Mastering Biology CH 17 homework

CH 17b

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Drag the terms on the left to the appropriate blanks on the right to complete the sentences.

1. A silent mutation does not change the wild-type amino acid sequence. 2. A nonsense mutation causes an early Stop codon to occur. 3. A missense mutation causes a wild-type amino acid to be replaced by a different amino acid.

The direction of synthesis of an RNA transcript is _____.

5' --> 3'

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 cap consisting of a modified guanine nucleotide is added to the 5' end of the pre-mRNA. 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.

Transcription begins at a promoter. What is a promoter?

A site in DNA that recruits the RNA Polymerase

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.

In the diagram below, the two blue strands represent _____.

DNA

Place the events in the transcription of a gene in their proper order from left (first event) to right (last event). Rank from first event to last event.

First event RNA polymerase binds promoter RNA polymerase transcribes gene RNA polymerase reaches terminator RNA polymerase exits gene, RNA is released Last event

Which of these correctly illustrates the pairing of DNA and RNA nucleotides?

GTTACG CAAUGC

What happens to RNA polymerase II after it has completed transcription of a gene?

It is free to bind to another promoter and begin transcription.

During translation, nucleotide base triplets (codons) in mRNA are read in sequence in the 5' → 3' direction along the mRNA. Amino acids are specified by the string of codons. What amino acid sequence does the following mRNA nucleotide sequence specify? 5′−AUGGCAAGAAAA−3′ Express the sequence of amino acids using the three-letter abbreviations, separated by hyphens (e.g., Met-Ser-Thr-Lys-Gly).

Met-Ala-Arg-Lys

Before a molecule of mRNA can be translated into a protein on the ribosome, the mRNA must first be transcribed from a sequence of DNA. What amino acid sequence does the following DNA nucleotide sequence specify? 3′−TACAGAACGGTA−5′ Express the sequence of amino acids using the three-letter abbreviations, separated by hyphens (e.g., Met-Ser-His-Lys-Gly).

Met-Ser-Cys-His

The DNA in a cell's nucleus encodes proteins that are eventually targeted to every membrane and compartment in the cell, as well as proteins that are targeted for secretion from the cell. For example, consider these two proteins: Phosphofructokinase (PFK) is an enzyme that functions in the cytoplasm during glycolysis. Insulin, a protein that regulates blood sugar levels, is secreted from specialized pancreatic cells. Assume that you can track the cellular locations of these two proteins from the time that translation is complete until the proteins reach their final destinations. For each protein, identify its targeting pathway: the sequence of cellular locations in which the protein is found from when translation is complete until it reaches its final (functional) destination. (Note that if an organelle is listed in a pathway, the location implied is inside the organelle, not in the membrane that surrounds the organelle.)

PFK: cytoplasm only Insulin: ER --> Golgi --> outside cell

In the diagram below, the gray unit represents _____.

RNA polymerase

Which of the following statements best describes the promoter of a protein-coding gene?

The promoter is a nontranscribed region of a gene.

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.

Suppose that a portion of double-stranded DNA in the middle of a large gene is being transcribed by an RNA polymerase. As the polymerase moves through the sequence of six bases shown in the diagram below, what is the corresponding sequence of bases in the RNA that is produced? 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. Select all that apply.

UGC, UGU

During RNA processing a(n) _____ is added to the 3' end of the RNA.

a long string of adenine nucleotides

Which of the following terms best describes the relationship between the newly synthesized RNA molecule and the DNA template strand?

complementary

Translation occurs in the _____.

cytoplasm

Which of the following mutations would likely be most dangerous to a cell?

deletion of one nucleotide

The RNA segments joined to one another by spliceosomes are _____.

exons

RNA processing converts the RNA transcript into _____.

mRNA

During RNA processing a(n) _____ is added to the 5' end of the RNA.

modified guanine nucleotide

DNA does not store the information to synthesize which of the following?

organelles

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

promoter terminator gene

Indicate at which step of the replication-transcription-translation process each type of RNA first plays a role. During which step of the replication-transcription-translation process does each type of RNA first play a role? Drag each item to the appropriate bin. (Not every bin has to be filled.)

replication: nothing transcription/RNA processing: mRNA translation: rRNA, tRNA

In eukaryotic cells, the processes of protein synthesis occur in different cellular locations. Drag the labels to the appropriate targets to identify where in the cell each process associated with protein synthesis takes place.

see image

Use the table to sort the following ten codons into one of the three bins, according to whether they code for a start codon, an in-sequence amino acid, or a stop codon. Drag each item to the appropriate bin.

start/methionine: AUG stop codon: UAA, UAG, UGA amino acid: AAA, AUC, CAC, GCA, ACU, UGC

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

In the diagram below, the green unit represents _____.

the promoter

Complete the following vocabulary exercise related to the process of translation of mRNA to protein by the ribosome. Match the words in the left-hand column with the appropriate blank in the sentences in the right-hand column.

1. Initiation of translation always happens at the start codon of the mRNA. 2. Termination of translation happens when the ribosome hits a stop codon on the mRNA. 3. The RNA that has an amino acid attached to it, and that binds to the codon on the mRNA, is called a tRNA. 4. The process, performed by the ribosome, of reading mRNA and synthesizing a protein is called translation. 5. Amino acids are attached to tRNA by enzymes called aminoacyl-tRNA synthetase

Life as we know it depends on the genetic code: a set of codons, each made up of three bases in a DNA sequence and corresponding mRNA sequence, that specifies which of the 20 amino acids will be added to the protein during translation. Imagine that a prokaryote-like organism has been discovered in the polar ice on Mars. Interestingly, these Martian organisms use the same DNA → RNA → protein system as life on Earth, except that 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

What determines which base is to be added to an RNA strand during transcription?

Base pairing between the DNA template strand and the RNA nucleotides

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 average length of a transcription unit 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?

Most eukaryotic genes and their RNA transcripts have long noncoding stretches of nucleotides that are not translated.

What name is given to the process in which pre-mRNA is edited into mRNA?

RNA processing

The diagram below shows an mRNA molecule that encodes a protein with 202 amino acids. The start and stop codons are highlighted, and a portion of the nucleotide sequence in the early part of the molecule is shown in detail. At position 35, a single base-pair substitution in the DNA has changed what would have been a uracil (U) in the mRNA to an adenine (A). 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

Cystic fibrosis is the most common lethal genetic disease in the United States. It strikes one out of every 2,500 people of European descent, though it is less common in other groups. Cystic fibrosis is the result of mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Over 1,800 different mutations have been identified that can cause cystic fibrosis. People who inherit two recessive CFTR alleles have the disease. Below is a partial mRNA and amino acid sequence for the wild-type CFTR protein. In this activity, you will examine two specific nucleotide-pair deletion mutations that affect this region of the CFTR sequence: [delta]F508 and 1660delG. Drag the amino acids to the targets of Group 1 to indicate what each mRNA codon codes for. (You will probably need to consult the codon table for mRNA.) Drag the labels of Group 2 to indicate the effect on the polypeptide's primary structure. Be sure to compare the mutant amino acid sequence to the wild-type sequence above.

a: Ile b: Gly c: Val d: Ser e: Phe f: Pro g: no frameshift h: frameshift--extensive missense

The instructions for assembling polypeptides are contained in DNA. Consequently, mutations in DNA sometimes affect protein structure. A mutation will initially affect a protein's primary structure, but changes at higher levels of structure may follow. Point mutations are mutations that affect a single nucleotide pair in DNA. The figure below shows different types of point mutations and the effects they have on protein primary structure. In this activity, you will examine three different mutations. Drag the white labels of Group 1 to indicate what each mutant mRNA codon codes for. (You will probably need to consult the codon table for mRNA .) Drag the pink labels of Group 2 to indicate the type of mutation. Drag the blue labels of Group 3 to indicate the effect on the polypeptide's primary structure.

a: Val b: substitution c: missense d: Glu e: substitution f: silent g: Stop h: substitution i: nonsense

Polypeptides are assembled from _____.

amino acids

The four levels of protein structure are primary, secondary, tertiary, and quaternary structure. Review the levels of protein structure by clicking the image below. Drag each label into the appropriate bin depending on whether it applies to primary, secondary, tertiary, or quaternary structure.

primary structure: amino acid sequence secondary structure: a helix b pleated sheet results from hydrogen bonding between the backbone constituens of the polypeptide tertiary structure: results from interactions between side chains(R groups) of amino acids the overall shape of a polypeptide quaternary structure: the aggregation of multiple polypeptide subunits

Ribosomes provide the scaffolding on which tRNAs interact with mRNA during translation of an mRNA sequence to a chain of amino acids. A ribosome has three binding sites, each of which has a distinct function in the tRNA-mRNA interactions. Drag the appropriate tRNAs to the binding sites on the ribosome to show the configuration immediately before a new peptide bond forms. Note that one of the binding sites should be left empty.

see image

The following eukaryotic structural gene contains two introns and three exons. The table below shows four possible mRNA products of this gene. Use the labels to explain what mutation(s) may have resulted in each mRNA. Drag the correct label to each location in the table. Labels may be used once, more than once, or not at all.

see image

Spliceosomes are composed of _____.

small RNAs and protein

Sort each description by the type of RNA it describes. Drag each item to the appropriate bin.

tRNA: contains an anticodon has amino acids covalently attached mRNA: contains exons specifies the amino acid sequence for a protein rRNA: is a component of ribosomes is the most abundant form of RNA

What is the process called that converts the genetic information stored in DNA to an RNA copy?

transcription

What name is given to the process in which a strand of DNA is used as a template for the manufacture of a strand of pre-mRNA?

transcription

RNA plays important roles in many cellular processes, particularly those associated with protein synthesis: transcription, RNA processing, and translation. Drag the labels to the appropriate bins to identify the step in protein synthesis where each type of RNA first plays a role. If an RNA does not play a role in protein synthesis, drag it to the "not used in protein synthesis" bin.

transcription/RNA processing: snRNA, pre-mRNA, mRNA translation: tRNA, rRNA not used in protein synthesis: RNA primers

What name is given to the process in which the information encoded in a strand of mRNA is used to construct a protein?

translation

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

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