Chapter 3:
Question #3:
Use the codon dictionary (Figure 3-18 in text) to complete the following table. Assume that reading is from left
to right and that the columns represent transcriptional and translational alignments.
▪While completing table, be sure and label the 5’ and 3’ ends of the DNA and RNA as well as the amino and
carboxy ends of the protein
3’
C
G
T
A
C
C
A
C
T
G
C
A
5’
G
C
A
T
G
G
T
G
A
C
G
T
5’
G
C
A
U
G
G
U
G
A
C
G
U
mRNA transcribed
3’
C
G
U
A
C
C
A
C
U
G
C
A
Appropriate tRNA anticodon
Amino
Ala
Trp
Stop
DNA Double Helix
Amino acid incorporated into
protein
This question definitely gets you to think about the relationship between DNA, mRNA, and proteins
produced…See Figure 3-2 in text
Question #11:
A certain Drosophila protein-coding gene has one intron. If a large sample of null alleles of the gene is
examined, will any of the mutant sites be EXPECTED:
First, what is a null mutation?! A null mutation is one that results in complete absence of function of the
geneResults in no protein function (see page 72 in text)
a.) in the exons? So, ask yourself—Can a mutation occur in the exon that would result in creation of a nonfunctional protein? YES! A missense, nonsense, deletion, or frameshift could occur that would disrupt the
reading frame resulting in a non-functional protein
b.) in the introns? Generally speaking…No. BUT! There are those CRITICAL consensus splice junction
sequences at the exon-intron boundary that are necessary for proper splicing! So, the book says Yes.
c.) in the promoter? Ask yourself—What acts at the promoter?! RNA Polymerase…Okay, there are some
critical regions in the promoter (namely –10 and –35) that serve as binding sites for RNA Polymerase. If those
were mutated, could that possibly result inproduction of a non-functional protein? YES! Mutation at a promoter
may disrupt the binding of RNA Polymerase. So where once a protein SHOULD have been produced, now NO
protein is produced…
d.) in the exon-intron boundary? See “b” YES! Disruption of consensus splice sites may lead to production of
truncated proteins or proteins that are longer than they should be.
The POINT of this question is best represented in Figure 3-25 of your text—Mutant sites have different consequences!!
Question #23:
List three examples of proteins that act on nucleic acids…
With what nucleic acids are we familiar? DNA and RNA! So, what proteins bind to DNA and RNA?? Don’t
forget that an enzyme is a protein!
-histones, DNA/RNA polymerases, topoisomerase, ligase, restriction enzymes, ribosomal proteins (to name a
few…)