Question 1. List the following items in order
of size from the smallest to largest:
• A. Nucleosome
• B. Mitochondrion
• C. Diameter of a DNA molecule
smallest__C_____
__A_____
Largest__B_____
Question 2. Give experimental evidence to
support that DNA, and not protein, is a
genetic material.
• See experiments by Griffiths and Avery et
al. on R and S strains of Streptococcus
pneumoniae [Figs. 5-3 and 5-4] or
• Experiment by Hershey and Chase on T2
virus infecting E. coli cell [Fig. 5-5].
Griffith’s experiment regarding DNA’s
characteristics.
Fig. 5-3, p. 173
Fig. 5-4: DNA is genetic material (Avery et al.).
Is the genetic material protein or DNA?
Hershey and Chase expt. (Fig. 5-5, p. 174)
Question 3. Fill in the blanks:
• Disulfide bonds can form between two
cysteine side chains in proteins.
• The 5’end of RNA is capped by the
addition of 7-methylguanosine .
• Nucleotides are joined together by
phosphodiester linkage between 5’and 3’
carbon atoms to form nucleic acids.
Question 4. Short answers.
A. Cholesterol comprises up to 50% of membrane lipids in
many animal cells. Explain in no more than two
sentences why it is not possible to form lipid bilayers with
cholesterol alone.
• Membranes are stabilized by phospholipids which are
strongly amphipathic, that is with very strong hydrophilic
(charged, both (+) and (-) as well as with polar groups)
and very strong hydrophobic hydrocarbon chains of 1222 carbons in length. Cholesterol is not sufficiently
amphipathic to form a stable bimolecular leaflet in which
the only hydrophilic group is the hydroxyl, with is only
weakly polar. The rest of the molecule is completely
hydrophobic.
Question 4. Short answers.
b. RNA splicing is considered an important
rather than a wasteful process? Explain.
RNA splicing makes genetic recombination
between exons of different genes more
likely, leading to formation of different
mRNAs and evolution of genes for new
proteins.
Question 5. Briefly describe the structurefunction relationship for each of the
following terms:
A. Small nuclear ribonucleoprotein
particles: The snRNPs are special kind of
enzymes which are composed of a
complex of proteins and RNA. They
catalyze removal of introns from RNA
(RNA splicing). Different types of snRNPs
recognize different regions of introns by
complemetary base-pairing (e.g. U1
snRNP recognize 5’splice site).
b. Aminoacyl-tRNA synthetases: are the
enzymes with two binding sites, one for a
specific amino acid and the other for a
specific tRNA. These enzymes catalyze
the ATP-mediated covalent coupling of
an amino acid to its appropriate set of
tRNA molecules.
c. Lysosomes: Lysosomes have a number
of hydrolytic enzymes e.g. proteases
which function at acidic pH and cause
hydrolysis of macromolecules. Low pH in
lysosme is maintained by influx of proton
by H+-ATPase pumps on lysosome
membrane.
Transcription of two genes seen be EM [Fig. 7-8]
1.
2.
3.
4.
5.
Where are Polymerases?
Where are transcription start/stop sites?
Where are the 3’ and 5’ ends of the transcript?
Which direction are the RNA polymerases moving?
Why are the RNA transcripts so much shorter than the length of the DNA that
encodes them?
See Figs. 7-9 and 7-17 for answer to this question.
Question 7: Write a short essay on the biological
information flow (DNA  RNA  protein) in
eucaryotes.
The essay should contain these points: [Fig. 7-20]
• Transcription of a gene by RNA polymerase (Fig.
7-9)
• mRNA processing e.g. 5’ RNA capping, splicing,
3’ polyadenylation [Figs. 7-12, 7-17]
• mRNA transport to cytosol [Fig. 7-19]
• precise role of genetic code, tRNA, ribosomes,
mRNA in translation [Figs. 7-26, 7-32].
Question 8. Which of the following statements are
correct? Explain your answers.
• Lipids in a lipid bilayer do not rotate rapidly
around their long axis.
• Lipids in a lipid bilayer do not flip flop readily
from one lipid monolayer to the other.
• Glycolipids move through different membraneenclosed compartments during their synthesis
but remain restricted to one side of the lipid
bilayer.
See question 11-9 and its answer in your text book
(Pages 387, A:30)
Problem Solving: Shown in the table below are the
sequences of selected amino acids from different types of
human hemoglobin (abbreviated Hb). Some forms of
hemoglobin are defective, while others are not. From what you
know about protein structure, explain why Sickle Cell and
Hammersmith Hbs are defective while delta Hb is not.
Amino acid number
Type of Hemoglobin (Hb)
3
4 5 6.. 9... 40 41 42 43
Normal beta Hb
Leu Thr Pro Glu Ser Gln Arg Phe Glu
Sickle Cell Hb (defective)
Leu Thr Pro Val Ser Gln Arg Phe Glu
Hammersmith Hb (defective)
Leu Thr Pro Glu Ser Gln Arg Ser Glu
Normal delta Hb
Leu Thr Pro Glu Thr Gln Arg Phe Glu
Panel 2-5, p75
Acid side chainsnegatively charged
Panel 2-5, p75
Polar side chains-interact
well with water, can form
H-bonds
Panel 2-5, p75
Nonpolar groups-energetically
unfavorable for them to contact water