BISC 202 Lecture Notes - Lecture 6: Start Codon, Frameshift Mutation, Transversion

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burgundycoyote951

5 Oct 2016

School

Simon Fraser University

Department

Biological Sciences

Course

BISC 202

Professor

Michael Hart

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Document Summary

Bisc 202 lecture 6: the genetic code (and mutations) We wanted to understand how the genetic code works so we needed to make a genetic code chart that was able to translate the genetic information on mrna to a specific protein. This chart allows us to take the sequence of any gene and predict the amino acid sequences of the protein. We can also predict how a mutation affects a protein. The challenge was connecting the two very different languages of dna/rna and polypeptides (4 different nucleotides vs. 20 different amino acids) Reading 3 nucleotide bases at a time with 4 different types of nucleotides means there are 43 = 64 combinations. Reading 3 bases at a time is logical because 1 or 2 would be too little, and 4 would be too many combinations (44 = 256 words), which is inefficient. Brenner and crick"s initially worked with mutagens that cause single base-pair insertions and deletions in dna.

Related Questions

An extraterrestrial organism (ET) is discovered whose basic cellbiology seems pretty much the same as that of
terrestrial organisms except that it uses a different genetic codeto translate RNA into protein. You set out to break the
code by translation experiments using RNAs of known sequence andcell-free extracts of ET cells to supply the necessary
protein-synthesizing machinery. In experiments using the RNAsbelow, the following results were obtained when the 20
possible amino acids were added either singly or in differentcombinations of two or three:
RNA 1: 5?-GCGCGCGCGCGCGCGCGCGCGCGCGCGC-3?
RNA 2: 5?-GCCGCCGCCGCCGCCGCCGCCGCCGCCGCC-3?
Using RNA 1, a polypeptide was produced only if alanine and valinewere added to the reaction mixture. Using RNA 2, a polypeptide wasproduced only if leucine and serine and cysteine were added to thereaction mixture. Assuming that protein synthesis can startanywhere on the template, that the ET genetic code isnonoverlapping and linear, and that each codon is the same length(like the terrestrial triplet code), how many nucleotides does anET codon contain?
(a)2 (b)3 (c)4 (d)5 (e)6

Its one problem with 7 questions

A) Most eukaryotic cells transcribe a relatively high portion of their genome, but most of those RNA transcripts are likely not encoding for proteins. Elucidating the function(s) of that "junk" RNA is one of the next big challenges in molecular cell biology. You isolate one of those transcripts and determine that its sequence consists of 50% C, 30% U, and 20% A. What is the percentage of Gs in this transcript? (don't write the unit)

B) Which stop codon(s) can be encoded by the RNA in the previous question ("How many times do we need to tell you to stop? 1").
List the codon(s) alphabetically. If you need to enter fewer codons than the alloted number of "blanks", enter N/A .

C) From what you can tell, the sequence of the transcript you isolated in the previous question* appears quite random. Assuming that it is random, you can expect to see the various combinations of any three nucleotides at a probability that depends of the frequency of each of the nucleotides. For example, you naturally should expect to see the triplet CCC more times than AAA. What is the expected percentage of triplets corresponding to stop codon(s) in this transcript (round to one decimal place and enter just the number without "%")? *(How many times do we need to tell you to stop? 1)

D) If the length of the transcript in the previous two questions is 2,500 nucleotides, how many stop codons do you expect to find in it, based on the frequency you calculated above?

E) On average, how many bases separate each of the occurrence of the stop codon(s) (round to the nearest integer).

F) The sequence between two potential stop codons is an "open reading frame" (ORF*). Upon closer examination of the RNA sequence from the previous questions** you determine the presence of an ORF that may encode for a putative protein which is 600 amino acid residues-long. How long is the ORF?

*Open reading frame: a stretch of DNA or RNA which is uninterrupted by a stop codon and may therefore encode for a protein.

**Questions "How many times do we need to tell you to stop" 1 through 5.

		27 bases
		1,800 bases
		2,500 bases
		259 bases
		600 bases
		83 bases
		200 bases

G) What may be the ramifications of your analyses of the RNA you isolated*? It is clearly containing an ORF which is longer than what you expected to find based on the sequence analysis you have conducted. What would be a logical conclusions based on the comparison of the lengths of the actual and predicted ORFs? Questions "How many times do we need to tell you to stop" 1 through 6. Pick 1, 2 or 3 below

		1) The difference between the actual and predicted sizes of the ORF is not big enough to be significant and therefore your initial hypothesis that sequence is random is clearly random, is supported.
		2) Nature is random and your results, using the Bard's words, may be "full of sound and fury" but are really "signifying nothing".
		3) The difference between the actual and predicted sizes of the ORF is rather big and may suggest that the sequence of the RNA may not be as random as it first appeared. This raises the hypothesis that what started as piece of "junk" RNA may be actually encoding for a protein.

sapphiregrasshopper651

Which of the following is NOT a direct consequence of the fact that DNA polymerase can only build onto the end of an existing nucleic acid?

Question 6 options:

	DNA replication requires primers
	Bits of DNA are lost from the ends of your chromosomes in each successive round of replication
	RNA is involved in DNA replication
	The enzyme "primase" is needed for DNA replication
	There are multiple origins of replication on each eukaryotic chromosome

How does a nucleotide sequence code for a protein in nearly all living organisms?

Question 7 options:

	a sequence of 3 nucleotides can code for one of 64 different amino acids
	a sequence of 2 nucleotides can code for one of 64 different amino acids
	a sequence of 2 nucleotides can code for one of 20 different amino acids
	a sequence of 3 nucleotides can code for one of 20 different amino acids
	a sequence of 3 nucleotides can code for 3 different amino acids

Fill in the blanks. To make one strand of DNA, _________ monomers are linked together in a chain, forming a polymer we call a(n) ________ .

Question 8 options:

	nitrogenous bases, hydrogen bond
	nucleotide, nucleic acid
	amino acid, nucleic acid
	nucleotide, nitrogenous base
	amino acid, protein

Which of the following was NOT part of the ideas that Darwin used in his book On the Origin of Species?

Question 9 options:

	organisms vary in characteristics that affect survival and reproduction
	variation in traits is often heritable
	descent with modification explains life's unity and life's diversity
	organisms inherit characteristics from their parents that the parents acquired in their own lifetimes
	natural selection is a cause of adaptive evolution

Here is a hypothetical mRNA sequence:

5' G G A U G C U A G U A U G A 3'

What is the amino acid sequence encoded by this mRNA?

Question 10 options:

	Met-Ile-Val
	Asp-Ala-Ser-Met
	Met-Leu-Val
	Ser-Met-Ile-Val
	Gly-Cys

BISC 202 Lecture Notes - Lecture 6: Start Codon, Frameshift Mutation, Transversion

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