Unit 4 Review: Molecular Genetics
1) Fill in the following chart, which highlights the scientist who helped to establish DNA as the genetic
material.
Investigator(s)
Experimental Organisms/Design and Conclusions
S vs R strain of bacteria; something in heat-killed dangerous bacteria transformed
Griffith
living not dangerous bacteria into killer bacteria. Implied not a protein because heat
would have denatured the protein.
Avery
Hershey and Chase
Tested one component of Griffith’s experiment at a time; only DNA transformed the
non-dangerous bacteria into killer bacteria
Radioactively labeled P in 1 batch of virus and S in a 2 nd batch of virus; let each group
infect a separate colony of bacteria. The only bacteria that had radiation inside where
the group infected by radioactively labeled Phosphorus (P in DNA)
Chargaff
-Each species has a unique % of A, T, C, & G
-% of C = % of G and % of T = % of A
Franklin
Made the diffraction picture of crystallized DNA that Watson & Crick used to help
them identify the structure of DNA as a double helix
2) Summarize the evidence and techniques Watson and Crick used to deduce the double helix structure of
DNA.
-model building (wire & sticks)
-used Rosalind Franklin’s X-Ray diffraction picture which showed the width of the helix (2nm),
distance between base pairs (0.34nm), & the length of a full twist (3.4nm)
3) Label the following structure of DNA using
the list below:
 nucleotide
 cytosine
 guanine
 adenine
 thymine
 purine base
 pyrimidine base
 5’ end of chain
 sugar-phosphate backbone
 3’ end of chain
 hydrogen bonds
 deoxyribose
 phosphate group
a) sugar-phosphate backbone
b) 3’ end
c) pyrimidine
d) purine
e) H- bond
f) cytosine
g) guanine
h) adenine
i) thymine
j) 5’ end
K) nucleotide
l) deoxyribose
m) phosphate group
4) In the following diagram showing the replication of DNA, label the following items: leading strand, lagging
strand, Okazaki fragment, DNA polymerase, DNA ligase, Helicase, Primase, single-stranded binding
proteins, RNA primer, replication fork, and 5’ and 3’ ends of parental DNA.
a) helicase
b) single-stranded binding protein
c) DNA polymerase III
d) leading strand
e) lagging strand
f) DNA ligase
g) DNA polymerase I
h) Okazaki fragment
i) primer
j) replication fork
K) primase
l) 3’ end
m) 5’ end
5) Determine the amino acid sequence for a polypeptide coded for by the coded for by the following DNA
antisense strand (HINT: first determine the mRNA sequence that will be transcribed).
DNA
3’- T A C G G A C T G A A A T T C A C T- 5’
mRNA
5’- A U G C C U G A C U U U A A G U G A- 3’
a.a. seq
Met- Pro- Asp- Phe- Lys- STOP
6) What determines if a ribosome remains free in the cytosol?
If the beginning of the amino acid sequence is recognized by a SRP (signal recognition particle), the
SRP binds to the elongating amino acid chain and drags the entire unit (elongating amino acid chain
& ribosome) to the rough ER and binds the ribosome to the rough ER. If the initial amino acid
sequence isn’t recognized by the SRP, it stays “free” in the cytosol.
7) Using the chart in your textbook (p. 314), fill in the following table:
DNA triplet
GGG
CTT
TTT or TTC
AGC
GAA, GAC, AAT, GAG,
GAT, AAC
ATA
AAA
GTT
mRNA codon
CCC
GAA
AAA or AAG
UCG
CUU, CUG, UUA, CUC,
CUA, UUG
UAU
UUU
CAA
tRNA Anticodon
GGG
CUU
UUU or UUC
AGC
GAA, GAC, AAU, GAG,
GAU, AAC
AUA
AAA
GUU
Amino Acid
Pro
Glu
Lysine
Ser
Leucine
Tyr
Phe
Gln
8) Define the following and explain what type of point mutation could cause each of these mutations:
a) silent mutation: base-pair substitution with no effect (ex: the amino acid is the same due
to redundancy of the code or the amino acid is really similar in chemical properties)
b) missense mutation: substitute base-pair with some effects (new amino acid but some
differences in folding; ex: hemoglobin & Sickle Cell makes sense, just not the “right”
sense
c) nonsense mutation: a point mutation results in a STOP codon; translation ends
prematurely
d) frameshift mutation: insertion or deletion that changes the reading frame (groups of 3
mRNA nucleotides); as a result, all amino acids are wrong after the mutation
9) Eukaryotic cells modify mRNA after transcription. Describe how the pre-mRNA is modified with respect
to:
a) the 5’ ends and 3’ ends
 5’ end: modified G cap
 3’ end: poly A-tail

b) RNA splicing of interior sections (introns vs. exons)
Spliceosome (snRNA & proteins): splice/cut out Introns & join Exons into one continuous coding
sequence
10) Sketch and describe the anatomy of a ribosome. Include in your labeled sketch and/or your description
the following: large ribosomal unit (50s), small ribosomal subunit (30s), E site, P site, A site, mRNA
binding site, and growing polypeptide.