ejected from the ribosome

false

T/f Most codons code for more than one amino acid.

false

T/f Only 20 different codons are used to code for amino acids

false

An addition or deletion that alters the codons downstream from the mutation

frameshift mutation

___________: A tRNA molecule charged with its amino acid joins to the first AUG codon in the mRNA strand

initiation

_______________: the small ribosomal subunit binds to mRNA

initiation

________________: the large ribosomal subunit binds to the small ribosomal subunit

initiation

Segments of a chromosome that are broken in 2 places, reversed, and then put back together are called _______________

inversions

A small ribosomal subunit binds to a molecule of ___________ near its 5' end.

mRNA

During protein synthesis in eukaryotes, which molecule passes from the nucleus to the cytoplasm and specifies the sequence of amino acids in the new polypeptide? mRNA DNA tRNA RNA polymerase rRNA

mRNA

The Shine-Dalgarno sequence is found on the ________. small ribosomal subunit large ribosomal subunit initiator tRNA mRNA IF3

mRNA

____________ is translated by the ribosomes and contains the code that specifies the sequence of amino acids in a polypeptide chain.

messenger RNA

All nascent proteins being with what amino acid? Methionine Guanine Phenylalanine Valine Different proteins begin with different amino acids

methionine

____________acts to cleave target mRNAs or inhibit the translation of target mRNAs present in the cytoplasm of eukaryotes.

micro RNA

Changes a codon for one amino acid into a codon for a different amino acid.

missense mutation

During translation, translocation refers to -moving the ribosome along the mRNA molecule. -releasing a tRNA molecule from the ribosome. -joining an amino acid to a tRNA molecule. -joining an amino acid to the next amino acid in the chain. -joining a tRNA molecule to the ribosome.

moving the ribosome along the mRNA molecule.

Changes a codon for one amino acid into a stop codon.

nonsense mutation

The location of translation in prokaryotic cells is on chromosomes on mesosomes. on the plasma membrane. in the nucleoid. on ribosomes.

on ribosomes

The amino acids carried by the transfer RNA are joined by ionic bonds. covalent bonds. polar bonds. peptide bonds. nonpolar bonds.

peptide bonds

The release factor breaks the covalent bond that links the newly synthesized __________________ to the tRNA in the P site.

polypeptide chain

Translation is the synthesis of mRNA from DNA. mRNA from proteins. proteins from DNA proteins from mRNA proteins from tRNA

proteins from mRNA

If two chromosomes are broken and they exchange non-homologous segments, this is called a __________________ translocation.

reciprocal

The protein that promotes translation termination is called terminator. polypeptidase. release factor. doomsday factor. X factor.

release factor

When the ribosome encounters a stop codon, a ____________________ binds to the A site.

release factor

Codons that serve as "stop" signals for translation are recognized by -anticodons. -aminoacyl-tRNA synthetases -translation terminators. -tRNA. -release factors.

release factors

RNA is used as a template to make a complementary strand of DNA.

reverse transcription

________________ combines with protein to form the 2 ribosomal subunits.

ribosomal RNA

The polypeptide-making organelles, which consist of protein combined with RNA, are called mitochondria. centrosomes. Golgi bodies. ribosomes. lysosomes.

ribosomes

Changes a codon for one amino acid into a different codon for the same amino acid.

silent mutation

A large ribosomal subunit associates with the________________ribosomal subunit.

small

_____________plays a key role in the splicing reaction that removes introns from eukaryotic pre-mRNA.

small nuclear RNA

One or a few base pairs are replaced by different base pairs

substitution

A charged ________ molecule with a UAC anticodon binds to the first AUG codon in the mRNA strand

tRNA

If a duplication occurs directly next to the original segment, it is termed a ___________ duplication.

tandem

_____________: the mRNA, tRNA, and 2 ribosomal subunits dissociate from each other

termination

_______________: a release factor breaks the covalent bond that links the polypeptide chain to the P site tRNA

termination

_______________: a release factor enters the A site of the ribosome

termination

The A, P, and E sites are progressively occupied by amino acids being assembled into a polypeptide. These sites are part of -tRNA. -the spliceosome. -DNA. -the large ribosomal subunit. -mRNA.

the large ribosomal subunit

Which of the following occurs as the ribosome shifts down the mRNA by a distance of three nucleotides? -the tRNA that was in the A site moves into the E site -the tRNA that was in the P site moves into the A site -the tRNA that was in the E site moves into the P site -the tRNA that was in the E site moves into the A site -the tRNA that was in the P site moves into the E site

the tRNA that was in the P site moves into the E site

DNA is used as a template to make a complementary strand of RNA

transcription

______________ transports amino acids to the ribosomes for use in protein synthesis.

transfer RNA

At the E site -transfer RNA is released -anticodons match with codons -peptide bonds are formed between amino acids -transcription occurs

transfer RNA is released

RNA is used as a template to make a polypeptide.

translation

Ribosome movement along the mRNA is called transcription. translocation. initiation. replication. activation.

translocation

Segments of a chromosome that break off and attach to another chromosome are called ___________________

translocations

This type of mutation causes Huntington's disease and has only been observed in humans and mice.

triplet repeat expansion

T/f A peptide bond forms between the amino acid attached to a tRNA in the A site and the growing polypeptide attached to a tRNA in the P site

true

T/f In some cases, it is possible to change the sequence of bases in a codon and it will still code for the same amino acid

true

T/f No more than 2 tRNA molecules are bound to a ribosome at any given time.

true

T/f Uncharged tRNA molecules in the E site are ejected from the ribosome.

true

T/f. The start codon has a dual function because it also codes for an amino acid.

true