STUDY QUESTIONS: LEC 1-4
1. What information(s) could you obtain from a genetic approach
of studying mutants defective in a particular process?
A. Function and importance of a protein (isolation, identification,
permissiveness of mutation)
B. Number of genes involved in a certain process
C. Location/order of the genes in the process (complementation
D. Interactions between different genes by using genetic suppression.
NOTE: B, C and D are carried out by the Lac Operon
2. How would you define permissive conditions in respect to
temperature sensitive mutants?
Permissive conditions are those under which a mutation is silenced. Eg:
In temperature sensitive mutations, at low temperature (permissive
conditions), the mutation will be almost silent and the organism will be
able to survive. On the other hand, at higher temperatures, the
organism will fail to survive due to loss of function.
3. Define: a) gene expression; transcription; replication;
translation; b) gene; allele
Gene Expression Transcriptio Replication Translatio
Definitio Process by which The process The process of The
n information from a of formation forming process of
gene is used in the of RNA from multiple formation
synthesis of a DNA by RNA copies of DNA of protein
functional protein polymerase by semi- from
or RNA product. conservative mRNA.
Steps DNA replication,
Cell Mainly in S phase All phases
Cycle interphase of the cell
Genes are sequences of nucleotides in a genome that contain
information coding for the synthesis of a functional protein or RNA
product. Alleles are alternative sequences of a particular gene; more
specifically, two homologous chromosomes may contain different
sequences of a specific gene at a particular locus, and thus contain
4. Explain by using your own words the meaning/significance of
gene expression. Gene expression forms the central dogma of life. Without gene
expression, there would be no passing of genetic information to off
springs, no formation of proteins and life will cease to exist. Moreover,
all cells in an organism contain the same DNA, however, not all cells
carry out the same functions. The process of gene expression is
selective. Different tissue types express different proteins depending on
their function. This selectivity of the gene expression helps the cell
conserve energy and resources by not forming unwanted proteins and
therefore, increases the viability of the cell.
5. What are the roles of model organisms in molecular biology
studies? Choose two model organisms and explain your
Model organisms are used in molecular biology studies because they
have many benefits, including simplicity, relative ease to use,
cheapness, and often short reproductive times. They are also used as
standards because so much information has been collected on them and
continue to be collected. In this way, vast and specific amounts of
information about these model organisms are obtained, and can be
extrapolated to other organisms, including humans. For example, mice
can be used to model mammalian species such as humans due to highly
conserved biological pathways and processes, and they have relatively
quick turnover rates compared to other similar organisms. Escherichia
coli are used to model metabolic processes due to their simplicity, and
the conservation of metabolic processes throughout many species.
6. What are three main functions of DNA? Explain the importance
of each of them.
Stores information â for the production of all proteins required for life.
These instructions are then passed on to daughter cells providing them
with the essential information to synthesize their own required proteins.
Replicates faithfully â by a semi-conservative mechanism. The two
strands separate and each is used to form a second strand. This
mechanism ensures that both the parent and the new strand are exactly
identical. It also ensures that if a mutation were to occur, it would only
be replicated on one of the two new strands.
Can mutate - The only source of variability in DNA is mutations. Mutation
can lead to the formation of new alleles which if selected for by the
natural selection process can result in evolution.
7. What is (are) the role(s) of phospho-diester bonds in DNA
structure? What is (are) the role(s) of hydrogen bonds in DNA
structure? What is (are) the role(s) of hydrophobic interactions
in DNA structure?
Phosphodiester bonds provide the rigid backbone for DNA structure, and
also help stabilize the molecule as they are negatively charged and repel
from each other, allowing H-bonding to occur between the bases
instead. Hydrogen bonds in DNA structure provide minimal stabilization,
but also allow for hybridization between strands due to complementary
hydrogen bonding between A and T, and between G and C. Hydrophobic interactions make it favourable for DNA strands to be hybridized in order
to minimize the water molecules that form the cage around the molecule
â thus, provide an entropically favorable way for DNA duplex formation.
8. What noncovalent interactions are involved in maintaining the
double-helical conformation of DNA?
Ionic bonds, hydrogen bonds, van der Waals interactions, and
â¢ Ionic bonds are formed between the negatively charged phosphate
groups on DNA and the positively charged ions. They help reduce
the repulsion between the 2 DNA strands and therefore