BISC 110 Exam 2 Review Questions
with Verified Answers
In what type of cells and what phase do holliday junctions occur? - ANSWERSGerm
cells; prophase
Why is sexual reproduction more beneficial to a species living in an unpredictable
environment than to one living in a constant environment? - ANSWERSThe real benefit
in sexual reproduction seems to be that parents produce children that are genetically
unlike either parent and that are not genetically identical to each other. This provides
more variation in the population than asexual reproduction could provide, and is an
advantage if the environment is variable, since any one combination of the parents'
characteristics, however well adapted to the prevailing conditions, may or may not be
the best in a new situation.
The diploid human genome comprises 6.4 x 109 bp, and fits into a nucleus that is 6 μm
in diameter.
a. If base pairs occur at intervals of 0.34 nm along the DNA helix, what is the length of
DNA in a human cell?
b. If the diameter of the DNA helix is 2.4 nm, what fraction of the volume of the nucleus
is occupied by DNA? Remember that the volume of a sphere is (4/3)πr3 and the volume
of a cylinder is πr2h. - ANSWERSa) The DNA in a human cell is about 2.2 meters in
length: 6.4 x 109 bp x 0.34 nm/bp x 1 m/109 nm = 2.18 m
b) DNA occupies about 9% of the volume of the nucleus. The volume of the nucleus is:
(4/3)(3.14)(3x103 nm)3 = 1.13 x 1011 nm3 The volume of DNA is: (3.14)(1.2
nm)2(2.2x109 nm) = 9.95 x 109 nm3 The ratio of DNA volume to nuclear volume is:
(9.95 x 109 nm3)/(1.13 x 1011 nm3) ≈ 0.09
The mechanism of DNA replication gives rise to the "end-replication problem" for linear
chromosomes. Over time, tis problem leads to loss of DNA from the ends of
chromosomes. In human germ cells, loss of nucleotides during replication is balanced
by addition of nucleotides by telomerase. However, in human somatic cells, telomerase
is turned off early in development, so that chromosomes become shorter with increasing
rounds of replication. Consider one round of replication in a human somatic cell.
Describes the status of the two daughter chromosomes relative to the parent
chromosome. - ANSWERSE. The two daughter chromosomes will be shorter at
opposite ends. This outcome is illustrated in the figure below, which, for simplicity's
sake, shows replication from a single origin to the ends of the chromosome (multiple
origins do not affect the outcome). The leading strand can continue all the way to the
end of the chromosome, but the lagging strand cannot. The very last RNA primer
cannot be replaced by DNA because there is no upstream primer for the DNA
polymerase to extend.
, What would happen to a cell if, due to a genetic mutation, its chromosomes completely
lacked telomeres? Please be as specific as possible in stating your prediction (e.g. "The
cell would die immediately," etc.) and briefly justify your prediction. - ANSWERSIf a cell
completely lacked telomeres, that cell would experience no adverse effects during its
lifetime. However, when the cell attempted to replicate its genome prior to cell division, it
would almost certainly lose some DNA from the two ends of each of its chromosomes.
Because the resulting daughter cells will not have a complete genome, they are likely to
be somewhat impaired in their normal cellular functions. This impairment will
presumably get progressively worse with each subsequent cell division, eventually
leading to a cell that dies due either to the loss of an essential gene or to the loss of
several important (but non-essential) genes.
Chemical reactions that lead to a release of free energy are referred to as "energetically
favorable." Another common way in which these reactions are described is
_____________.
a) uphill
b) uncatalyzed
c) spontaneous
d) activated - ANSWERSc. spontaneous
Which one of the following is true for all exergonic reactions?
a) The products have more total energy than the reactants.
b) The reaction proceeds with a net release of free energy.
c) The reaction goes only in a forward direction: all reactants will be converted to
products, but no products will be converted to reactants.
d) A net input of energy from the surroundings is required for the reactions to proceed.
e) The reactions are rapid. - ANSWERSb. The reaction proceeds with a net release of
free energy
A chemical reaction that has a positive delta G is correctly described as - ANSWERSa)
endergonic
The figure on the right is an energy diagram for the reaction X→Y. Which equation
below provides the correct calculation for the amount of free-energy change when X is
converted to Y?
(a and X medium; b high; c and Y low) - ANSWERSd) c- a
Provide the name for a term that satisfies the following descriptions.
i. Extra energy that must be possessed by atoms or molecules in addition to their initial
energy in order to undergo a particular chemical reaction.
ii. Protein that catalyzes a specific chemical reaction.
iii. The energy that can be extracted from a system to drive reactions. - ANSWERSi.
activation energy
ii. enzyme
iii. Gibbs free energy
with Verified Answers
In what type of cells and what phase do holliday junctions occur? - ANSWERSGerm
cells; prophase
Why is sexual reproduction more beneficial to a species living in an unpredictable
environment than to one living in a constant environment? - ANSWERSThe real benefit
in sexual reproduction seems to be that parents produce children that are genetically
unlike either parent and that are not genetically identical to each other. This provides
more variation in the population than asexual reproduction could provide, and is an
advantage if the environment is variable, since any one combination of the parents'
characteristics, however well adapted to the prevailing conditions, may or may not be
the best in a new situation.
The diploid human genome comprises 6.4 x 109 bp, and fits into a nucleus that is 6 μm
in diameter.
a. If base pairs occur at intervals of 0.34 nm along the DNA helix, what is the length of
DNA in a human cell?
b. If the diameter of the DNA helix is 2.4 nm, what fraction of the volume of the nucleus
is occupied by DNA? Remember that the volume of a sphere is (4/3)πr3 and the volume
of a cylinder is πr2h. - ANSWERSa) The DNA in a human cell is about 2.2 meters in
length: 6.4 x 109 bp x 0.34 nm/bp x 1 m/109 nm = 2.18 m
b) DNA occupies about 9% of the volume of the nucleus. The volume of the nucleus is:
(4/3)(3.14)(3x103 nm)3 = 1.13 x 1011 nm3 The volume of DNA is: (3.14)(1.2
nm)2(2.2x109 nm) = 9.95 x 109 nm3 The ratio of DNA volume to nuclear volume is:
(9.95 x 109 nm3)/(1.13 x 1011 nm3) ≈ 0.09
The mechanism of DNA replication gives rise to the "end-replication problem" for linear
chromosomes. Over time, tis problem leads to loss of DNA from the ends of
chromosomes. In human germ cells, loss of nucleotides during replication is balanced
by addition of nucleotides by telomerase. However, in human somatic cells, telomerase
is turned off early in development, so that chromosomes become shorter with increasing
rounds of replication. Consider one round of replication in a human somatic cell.
Describes the status of the two daughter chromosomes relative to the parent
chromosome. - ANSWERSE. The two daughter chromosomes will be shorter at
opposite ends. This outcome is illustrated in the figure below, which, for simplicity's
sake, shows replication from a single origin to the ends of the chromosome (multiple
origins do not affect the outcome). The leading strand can continue all the way to the
end of the chromosome, but the lagging strand cannot. The very last RNA primer
cannot be replaced by DNA because there is no upstream primer for the DNA
polymerase to extend.
, What would happen to a cell if, due to a genetic mutation, its chromosomes completely
lacked telomeres? Please be as specific as possible in stating your prediction (e.g. "The
cell would die immediately," etc.) and briefly justify your prediction. - ANSWERSIf a cell
completely lacked telomeres, that cell would experience no adverse effects during its
lifetime. However, when the cell attempted to replicate its genome prior to cell division, it
would almost certainly lose some DNA from the two ends of each of its chromosomes.
Because the resulting daughter cells will not have a complete genome, they are likely to
be somewhat impaired in their normal cellular functions. This impairment will
presumably get progressively worse with each subsequent cell division, eventually
leading to a cell that dies due either to the loss of an essential gene or to the loss of
several important (but non-essential) genes.
Chemical reactions that lead to a release of free energy are referred to as "energetically
favorable." Another common way in which these reactions are described is
_____________.
a) uphill
b) uncatalyzed
c) spontaneous
d) activated - ANSWERSc. spontaneous
Which one of the following is true for all exergonic reactions?
a) The products have more total energy than the reactants.
b) The reaction proceeds with a net release of free energy.
c) The reaction goes only in a forward direction: all reactants will be converted to
products, but no products will be converted to reactants.
d) A net input of energy from the surroundings is required for the reactions to proceed.
e) The reactions are rapid. - ANSWERSb. The reaction proceeds with a net release of
free energy
A chemical reaction that has a positive delta G is correctly described as - ANSWERSa)
endergonic
The figure on the right is an energy diagram for the reaction X→Y. Which equation
below provides the correct calculation for the amount of free-energy change when X is
converted to Y?
(a and X medium; b high; c and Y low) - ANSWERSd) c- a
Provide the name for a term that satisfies the following descriptions.
i. Extra energy that must be possessed by atoms or molecules in addition to their initial
energy in order to undergo a particular chemical reaction.
ii. Protein that catalyzes a specific chemical reaction.
iii. The energy that can be extracted from a system to drive reactions. - ANSWERSi.
activation energy
ii. enzyme
iii. Gibbs free energy
