BIO 3102 Study Guide - Protein Structure, Reading Frame, Nonsense Mutation

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10 Jul 2014

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Dna bases in genes is directly related to the structure & function of the polypeptides that they encode. Small changes in the dna sequence might affect protein structure. Mutations:- are changes in the sequence of bases in the genetic material. Base-pair substitution mutation involve a change of one particular base to another in the genetic material there are 4 types of them. This will cause a change in a base in a codon in mrna. If a mutation alters the codon to specify a different amino acid. Then the resulting protein will have a different amino acid sequence. This is called the 1- missense mutation:- because although an amino acid is placed in the polypeptide it is the wrong one. Whether the polypeptide function is altered significantly or not depends on which amino acid changed and what it is changed to. 2-nonsense mutation :- the mutation changes an amino acid coding(sense) to nonsense (termination) codon in the mrna.

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Part B

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?

a) It could cause a frameshift nonsense or frameshift missense mutation because it would change the reading frame of the codon triplet.

b) 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.

c) It could cause a nonsense mutation because the sequence would no longer be the same, so the protein would be shorter and non-functional.

d) It could cause a silent mutation because A and T are complementary to each other so it is not really a substitution mutation.

Part C

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) A substitution missense mutation causes the protein to be shorter and thus non-functional.

b) A frameshift missense will cause the codons to be out of order, but a substitution missense does not change the order of the codons.

c) A frameshift missense mutation will cause an early Stop codon, but a substitution missense might be silent.

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

Part D

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

a) wild-type	5â-AUGCAUACAUUGGAGUGA-3â
mutant	5â-AUGCAUACAGAGUGA-3â

b) wild-type	5â-AUGCAUACAUUGGAGUGA-3â
mutant	5â-AUGCAUACGUUGGAGUGA-3â

c) wild-type	5â-AUGCAUACAUUGGAGUGA-3â
mutant	5â-AUGCAUACAUCUGGAGUGA-3â

d) wild-type	5â-AUGCAUACAUUGGAGUGA-3â
mutant	5â-AUGCAUGUGACAUUGGAGUGA-3â

Part F

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?

5â-ATGCTAGCCTATCGTAAC-3â

a) 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.

b) The entire amino acid sequence would be altered due to the frameshift.

c) All of the amino acids after the deletion would be altered due to the frameshift.

d) All of the amino acids up to the deletion would be altered due to the frameshift.

mauvetrout554

Fill in the blank. Elongation during translation does NOT involve ____________.

Question 16 options:

	the translation of codons according to the genetic code
	the formation of bonds catalyzed by the ribosome
	complementary base pairing between RNA molecules
	amino acids being linked together in a polypeptide
	reading the DNA template 3' to 5'

For a given gene, what establishes the reading frame for translation?

Question 17 options:

	the location of the enhancer relative to the gene
	the first three nucleotides at the 5' end of the mRNA
	the first three nucleotides at the 3' end of the mRNA
	the start codon in the mRNA
	the location of the promoter relative to the gene

Which of the following is the LEAST likely direct consequence of a substitution mutation?

Question 18 options:

	changing the length of a protein coded for by a gene
	changing one amino acid in a protein
	creating a stop codon
	eliminating a start codon
	changing the length of the DNA molecule containing a gene

Suppose that the pre-mRNA transcript from a eukaryotic gene is 30,000 nucleotides long, and the gene codes for a sequence of 300 amino acids. What is the best explanation for the relationship between these numbers?

Question 19 options:

	only the first 900 nucleotides of the pre-mRNA transcript are translated
	it takes 100 nucleotides to specify a single amino acid
	300 of the nucleotides in the transcript are important, and the rest are "junk"
	only the last 900 nucleotides of the pre-mRNA transcript are translated
	large portions of pre-mRNA transcripts are cut out during RNA processing

Suppose an individual is born into a population with a novel mutation. Is the new mutation an evolutionary change, and why?

Question 20 options:

	no, because it is not a big enough change to count
	yes, because new mutations are always adaptive
	yes, because the appearance of a new genetic variant is a genetic change in a population
	no, because not enough individuals have the mutation for it to matter
	no, because most mutations are not adaptive

PART C IS THE PART I NEED HELP WITH PLEASE

Below is a partial mRNA sequence. Use it to answer the following questions.

5' - GCCGAUCGAACU - 3'

What is the correct reading frame for this mRNA?

5' - G | CCG | AUC | GAA | CU - 3'

If a single base-pair deletion occurred in the part of the gene that corresponds to the mRNA above and the resulting partial amino acid sequence was (N-term-...P-M-N...-C-term), which new partial mRNA sequence would be consistent with this change?

5' - G | CCG | AUG | AAC | U - 3'

Part C

The amino acids in the original partial sequence (N-term-...P-I-E...-C-term) have little to no impact on protein structure and function. However the amino acid sequence near the C-terminal end of the protein is required for normal function. Any amino acid changes in this region of the protein will result in a nonfunctional protein.

Given this information, which reversion mutation in the gene would restore the normal function of the protein?

Select all that apply.

Insertion of 2 base-pairs in the region of the proline codon

Deletion of 5 base-pairs in the region of the proline codon

Deletion of 2 base-pairs in the region of the proline codon

Deletion of 1 base-pair in the region of the proline codon

Insertion of 1 base-pair in the region of the proline codon

Insertion of 4 base-pairs in the region of the proline codon

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BIO 3102 Study Guide - Protein Structure, Reading Frame, Nonsense Mutation

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