POLE 2 :
Training
&
Exercises
II.SCIENTIFIC REASONING:
Test your understanding by answering
the following exercises
Exercice 1:
In order to determine the origin of a mutation and the mode of transmission of a mutant allele in two types of living
beings, the following data are proposed:
I- In order to determine the origin of the resistance of a strain of Pa bacteria (Pseudomonas aeruginosa) to a type
of antibiotic called macrolids, we propose the exploitation of the following observations:
-After the infiltration of macrolides inside Pa bacteria, these molecules bind to the ribosomes, which inhibits the
synthesis of certain proteins essential to the multiplication of these bacteria.
Document I represents the concentration of macrolids (in arbitrary units) inside and outside of two strains of Pa
bacteria: a wild strain and a mutant strain, placed in a medium containing the same concentration of these
antibiotics.
-Pa bacteria have a membrane protein called MexAB-OprM which acts as a pump that rejects macrolides outside
the Pa bacteria. Document 2 presents the concentration of this membrane protein in the two Pa bacterial strains
studied.
Wild Mutant
strain strain
Concentration of macrolids inside the
bacterium in A.U.
17
Concentration of macrolids outside
the bacterium in A.U.
3
Wild
strain
Mutant
strain
low
high
Number of
protein
4
MexAB-OprM
16
1. Based on the comparison of the results shown in documents 1 and 2, explain the resistance of the mutant
strain to macrolids
The Mex.R protein inhibits the synthesis of a large amount of the MexAB-OprM protein. Document 3 presents
part of the untranscribed strand of the gene that controls the synthesis of the Mex.R protein in both wild and
mutant strains, while document 4 represents an extract of the genetic code.
107
108
109
110
111
112
113
114
115
Wild strain :
CAT GCG GAA GCC ATC ATG TCA TGC GTG
Mutant strain : CAT GCG GAA GCC ATC ATG TCA TGA GTG
Codons
GUG
GUA
UGC
UGU
CAU
CAC
GCG
GCC
ACU
ACC
UCA
UCG
GAG
GAA
AUG
Amino
acids
Val
Cys
His
Ala
Thr
Ser
Glu
Met
UGA
UAG
Non
sens
AUC
AUA
Ile
2. Using the data from Papers 3 and 4, determine the amino acid sequence corresponding to each part of the
gene controlling Mex.R protein synthesis in the two bacterial strains studied, and explain the hereditary origin of
the resistance observed in the mutant strain.
Exercice 2:
There are two strains of Japanese Quail (Coturnix japonica): black-brown and red-yellow speckled plumage
strains.
To determine the cause of the difference in plumage color in Japanese quail, studies were conducted on two
alleles of the McI-R gene: a normal allele coding for the synthesis of eumelanin pigments responsible for blackbrown spotted plumage, and a mutated allele coding for the synthesis of pheomelanin responsible for the redyellow spotted plumage.
Document I presents part of the un-transcribed strand of the normal allele in Japanese quail.
225 226 227 228 229 230 231 232 233 234 235
Nucleotide sequence: CAG CCC ACC ATC TAC GSC ACC AGC ACC CTG A
1. Using the genetic code table (document 2), give the
mRNA strand and amino acid sequence corresponding
to the part of the allele encoding the synthesis of
eumelanin pigment from triplet 225 to triplet 234.
2. A mutation by deletion of several nucleotides in the McIR gene leads to the appearance of a mutant allele
controlling the synthesis of pheomelanin pigment.
document 3 shows part of the un-transcribed strand of
the mutant allele and the sequence of amino acids
corresponding to it
225 226 227 228
Nucleotide sequence
Amino acids sequence
229
230
231 232
CAG CCC ACC GCA CCA GCA GCC TGA
Gln - Pro - Thr - Ala -Pro - Ala -Ala
3. Determine the location and number of nucleotides lost by deletion that cause The Appearance of the
mutant allele, then show the character-gene relationship
Exercice 3 ;
Xeroderma pigmentosum type B is a rare genetic disease, characterized by a hypersensitivity to UV rays,
and causes skin and eye damage that may evolve into cancers. This disease is the consequence of the loss
of the cells' ability to repair the DNA errors.
UV light causes changes in the structure of DNA by forming covalent bonds between 2 successive thymines
(T) of the same DNA strand.
In the normal state, this aberration is corrected by the intervention of a enzyme called ERCC3 before
duplication of DNA. Document 2 summarizes the mode of action of this enzyme.
DNA strand Recognition and
binding at the error location
Repair
Covalent bond
Dna strand
Document 3 presents the nucleotide sequence of a portion of the gene coding for the ERCC3 enzyme in a
healthy individual and another individual with XPB. The table in document 4 gives an extract of the genetic
code
Healthy
individual
Un-transcribed strain
Transcribed strain
XPB
individual
Un-transcribed strain
Transcribed strain
A.A
1-Using the data in document 2, 3 and 4, determine the amino acid sequence corresponding to each patty of
the gene controlling the synthesis of the ERCC3 protein in the two individuals studied, and explain the
genetic origin of this disease.
Exercice 4;
Maturity Onset Diabetes of the Young (Mody,2) affects some people before they reach the age of. 20 years.
People with this disease suffer from permanent hyperglycemia. In order to highlight the genetic origin of this
disease the following data is proposed:
Glucose is stored in the liver in the form of glycogen (glycogenogenesis) by the intervention of a a set of
enzymes of which glucokinase is one. Document I shows the level of intervention of the glucokinase in the
reaction chain of glycogenogenesis.
glycogen
The measurement of glucokinase activity in an healthy individual and one with MODY-2 disease gave the
results presented in Document 2.
I. From documents I and 2 :
Glucokinase activity in
Describe the variations in glucokinase activity.
in the healthy individual and the individual affected by
Mody-2.
b. Explain permanent hyperglycemia in the individual.
reached by Mody-2.
To establish the genetic origin of this disease, one can
proposes the documents 3 ct 4.
Blood sugar levels
Document 3 presents part of the transcribed strand of the glucokinase gene in a healthy individual and
another with Mody.2, and document 4 presents an extract from the genetic code of the glucokinase gene.
Healthy individual :
Mody2 individual
2. Based on documents 3 4, determine the amino
acid sequence of each part of the glucokinasc
gene in the healthy and Mody-2 affected
individual.
3. From the above explain the genetic origin of
the Mody-2 type diatbete.