BIO 161 Chapter 17

Define TATA Box

crucial promoter DNA sequence

Distinguish between transcription and translation

Transcription - is the synthesis of RNA using information in the DNA Translation - is the synthesis of a polypeptide using the information in the mRNA

Define P-Site (ribosome binding site)

holds the tRNA carrying the growing polypeptide chain

Define A-Site (ribosome binding site)

holds the tRNA carrying the next amino acid to be added to the chain

Define missense mutation

substitutionsew that change one amino acid to another one

Define triplet code

- Is the flow of information from gene to protein - is the genetic instructions for a polypeptide chain that is written in the DNA as a series of nonoverlapping, three-nucleotide words.

Functions of a Poly-A tail

- they seem to facilitate the export of the mature mRNA from the nucleus. - they help protect the mRNA from degradation by hydrolytic enzymes. - they help ribosomes attach to the 5' end of the mRNA once the mRNA reaches the cytoplasm

Describe the significance of polyribosomes.

-Are a number of ribosomes trailing along the mRNA due to a second ribosome that attaching to the mRNA -Found in both bacteria and eukaryotic cells -they enable a cell to make many copies of a polypeptide very quickly

Because codons are nucleotide triplets, the number of nucleotides making up the genetic message must be...

3x the number of amino acids in the protein product ex) it take 300 nucleotides along an mRNA strand to code for the amino acids in a polypeptide that is 100 amino acids long

Choose the answer that has these events of protein synthesis in the proper sequence. 1. An aminoacyl-tRNA binds to the A site. 2. A peptide bond forms between the new amino acid and a polypeptide chain. 3. the uncharged tRNA leaves the ribosome 4. A small ribosomal subunit binds with mRNA. 5. tRNA with the peptide chain translocates to the P site.

4, 1, 2, 5, 3

Which of the following is not true of RNA processing? A) Exons are cut out before mRNA leaves the nucleus. B) Nucleotides may be added at both ends of the RNA. C) Ribozymes may function in RNA splicing. D) RNA splicing can be catalyzed by spliceosomes. E) A primary transcript is often much longer than the final RNA molecule that leaves the nucleus.

A. Exons ar ecut out before mRNA leaves the nucleus

Which of the following is NOT true of the RNA processing? A. Exons are cut out before mRNA leaves the nucleus B. Nucleotides may be added at both ends of the RNA C. Ribozymes may function in RNA splicing D. RNA splicing can be catalyzed by spliceosomes E. A primary transcript is often much longer than the final RNA molecule that leaves the nucleus

A. Exons are cut out before mRNA leaves the nucleus

What is the function of GTP in translation? A) GTP energizes the formation of the initiation complex, using initiation factors. B) GTP hydrolyzes to provide phosphate groups for tRNA binding. C) GTP hydrolyzes to provide energy for making peptide bonds. D) GTP supplies phosphates and energy to make ATP from ADP. E) GTP separates the small and large subunits of the ribosome at the stop codon.

A. GTP energizes the formation of the inititation complex, using initiation factors

Which of the following DNA mutations is the most likely to be damaging to the protein it specifies? A) a base-pair deletion B) a codon substitution C) a substitution in the last base of a codon D) a codon deletion E) a point mutation

A. a base-pair deletion

A mutation results in a defective enzyme A in the pathway below. Which of the following would be a consequence of that mutation? Alpha------> Beta ------> Gamma -------> Delta A B C A) an accumulation of A and no production of B and C B) an accumulation of A and B and no production of C C) an accumulation of B and no production of A and C D) an accumulation of B and C and no production of A E) an accumulation of C and no production of A and B

A. an accumulation of A and no production of B and C

The anticodon of a particular tRNA molecule is... A complementary to the corresponding mRNA codon B. complementary to the corresponding triplet in rRNA C. The part of tRNA that bonds to a specific amino acid D. Changeable, depending on the amino acid that attaches to the tRNA. E. Catalytic, making the tRNA a ribozyme

A. complementary of the corresponding mRNA codon

The anticodon of a particular tRNA molecule is A) complementary to the corresponding mRNA codon. B) complementary to the corresponding triplet in rRNA. C) the part of tRNA that bonds to a specific amino acid. D) changeable, depending on the amino acid that attaches to the tRNA. E) catalytic, making the tRNA a ribozyme.

A. complementary to the corresponding mRNA codon.

Once transcribed, eukaryotic mRNA typically undergoes substantial alteration that includes A) excision of introns. B) fusion into circular forms known as plasmids. C) linkage to histone molecules. D) union with ribosomes. E) fusion with other newly transcribed mRNA.

A. excision of introns

The TATA sequence is found only several nucleotides away from the start site of transcription. This most probably relates to which of the following? A) the number of hydrogen bonds between A and T in DNA B) the triplet nature of the codon C) the ability of this sequence to bind to the start site D) the supercoiling of the DNA near the start site E) the 3-D shape of a DNA molecule

A. the number of hydrogen bonds between A and T in DNA

Explain how RNA is modified after transcription in eukaryotic cells.

Alteration of mRNA ends: The 5' end is synthesized first, it receives a 5' cap, a modified form of a guanine nucleotide. The 3' end of the pre-mRNA, an enzyme adds more adenine nucleotides, forming a poly-A tail. RNA splicing: removal of large portions of the RNA molecule that is initially synthesized. The remaining parts splice together

RNA polymerase moves in which direction along the DNA? A.5' → 3' along the double-stranded DNA B.3' → 5' along the template strand C.3' → 5' along the coding (sense) strand D.5' → 3' along the template strand

B. 3' → 5' along the template strand

Which component is not directly involved in translation? A) mRNA B) DNA C) tRNA D) ribosomes E) GTP

B. DNA

Which of the following is required only by eukaryotes for transcription? A) uracil B) transcription factors C) promoter D) RNA polymerase E) terminator

B. Transcription factors

Using RNA as a template for protein synthesis instead of translating proteins directly from the DNA is advantageous for the cell because A. only one mRNA molecule can be transcribed from a single gene, lowering the potential rate of gene expression. B.RNA acts as an expendable copy of the genetic material. C.mRNA molecules are subject to mutation but DNA is not. D.tRNA, rRNA and others are not transcribed. E.RNA is much more stable than DNA.

B. RNA acts as an expendable copy of the genetic material

Which of the following statements is true about protein synthesis in prokaryotes? A) Extensive RNA processing is required before prokaryotic transcripts can be translated. B) Translation can begin while transcription is still in progress. C) Prokaryotic cells have complicated mechanisms for targeting proteins to the appropriate cellular organelles. D) Translation requires antibiotic activity. E) Unlike eukaryotes, prokaryotes require no initiation or elongation factors.

B. Translation can begin while transcription is still in progress

Alternative RNA splicing A) is a mechanism for increasing the rate of transcription. B) can allow the production of proteins of different sizes from a single mRNA. C) can allow the production of similar proteins from different RNAs. D) increases the rate of transcription. E) is due to the presence or absence of particular snRNPs.

B. can allow the production of proteins of different sizes from a single mRNA.

A mutation in which of the following parts of a gene is likely to be most damaging to a cell? A) intron B) exon C) 5' UTR D) 3' UTR E) All would be equally damaging.

B. exons

In eukaryotic cells, transcription cannot being until... A. the two DNA strands have completely separated and exposed the promoter B. several transcription factors have bound to the promoter C. the 5' caps are removed from the mRNA D. the DNA introns are removed from the template E. It is the basic until of the genetic code

B. several transcription factors have bound to the promoter

There are 61 mRNA codons that specify an amino acid, but only 45 tRNAs. This is best explained by the fact that A) some tRNAs have anticodons that recognize four or more different codons. B) the rules for base pairing between the third base of a codon and tRNA are flexible. C) many codons are never used, so the tRNAs that recognize them are dispensable. D) the DNA codes for all 61 tRNAs but some are then destroyed. E) competitive exclusion forces some tRNAs to be destroyed by nucleases.

B. the rules for base pairing between the third base of a codon and tRNA are flexible.

According to Beadle and Tatum's hypothesis, how many genes are necessary for this pathway? Enzyme A Enzyme B A-------------->B------------> C A) 0 B) 1 C) 2 D) 3 E) It cannot be determined from the pathway.

C. 2

If a protein is coded for by a single gene and this protein has six clearly defined domains, which number of exons below is the gene likely to have? A) 1 B) 5 C) 8 D) 12 E) 14

C. 8

A part of the promoter, called the TATA box, is said to be highly conserved in evolution. Which of the following might this illustrate? A) The sequence evolves very rapidly. B) The sequence does not mutate. C) Any mutation in the sequence is selected against. D) The sequence is found in many but not all promoters. E) The sequence is transcribed at the start of every gene.

C. Any mutation in the sequence is selected against

Transcription occurs in A) the cytoplasm. B) a lysosome. C) the nucleus. D) a mitochondrion. E) a nucleoplasm.

C. Nucleus

During splicing, which molecular component of the spliceosome catalyzes the excision reaction? A) protein B) DNA C) RNA D) lipid E) sugar

C. RNA

Which of the following is true for both prokaryotic and eukaryotic gene expression? A) After transcription, a 3' poly-A tail and a 5' cap are added to mRNA. B) Translation of mRNA can begin before transcription is complete. C) RNA polymerase binds to the promoter region to begin transcription. D) mRNA is synthesized in the 3' → 5' direction. E) The mRNA transcript is the exact complement of the gene from which it was copied.

C. RNA polymerase binds to the promoter region to begin transcription.

In eukaryotes there are several different types of RNA polymerase. Which type is involved in transcription of mRNA for a globin protein? A) ligase B) RNA polymerase I C) RNA polymerase II D) RNA polymerase III E) primase

C. RNA polymerase ll

A particular triplet of bases in the coding sequence of DNA is AAA. The anticodon on the tRNA that binds the mRNA codon is A) TTT. B) UUA. C) UUU. D) AAA. E) either UAA or TAA, depending on first base wobble.

C. UUU

What is the effect of a nonsense mutation in a gene? A) It changes an amino acid in the encoded protein. B) It has no effect on the amino acid sequence of the encoded protein. C) It introduces a premature stop codon into the mRNA. D) It alters the reading frame of the mRNA. E) It prevents introns from being excised.

C. it introduces a premature stop codon into the mRNA

Base-pair substitutions involving the third base of a codon are unlikely to result in an error in the polypeptide. This is because A) substitutions are corrected before transcription begins B) substitutions are restricted to introns C) the base-pairing rules are less strict for the third base of codons and anticodons D) a signal-recognition particle corrects coding errors E) transcribed errors attract snRNPs, which then stimulate splicing and correction

C. the base-pairing rules are less strict for the third base of codons and anticodons

Define codon and explain the relationship between the linear sequence of codons on mRNA and the linear sequence of amino acids in a polypeptide.

Codon - mRNA nucleotide triplets, which are customarily written in the 5' -> 3' direction During translation, the sequence of codons along an mRNA molecule is decoded, or translated, into a sequence of amino acids making up a polypeptide chain. The codons are ready by the translation 5'-> 3' direction along with mRNA. Each codon specifies which one of the 20 amino acids will be incorporated at the corresponding position along a polypeptide.

Define E-Site (ribosome binding site)

Exit site for discharged tRNAs to leave the riobsome

What amino acid sequence will be generated, based on the following mRNA codon sequence? 5' AUG-UCU-UCG-UUA-UCC-UUG 3' A) met-arg-glu-arg-glu-arg B) met-glu-arg-arg-glu-leu C) met-ser-leu-ser-leu-ser D) met-ser-ser-leu-ser-leu E) met-leu-phe-arg-glu-glu

D) met-ser-ser-leu-ser-leu

A particular triplet of bases in the coding sequence of DNA is AAA. The anticodon on the tRNA that binds the mRNA codon is A) TTT. B) UUA. C) UUU. D) AAA. E) either UAA or TAA, depending on first base wobble.

D. AAA

What are the non-coding segments of a eukaryotic gene called? A.exons B.transposons C. codons D.introns

D. Itrons

Which component is NOT directly involved in translation? A. mRNA B. DNA C.tRNA D. ribosomes E. GTP

D. Ribosomes

Which of the following is NOT true of a codon? A. It consists of three nucleotides B. It may code for the same amino acid as another codon C. It never codes for more than one amino acid D. It extends from one end of a tRNA molecule E. IT is the basic until of the genetic code

D. it extends from one end of a tRNA

A possible sequence of nucleotides in the template strand of DNA that would code for the polypeptide sequence phe-leu-ile-val would be A) 5' TTG-CTA-CAG-TAG 3'. B) 3' AAC-GAC-GUC-AUA 5'. C) 5' AUG-CTG-CAG-TAT 3'. D) 3' AAA-AAT-ATA-ACA 5'. E) 3' AAA-GAA-TAA-CAA 5'.

E) 3' AAA-GAA-TAA-CAA 5'.

Which of the following helps to stabilize mRNA by inhibiting its degradation? A) TATA box B) spliceosomes C) 5' cap D) poly-A tail E) both C and D

E. both C and D

Which of the following mutations would be most likely to have a harmful effect on an organism? A. A nucleotide-pair substitution B. A deletion of three nucleotides near the middle of a gene C. A single nucleotide deletion in the middle of an intron D. a single nucleotide deletion near the end of the coding sequence E. A single nucleotide insertion downstream of, and close to, the start of the coding sequence

E. A single nucleotide insertion downstream of, and close to, the start of the coding sequence

In comparing DNA replication with RNA transcription in the same cell, which of the following is true only of replication? A) It uses RNA polymerase. B) It makes a new molecule from its 5' end to its 3' end. C) The process is extremely fast once it is initiated. D) The process occurs in the nucleus of a eukaryotic cell. E) The entire template molecule is represented in the product.

E. The entire template molecule is represented in the product

Accuracy in the translation of mRNA into the primary structure of a polypeptide depends on specificity in the A) binding of ribosomes to mRNA. B) shape of the A and P sites of ribosomes. C) bonding of the anticodon to the codon. D) attachment of amino acids to tRNAs. E) bonding of the anticodon to the codon and the attachment of amino acids to tRNAs.

E. bonding of the anticodon to the codon and the attachment of amino acids to tRNAs.

A particular triplet of bases in the template strand of DNA is 5' AGT 3'. The corresponding codon for the mRNA transcribed is A. 3'ACU 5'. B. 5' ACU 3'. C. 5' TCA 3'. D.3' UGA 5'. E.either UCA or TCA, depending on wobble in the first base.

E. either UCA or TCA, depending on wobble in the first base.

Which of the following is the first event to take place in translation in eukaryotes? A) elongation of the polypeptide B) base pairing of activated methionine-tRNA to AUG of the messenger RNA C) binding of the larger ribosomal subunit to smaller ribosomal subunits D) covalent bonding between the first two amino acids E) the small subunit of the ribosome recognizes and attaches to the 5' cap of mRNA

E. the small subunit of the ribosome recognizes and attaches to the 5' cap of mRNA

Explain the process of elongation transcription

Elongation: The polymerase moves downstream, unwinding the DNA and elongating the RNA transcript 5' -> 3'. In the wake of transcription, the DNA strands re-form a double helix

Describe the process of translation elongation, and explain which enzyme, protein factors, and energy sources are needed

Elongation: amino acids are added one by one to the previous amino acid at the C-terminus of the growing chain. - proteins needed are called elongation factors

Explain the reasoning that led Archibald Garrod to first suggest that genes dictate phenotypes through enzymes

He hypothesized that the symptoms of an inherited disease reflect a persons inability to make a particular enzyme.

Briefly explain how information flows from gene to protein

In DNA, or RNA, the monomers are the four types of nucleotides, which differ in their nitrogenous bases.Genes has a specific sequence of nucleotides. Each polypeptide of a protein also has monomers arranged in a particular linear order, but its monomers are amino acids. Thus, nucleic acids and proteins contain information written in two different chemical languages. Getting from DNA to protein requires transcription and translation.

Explain the process of initiation trancription

Initiation: After RNA polymerase binds to the promoter, the DNA strands unwind, and the polymerase initiates RNA synthesis at the start point on the template strand.

Describe the process of translation initiation and explain which enzymes, protein factors, and energy sources are needed for each stage.

Initiation: brings together mRNA, a tRNA bearing the first amino acid of the polypeptide, and two subunits of a ribosome. - energy obtained by hydrolysis of a GTP molecule to form this complex

Describe what an Intron is, the and functional and evolutionary significance them

Introns: noncoding segment of nucleic acid that lie between coding regions Function: contain sequences that regulate gene expression, and many affect gene products. Evolutionary: may facilitate new and potentially beneficial proteins as a result of exon shuffling. Introns increase the probability of crossing over between the exons of alleles of a gene.

Explain the evolutionary significance of a nearly universal genetic code

It has made it possibly for Insertion of human genes to synthesize certain human proteins made for medical use.

Explain the significance of the reading frame during translation

Its important in the reading of the molecular language of cells

Explain the early techniques used to identify what amino acids are specified by the triplets UUU, AAA, GGG, and CCC.

Nirenberg synthesized an artificial mRNA by linking identical RNA nucleotides containing uracil as their base. No matter where this message started or stopped, it could contain only one codon in repetition: UUU. He added this "poly-U" to a test-tube mixture containing amino acids, ribosomes, and the other components required for protein synthesis. He determined that the mRNA codon UUU specifies the amino acid phenylalanine. He was then able to specify the codons AA, GGG, CCC.

Distinguish between the "one gene-one enzyme" hypothesis and the "one gene-one polypeptide" hypothesis and explain why the original hypothesis was changed.

One gene-one enzyme hypothesis - states that the function of a gene is to dictate the production of a specific enzyme One gene-one polypeptide hypothesis - states that the function of a gene is to specify polypeptides, and code for proteins.

Define point mutations.

Point Mutations: a mutation that causes a change in a single nucleotide pair of genes - can be transmitted to offspring

Explain how RNA differs from DNA

RNA: contains ribose as sugar, has uracil as nitrogenous base DNA contains doxyribose as sugar, has thymine as nitrogenous base

Define and explain the role of ribozymes

Ribozymes: RNA molecules that function as enzymes. - The intron RNA functions as a ribozyme and catalyzes its own excision - The discovery of ribozymes rendered the idea that all biological catalysts are proteins

Explain how RNA polymerase recognizes where transcription should begin. Describe the promoter, the terminator, and the transcription unit.

Specific sequences of nucleotides along the DNA mark where transcription of a gene begins and ends. Promoter- Is the DNA sequence where RNA polymerase attaches and initiates transcription Terminator- Is the DNA sequence that signals the end of transcription Transcription unit- Is the stretch of DNA that is transcribed into an RNA molecule

Describe the structure and functions of tRNA.

Structure: the tRNA molecules are not all identical, and each type of tRNA molecules translates a particular mRNA codon into a particular amino acid. -when it arribes at the ribosome, one end is has a specific amino acid, while the other end is an anticodon. Function: to transfer amino acids from the cytoplasmic pool of amino acids to a growing polypeptide in a ribosome.

Explain the process of termination transcription

Termination: Eventually, the RNA transcript is released, and the polymerase detaches from the DNA. - in bacteria

Describe the process of translation termination and explain which enzymes, protein factors, and energy sources are needed for each stage.

Termination: elongation continues until a stop codon in the mRNA reaches the A site of the ribosome. - protein: release factor- binds directly to the stop codon in the A site. - causes addition of water molecule

Explain the general process of transcription

The promoter of a gene includes the transcription start point, where RNA synthesis actually beings. RNA polymerase binds to a precise location and orientation on the promoter, determining where transcription starts and which of the two strands of the DNA helix is used as the template. Transcription factors mediate the binding of RNA polymerase and the initiation of transcription. Three steps: Initiation, elongation, and termination

Describe Beadle and Tatum's experiments with Neurospora (bread mold) and explain the contribution they made to our understanding of how genes control metabolism.

They bombarded neurospora with x-rays, then looked among the survivors for mutants that differed in their nutritional needs from the wild-type bread mold. They identified mutants that could not survive on minimal medium (when the mold cells would use their metabolic pathways to produce all the other molecules they needed), apparently because they were unable to synthesize certain essential molecules from the minimal ingredients. They allowed the survivors to grow on complete growth medium, which consisted of 20 amino acids and a few other nutrients. They took samples from the mutant growing on the complete medium and distributed them to a number of different vials. Each vial contained minimal medium plus a single additional nutrient. The particular supplement that allowed growth indicated the metabolic defect. Because each mutant was defective in a single gene, they say that the collected results provided strong support that a gene is to dictate the production of a specific enzyme (one gene-one enzyme hypothesis)

Explain how tRNA is joined to the appropriate amino acid.

Through Aminoacyl-tRNA synthetases- the active site of each one fits only a specific combination of amino acid and tRNA.

Compare where transcription and translation occur in prokaryotes and in eukaryotes.

Translation (eukaryotic)- occurs in the nucleus Transportation (eukaryotic) - occurs in cytoplasm

Explain what it means to say that the genetic code is redundant and unambiguous.

Two codons could both specify an amino acid, but neither of them ever specifies any other amino acid

Define frameshift mutation

alteration of the reading frame of the genetic message whenever the number of nucleotides inserted or deleted is of a multiple of three

Distinguish between base-pair substitutions and base-pair insertions.

base- pair substitutions: is the replacement of one nucleotide and its partner with another pair of nucleotides. base-pair insertions: are additions of nucleotide pairs in a gene. - can cause a huge effect on the resulting proteins by altering the reading frame of the genetic message

Explain why polypeptides begin with methionine when they are synthesized

because it signals the protein-synthesizing machinery to begin translating the mRNA at that location.

Define silent mutation

change in a nucleotide pair which would transform one codon into another that is translated into the same amino acid. - can occur outside of genes

Describe the structure and functions of ribosomes.

function: bringing mRNA together with tRNAs carrying amino acids

Define mutagens

is a number of physical and chemical agents that interact with DNA in ways that cause mutations

Define snRNA

is the RNA in a snRNP particles

Define splicosome

is the joining of several different snRNPs with additional proteins to form an even larger assembly

Define Gene expression

is the process by which DNA directs the synthesis of proteins.

Explain the significance of wobble.

it explains why the synonymous codons for a given amino acid most often differ in their third nucletide base, but not in the other bases. - ex: anticodon : 3'-UGU-5' can base pair with either the mRNA codon 5'-AGA-3' or 5'-AGG-3'

Define Signal Peptide

marks the polypeptides of proteins designed for the ER system, and targets the protein to the ER

Define snRNPS

recognize splice sites from the short nucleotide sequences at each end of an intron. -Are located in cell nucleus and are composed of RNA and protein moleucles

Define signal-recognition particles (SRP)

recognizes the sequence of about 20 amino acids at or near the leading end of the polypeptide as it emerges from the riobsome

What is tRNA?

the translator of the message of codons along an mRNA molecule.

Define nonsense mutation

when a point mutation can also change a codon for an amino acid into a stop codon