BIOLOGY 1A03 Chapter 2: The Genetic Code

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BIOLOGY 1A03 Full Course Notes

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Details of the genetic code determined from experiments. Translation of the genetic code into a protein sequence. 3 nucleotides make up a codon which codes for a speci c amino acid. Codons are written in a 5" to 3" direction. The non template strand is called the coding strand and it contains the same codons as the mrna while the template strand contains the complementary anti-codons. Aug (methionine only coded by one sequence) is a start codon (the rst triplet in every protein coding sequence. Ugg (tryptophan) is also only coded by one codon. Some amino acids are coded for by more than one sequence (ex: serine) Generally found at the end of a coding sequence to signal the end of translation (translation stop codons include uaa, uag, and uga) Open reading frame: entire continuous sequence of a gene that begins at a triplet start codon and ends with a triplet stop codon.

Related Questions

36. The term used to describe the relationship between the two strands in a DNA double helix is:
A. opposite
B. an exact duplicate
C. colinear
D. complementary
E. antagonistic

37. The sequence of one strand of a DNA molecule is 5'-AGCGCT. What is the sequence of the other DNA strand?
A. 3'-AGCGCT
B. 3'-GCTGCA
C. 5'-TCGCGA
D. 5'-AGCGCT
E. none of the above

38. The elongation of the leading strand during DNA replication:
A. progresses away from the replication fork
B. occurs in the 3' --> 5' direction
C. produces many Okazaki fragments, which subsequently are joined together
D. depends primarily on the activity of DNA polymerase
E. does not require a template strand

39. Which statement about the genetic code is FALSE?
A. the genetic code is essentially identical in all living organisms
B. there are six codons for arginine (Arg)
C. amino acids are encoded by 64 different codons
D. several amino acids are encoded by more than one codon
E. the start codon is usually AUG, the only codon for methionine

40. Approximately what fraction of the human genome corresponds to coding regions of genes (exons)?
A. 100%
B. 48%
C. 19%
D. 1.5%
E. 0.1%

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

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

BIOLOGY 1A03 Chapter 2: The Genetic Code

BIOLOGY 1A03 Full Course Notes

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