MIT Biology Department

7.012: Introductory Biology - Fall 2004

Instructors: Professor Eric Lander, Professor Robert A. Weinberg, Dr. Claudette Gardel

Final Exam Practice

Final Exam is on Monday, DECEMBER 13 9:00 AM - 12 NOON

BRING PICTURE I.D.

Exam Review on Thursday, Dec. 9 (new

material only)

7-9 PM

Exam Tutorial Friday, Dec 10th

Spring 2004 Final Exam Practice

1-3 PM

Question 1
In the space provided next to each definition or description, clearly write the letter of the
appropriate term from the list of terms given on the last page.
____

A short, single-stranded DNA that serves as the necessary starting material

for the synthesis of the new DNA strand in PCR

____

The synthesis of DNA using DNA as a template

____

The building blocks of DNA and RNA

____

The synthesis of protein using information encoded in mRNA

____

The location in a eukaryotic cell where the electron transport chain occurs

____

The major component of cell membranes

____

The genetic composition of an organism

____

A gene that lies on one of the sex chromosomes

____

An organism without membrane-bound organelles

____

A cell with 1n chromosomes

____

The building blocks of proteins

____

A cell with 2n chromosomes

____

A major source of energy that has the general formula (CH2O)n

____

An enzyme needed for completion of lagging strand synthesis, but not

leading strand synthesis

____

The synthesis of RNA using one strand of DNA as a template

____

An observed characteristic of an organism

Spring 2004 Final Exam Practice

Question 1, continued
____

A DNA molecule that is distinct from the chromosome; this molecule can be
used to move foreign DNA in or out of a cell

____

The DNA from a eukaryote formed by the enzyme reverse transcriptase; this
DNA lacks introns

____

An organism with 2 identical alleles for the same gene

____

A membrane protein involved in signal transduction; activation involves

binding a GTP molecule

____

An organism with genetic material inside a nucleus

____

An organism with 2 different alleles for the same gene

____

A measure of the affinity of an enzyme for its substrate

____

A gene that lies on any chromosome except the sex chromosomes

____

The membrane that surrounds the cell

____

One of the alternate forms of a gene found at a given locus on a

chromosome

____

A technique for the rapid production of millions of copies of a particular

region of DNA

____

Proteins with a signal sequence are directed to this cellular organelle

Spring 2004 Final Exam Practice

Question 2
The following double-stranded DNA contains sequence of a eukaryotic gene:

b
1
2
3
5'-ATGGCCTTCACACAGGAAACAGCTATGGCCATGAGCACGC
1 ---------+---------+---------+---------+ 40
3'-TACCGGAAGTGTGTCCTTTGTCGATACCGGTACTCGTGCG
ii

CAGTCTCGGCATTATCCTATTAAAGGGAACTGAGGTGA-3'
41 ---------+---------+---------+---------+ 80
GTCAGAGCCGTAATAGGATAATTTCCCTTGACTCCACT-5'
i

a) Transcription begins at the underlined A/T at base pair 17 (b) and proceeds to the right.
What are the first 12 nucleotides of the resulting mRNA? Indicate the 5' and 3' ends of the
mRNA.
b) The first 7 amino acids of the protein encoded by this gene are:
NH3+ -met-ala-met-ser-thr-pro-his-tyr....COOi) underline the nucleotides which correspond to the 5' untranslated region of the primary
RNA transcript made from this gene.
ii) draw a box around the intron region in this gene.

c) Consider each of the following three mutations independently.

i) How would the resulting protein change if the underlined G/C base pair at position 22 (1)
was deleted from the DNA sequence? Briefly explain.

ii) How would the resulting protein change if the underlined G/C base pair at position 27 (2)
was changed to a C/G base pair? Briefly explain.

iii) How would the resulting protein change if the underlined A/T base pair at position 31
(3) was deleted from the DNA sequence? Briefly explain.

Spring 2004 Final Exam Practice

Question 2, continued
d) Puromycin is an antibiotic that has an effect on both prokaryotes and eukaryotes.
Puromycin, which is structurally similar to the aminoacyl terminus of an aminoacyl-tRNA (see
diagram), inhibits protein synthesis by releasing nascent polypeptide chains before their
synthesis is completed.

R represents the side group of the amino acid

R' is the remainder of the tRNA

Explain how puromycin can affect this result on growing polypeptide chains and why the
peptide chain is released.
Question 3
a) Many patients are coming into the emergency room with a disease caused by an unknown
pathogen! A doctor studies this pathogen in order to create a vaccine against it. She discovers
that the infectious agent is an intracellular bacterium and its cell surface is coated with humanlike proteins. Considering the mechanism of the pathogen, the doctor decides to generate a
live-attenuated vaccine instead of a heat-killed vaccine.
i) What are the two advantages of using a live-attenuated vaccine vs. a heat killed vaccine in
this case?
ii) What is a disadvantage of using a live-attenuated vaccine?

b) When a rabbit protein is injected into rabbits, no antibodies against this protein are
generated. If, however, the same rabbit protein is injected into guinea pigs, the guinea pigs
generate antibodies against the rabbit protein. Briefly (in one or two sentences) explain this
observation.

c) The genomes contained in almost all of the somatic cells in an adult human are identical.
Name one (diploid) cell type that is an exception to this and specify the process by which the
genetic variation occurred.
d) Will siblings have the exact same antibody repertoire? What about identical twins? Briefly
explain your reasoning.
Spring 2004 Final Exam Practice

Question 4
a) Below is the pedigree for a family with an autosomal recessive disease, disease X.
= unaffected female

= affected female
= unaffected male

= affected male

?
i) What is the genotype of individual A at the disease X locus? Use + to indicate the
wildtype allele and - to indicate the mutant allele.
ii) What is the probability that individual B is a carrier of disease X?

iii) Individuals C and D decide to have a child. What is the probability that the child will have
disease X?

iv) What is the probability that the child of individuals C and D will be a carrier of disease X?

b) The most common mutant allele of the disease X gene is a deletion of three nucleotides
which eliminates a phenylalanine at amino acid residue 508. Although the mutant X protein is
made, it is not localized to the plasma membrane.
i) Assuming the altered X protein is stable, where might it be found?

ii) Describe another mutation in this gene that could prevent the disease X protein from
localizing to the plasma membrane.

Spring 2004 Final Exam Practice

Question 4, continued
c) Researchers are currently working on gene therapy for disease X patients. The most
promising therapy has involved incorporating the disease X gene into an adenovirus. Because
adenovirus is a double-stranded DNA virus that targets lung epithelial cells, it can be used to
deliver the disease X gene to the lung cells of the affected individual.
i) The adenovirus used in these studies is able to produce gp19, a protein that inhibits the
display of MHC I molecules on the surface of cells. Why is this a desirable property of the
virus used to deliver the disease X gene?

ii) Using the plasmids and restriction enzymes provided, design a procedure to create a,
double-stranded DNA to incorporate into the adenovirus particle. The final product should
be linear, contain the majority of the virus genome and have the disease X gene under
control of the E1 promoter (PE1). NheI and SpeI create the same sticky ends. All the other
restriction enzymes create unique cuts.
BamHI

P E1
NheI
HindIII

SpeI
start

SpeI
disease X cDNA

pBR-Ad2-7

BamHI

Spring 2004 Final Exam Practice

Adenovirus
genome

pCMV-diseaseX

stop

HindIII

EcoRI

Question 5
The figure below shows GDP in the binding pocket of a G protein.
O
N
O
O-

O-

+
NH 3

Lys

H 2N

NH

O
O

CH 2

NH

O-

+
NH 2

NH

HO

OH

OH

Tyr

Arg
Asp
a) Circle the strongest interaction that exists between:

Glu

i) the side chain of Lys and the phosphate group of GDP

van der Waals

covalent

hydrogen bond

ionic

ii) the side chain of Glu and the ribose group of GDP
van der Waals

covalent

hydrogen bond

ionic

iii) the side chain of Tyr and the guanine base of GDP
van der Waals

covalent

hydrogen bond

ionic

b) You make mutations in the GDP-binding pocket of the G protein and examine their effects on
the binding of GDP. Consider the size and the nature (e.g. charge, polarity, hydrophilicity,
hydrophobicity) of the amino acid side chains and and give the most likely reason why each
mutation has the stated effect. Consider each mutation independently.
i) Arg is mutated to a Lys, resulting in a G protein that still binds GDP.

ii) Asp is mutated to a Tyr, resulting in a G protein that cannot bind GDP.

Spring 2004 Final Exam Practice

Question 6
The bos/seven receptor is required for differentiation of a particular cell, called R7. It is a
receptor tyrosine kinase with the structure below. As a monomer, the protein is inactive.
Binding of ligand causes the receptor to dimerize, causing phosphorylation of the intracellular
domain, activating the protein. During processing of the protein, the extracellular domain is
cleaved and a disulfide bridge forms between two cysteines, tethering the ligand-binding
domain to the rest of the protein.
ligand-binding
domain

extracellular
-S-S-

ligand
-S-S-

-S-S-

membrane
intracellular

INACTIVE

ACTIVE

a)
i) How would receptor activity be affected by changing one of the two cysteines shown
above to an alanine? Explain.

ii) What effect would this mutation have on the differentiation of R7?

b) Name three amino acids that would be likely to be found in the transmembrane domain.
What property do those amino acids have in common, and why do they cause the
transmembrane domain to stay in the membrane?

d) Draw a schematic of the receptor tyrosine kinase (discussed above) prior to any cleavage or
modification using the template below. Include the domains of this protein that are required
for targeting to and insertion in the plasma membrane. Also label the intracellular and
extracellular domains.
N

e) Activation of the above receptor causes Ras to exchange GDP for GTP, thereby activating it.
This activated Ras can activate a signal transduction cascade, which ultimately results in the
Spring 2004 Final Exam Practice

transcription of genes required for R7 differentiation. In different cells in the same animal, Ras
can be activated by an activated growth factor receptor. This leads to transcription of genes
required for cell division.
EGF

boss/sev

EGF
receptor

Ras

Ras

GDP

GDP

GTP

GTP

transcription of genes
for R7 development

transcription of genes
for cell division

i) How is it possible for the activation of Ras to lead to transcription of different sets of
genes?

ii) Given that these cells exist in the same animal, name one component in the pathway that
could be mutated to give each of the following results (consider each situation
independently). Describe how the mutant component differs from the wild-type
component, and whether it is a loss-of-function or gain-of-function mutation.

You never see differentiation of R7 cells.

You see uncontrolled cell proliferation.

Question 7
You are studying a common genetic condition. The mutant allele differs from the wild-type
allele by a single base-pair (bp) substitution. This substitution eliminates a NheI restriction site
that is present in the wild-type allele. (The mutant allele is not cut by NheI.) A pedigree of a
family exhibiting this condition is shown below:
normal male

Spring 2004 Final Exam Practice

affected male

normal female
affected female

10

You isolate DNA from four individuals in the pedigree. Using PCR techniques, you amplify a
1000 bp portion of their DNA that includes the site affected by the mutation. You digest the
PCR products with NheI and analyze the resulting DNA fragments on a gel:
Individual:

NheI

NheI

NheI

NheI

1000 bp

600 bp

400 bp

a) Based on these data, is this gene located on an autosome or the X-chromosome? Briefly justify
your reasoning.

b) Based on these data, is the mutant phenotype dominant or recessive to wild-type and why?

c) If individuals 3 and 4 have a daughter, what is the probability that she will be affected?
Justify your reasoning.

You sequence the region around the NheI site in the wild-type PCR product. You then
sequence the corresponding region in the mutant PCR product and discover that not only did
the mutation eliminate the NheI site in the mutant allele but it has created a new PvuII
restriction site. The recognition sites for the two enzymes are indicated below.
NheI cuts at:

5' GCTAGC 3'

3' CGATCG 5'

PvuII cuts at:

5' CAGCTG 3'

3' GTCGAC 5'

A portion of one strand of the wild-type DNA sequence is shown below:

5....GCTAGCTG...3
d) What is the sequence of this same region in the mutant allele?
Indicate the 5' and the 3' ends of the DNA sequence.

Spring 2004 Final Exam Practice

11

e) Individuals 1 and 2 have another child, 9, who is affected by the genetic condition.
1

You PCR amplify the 1000 bp region affected by the mutation from individuals 1, 2, and 9,
digest the PCR products with NheI or PvuII, and analyze the restriction fragments on a gel:

NheI PvuII

NheI PvuII

NheI PvuII

Individual:

1000 bp

600 bp

400 bp

What event occurred and how does this explain the data shown above?

Spring 2004 Final Exam Practice

12

Question 8
While walking through the sub-basement of the Infinite Corridor late one night you come
upon an enclave of gnomes. You are struck by the color of their beards, which are all blue.
(Gnomes are diploid organisms, both male and female gnomes have beards, and you can
assume that the gnomes are true-breeding for this trait.) The following week you are busy
pulling a hack at Harvard when you spy another enclave of gnomes. All of these gnomes
have yellow beards. (Again assume that the gnomes are true-breeding for this trait.) Curious,
you collect a few yellow-bearded gnomes from Harvard and bring them back to MIT. Later
you discover that several of the yellow-bearded gnomes and blue-bearded gnomes have
mated. The offspring of these matings are all green-bearded. Below are two possible
explanations for these results.
a) Possibility 1: Beard color is controlled by a single locus. Give the genotypes in the blanks
below.
X
Yellow beards

Blue beards

Green beards
b) Possibility 2: Beard color is controlled by a pathway of two distinct enzymes encoded by
the A and Q genes.
i) Give one genotype in each of the blanks below. Use A and Q to designate the wild-type
alleles. Use a and q to designate the loss-of-function alleles.
X
Yellow beards

Blue beards

Green beards
ii) When two F1 green-bearded gnomes mate, they produce 64 green-bearded gnomes, 27
blue-bearded gnomes, and 22 yellow-bearded gnomes. Given your answer to i) above, draw
the pathway for beard color. Be sure to include at which step each of the genes functions.

Spring 2004 Final Exam Practice

13

Question 9
Bob, a sophomore at MIT, failed 8.01 his freshman year. His parents are both physicists, but he remembers that his greatgrandfather also failed physics. Bob constructs the following family pedigree and is convinced that his poor performance in
physics is an inherited genetic trait.

unaffected male

unaffected female

affected male

affected female
1

10

Bob
a) If Bob's hypothesis is true, what is the most likely mode of inheritance?_____________
b) Individuals marrying into the family are homozygous for the wild-type allele. Complete the table below.
Use G or g to denote the alleles of this gene. Be sure to note any ambiguities.

individual

genotype

2
3
4
9
10
c) Bob meets Leah in his remedial physics class. Bob is a hard worker (homozygous for the H allele). Leah is
lazy (homozygous for the h allele). The H locus is linked to a chromosomal marker, which exists in two forms
+ or - . Circle the non-recombinant genotypes of Bob and Leah's grandchildren.

hh ++

HH--

Leah

Bob
hh --

?
genotypes
hh++

hh-HH+-

Spring 2004 Final Exam Practice

hh+Hh++

HH++

HH--

Hh-- Hh+14

Question 10
The following is a plot of an action potential measured at a single spot along an axon. Four
points are highlighted along the curve, , , , .

+50

Membrane
Potential
(mV)

-70

Time

a) On the table below, identify which ion (Na+, K+, Ca++, Cl-) is undergoing the greatest net
flow across the membrane at the points indicated and state the direction that the ion is moving
(into the cell or out of the cell).
Point

Ion

Direction (in/out)

b) The membrane potential is -70 mV at points and , on the plot above. Which of the
voltage-gated ion channels is closed at point , but open at point ?
c) What dictates the closing of the voltage-gated channel that is open at point ?

d) There are at least three states in which the voltage-dependent Na+ channel exists.
At on the above plot, the majority of voltage-dependent Na+ channels would be in which
state? Circle the best answer.

Open

Spring 2004 Final Exam Practice

Closed

Inactivated

15

Question 11 continued
Two different pre-synaptic neurons, neuron 1 and neuron 2, synapse onto cell W as shown
below. When neuron 1 is stimulated, the membrane of cell W is locally depolarized. When
neuron 2 is stimulated, the membrane of cell W is locally depolarized to exactly the same
extent as seen with neuron 1.
Neuron 1

Cell W

Neuron 2

e) Circle the one correct statement below.

If stimulated equally, neuron 1 is more likely to result in an action potential in cell W
than neuron 2.

If stimulated equally, neuron 2 is more likely to result in an action potential in cell W

than neuron 1.

If stimulated equally, neuron 1 and neuron 2 are equally as likely to result in an action
potential in cell W.
f) If you were exposed to a toxin that irreversibly blocked voltage-gated Ca++ channels,
indicate whether the following statements would be TRUE or FALSE.
T

Secretory vesicles filled with neurotransmitters would stay in the nerve.

Your muscles would end up in a rigid contraction.

Secretory vesicles filled with neurotransmitters would fuse with the plasma membrane.

Spring 2004 Final Exam Practice

16

Question 11
To investigate the yeast metabolic pathway for serine biosynthesis, you screen for serine
auxotrophs (mutants which are unable to grow without serine supplied in their growth
medium).
You isolate four such mutants, which are recessive to the wild-type strain, and you test them
for growth on medium supplemented with several intermediates (A, B and C) known to be
part of the pathway. The results are shown below ("+" represents growth,
"-" represents no growth).
Strain

minimal
medium

minimal
+ A

minimal
+ B

minimal
+ C

minimal
+ serine

wild-type

m1

m2

m3

m4

You then mate the haploid m1 strain with the haploid m4 strain to create a diploid yeast strain
carrying both the m1 and the m4 mutations. You test the diploid for growth on the same
conditons as above and observe that the diploid exhibits the same growth requirements as the
m1 or the m4 haploid.
a) Are the m1 and m4 mutations in the same gene or in different genes? Briefly explain your
reasoning.

b) Draw the metabolic pathway for the synthesis of serine, consistent with the data given
above. Include the intermediates (A, B, and C) and serine, and indicate which mutants (m1,
m2, m3, m4) are defective at each step in the pathway.

c) You create a haploid strain that has both the m1 and m3 mutations.
i) This haploid mutant will grow on media supplemented with which of the following
intermediate(s): A, B and/or C?
ii) When grown on minimal medium this haploid will accumulate which of the following
intermediate(s): A, B and/or C?

Spring 2004 Final Exam Practice

17

Solutions
Question 1
AA

A short, single-stranded DNA that serves as the necessary starting material for the synthesis of
the new DNA strand in PCR

DD

The synthesis of DNA using DNA as a template

S
HH

The building blocks of DNA and RNA

The synthesis of protein using information encoded in mRNA

The location in a eukaryotic cell where the electron transport chain occurs

The major component of cell membranes

The genetic composition of an organism

FF

A gene that lies on one of the sex chromosomes

BB

An organism without membrane-bound organelles

A cell with 1n chromosomes

The building blocks of proteins

A cell with 2n chromosomes

A major source of energy that has the general formula (CH2O)n

An enzyme needed for completion of lagging strand synthesis, but not leading strand synthesis.

GG

The synthesis of RNA using one strand of DNA as a template

An observed characteristic of an organism

A DNA molecule that is distinct from the chromosome; this molecule can be used to move foreign
DNA in or out of a cell

The DNA from a eukaryote formed by the enzyme reverse transcriptase; this DNA lacks introns

An organism with 2 identical alleles for the same gene

A membrane protein involved in signal transduction; activation involves binding a GTP molecule

An organism with genetic material inside a nucleus

An organism with 2 different alleles for the same gene

A measure of the affinity of an enzyme for its substrate

A gene that lies on any chromosome except the sex chromosomes

The membrane that surrounds the cell

One of the alternate forms of a gene found at a given locus on a chromosome

A technique for the rapid production of millions of copies of a particular region of DNA

Proteins with a leader peptide are directed to this cellular organelle

Spring 2004 Final Exam Practice

18

Question 2
a)

5' AAACAGCUAUGG 3'

5'- ATGGCCTTCACACAGGAAACAGCTATGGCCATGAGCACGC
---------+---------+---------+---------+
3'- TACCGGAAGTGTGTCCTTTGTCGATACCGGTACTCGTGCG
CAGTCTCGGCATTATCCTATTAAAGGGAACTGAGGTGA -3'
---------+---------+---------+-------GTCAGAGCCGTAATAGGATAATTTCCCTTGACTCCACT -5'

b)
c) Consider each of the following three mutations independently.
i) The mutation is before the start codon so does not change the protein sequence.
ii) The start codon (at nucleotides 25 - 27) would be changed and protein synthesis would now
start at the next start codon (position 31 - 33). The protein would be shorter by two amino
acids.
iii) This frameshift mutation will result in the protein being terminated prematurely because a
new stop codon was created. As a result of this deletion, the new sequence of the peptide would
be : H3N+-methionine-alanine-COOd) Puromycin functions by entering the A site of the ribosome. Here, because puromycin is
structurally similar to the aminoacyl-tRNA, it can participate in formation of a peptide bond with the
nascent polypeptide chain. Puromycin causes peptide release from the ribosome because there is no tRNA anticodon to link the mRNA to the peptide chain.
Question 3
i) What are the two advantages of using a live-attenuated vaccine vs. a heat killed vaccine in this case?

Itll mimic the disease by invading cells, thus it will illicit both a humoral and cellular response.
Surface proteins will not be denatured by heat.
ii) What is a disadvantage of using a live-attenuated vaccine?
Could acquire virulence factors, Need a cold chain (expensive refrigeration), it may make people sick.
b) The rabbit protein is recognized as foreign (non-self) by the guinea pig.
c) B cells, by gene rearrangement of Ab genes (VDJ rearrangement). Also, T cells (by
rearrangement of T cell receptor genes).
d) Neither siblings nor identical twins will produce the same antibodies, because the DNA
rearrangement process that produces the antibody repertoire is a random event in each B cell.
Question 4
a)

i)

+/-

ii) 2/3. B is not affected, therefore must be either +/+ or +/-.

+
cf
+ +/+ +/cf
cf +/cf cf/cf
Spring 2004 Final Exam Practice

19

iii) Since both parents are carriers (+/cf), the probability of an affected child is 1/4.
iv) Again, both parents are carriers, the probability of having a child who is a carrier is 1/2.
b)

i) Since the signal sequence would be unaffected by the mutation, the protein could be found in
either the Golgi, the ER, or some membrane vesicle.
ii) Deletion or mutation of the signal sequence would create a protein which would not be
translated into the ER.

c)
i) Since gp19 prevents MHC I display, virus-infected cells which are expressing the wild-type disease
X gene would not be attacked by the cellular immune system.
ii)
1) Digest pBR-Ad2-7 with NheI and HindIII.
2) Digest pCMV-disease X with SpeI and HindIII. Isolate the CFTR cDNA fragment.
3) Ligate the products of steps 1 and 2.
4) Cut the resulting plasmid with BamHI to obtain a linear fragment with disease X gene at the PE1
promoter.
Question 5
treat the substrate with DTT (a compound that disrupts disulfide bonds) and test the enzyme E activity again.
This time the substrate is cleaved by enzyme E.
Why was enzyme E able to cleave the protein substrate only after the substrate was treated with DTT?
Enzyme X binds and cuts at specific sites. These site are not present on the exterior of the substrate when the
substrate is properly folded. When the disulfide bonds within the substrate protein are disrupted, the 3
dimensional shape is altered, and the protein unfolds. This allows enzyme X access to sites that were

previously protected within the substrate protein.

c) You conduct mutational studies of enzyme E. You examine the kinetics of the various mutants as compared to the normal enzyme. The
data from your experiments is shown below.

ii) Which mutant has the same affinity for the substrate as the normal enzyme?

mutant 2

iii) Which mutant has the same catalytic activity as the normal enzyme?

mutant 1
Question 5
b)
a)

b)

i) van der Waals

covalent

hydrogen bond

ionic

ii) van der Waals

covalent

hydrogen bond

ionic

iii) van der Waals

covalent

hydrogen bond

ionic

i) Arg and Lys are both positively charged, thus the ionic interaction with the phosphate group
is preserved. The side chains of both amino acids are also of similar size.
ii) Tyr is much larger than Asp. Although Tyr can form a hydrogen bond, GDP will no longer
fit into the binding pocket. The Tyr side chain is also much more hydrophobic than the Asp side
chain.

Spring 2004 Final Exam Practice

20

Question 6
a)

i) This would eliminate the disulfide bridge tethering the ligand-binding domain to the rest of the
protein. The receptor would be inactive.
ii) This would prevent the differentiation of the R7 cell type.

b) Leucine, alanine, isoleucine, valine, phenylalanine, glycine, tryptophan are all hydrophobic amino
acids. The hydrophobic effect causes these amino acids to cluster away from water and stay in the
interior of the plasma membrane.
d)
extracellular

intracellular

C
signal
sequence

e)

transmembrane
domain

i) Ras can activate several different proteins, each of which leads to a different signal
transduction cascade. Different cells express different genes, and the specific protein that a
given cell expresses will determine the outcome of Ras activation.
ii) You never see diferentiation of R7 cells.
A loss-of function mutation in the boss/sev receptor would prevent signaling through
Ras and activation of the differentiation pathway.

You see uncontrolled cell proliferation.

A gain-of function mutation in the EGF receptor such that it signals to Ras in the
absence of growth factor would allow uncontrolled cell division.
Question 7
a) An autosome, because individual 6, a male, has 2 alleles.
b) The mutant phenotype is recessive, because individuals 5 and 6 each have one copy of the mutant
allele, m, and are both phenotypically normal.
c) 1/4. Since individuals 3 and 4 already have an affected child, then they must both be heterozygotes.
d)
5...GCCAGCTG...3
e) A mutation occurred which led to the production of a new mutant allele, m*. This mutant allele has a
recessive phenotype and its PCR product is cut by neither NheI nor PvuII. Individual 9 has the
genotype m/m*.
Question 8

Below are two possible explanations for these results.

a) Possibility 1: Beard color is controlled by a single locus. Give the genotypes in the blanks below.

ByB y

Yellow beards

BbB b
Blue beards

ByB b
Green beards
b) Possibility 2: Beard color is controlled by a pathway of two distinct enzymes encoded by
the A and Q genes.
Spring 2004 Final Exam Practice

21

i) Give one genotype in each of the blanks below. Use A and Q to designate the
designate the loss-of-function alleles.
AAqq

A)

wild-

type alleles. Use a and q to

aaQQ

Yellow beards

Blue beards

AaQq
Green beards

AAqq

aaQQ

B)

Yellow beards

Blue beards

AaQq
Green beards
ii) Given your answer to i) above, draw the pathway for beard color. Be sure to include at which step each of the genes functions.

gene or enzyme A

gene or enzyme Q

If A)

blue --------------> yellow--------------> green

If B)
Question 9

blue --------------> yellow--------------> green

gene or enzyme Q

gene or enzyme A

a) Autosomal Recessive
b)

individual

genotype

gg

Gg

Gg

Gg

10

GG or Gg

c)
genotypes:
hh++

hh--

hh+-

HH++

HH--

HH+-

Hh++

Hh--

Hh+-

Spring 2004 Final Exam Practice

22

Question 10
The following is a plot of an action potential measured at a single spot along an axon. Four
points are highlighted along the curve, , , , .
+50

Membrane
Potential
(mV)

-70

Time

a) On the table below, identify which ion (Na+, K+, Ca++, Cl-) is undergoing the greatest net
flow across the membrane at the points indicated and state the direction that the ion is moving
(into the cell or out of the cell).
Point

Ion

Direction (in/out)
+

Na
K+

in
out

b) The membrane potential is -70 mV at points and , on the plot above. Which of the
voltage-gated ion channels is closed at point , but open at point ?
voltage-gated K+ channel
c) What dictates the closing of the voltage-gated channel that is open at point ?
TIME
d) There are at least three states in which the voltage-dependent Na+ channel exists.
At on the above plot, the majority of voltage-dependent Na+ channels would be in which
state? Circle the best answer.

Open

Closed

Inactivated

e) Circle the one correct statement below.

Spring 2004 Final Exam Practice

23

If stimulated equally, neuron 1 is more likely to result in an action potential in cell W

than neuron 2.

If stimulated equally, neuron 2 is more likely to result in an action potential in cell W

than neuron 1.

If stimulated equally, neuron 1 and neuron 2 are equally as likely to result in an action
potential in cell W.

f) If you were exposed to a toxin that irreversibly blocked voltage-gated Ca+ + channels, indicate whether the
following statements would be TRUE or FALSE.

T
T

Secretory vesicles filled with neurotransmitters would stay in the nerve.

Your muscles would end up in a rigid contraction.

Secretory vesicles filled with neurotransmitters would fuse with the plasma membrane.

Question 11
a) The m1 and m4 mutations are in the same gene. This is a complementation test. The diploid strain
has the same growth phenotype as the haploid single mutants; the two mutations fail to complement (fail
to produce the wild-type phenotype) in the double heterozygote. The m1 and m4 mutations must both
inactivate the same gene (which codes for an enzyme essential for serine biosynthesis) so that the diploid
double mutant has two mutant alleles of the same gene.
b)
c)

m1, m4

m3

m2

serine

i) This haploid mutant will grow on media supplemented with intermediate A.

ii) Intermediate C will accumulate when this haploid mutant is grown on minimal medium.

UUU
UUC
UUA
UUG
CUU
CUC
CUA
CUG
AUU
AUC
AUA
AUG
GUU
GUC
GUA
GUG

U
phe
phe
leu
leu
leu
leu
leu
leu
ile
ile
ile
met
val
val
val
val

(F)
(F)
(L)
(L)
(L)
(L)
(L)
(L)
(I)
(I)
(I)
(M)
(V)
(V)
(V)
(V)

Spring 2004 Final Exam Practice

UCU
UCC
UCA
UCG
CCU
CCC
CCA
CCG
ACU
ACC
ACA
ACG
GCU
GCC
GCA
GCG

C
ser
ser
ser
ser
pro
pro
pro
pro
thr
thr
thr
thr
ala
ala
ala
ala

(S)
(S)
(S)
(S)
(P)
(P)
(P)
(P)
(T)
(T)
(T)
(T)
(A)
(A)
(A)
(A)

UAU
UAC
UAA
UAG
CAU
CAC
CAA
CAG
AAU
AAC
AAA
AAG
GAU
GAC
GAA
GAG

A
tyr (Y)
tyr (Y)
STOP
STOP
his (H)
his (H)
gln (Q)
gln (Q)
asn (N)
asn (N)
lys (K)
lys (K)
asp (D)
asp (D)
glu (E)
glu (E)

UGU
UGC
UGA
UGG
CGU
CGC
CGA
CGG
AGU
AGC
AGA
AGG
GGU
GGC
GGA
GGG

G
cys (C)
cys (C)
STOP
trp (W)
arg (R)
arg (R)
arg (R)
arg (R)
ser (S)
ser (S)
arg (R)
arg (R)
gly (G)
gly (G)
gly (G)
gly (G)

U
C
A
G
U
C
A
G
U
C
A
G
U
C
A
G

24

STRUCTURES OF AMINO ACIDS at pH 7.0

O

O
H

NH3
+

C CH2CH2CH2 N

C
H

NH3
+

C
H

C CH2
NH3
+

H
H

O-

C CH2CH2

C C CH2CH3

CH3

NH3
+

METHIONINE
(met)
O-

C C CH3
NH3 OH
+

THREONINE
(thr)

C CH2

C CH3

C CH2

NH3+

O-

O
C

H C CH2
CH2
H
N
CH
2
H +

C CH2

OH

NH3
+

SERINE
(ser)

PROLINE
(pro)

H
H

NH3
+

Spring 2004 Final Exam Practice

OC

C CH2CH2CH2CH2

LYSINE
(lys)

O
H

NH3
+

CH3

TRYPTOPHAN
(trp)

LEUCINE
(leu)

GLYCINE
(gly)

PHENYLALANINE
(phe)
O

O
OC H

C CH2
NH3
+

C H
NH3
+

C
S

H
NH2

NH3
+

O-

ISOLEUCINE
(ile)

HISTIDINE
(his)
O

O
C H

O
C

C CH2CH2

O-

ASPARTIC ACID
(asp)

GLUTAMINE
(gln)

NH3 CH3
+

NH3
+

NH3
+

GLUTAMIC ACID
(glu)
H

NH2

C
H

O-

NH3
+

CYSTEINE
(cys)
O

C CH2 C

O-

C CH2CH2

ASPARAGINE
(asn)

C CH2 SH

NH3
+

O-

C CH2 C

NH2
+

ARGININE
(arg)

NH2

O-

NH3
+

ALANINE
(ala)

C CH3

C
H

C CH2

OH

NH3
+
H

TYROSINE
(tyr)

C C
NH3 H
+

CH3
CH3

VALINE
(val)

25

List of terms for Question 1.

You may detach this page from the exam.
A.
B.
C.
D.
E.
F.
G.
H.
J.
K.
L.
M.
N.
O.
P.
Q.
R.
S.
T.
U.
W.
X.
Y.
Z.
AA.
BB.
CC.
DD.
EE.
FF.
GG.
HH.

allele
amino acids
autosomal gene
carbohydrate
cDNA
competitive inhibitor
diploid
endoplasmic reticulum
eukaryote
G protein
genotype
haploid
heterozygote
homozygote
KM
mitochondria
non-competitive inhibitor
nucleotides
DNA ligase
phenotype
phospholipids
plasma membrane
plasmid
polymerase chain reaction
primer
prokaryote
DNA polymerase
replication
repressor protein
sex-linked gene
transcription
translation

Spring 2004 Final Exam Practice

26