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137 terms

Exam 2

Describe the main purpose of the combined processes of glycolysis and cellular respiration
transforming the energy in glucose and related molecules in a chemical form that cells can use for work
In the combined processes of glycolysis and cellular respiration, what is consumed and what is produced?
Glucose is consumed, and carbon dioxide is produced.
The molecule that functions as the reducing agent (electron donor) in a redox or oxidation-reduction reaction
loses electrons and loses potential energy.
When a molecule of NAD+ (nicotinamide adenine dinucleotide) gains a hydrogen atom (not a proton), the molecule becomes
The ATP made during glycolysis is generated by
substrate-level phosphorylation
The oxygen consumed during cellular respiration is involved directly in which process or event?
accepting electrons at the end of the electron transport chain
Why are carbohydrates and fats considered high energy foods?
They have a lot of electrons associated with hydrogen.
Which process in eukaryotic cells will proceed normally whether oxygen () is present or absent?
Among the products of glycolysis, which compounds contain energy that can be used by other biological reactions?
pyruvate, ATP, and NADH
In addition to ATP, what are the end products of glycolysis?
NADH and pyruvate
In glycolysis, for each molecule of glucose oxidized to pyruvate
two molecules of ATP are used and four molecules of ATP are produced.
What enters the citric acid cycle?
acetyl CoA
In the citric acid cycle, ATP molecules are produced by _____.
substrate-level phosphorylation
Which of these is NOT a product of the citric acid cycle?
acetyl CoA
A glucose molecule is completely broken down to carbon dioxide and water in glycolysis and the citric acid cycle, but together these two processes yield only a few molecules of ATP. What happened to most of the energy that the cell obtains from the oxidation of glucose?
It is stored in NADH and FADH2
During cellular respiration, acetyl CoA accumulates in which location?
mitochondrial matrix
Carbon dioxide is released during which of the following stages of cellular respiration?
oxidation of pyruvate to acetyl CoA and the citric acid cycle
During aerobic respiration, electrons travel downhill in which sequence?
food → NADH → electron transport chain → oxygen
Starting with one molecule of isocitrate and ending with fumarate, how many ATP molecules can be made through substrate-level phosphorylation (see the figure)?
Carbon skeletons for amino acid biosynthesis are supplied by intermediates of the citric acid cycle. Which intermediate would supply the carbon skeleton for synthesis of a five-carbon amino acid (see the figure)?
For each mole of glucose oxidized by cellular respiration, how many moles of carbon dioxide are released in the citric acid cycle
In the presence of oxygen, the three-carbon compound pyruvate can be catabolized in the citric acid cycle. First, however, the pyruvate (1) loses a carbon, which is given off as a molecule of CO2, (2) is oxidized to form a two-carbon compound called acetate, and (3) is bonded to coenzyme A.
These three steps result in the formation of
acetyl CoA, NADH,H+ , and CO2.
For each glucose that enters glycolysis, _____ acetyl CoA enter the citric acid cycle.
For each glucose that enters glycolysis, _____ NADH + H+ are produced by the citric acid cycle.
In cellular respiration, most ATP molecules are produced by _____.
oxidative phosphorylation
The final electron acceptor of cellular respiration is _____.
During electron transport, energy from _____ is used to pump hydrogen ions into the _____.
NADH and FADH2 ... intermembrane space
The proximate (immediate) source of energy for oxidative phosphorylation is _____.
kinetic energy that is released as hydrogen ions diffuse down their concentration gradient
The electrons stripped from glucose in cellular respiration end up in which compound?
Which one of the following statements about the redox reactions of the electron transport chain is correct?
The redox reactions of the electron transport chain are directly coupled to the movement of protons across a membrane.
The primary role of oxygen in cellular respiration is to
act as an acceptor for electrons and hydrogen, forming water.
When hydrogen ions are pumped from the mitochondrial matrix across the inner membrane and into the intermembrane space, the result is the
creation of a proton-motive force.
It is possible to prepare vesicles from portions of the inner mitochondrial membrane. Which one of the following processes might still be carried on by this isolated inner membrane?
oxidative phosphorylation
Exposing inner mitochondrial membranes to ultrasonic vibrations will disrupt the membranes. However, the fragments will reseal "inside out." The little vesicles that result can still transfer electrons from NADH to oxygen and synthesize ATP.These inside-out membrane vesicles
will become acidic inside the vesicles when NADH is added.
In the absence of oxygen, yeast cells can obtain energy by fermentation, resulting in the production of
ATP, CO2, and ethanol (ethyl alcohol).
A mutation in yeast makes it unable to convert pyruvate to ethanol. How will this mutation affect these yeast cells?
The mutant yeast will be unable to grow anaerobically.
Which of these equations best summarizes photosynthesis?
6 CO2 + 6 H2O → C6H12O6 + 6 O2
Where does the Calvin cycle occur?
The light reactions of photosynthesis use _____ and produce _____.
When oxygen is released as a result of photosynthesis, it is a direct by-product of
splitting water molecules.
An action spectrum plots the rate of photosynthesis at various wavelengths of visible light, and it shows that blue light with a wavelength of about 490 nm is effective in driving photosynthesis. Based on this information and the absorption spectra shown at left, what role may chlorophyll b and carotenoids play in photosynthesis?
These pigments are able to absorb more wavelengths of light (and thus more energy) than chlorophyll a alone can absorb. As part of light-harvesting complexes in photosystems, they broaden the range of light that can be used in the light reactions.
Assume a thylakoid is somehow punctured so that the interior of the thylakoid is no longer separated from the stroma. This damage will have the most direct effect on which of the following processes?
the synthesis of ATP
P680+ is said to be the strongest biological oxidizing agent. Given its function, why is this necessary?
It obtains electrons from the oxygen atom in a water molecule, so it must have a stronger attraction for electrons than oxygen has.
In thylakoids, protons travel through ATP synthase from the thylakoid space to the stroma. Therefore, the catalytic "knobs" of ATP synthase would be located
on the stromal side of the membrane.
Halobacterium has a photosynthetic membrane that appears purple. Its photosynthetic action spectrum is the inverse of the action spectrum for green plants. (That is, the Halobacterium action spectrum has a peak where the green plant action spectrum has a trough.) What wavelengths of light do the Halobacterium photosynthetic pigments absorb?
green and yellow
Carbon fixation involves the addition of carbon dioxide to _____.
After 3-PGA is phosphorylated, it is reduced by _____.
How many carbon dioxide molecules must be added to RuBP to make a single molecule of glucose?
In the Calvin cycle, how many ATP molecules are required to regenerate RuBP from five G3P molecules?
Where do the enzymatic reactions of the Calvin cycle take place?
stroma of the chloroplast
What is the primary function of the Calvin cycle?
synthesize simple sugars from carbon dioxide
In the process of carbon fixation, RuBP attaches a CO2 to produce a six-carbon molecule, which is then split to produce two molecules of 3-phosphoglycerate. After phosphorylation and reduction produces glyceraldehyde 3-phosphate (G3P), what more needs to happen to complete the Calvin cycle?
regeneration of RuBP
The phylogenetic distribution of the enzyme rubisco is limited to
all known photoautotrophs, both bacterial and eukaryotic.
C4 plants occur more commonly in desert conditions because _____.
they can fix carbon at the lower CO2 concentrations that develop when the stomata are closed
Why are C4 plants able to photosynthesize with no apparent photorespiration?
They use PEP carboxylase to initially fix CO2.
What would be the expected effect on plants if the atmospheric CO2 concentration was doubled?
C3 plants will have faster growth; C4 plants will be minimally affected.
When a glucose molecule loses a hydrogen atom as the result of an oxidation-reduction reaction, the molecule becomes
During glycolysis, when each molecule of glucose is catabolized to two molecules of pyruvate, most of the potential energy contained in glucose is
retained in the two pyruvates.
A young animal has never had much energy. He is brought to a veterinarian for help and is sent to the animal hospital for some tests. There they discover his mitochondria can use only fatty acids and amino acids for respiration, and his cells produce more lactate than normal. Of the following, which is the best explanation of his condition?
His mitochondria lack the transport protein that moves pyruvate across the outer mitochondrial membrane.
Inside an active mitochondrion, most electrons follow which pathway?
citric acid cycle → NADH → electron transport chain → oxygen
Which of the following is a product of the light reactions of photosynthesis?
oxygen, ATP, and NADPH
Photosynthesis is a redox reaction. This means that H2O is _____ during the light reactions and CO2 is _____ during the Calvin cycle.
Which statement describes the functioning of photosystem II?
The electron vacancies in P680+ are filled by electrons derived from water.
Which of the following statements best describes the relationship between photosynthesis and respiration?
Photosynthesis stores energy in complex organic molecules, whereas respiration releases it.
Proteins that end up in the plasma membrane are
by ribosomes on the rough ER
Water will enter a cell by osmosis if:
dissolved substances are more concentrated inside the cell than
outside the cell.
.Which ofthe following isin the correct order with respect
to the ability ofthe listed moleculesto crossthe cell membrane?
Most permeable<----------> Least permeable
water glycerol amino acids sodium ions
TheNa/K Pump
indirectly providesthe energy forthe uptake of moleculeslike
sugars and amino acidsinto animal cells
The second Law of Thermodynamics states that:
energy spontaneously moves from a more organized state to a less
organized state.
Which of the following statements about catabolic
pathways is true?
They are exergonic reactions that break complex molecules into
simpler ones.
If a chemical reaction has a negative deltaG it:
is spontaneous
The hydrolysis of ATP to ADP + PO4
is spontaneous and releases energy, is used by cells to drive forward chemical reactions that have a positive deltaG, is exergonic.
The active site of an enzyme:
can bind competitive inhibitors as well as the enzyme's substrate.
A cell that contains 0.4M sucrose and 0.4M glucose is
placed in a solution of 0.1M sucrose + 0.1M glucose. If the cell membrane is impermeable to sucrose but is highly permeable to water and glucose what will happen?
glucose will diffuse out of the cell and water will diffuse in, the
cell will swell
A compound that binds to an enzyme, at a site other than
the enzyme's active site, and inhibits the enzyme's activity is called
an allosteric inhibitor
Which of the following choices correctly matches a tool and its proper application?
cell fractionation to study the function of specific organelles
When biologists wish to study the internal ultrastructure of cells, they can achieve the finest resolution by using
a transmission electronic microscope.
A biologist wants specifically to examine the surfaces of different types of cells in kidney tubules of small mammals. The cells in question can be distinguished by external shape, size, and 3-D characteristics. Which of the following would be the optimum method for her study?
scanning electron microscopy
_____ are surface appendages that allow a bacterium to stick to a surface.
What is the function of a bacterium's capsule?
Where is a bacterial cell's DNA found?
nucleoid region
In a bacterium, where are proteins synthesized?
What name is given to the rigid structure, found outside the plasma membrane, that surrounds and supports the bacterial cell?
cell wall
The _____ is the bacterial structure that acts as a selective barrier, allowing nutrients to enter the cell and wastes to leave the cell.
plasma membrane
Which of the following clues would tell you if a cell is prokaryotic or eukaryotic?
whether or not the cell is partitioned by internal membranes
If radioactive deoxythymidine triphosphate (dTTP) is added to a culture of rapidly growing bacterial cells, where in the cell would you expect to find the greatest concentration of radioactivity?
ECM proteins are made by ribosomes in which part of a eukaryotic cell?
rough ER
Beginning within the nucleus, the first step leading to the synthesis of a polypeptide is _____.
transferring of information from DNA to messenger RNA
All of the following are part of a prokaryotic cell except
an endoplasmic reticulum.
A cell with a predominance of free ribosomes is most likely
producing primarily cytoplasmic proteins.
Which organelle plays a role in intracellular digestion?
Which one of the following statements about the endomembrane system is correct?
Proteins that will be secreted from the cell are likely to be found in closed spaces bounded by membranes of the endomembrane system.
A cell has formed a food vacuole as it ingested a food particle. Which of the following events is associated with the breakdown of that food particle?
Digestion of the food particle occurs in a vesicle enclosed by a membrane that separates the digestion from the cytoplasm.
Which type of organelle or structure is primarily involved in the synthesis of oils, phospholipids, and steroids?
smooth endoplasmic reticulum
Which structure is the site of the synthesis of proteins that may be exported from the cell?
rough ER
Hydrolytic enzymes must be segregated and packaged to prevent general destruction of cellular components. Which of the following organelles contains these hydrolytic enzymes in animal cells?
Mitochondria are found in _____.
plant and animal cells
Which organelle is the primary site of ATP synthesis in eukaryotic cells?
Why isn't the mitochondrion classified as part of the endomembrane system?
Its structure is not derived from the ER or Golgi.
A biologist ground up some plant leaf cells and then centrifuged the mixture to fractionate the organelles. Organelles in one of the heavier fractions could produce ATP in the light, whereas organelles in the lighter fraction could produce ATP in the dark. The heavier and lighter fractions are most likely to contain, respectively,
chloroplasts and mitochondria.
All of the following serve an important role in determining or maintaining the structure of plant cells. Which of the following are distinct from the others in their composition?
plant cell walls
What is the most likely pathway taken by a newly synthesized protein that will be secreted by a cell?
ER--> Golgi--> vesicles that fuse with plasma membrane
Describe the structure of a biological membrane.
two layers of phospholipids with proteins either crossing the layers or on the surface of the layers
What is one of the ways that the membranes of winter wheat are able to remain fluid when it is extremely cold?
by increasing the percentage of unsaturated phospholipids in the membrane
The permeability of a biological membrane to a specific polar solute may depend on_________
the types of transport proteins in the membrane
What kinds of molecules pass through a cell membrane most easily?
small and hydrophobic
What would likely move through the lipid bilayer of a plasma membrane most rapidly?
Water passes quickly through cell membranes because
it moves through aquaporins in the membrane.
Celery stalks that are immersed in fresh water for several hours become stiff and hard. Similar stalks left in a 0.15 M salt solution become limp and soft. From this we can deduce that
the fresh water is hypotonic and the salt solution is hypertonic to the cells of the celery stalks.
Correctly describe the normal tonicity conditions for typical plant and animal cells?
The animal cell is in an isotonic solution, and the plant cell is in a hypotonic solution.
If the concentration of phosphate in the cytosol is 2.0 mM and the concentration of phosphate in the surrounding fluid is 0.1 mM, how could the cell increase the concentration of phosphate in the cytosol?
active transport
The movement of glucose into a cell against a concentration gradient is most likely to be accomplished by which of the following?
cotransport of the glucose with a proton or sodium ion that was pumped across the membrane using the energy of ATP hydrolysis
Active and passive transport of solutes across a membrane typically differ in which of the following ways?
Active transport always involves the utilization of cellular energy, whereas passive transport does not require cellular energy.
The movement of potassium into an animal cell requires
an energy source such as ATP.
Ions diffuse across membranes through specific ion channels
down their electrochemical gradients.
A bacterium engulfed by a white blood cell through phagocytosis will be digested by enzymes contained in
What membrane activities requires energy from ATP hydrolysis?
movement of Na+ ions from a lower concentration in a mammalian cell to a higher concentration in the extracellular fluid
The difference between pinocytosis and receptor-mediated endocytosis is that
pinocytosis is nonselective in the molecules it brings into the cell, whereas receptor-mediated endocytosis offers more selectivity.
The process of cellular respiration, which converts simple sugars such as glucose into CO2 and water, is an example of _____.
a catabolic pathway
the covalent bonds of a sugar molecule have what type of energy?
potential energy
Which of the following is (are) true for anabolic pathways?
They consume energy to build up polymers from monomers.
Which of the following is a statement of the first law of thermodynamics?
Energy cannot be created or destroyed.
Which of the following statements is a logical consequence of the second law of thermodynamics?
Every chemical reaction must increase the total entropy of the universe.
Which of the following is an example of potential rather than kinetic energy?
a molecule of glucose
What is true for all exergonic reactions?
The reaction proceeds with a net release of free energy.
A chemical reaction that has a positive ΔG is best described as
Which part of the adenosine triphosphate molecule is released when it is hydrolyzed to provide energy for biological reactions?
the terminal phosphate
What type of reaction breaks the bonds that join the phosphate groups in an ATP molecule?
When chemical, transport, or mechanical work is done by an organism, what happens to the heat generated?
It is lost to the environment.
The binding of a compound to an enzyme is observed to slow down or stop the rate of the reaction catalyzed by the enzyme. Increasing the substrate concentration reduces the inhibitory effects of this compound. Which of the following could account for this observation?
The compound is a competitive inhibitor.
Which of the following statements is true about enzyme-catalyzed reactions?
The reaction is faster than the same reaction in the absence of the enzyme.
Reactants capable of interacting to form products in a chemical reaction must first overcome a thermodynamic barrier known as the reaction's
activation energy.
The active site of an enzyme is the region that
is involved in the catalytic reaction of the enzyme.
How does a noncompetitive inhibitor decrease the rate of an enzyme reaction?
by changing the shape of the enzyme's active site
Succinate dehydrogenase catalyzes the conversion of succinate to fumarate. The reaction is inhibited by malonic acid, which resembles succinate but cannot be acted upon by succinate dehydrogenase. Increasing the ratio of succinate to malonic acid reduces the inhibitory effect of malonic acid. Based on this info, which of the following is correct?
Succinate is the substrate, and fumarate is the product.
Protein kinases are enzymes that catalyze phosphorylation of target proteins at specific sites, whereas protein phosphatases catalyze removal of phosphate(s) from phosphorylated proteins. Phosphorylation and dephosphorylation can function as an on-off switch for a protein's activity, most likely through
the change in a protein's charge leading to a conformational change.
A series of enzymes catalyze the reaction X → Y → Z → A. Product A binds to the enzyme that converts X to Y at a position remote from its active site. This binding decreases the activity of the enzyme.

With respect to the enzyme that converts X to Y, substance A functions as
an allosteric inhibitor