BIL 150 Lecture Notes - Lecture 19: Point Mutation, Molecular Genetics, Methionine

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amaranthgiraffe480

17 Dec 2018

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@3bil 150: molecular genetics continued: the genetic code. A sequence of nucleotides in dna, but it is shown as mrna code. Mrna specifies the sequence of amino acids linked in a protein. Pairing of mrna is antiparallel just like in dna. But pairing is weak at third base due to loop shape. This allows for multiple codons to be made by the third base changing. Recognize the three letter codons for each amino acid. A change in dna nucleotide sequence= a change in mrna. Mutation: a permanent change in an organism"s dna that results in a different codon. Point mutation: only one single nucleotide base pair changes. Hot spots: places that are very susceptible to point mutations (evidence for triplet codons) Loop out structures form, lead to repeats. Non sense: change to no amino acid. Inherited as recessive trait; abnormal b globin protein is made. Forms non polar aa instead of polar to change the shape.

Related Questions

5). The table shows five different mutations of a small section of a gene.

Use the base-pairing rules to complete the second column. For each mutation, write the sequence for any mRNA codons that will be changed as a result of the mutation in bold. Write any codons that wonât be changed in regular font.

Using the genetic code chart from question #3, identify any stop codons in the mRNA molecules â write these codons in red

For each mutation, write any amino acids that will be changed in the last column in bold font. Use red XXXs to indicate any amino acids that will be missing as a result of stop codons and use use regular font indicate any amino acids that will not be changed.

DNA (Template Strand)	mRNA codon	Polypeptide
Original DNA = GCAAGTACCTGA	CGU UCA UGG ACU	arg â ser â trp â thr
Mutation = GCCAGTACCTGA (nucleotide change underlined)	____ ____ ____ ____	___ ___ ___ ___
Mutation = GCACGTACCTGA (nucleotide change underlined)	____ ____ ____ ____	___ ___ ___ ___
Mutation = GCAAGTACTTGA (nucleotide change underlined)	____ ____ ____ ____	___ ___ ___ ___
Mutation = GAAGTACCTGA (first C deleted)	____ ____ ____ ____	___ ___ ___ ___
Mutation = GCAAGTACTGA (second C deleted)	____ ____ ____ ____	___ ___ ___ ___

ambergnu488

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 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.

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BIL 150 Lecture Notes - Lecture 19: Point Mutation, Molecular Genetics, Methionine

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