Ch 17

1. translation2. RNA processing3. transcription4. modification of protein

3, 2, 1, 4

there are only 2 bases (A and T) in the Martian DNA, and there are only 17 amino acids found in Martian proteins. Based on this information, what is the minimum size of a codon for these hypothetical Martian life-forms?

5 bases

Why is a frameshift missense mutation more likely to have a severe effect on phenotype than a nucleotide-pair substitution missense mutation in the same protein?

A substitution missense affects only one codon, but a frameshift missense affects all codons downstream of the frameshift.

Which type of mutation is least likely to affect protein function

Base-pair substitution

Who formulated the one gene-one enzyme hypothesis?

Beadle and Tatum

Which accurately describes the usual process of eukaryotic transcription?

Both introns and exons are transcribed, but the RNA transcribed from introns does not leave the nucleus.

Two different proteins with mostly different structures are translated from two different mRNAs. These mRNAs, however, were transcribed from the same gene. Which mechanism could best account for this?

Exons from the same gene could be spliced in different ways to make different mRNAs.

Question 5:Generally speaking, how many genetic codes are there?

One

Suppose that the triplet of nucleotides indicated in bold (AGC) spans two codons, that is, CTA and GCC. If the triplet AGC were deleted from this DNA coding sequence, what effect would it have on the resulting protein? 5'-ATGCTAGCCTATCGTAAC-3'

The two flanking codons would be altered, but the rest of the amino acid sequence would be the same because there would be no frameshift.

When RNA is being made, the RNA base __________ always pairs with the base __________ in DNA.

U; A

Enter the sequence of bases as capital letters with no spaces and no punctuation. Begin with the first base added to the growing RNA strand, and end with the last base added.

UGAGCC

Use the codon table to determine which mRNA triplets code for the amino acid cysteine, Cys.

UGU UGC

Ultraviolet (UV) radiation is damaging to cells because it ___

causes mutations in the DNA

At one point, as a cell carried out its day-to-day activities, the nucleotides GAT were paired with the nucleotides CUA. This pairing occurred __________

during transcription

A point mutation in which a single base pair is inserted or deleted from DNA is called a(n) ______

frameshift mutation

Polysomes may be defined as ________

groups of ribosomes translating the same mRNA

Which statement correctly describes mRNA processing?

introns are cut out of the primary transcript, and the resulting exons are spliced together.

One strand of a DNA molecule has the following sequence: 3′-AGTACAAACTATCCACCGTC-5′. In order for that strand to be transcribed, there would have to be a specific recognition sequence, called a(n) __________, to the left of the DNA sequence indicated.

promoter

Which of the following terms associated with transcription describe regions of nucleic acid?

promoter terminator gene

In many cases, more than one codon codes for the same amino acid. Because of this, we say that the code is __________

redundant

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 poly-A tail (50-250 adenine nucleotides) is added to the 3' end of the pre-mRNA. Noncoding sequences called introns are spliced out by molecular complexes called spliceosomes. A cap consisting of a modified guanine nucleotide is added to the 5' end of the pre-mRNA.

Which statement regarding the structure and function of tRNA is false

Although each tRNA consists of a relatively short, single RNA strand, this single strand can achieve a three-dimensional structure by folding back upon itself and forming covalent bonds between complementary bases.

How many nucleotides are needed to code for a protein with 450 amino acids?

At least 1,350

Which is a post-translational modification of a polypeptide

Cleavage of a polypeptide into two or more chains

What is a key difference between eukaryotic and prokaryotic gene expression?

In prokaryotic cells, the RNA transcript is immediately available as mRNA without processing.

Think about the DNA coding sequence of a gene. If an A were swapped for a T, what kind of mutation could it cause and why?

It could cause a silent, missense, or nonsense mutation because those are the types that can be caused by a nucleotide-pair substitution like this one.

The P site of a ribosome does which of the following?

It holds the tRNA carrying the growing polypeptide chain.

Which summary of protein synthesis is correct?

Messenger RNA is made on a DNA template, and then amino-acid-bearing transfer RNAs bind to the mRNA through codon-anticodon pairing.

5′−AUGGCAAGAAAA−3′

Met-Ala-Arg-Lys

3′−TACAGAACGGTA−5′

Met-Ser-Cys-His

There are two general targeting pathways for nuclear-encoded proteins in eukaryotic cells.

Proteins that will ultimately function in the cytoplasm (PFK, for example) are translated on free cytoplasmic ribosomes and released directly into the cytoplasm. Proteins that are destined for the membranes or compartments of the endomembrane system, as well as proteins that will be secreted from the cell (insulin, for example), are translated on ribosomes that are bound to the rough ER. For proteins translated on rough ER, the proteins are found in one of two places at the end of translation. If a protein is targeted to a membrane of the endomembrane system, it will be in the ER membrane. If a protein is targeted to the interior of an organelle in the endomembrane system or to the exterior of the cell, it will be in the lumen of the rough ER. From the rough ER (membrane or lumen), these non-cytoplasmic proteins move to the Golgi apparatus for processing and sorting before being sent to their final destinations.

Genetic information of eukaryotic cells is transferred from the nucleus to the cytoplasm in the form of __________.

RNA

What catalyzes the linkage between ribonucleotides to form RNA during gene expression?

RNA polymerase

In eukaryotes, which mechanism operates after transcription, but before translation of mRNA into protein?

RNA splicing

There are three principles to keep in mind when predicting the sequence of the mRNA produced by transcription of a particular DNA sequence.

The RNA polymerase reads the sequence of DNA bases from only one of the two strands of DNA: the template strand. The RNA polymerase reads the code from the template strand in the 3' to 5' direction and thus produces the mRNA strand in the 5' to 3' direction. In RNA, the base uracil (U) replaces the DNA base thymine (T). Thus the base-pairing rules in transcription are A→U, T→A, C→G, and G→C, where the first base is the coding base in the template strand of the DNA and the second base is the base that is added to the growing mRNA strand.

Based on the genetic code chart above, which of the following would be the result of this single base-pair substitution?

a nonsense mutation resulting in early termination of translation

A particular mutation had no effect on the polypeptide encoded by a gene. This mutation probably involves ___

a silent or neutral mutation

The function of tRNA during protein synthesis is to _____

deliver amino acids to their proper site during protein synthesis

The bonds that hold tRNA molecules in the correct three-dimensional shape are _________

hydrogen bonds

In a eukaryotic cell, transcription takes place __________.

in the nucleus

A virus infects a cell and randomly inserts many short segments of DNA containing a stop codon throughout an organism's chromosomes. This will probably cause __________

manufactured proteins to be short and defective

The first amino acid inserted into a new polypeptide chain in eukaryotic cells is usually __________

methionine

During translation in a eukaryotic cell, _________

polypeptides are synthesized at ribosomes, according to instructions carried by mRNA

The codons AAA, CCC, GGG, and UUU specify the amino acids lysine, proline, glycine, and phenylalanine, respectively. If the base sequence 5′-CCCAAATTTGGG-3′ is present in the coding strand of a stretch of DNA, what polypeptide sequence would be encoded by the corresponding template strand?

pro-lys-phe-gly

Cells are able to distinguish proteins destined for secretion or for segregation to specific intracellular compartments from those that will remain in the cytoplasm because _______

some proteins, as they begin to be synthesized, contain a signal region that causes the ribosome with its growing polypeptide to attach to the ER and translocate the polypeptide into the lumen (space) of the ER

In transcription, __________

the RNA nucleotides used are produced by the cell the promoter region acts as an initial binding site for RNA polymerase only one of the DNA strands is used as the template

During transcription in eukaryotes, a type of RNA polymerase called RNA polymerase II moves along the template strand of the 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?

the base sequence of the gene's promoter

Bacteria can transcribe and translate human genes to produce functional human proteins because __________.

the genetic code is nearly universal

During translation, amino acid chain elongation occurs until __________

the ribosome encounters a "stop" codon

The mRNA codons 5′-CAA-3′ or 5′-CAG-3′ are translated as the amino acid glutamine by __________

the same tRNA with the anticodon 3′-GUU-5′

The number of nucleotide bases "read" together on the mRNA to designate each amino acid is __________; this unit is called a(n) __________

three; codon

Each amino acid in a protein is coded for by three bases in the DNA.

true

Transcription factors are required to initiate transcription in eukaryotes. In bacteria, the RNA polymerase alone can bind to the promoter site of a gene.

true

Which of the following sequences shows a frameshift mutation compared to the wild-type mRNA sequence?

wild-type5'-AUGCAUACAUUGGAGUGA-3'mutant5'-AUGCAUACAUCUGGAGUGA-3'