Homeostasis and Cell signalling
Multiple Choice Questions1Viral genomes vary greatly in size
ranging from four genes to several hundred genes. Which of the
following viral features is most apt to correlate with the size of
the genome?
Asize of the viral capsomeres
BRNA versus DNA genome
Cdouble stranded versus single stranded genomes
Dsize and shape of the capsid
2Emerging viruses arise by
Amutation of existing viruses.
Bthe spread of existing viruses to new host species.
Cthe spread of existing viruses more widely within their host
species.
Dall of the above.
3To cause a human pandemic, the H5N1 avian flu virus would have
to
Abecome capable of human to human transmission.
Bdevelop into a virus with a different host range.
Cbecome much more pathogenic.
Dundergo an antigenic shift.
4A bacterium is infected with an experimentally constructed
bacteriophage composed of T2 phage protein coat and T4 phage DNA.
The new phages produced would have
AT2 protein and T2 DNA
BT2 protein and T4 DNA
CT4 protein and T2 DNA
DT4 protein and T4 DNA
5Some statements about the lytic cycle of a T4 bacteriophage are
listed below.
1 Bacteriophage tail fibres attach to receptors on the bacterial
cell membrane. 2 Bacteriophage enzymes break down bacterial DNA. 3
Bacteriophage nucleic acid, enzymes and other proteins are injected
into the bacterial cell. 4 New bacteriophages assembled. 5
Bacteriophage DNA replicates and codes for new bacteriophage
proteins. 6 Release of bacteriophages.
Which sequence of these statements correctly describes the lytic
cycle?
A1, 2, 3, 4, 5, 6
B1, 3, 2, 4, 5, 6
C1, 3, 2, 5, 4, 6
D1, 3, 5, 2, 4, 6
6The graph shows the changes in the core protein (capsid)
concentration of the human immunodeficiency virus (HIV) in the
blood stream after an HIV infection. The protein is detected using
antibodies.
What explains the apparent absence of the protein between three
months and seven years?
AThe core protein attaches to a CD4 receptor, therefore, it is
not found in plasma.
BThe lipid bilayer envelope masks the core protein.
CThe patients own antibodies destroy the core protein.
DThe virus enters the latent phase.
7A mutated lacI gene resulting in the failure of allolactose
binding to the repressor protein would cause
Areduced expression of operon.
Bconstitutive expression of the operon.
Creversible binding of lac repressor protein to operon when
lactose is present.
Dpermanent binding of lac repressor protein to operon when
lactose is present.
8In generalised transduction, defective virus are formed as a
result of
Aviral enzymes cutting the host DNA such that the host DNA is
assembled into the new virus.
Bproduction of host enzymes by virus which nicks its own DNA
such that it can be assembled into the new virus.
C no shut down of host DNA production such that host DNA or the
virus DNA can either be assembled into the new virus.
D integrate of virus DNA into host DNA and during excision the
viral genome carries along with it the host DNA to be assembled
into the new virus.
9The diagram shows the lac operon.
PILacI
PlacOLacZLacYLacA
Mutation in which of the following DNA sequence(s) would result
in the constitutive synthesis of -galactosidase?
ALacZ and LacY
BLacI and Plac
CO and LacI
DPI and Plac
10Which component/s make up a virus?
Aprotein particles only
BDNA or RNA and a protein coat
CDNA and RNA and a protein coat
DDNA in a nucleus, RNA, ribosomes, plasma membrane, and a cell
wall
11Two strains of the bacterium Streptococcus pneumoniae were
used in an experiment on mice. The smooth (S) strain is a virulent
strain whereas the rough (R) strain is a non- virulent strain. The
diagram below shows the results of the experiment.
Which of the following accounts for the living S cells detected
in the mouse blood sample, even though the original injection
mixture contained only heat-killed S cells and living R cells?
ABinary fission
BConjugation
CTransduction
DTransformation
12A microbiologist analyzed the DNA of two E. coli cells, an F+
cell and an F- cell, before and immediately after their
conjugation. He found that ________________________________.
Aboth cells lost some genes and gained others
Bboth cells gained genes but lost none of their original
genes
Cone cell lost genes and the other gained genes
Done cell gained genes and the genes of the other were
unchanged
13How does a bacterial chromosome differ from a eukaryotic
chromosome?
Bacterial chromosomeEukaryotic chromosome
Aa circular, single-stranded DNA moleculea linear,
single-stranded DNA molecule with many associated proteins
Ba circular, double-stranded DNA molecule with associated
proteinsa linear, double-stranded DNA molecule with many associated
proteins, including histones
Ca circular, double-stranded DNA molecule with associated
histone proteinsa linear, double-stranded DNA molecule with many
associated proteins
Da linear, double-stranded DNA molecule with many associated
proteinsa circular, double-stranded DNA molecule with very few
attached protein molecules
14Which does not occur during the formation of bacterial
messenger RNA?
Aformation of hydrogen bonds
Binitiation of translation
Closs of water molecules
Dpolymerization of deoxyribonucleotides
15Which features of viruses account for them being obligate
parasites?
1. All viruses are very small, ranging in size from 20-300nm.2.
Each virus contains only one type of nucleic acid.3. Viruses can be
crystallised.4. Viruses cannot synthesise ATP.5. Viruses have no
cellular structure.6. Viruses have no enzymes involved in
metabolism outside a host cell.
A1, 3 and 5
B1, 4 and 6
C2, 3 and 5
D2, 4 and 6
Anglo-Chinese Junior CollegeRevision Package H2 Genetics of
Viruses & Bacteria
14
16Some events that take place during the reproductive cycle of
influenza virus are listed.
1. The virus enters the cytoplasm surrounded by a coated
vesicle.2. The nucleocapsid is released and viral RNA replicated by
RNA polymerase.3. Each replicated viral RNA is given a new
envelope.4. Viral hemagglutinin proteins bind to receptors in the
host cell surface membrane.5. Hemagglutinin and neuraminidase are
produced by the host cells ribosomes.6. The replicated viral RNA is
transcribed to mRNA.
Which sequence of events correctly describes the reproductive
cycle of the virus?
A1 2 3 6 5 4
B1 2 6 5 4 3
C4 2 5 1 6 3
D4 1 2 6 5 3
17The synthesis of the amino acid tryptophan is E. coli is
controlled by the trp operon. The amino acid tryptophan combines
with an inactive trp repressor protein to activate it. This trp
repressor protein binds to the operator controlling the expression
of structural genes for the production of tryptophan. What does
this system ensure?
ACells are able to absorb tryptophan.
BTryptophan is constantly manufactured.
CTryptophan is manufactured only when levels are low.
DTryptophan inhibits translation at the ribosome.
18Which statement CORRECTLY describes the control of
transcription of the genes involved in the breakdown of lactose in
Escherichia coli?
AA repressor protein binds to the operator and the genes are
switched on.
BA repressor protein binds to the operator and the genes are
switched off.
CA transcription factor binds to the promoter and the genes are
switched on.
DA transcription factor binds to the promoter and the genes are
switched off.
19Which drug would be most effective in treating viral
infections?
AOne that competes with the virus for the same binding site on
the host receptor.
BOne that induces the body to produce antibodies.
COne that inhibits the action of viral ribosomes.
DOne that interferes with the synthesis of viral nucleic
acids.
20Regarding prokaryotic reproduction, which statement is
correct?
AProkaryotes form gametes by meiosis.
BProkaryotes feature the fusion of haploid gametes, as do
eukaryotes.
CProkaryotes exchange some of their genes by conjugation, the
fusion of haploid gametes, and transduction.
DMutation is a primary source of variation in prokaryote
populations.
Structured Questions
1. (a) Briefly describe the structural components of viruses.
[1]
HIV enters blood cells via CCR5 receptor molecules in the cell
surface membranes. Fig. 1.1 shows a CCR5 receptor, which is a
protein.
Fig.1.1
Source: Samson M, Libert F et al. Nature 382 (6593) p722 1996(b)
Using information from Fig. 1.1, describe the protein structure of
the CCR5 receptor. [3]
(c) Some people carry a mutant form of a gene which results in a
different form of the CCR5 receptor. Suggest how this may result in
protection from HIV. [1]
(d) Four possible combinations for the binding of catabolite
activator protein (CAP) and Lac repressor are shown in Fig.
1.2.
For each of the four combinations, indicate on the left-hand
side of Fig. 1.2 which sugar(s) must be present (using + ) or
absent (using - ), and on the right hand side whether the operon is
expected to be turned On or Off .
Fig.1.2
(e) Bacterial cells can take up the amino acid tryptophan from
their surroundings. If the external supply is insufficient, they
can synthesize tryptophan from small molecules in the cell.
Tryptophan repressor inhibits transcription of the genes in trp
operon. Upon binding tryptophan, the tryptophan repressor binds to
a site in the promoter of the operon. Why is such
tryptophan-dependent binding to the operon a useful property for
tryptophan repressor? How does it illustrate that the trp operon is
a repressible system? [2]
(f) Fig. 1.3 shows how a trp-lac fusion operon is
constructed.
Explain the condition(s) required for beta galactosidase to be
expressed in bacteria cells that have been transformed with the
trp-lac fusion operon.[2]
[Total: 10]
2 (a) In a study to examine the effectiveness of bacteriophages
in treating colibacillosis, a fatal disease caused by E. coli in
poultry, broiler chickens were first subjected to an aerosol spray
containing bacteriophages on day 0. They were then separated into
five treatment groups. Each treatment group was subsequently
injected with E. coli on days 0, 1, 2, 3 and 4 respectively. The
mortality rate of each group was determined after 21 days. The
result of the study is represented by Fig. 2.1 below.
Fig. 2.1
Fig. 2.1(i) With reference to Fig. 2.1, compare the general
trends observed in the control groups and the groups that have been
treated with bacteriophages. [3]
(ii) Discuss ways in which the farmer can make use of the
results in Fig. 2.1 to treat colibacillosis in his poultry. [2]
(bi) Suggest why the use of bacteriophages is a better possible
alternative to antibiotic therapy for the chickens. [1]
(b) (i) A person infected with the H1N1 influenza virus does not
develop the symptoms. Physical examination shows that the persons
immune system has produced an antibody that binds to the
haemagglutinin molecules. Suggest why the person does not develop
influenza-like symptoms. [2]
(ii) After a few days, the person begins to develop influenza
symptoms. Tests for the antibody mentioned in (b) (i) show that it
is still present in the blood. Account for this observation and
comment on the implication of this observation for developing a
H1N1 influenza vaccine. [2]
[Total : 10]
3Fig. 3.1 shows the percentage of regulatory sites spanning the
indicated base positions in operons found in E. coli. Activator
binding sites% of regulatory sites at indicated positions in
different operonsBase position
Repressor binding sites
Fig. 3.1
(a)With reference to Fig. 3.1,
(i) indicate using on the x-axis of the graph the base position
of the promoter. [1]
(ii)outline the role of the repressor binding site in an operon.
[1]
(iii) state and explain whether the structure of the lac operon
conforms to the data shown. [3]
[Total: 5]4Fig. 4.1 shows the structure of the human
immunodeficiency virus, HIV.
Fig. 4.1
(a) Name the parts A to C. [3]
A: ____________________________B:
_____________________________C: _____________________________
HIV instructs the T-lymphocytes to reproduce more viruses.
During this process, the cell replicates viral DNA and produces
viral proteins, which will be used to make new viral particles.
These HIV particles will be released from the infected T-lymphocyte
through budding, so that more T-lymphocytes will be infected. Fig.
4.2 is an electron micrograph showing the process of HIV particles
leaving a T-lymphocyte.
Fig. 4.2(b) Suggest why an infected T-lymphocyte that is
producing HIV particles has a higher demand for amino acids than an
uninfected lymphocyte. [1]
(c) Describe how HIV acquires the outer envelope. [3]
(d) Upon the release of HIV from an infected T-lymphocyte, HIV
protease completes the maturation of the viruses by cutting viral
polyproteins to form the HIV structural proteins and enzymes of the
infective virus.
HIV protease inhibitors may be used to treat HIV patients.HIV
protease is composed of two identical protein chains which forms a
tunnel that wraps around the viral polyprotein chains, closing and
holding it while it is hydrolysed to form the hiv structural
proteins and enzymes.
Fig. 4.3 shows a molecular model of HIV protease with the
protease inhibitor (shaded) attached.Fig. 4.3
(i) Explain how HIV protease inhibitors work in the treatment of
HIV infection. [3]
(ii) Describe the structural properties of this inhibitor
required for its action. [2]
[Total: 12]
5In 1951, Joshua Lederberg and Norton Zinder were testing for
genetic recombination in the bacterium Salmonella typhimurium. The
researchers used two different strains of bacteria: one which only
grew when supplied with tryptophan and tyrosine, and a second
strain which only grew when supplied with methionine and histidine.
When either strain was plated on a minimal medium, no wild-type
cells were observed. However, after the two strains were mixed,
wild-type cells appeared at a frequency of about 1 in 105.
(a) Explain how genetic recombination typically occurs in
eukaryotes. [2]
(b) Describe three methods by which genetic recombination may
occur in bacteria. [3]
In a further U-tube experiment, the different strains of
bacteria were placed in two arms of a U-tube, separated by a filter
that prevents cell contact. The result of this experiment shows
that recombinant strains could also be obtained. By varying the
size of the pores in the filter, they found that the agent
responsible for recombination was about the size of the virus P22,
a known temperate phage of Salmonella.
(c) Explain what it means by temperate phage. [1]
(d) Outline the process by which a lytic bacteriophage leads to
genetic recombination in bacteria. [4]
[Total: 10]
Essays
1(a)Discuss whether viruses are living or non-living organisms
and explain why viruses are obligate parasites. [9]
(b)Some bacteriophages have both a lysogenic and a lytic cycle.
Suggest reasons why it may be advantageous for a bacteriophage to
have a lysogenic cycle. [4]
2(a)Distinguish between the reproductive cycles of lambda phage
and HIV. [5]
(b)Explain how HIV infection causes diseases in humans. [9]
3(a)Discuss the importance of operons in bacteria. [4]