Download MCDB 1030 – Spring 2003

MCDB 1030 – Spring 2005
Homework Set 1
Development of Ideas about Infectious Disease and Biological Macromolecules
1. (3 points) What are the three fundamental types of living organisms?
Bacteria, Archaea, and eukaryotes
2. (4 points) Define the following words:
a) Pathogen – an infectious agent that can cause disease
b) spontaneous generation – the hypothesis that life could appear spontaneously from
non-living matter
c) pasteurization – a process of heating that kills microorganisms in foods and
beverages
d) biogenesis – the idea that life must arise from other life
3.
(5 points) List some of the major contribution(s) of the following scientists:
a) Anton van Leeuwenhoek – the first person to discover microbial life by looking
through a microscope
b) Joseph Lister – introduced antiseptic techniques to prevent infection of wounds
c) Louis Pasteur – laid to rest the theory of spontaneous generation once and for all with
the famous swan-necked flask experiment; introduced the technique of pasteurization;
was one of the leaders in developing the germ theory of disease
e) Francesco Redi – designed the clever experiment shown in Figure 1.10 which proved
that spontaneous generation did not occur for macroscopic life forms
f) Ignaz Semmelweiss – introduced a requirement for handwashing in chlorinated lime
water in an obstetrical ward in Vienna, a practice which led to a dramatic decrease in
the number of deaths from puerperal fever, which was caused by introduction of
bacteria from the hands of doctors into the tissues of women who had given birth
3. (8 points) What are Koch’s postulates? Why were they an important breakthrough? Are
they always valid?
See text and lecture notes for Koch’s postulates
These postulates were an important breakthrough because they provided an intellectually
rigorous way of proving that a particular pathogen caused a particular disease. They are
not always valid, though. Viruses and prion cannot be grown in pure culture.
Furthermore, many bacteria cannot be grown in pure culture, probably because we don’t
understand their growth requirements. Thus, it may be impossible to isolate a bacterium
that is in fact that cause of a disease.
4. (6 points) a) What is the difference between a nucleotide and a polynucleotide?
A nucleotide is one building block of a polynucleotide that is polymer form. DNA strands
are polynucleotides, constructed from DNA nucleotides (monomers).
b) What are three important structural differences between DNA and RNA?
The ribose sugar in ribonucleotides (the building blocks for RNA) has an OH (hydroxyl)
group on the 2’-carbon, while the deoxyribose sugar of deoxyribonucleotides (the building
blocks for DNA) do not have an OH group on the 2’ carbon.
DNA is double-stranded, and RNA is usually single-stranded
DNA and RNA have the bases A, C and G, but DNA has T and RNA has U.
c) What is the role of DNA?
In living organisms it serves as the instructions for making protein and RNA products for
the cell. It is the heritable material that is passed from generation to generation.
5. (4 points) Are the following hydrophobic or hydrophilic?
a) ethanol (hydrophilic)
b) olive oil (hydrophobic)
c) vinegar (hydrophilic)
d) sugar (hydrophilic)
6. (8 points) a) Draw a triglyceride and a phospholipid. Circle the ester linkages.
See figures 2.15 and 2.18
b) What are the differences between these two types of molecules?
There are two fatty acid chains in a phospholipid and three fatty acid chains in a
triglyceride. (In a phospholipid, a phosphate group takes the place of one of the fatty acid
tails of a triglyceride.)
c) Why do phospholipids form bilayers?
Phospholipids have polar and non-polar regions (they are amphipathic). In water they
form bilayers so that the tails can associate with each other and “get away” from the water.
The heads face the water side because they are polar.
7. (3 points) What is the common feature in the following molecules: sucrose, glycogen, and
starch?
They are all made from the same monomer (glucose). They are all polymerized in different
ways.
8. (3 points) Define the following terms .
a) Replication
Formation of new DNA double strand using each of the parental DNA strains as a template
(utilizes a DNA-dependent DNA polymerase, primers etc).
b) Transcription
Processes involving the formation of an mRNA from a DNA template using an RNAdependent RNA polymerase.
c) Translation
The synthesis of a protein polymer using the information provided by a mRNA template on
a cytoplasmic ribosome.
9. (6 points) Draw a GC base pair and an AT base pair with the hydrogen bonds. Try to make
a GT base pair. Does it work?
See text and handout diagrams