Biochemistry Final Review Questions
The citric acid cycle is a stage of catabolism that oxidizes acetate into carbon dioxide and generates energy. There are eight enzymes involved in the citric acid cycle. Which enzymes produce NADH as a product? Select all that apply. (1) Which enzymes produce carbon dioxide as a product? Select all that apply. (2) Which enzymes produce coenzyme A as a product? Select all that apply. (3) Which enzymes have an α‑keto acid substrate? Select all that apply. (4) Which enzyme catalyzes a Claisen condensation?
(1) *α-ketoglutarate dehydrogenase *malate dehydrogenase *isocitrate dehydrogenase (2) *α-ketoglutarate dehydrogenase *isocitrate dehydrogenase (3) *citrate synthase *succinyl-CoA synthetase (4) *citrate synthase * α-ketoglutarate dehydrogenase Citrate synthase
In the presence of saturating amounts of oxaloacetate, the activity of citrate synthase from pig heart tissue shows a sigmoid dependence on the concentration of acetyl‑CoA. When succinyl‑CoA is added, the curve shifts to the right and the sigmoid dependence is more pronounced. Choose the statements that are reasonable explanations for the right‑ward shift of the velocity curve caused by succinyl-CoA.
* Succinyl‑CoA binds at a regulatory site other than the active site. * Succinyl‑CoA competes with acetyl‑CoA for binding at the active site.
Hexokinase catalyzes the first step of glycolysis, in which glucose is phosphorylated to form glucose‑6‑phosphate. Which of these statements are accurate?
- Hexokinase is a type of transferase that catalyzes the transfer of a phosphoryl group from ATP to a hexose. - Hexokinase consists of two domains, or lobes, that come together when glucose and the - The conformational shift that occurs when glucose, but not water, enters the active site prevents water from hydrolyzing ATP.
Select the true statements about the citric acid cycle.
- In the citric acid cycle, acetyl-CoA is degraded to produce NADHNADH and FADH2FADH2. - NADH, GTP, FADH2, and coenzyme. A molecules are produced by the citric acid cycle. - The citric acid cycle is an aerobic process.
Identify all statements that accurately describe the structure of the pyruvate dehydrogenase (PDH)(PDH) complex.
- Several copies each of E1E1 and E3E3 surround E2E2 . - The complex contains multiple copies of each of three enzymes. - E2 contains three domains. - A regulatory kinase and phosphatase are part of the mammalian PDHPDH complex.
1. Consider the given interconversion, which occurs in glycolysis. fructose 6-phosphate↽−−⇀glucose 6-phosphatefructose 6-phosphate↽−−⇀glucose 6-phosphate 𝐾′eq=1.97Keq′=1.97 What is Δ𝐺′∘ΔG′∘ for the reaction (𝐾′eqKeq′ measured at 25 °C)? 2. If the concentration of fructose 6‑phosphate is adjusted to 1.6 M1.6 M and that of glucose 6‑phosphate is adjusted to 0.50 M,0.50 M, what is Δ𝐺? 3. Which statements are consistent with the conditions at which Δ𝐺′∘ΔG′∘ is measured? CH 13 Q 11
1. Δ𝐺′∘=−𝑅𝑇ln(𝐾′eq)ΔG′∘=−RTln(Keq′) Δ𝐺′∘=−(8.315×10−3 kJ/mol⋅K)(298 K)ln(1.97)ΔG′∘=−(8.315×10−3 kJ/mol⋅K)(298 K)ln(1.97) Δ𝐺′∘=−1.68 kJ/molΔG′∘=−1.68 kJ/mol 2. Δ𝐺=Δ𝐺′∘+𝑅𝑇ln(𝑄)ΔG=ΔG′∘+RTln(Q) Δ𝐺=−1.68 kJ/mol+(8.315×10−3 kJ/mol⋅K)(298 K)ln(0.50 M1.6 M)ΔG=−1.68 kJ/mol+(8.315×10−3 kJ/mol⋅K)(298 K)ln(0.50 M1.6 M) Δ𝐺=−4.56 kJ/mol 3. The temperature is 298 K. The pressure is 101.3 kPa (1 atm). The pH is 7.
1. Which of the processes are coupled to the dephosphorylation of ATP? 2. One reason that ATP is a source of energy is that the products of ATP hydrolysis have less free energy than the reactants. Why?
1. - myosin action during muscle contraction - de novo (from scratch) anabolism of nucleotides - the endergonic reaction forming glucose‑6‑phosphate 2. - hydrogen bonding between free phosphate and water - resonance stabilization of free phosphate - electrostatic repulsion in ATP
The path of carbon through the glycolytic pathway is shown in the figure. Answer four questions about the steps in this pathway. 1. Which step of the pathway is the main control point? 2. What negative effector inhibits the enzyme in this step? 3. What positive effector activates the enzyme in this step? 4. Some of these steps are reversible and catalyzed by the same enzyme acting in either direction, glycolysis or gluconeogenesis. Which reaction steps are irreversible and require a different enzyme in gluconeogenesis than in glycolysis? Select every irreversible reaction step.
1. 3 2. ATP 3. AMP 4. 1, 3, 10
Hexokinase is an enzyme that catalyzes the ATP‑dependent phosphorylation of glucose to glucose 6‑phosphate. Watch the animation of hexokinase converting glucose into glucose 6‑phosphate and answer the questions. 1. Modify the glucose molecule to glucose 6‑phosphate. 2. The induced‑fit model describes the interaction between the hexokinase and glucose.
1. Ans Ch 14 Question 5 2. Induced fit model
Some cofactors participating in reactions of the citric acid cycle are given. Identify the position or positions each cofactor has in the cycle by selecting the appropriate letter or letters designating that position in the cycle diagram. NADH + H+: FADH2: GTP:
1. B,D,J 2. H 3. F
Complete the aldolase reaction of glycolysis by drawing the product or products. Which enzyme catalyzes the next reaction, interconverting two trioses?
1. CH 14 Q 8 2. triose phosphate isomerase
In the first step of glycolysis, the given two reactions are coupled. reaction 1: glucose+Pi⟶glucose-6-phosphate+H2O Δ𝐺= +13.8 kJ/mol reaction 2:ATP+H2O⟶ADP+Pi Δ𝐺= −30.5 kJ/molreaction 1. Is reaction 2 spontaneous or nonspontaneous? 2. Complete the net chemical equation. 3. Calculate the overall ΔG for the coupled reaction. 4. Is the first step in glycolysis spontaneous (favorable)?
1. spontaneous 2. ATP + glucose ⟶ glucose-6-phosphate + ADP 3. reaction 1Δ𝐺 = +13.8 reaction 2Δ𝐺 = −30.5 overall Δ𝐺 = −16.7 kJ/mol 4. yes
Consider the malate dehydrogenase reaction from the citric acid cycle. Given the listed concentrations, calculate the free energy change for this reaction at 37.0°C. Δ𝐺'∘ for the reaction is +29.7 kJ/mol. Assume that the reaction occurs at pH 7. The concentrations are as follows: malate=0.00112 M; oxaloacetate=0.000225 M; NAD+= 0.503 M; and NADH=0.122 M. Provide the answer in kJ/mol and to 3 significant figures. R=8.315J/molK. Answer to correct significant figures. This question is worth 2 points.
21.9
The path of carbon through the glycolytic pathway is shown in the figure. Which step of the pathway is the main control point and what is the negative effector that inhibits the enzyme at this step?
3 and ATP
Quiz 10 Q 1 : Select the structure of pyruvate showing its appropriate structure at pH 7.4. The structure should have a carbon highlighted in green and bold that corresponds to the original anomeric carbon (aldehyde carbon in the open-chain form) of glucose. Which structure fits the criteria?
A
Identify all statements that accurately describe the structure of the pyruvate dehydrogenase (PDH) complex.
A. A regulatory kinase and phosphatase are part of the mammalian PDH complex. B. The complex contains multiple copies of each of three enzymes. C. E2 contains three domains. E. Several copies of each of E1 and E3 surround E
Select the three true statements about the citric acid cycle.
A. The major reactants in the citric acid cycle are acetyl CoA, NAD+, GDP, and FAD. C. The citric acid cycle is an aerobic process E. In the citric acid cycle, acetyl-CoA is degraded to produce NADH and FADH2.
The citric acid cycle is a stage of catabolism that oxidizes acetate into carbon dioxide and generates energy. There are eight enzymes involved in the citric acid cycle. Which enzymes produce NADH as a product? Select all that apply.
A. isocitrate dehydrogenase C. malate dehydrogenase D. α-ketoglutarate dehydrogenase
The equation for ATP hydrolysis is ATP−→−−H2OADP+PiΔ𝐺∘′=−30.5 kJ/molATP→H2OADP+PiΔG°′=−30.5 kJ/mol Calculate Δ𝐺ΔG for ATP hydrolysis to arrange the conditions from most favorable to least favorable. Assume a temperature of 37.0 °C and 𝑅=8.315 J/(mol·K)R=8.315 J/(mol·K) .
ATP hydrolysis most favorable brain: [ATP]=2.6 mM[ATP]=2.6 mM ; [ADP]=0.7 mM[ADP]=0.7 mM ; [Pi]=2.7 mM[Pi]=2.7 mM muscle: [ATP]=8.1 mM[ATP]=8.1 mM ; [ADP]=0.9 mM[ADP]=0.9 mM ; [Pi]=8.1 mM[Pi]=8.1 mM liver: [ATP]=3.4 mM[ATP]=3.4 mM ; [ADP]=1.3 mM[ADP]=1.3 mM ; [Pi]=4.8 mM[Pi]=4.8 mM ATP hydrolysis least favorable
Fructose‑2,6‑bisphosphate is a regulator of both glycolysis and gluconeogenesis for the phosphofructokinase reaction of glycolysis and the fructose‑1,6‑bisphosphatase reaction of gluconeogenesis. In turn, the concentration of fructose‑2,6‑bisphosphate is regulated by many hormones, second messengers, and enzymes. Classify each condition according to its effect on glycolysis and gluconeogenesis
Activates glycolysis and inhibits gluconeogenesis increased levels of fructose‑2,6‑bisphosphate activation of PFK‑2 Activates gluconeogenesis and inhibits glycolysis activation of fructose‑2,6‑bisphosphatase (FBPase‑2) increased levels of cAMP increased glucagon levels
When considering free energy change, biochemists usually define a standard state, the biochemical standard state, which is modified from the chemical standard state to fit biochemical applications. Determine which of the phrases describe the biochemical standard state, the chemical standard state, or both. Ch 13 Q 2
Biochemical standard state Chemical standard state Δ𝐺° pH 0 Both
Ions, polar molecules, and large molecules cannot readily cross a lipid bilayer and are dependent on transport proteins to cross a membrane. Classify each of the seven images as an example of a uniport, symport, or antiport transport system.
CH 11 Q 15
Identify the parts of the G protein shown in the image.
CH 12 Q 3
Add coefficients to the reaction summary to show the net results of glycolysis from 1 mole of glucose. You do not need to add the water and hydrogen ions necessary to balance the overall reaction. 1 glucose + 2 ADP + 2 Pi + 2 NAD+ ⟶ 2 pyruvate + 2 ATP + 2 NADH Select the structure of pyruvate showing its appropriate structure at pHpH 7.4. The structure should have a carbon highlighted in green and bold that corresponds to the original anomeric carbon (aldehyde carbon in the open‑chain form) of glucose. Which structure fits the criteria?
CH 14 Q 10 2, 2, 2, 2, 2, 2 O O II II H3C-C-C-O_
Complete the glycolysis reaction. What is the enzyme that catalyzes this reaction?
CH 14 Q 9 1. ADP - ATP 2. phosphoglycerate kinase
The reactions of the citric acid cycle are shown. Identify the enzyme required for each step.
CH 16 Q 6
The pyruvate dehydrogenase complex converts pyruvate to acetyl‑CoA by oxidative decarboxylation of pyruvate followed by transfer of the acetyl group to coenzyme A. The net equation is pyruvate+CoA+NAD+⟶acetyl-CoA+CO2+NADHpyruvate+CoA+NAD+⟶acetyl-CoA+CO2+NADH Label the diagram of the pyruvate dehydrogenase complex reactions with the names of the enzymes and cofactors.
CH 16 q 3
The glycolysis pathway is shown. Place the enzymes used in each of the ten labeled steps of the pathway. Be sure to scroll down completely until pyruvate is formed.
Ch 14 Question 1
The structures of five of the compounds of glycolysis are given. Without using a reference, arrange them in order from the start of glycolysis to the end of glycolysis.
Ch 14 Question 2
There are a variety of mechanisms by which enzyme activity can be controlled. Match each example of enzyme regulation with the associated mechanism. CH 15 Q 1
Control by modulators feedback inhibition allosteric regulation Control by covalent modification zymogen activation regulation of chymotrypsin phosphorylation of glycogen phosphorylase Genetic control enzyme induction (synthesis) lactose stimulation of bacterial β‑galactosidase
The plasma membranes are composed of specific types of phospholipids that are asymmetrically distributed between the two monolayers of the lipid bilayer. For example, the inner monolayer of the human erythrocyte plasma membrane is primarily composed of phosphatidylethanolamine and phosphatidylserine. On the other hand, the outer monolayer mainly consists of phosphatidylcholine and sphingomyelin. The specific composition and distribution of phospholipids in the two monolayers is continuously maintained. Select the statements that describe how the transbilayer asymmetry in the lipid bilayer is achieved and maintained.
Diffusion of phospholipids between the two monolayers of the lipid bilayer exposes the polar or charged head group to a hydrophobic environment. This process requires a large positive change in free energy, thus making this type of movement unlikely without an input of energy. Membrane lipids are synthesized in the ER, then modified and targeted to specific locations in the inner and outer monolayers of the plasma membrane.
Animals are not able to convert fatty acids into carbohydrates. The net synthesis of 1 mol of oxaloacetate from 2 mol of acetyl‑CoA by the citric acid cycle does not occur because 1 mol of oxaloacetate is used in the cycle for each one generated. Plants are able to convert 2 mol of acetyl‑CoA into 1 mol of oxaloacetate with only two additional enzymes not found in animals. This process is called the glyoxylate cycle, and it occurs in organelles called glyoxysomes. Identify the enzyme in each step of the glyoxylate cycle. Not all the enzyme names will be used. ch 16 q 14
Enzyme A is citrate synthase Enzyme B is aconitase Enzyme C is isocitrate lyase Enzyme D is malate synthase Enzyme E is malate dehydrohgenase
Classify the enzymes based on whether they are found only in plants or are found in both plants and animals. Ch 16 Q15
Enzymes found in plants only isocitrate lyase malate synthase Enzymes found in plants and animals citrate synthase aconitase isocitrate dehydrogenase α‑ketoglutarate dehydrogenase succinyl‑CoA synthetase succinate dehydrogenase fumarase malate dehydrogenase
Some cofactors participating in reactions of the citric acid cycle are given. Identify the position of positions of GTP in the cycle by selecting the appropriate letter or letters designating the position in the cycle diagram.
F
Pyruvate dehydrogenase is a large, highly integrated complex containing many copies of three distinct enzymes. There are five coenzymes involved in its catalytic activity: NAD+NAD+ , FADFAD , coenzyme A, lipoamide, and thiamine pyrophosphate (TPP or TDP). The coenzymes can be classified depending on how they participate in an enzymatic reaction. A coenzyme prosthetic group is tightly bound to the enzyme and remains bound during the catalytic cycle. The original coenzymes are regenerated during the catalytic cycle. On the other hand, a coenzyme cosubstrate is loosely bound to an enzyme and dissociates in an altered form as part of the catalytic cycle. Its original form is regenerated not by the cycle, but by another enzyme. Which are coenzyme prosthetics?
FAD lipoamide TPPTPP or TDP
Classify the phrases based on whether they describe or give an example of facilitated transport, active transport, or both.
Facilitated transport: movement to area of lower concentration glucose transport into muscle cell Active transport: requires energy sodium ion transport out of cell Both: movement across a membrane movement assisted by proteins
Place these steps of the insulin signaling pathway in the correct order.
First binding of insulin to insulin receptor activation of insulin receptor phosphorylation of IRS‑1 phosphorylation of phosphoinositide 3‑kinase (PI‑3‑kinase) conversion of PIP2 to PIP3 activation of protein kinase B (PKB) Glut4 receptors are transported to cell membrane Last
Arrange the steps of a G protein signal transduction in the order that they occur.
First step A signal molecule binds to the receptor, activating it. The receptor changes conformation and binds an inactive G protein. The G protein is activated by the dissociation of GDPGDP and binding of GTPGTP . The G protein dissociates from the receptor. The G protein activates an effector protein, leading to a cellular response. Last step
Lipids in a bilayer can diffuse laterally at a relatively fast rate, but "flip‑flop" from one leaflet to the other very slowly without catalysis. Three protein families, flippases (or flipases), floppases, and scramblases, catalyze the movement of lipids across the bilayer. Classify each phrase as describing flippases, floppases, or scramblase
Flippases: translocate phosphatidylserine, preventing apoptosis and engulfment by macrophages translocate lipids from outer (extracellular) leaflet to inner (cytosolic) leaflet Floppases: move phospholipids from inner (cytoplasmic) leaflet to outer (extracellular) leaflet ABC transporter Scramblases: not ATP‑dependent move phospholipids across the lipid bilayer down the concentration gradient activation may result in increased membrane lipid symmetry
For the aqueous reaction dihydroxyacetone phosphate↽−−⇀glyceraldehyde−3−phosphatedihydroxyacetone phosphate↽−−⇀glyceraldehyde−3−phosphate the standard change in Gibbs free energy is Δ𝐺°′=7.53 kJ/molΔG°′=7.53 kJ/mol. Calculate Δ𝐺ΔG for this reaction at 298 K298 K when [dihydroxyacetone phosphate]=0.100 M[dihydroxyacetone phosphate]=0.100 M and [glyceraldehyde-3-phosphate]=0.00700 M[glyceraldehyde-3-phosphate]=0.00700 M.
For the reaction, dihydroxyacetone phosphate (DHAP)↽−−⇀glyceraldehyde-3-phosphate (G3P)dihydroxyacetone phosphate (DHAP)↽−−⇀glyceraldehyde-3-phosphate (G3P) the change in Gibbs energy is given by the equation Δ𝐺=Δ𝐺°′+𝑅𝑇ln([G3P][DHAP])ΔG=ΔG°′+RTln([G3P][DHAP]) where Δ𝐺ΔG is the change in Gibbs energy, Δ𝐺°′ΔG°′ is the standard change in Gibbs energy, 𝑅R is the ideal-gas constant 8.3145 J/(K⋅mol)8.3145 J/(K⋅mol), and 𝑇T is absolute temperature. To match the units of Δ𝐺°′ΔG°′, the ideal-gas constant must be converted to units of kJ/(K⋅mol) kJ/(K⋅mol). Insert the values given in the problem and solve for Δ𝐺ΔG. Δ𝐺=7.53kJmol+(8.3145JK⋅ mol×1 kJ1000 J)(298 K)(ln0.00700 M0.100 M)=0.941 kJ/mol 0.94
Pyruvate kinase catalyzes the transfer of a phosphoryl group from phosphoenolpyruvate to ADP in the last step of glycolysis, forming pyruvate in the process. Vertebrates have several isozymes of pyruvate kinase, which can be allosterically inhibited by compounds including ATP and acetyl-CoA. What is an effect of cAMP-dependent protein kinase (PKA) inactivation of the liver isozyme but not the muscle isozyme?
Glycolysis is inhibited in the liver, but not muscle, when blood sugar is low.
Identify events that contribute to the termination of a response in the GPCR, or 7TM receptor, pathway. Select all that apply.
GαGα hydrolyzes GTPGTP to GDPGDP and PiPi . The receptor is inactivated by phosphorylation of Ser or other residues on its intracellular domain. The ligand dissociates from the receptor, which resumes its inactive conformation.
Which of the outcomes could potentially result if a mutation in the gene encoding the GαGα subunit eliminates its GTPase activity? Choose three outcomes.
GαGα would be activated for an extended period. The concentration of cAMPcAMP in the cell would be continuously elevated. The signaling pathway could be activated for an extended period, possibly resulting in undesirable cell proliferation.
Hydropathy plots show the hydrophobic nature of polypeptide regions. They can be used to locate α helical transmembrane segments in a polypeptide. Identify which segment or segments of the polypeptide characterized in the hydropathy plot below could belong to a transmembrane region of a protein. CH 11 Q 8
Identify which segment or segments of the polypeptide characterized in the hydropathy plot below could belong to a transmembrane region of a protein. C
In muscle tissue, the ratio of phosphorylase a to phosphorylase b determines the rate of conversion of glycogen to glucose 1‑phosphate. Classify how each event affects the rate of glycogen breakdown in isolated muscle tissue.
Increased rate treatment with epinephrine AMP allosteric binding activates phosphorylase b addition of a phosphatase inhibitor Decreased rate addition of phosphatase PP1 addition of a kinase inhibitor [ATP] exceeds [AMP] treatment with insulin No change treatment with glucagon
Classify the phrases. Does each phrase describe a kinase, a phosphatase, neither, or both?
Kinases catalyze phosphorylation reactions may use ATPATP as a phosphoryl group donor PKAPKA (protein kinase A) is an example Phosphatases: remove phosphoryl groups from proteins turn off signaling pathways triggered by kinases Neither: in eukaryotes, transfer phosphoryl groups to acidic amino acids catalyze reactions that are the reverse of dephosphorylation reactions Both: regulate the activity of other proteins
Researchers can manipulate the genes of a mouse so that a single gene in a single tissue either produces an inactive protein (a knockout mouse) or produces a protein that is always (constitutively) active. What effects on metabolism would you predict for mice with these genetic changes? CH 15 Q 10
Knockout of the FBPase‑2 domain of PFK‑2/FBPase‑2 in the liver: Effect on glucose metabolism: glycolysis stimulated Effect on glucose levels: lowered glucose Constitutively active PFK‑2 in the liver: Effect on glucose metabolism: glycolysis stimulated Effect on glucose levels: lowered glucose
Determine whether each phrase describes ligand‑gated ion channels, voltage‑gated ion channels, or both. ch 12 q 16
Ligand‑gated ion channels: an example is the acetylcholine receptor change conformation in response to a signal molecule binding Voltage‑gated ion channels: change conformation in response to changing membrane potential Both: is a form of passive transport may participate in an action potential
Citrate synthase is regulated by another metabolite that has the opposite effect (i.e., stimulates citrate synthase). Choose the description of a condition where a positive regulator activates citrate synthase.
Low [ATP/ADP] ratio. ADP is an allosteric activator of citrate synthase.
Membrane‑associated proteins can be distinguished by the types of interactions they have with the lipid bilayer and their structural motifs. Match each statement to the category of membrane‑associated protein it describes.
Membrane‑spanning α helix: composed of about 20 hydrophobic residues Membrane‑spanning β strands: amino acid sequence pattern: nonpolar R group, polar R group (repeats) Lipid‑anchored membrane protein: often contain a residue with covalently attached glycosyl phosphatidylinositol Peripheral membrane protein: can usually be released from membrane by concentrated salt solutions membrane attachment depends upon electrostatic interactions with membrane phospholipid head groups
The text describes the first three reactions of a metabolic pathway. Complete the sentences. Not all the terms will be placed. In reaction 1 of the Krebs cycle, acetyl-CoA formed in the pyruvate..........
Oxaloacetate to form citrate..... tricarboxylic acid isomerization to form isocitrate.... intermediate a-ketoglutarate .... NAD+
Which of the following events contributes to the termination of a signal generated by the binding of a ligand to a receptor tyrosine kinase?
Phosphatases hydrolyze key phosphorylated residues.
The neurotransmitter acetylcholine is released from presynaptic neurons in response to a nerve impulse and diffuses across the synaptic cleft, or neuromuscular junction, to a receptor on another neuron or a muscle cell. The nicotinic acetylcholine receptor is a pentamer containing four types of subunits, α2βγδ. Place the events in the correct order, from the release of acetylcholine from a neuron to receptor resensitization.
Presynaptic neuron is excited excited presynaptic neuron releases acetylcholineacetylcholine diffuses across synaptic cleft or neuromuscular junction one acetylcholine binds to a receptor; the gate is closed two acetylcholine bind to a receptor; the gate opens small cations pass through the open pore of the receptor the plasma membrane of the target cell is depolarized two acetylcholine are tightly bound to a receptor; the gate is closed acetylcholine is released from the binding sites
In biological systems, there are several membrane transport systems responsible for the passage of ions like Na+Na+ and K+K+, or small molecules like glucose and amino acids, through biological membranes. Classify each membrane transport system as either a primary active transporter, a secondary active transporter, or a passive transporter. CH 11 Q 16
Primary active transporter: the Na+/K+ ATPaseNa+/K+ ATPase of plasma membranes the Ca2+ ATPaseCa2+ ATPase of the sarcoplasmic reticulum Secondary active transporter: the amino acid−Na+−Na+ transporter of kidney cells the glucose−Na+−Na+ transporter of intestinal epithelial cells Passive transporter: the glucose transporter of erythrocytes
The protein content of most plasma membranes is, on average, about 50%50% by weight. Myelin has a protein content of about 18%18% , whereas the internal membranes of mitochondria may be composed of 75%75% protein. Label the membrane proteins on the diagram.
See Ch 11 Q 3
Signal transduction is part of a cell's response to an external signal. Although signal transduction pathways can differ in their details, there are some common elements. Select the six statements that accurately describe signal transduction pathways. CH 12 Q 1
Select the six statements that accurately describe signal transduction pathways. -A receptor may pass on a signal by interacting with another protein or by acting as an enzyme. - A receptor changes conformation upon binding, transmitting a signal across the cell membrane. - A second messenger may carry a signal from the cell membrane to an organelle. - Signal transduction cascades, often involving protein kinases, amplify a signal intracellularly. - Phosphatases remove phosphoryl groups from polypeptides, regulating a cell's response. - A ligand, such as a hormone, binds to a specific cell surface receptor on a target cell.
A rabbit fleeing a coyote and a duck's extended flight during migration both involve muscular activity with high demands for metabolic fuel. However, the source of fuel and the pathways for ATP production differ. A rabbit's short‑term need for ATP is supplied by the breakdown of stored glycogen and glycolysis under anaerobic conditions. ATP for a duck's extended flight is supplied by the breakdown of fats to acetyl-CoA, the citric acid cycle, and oxidative phosphorylation. The short‑term intense run and the long‑term flight require coordinated regulatory controls on the central metabolic pathways of glycolysis, citric acid cycle, and oxidative phosphorylation. Match the actions of metabolic regulators with the type of muscular activity.
Short‑term, intense muscular activity low [citrate] results in higher PFK‑1 activity high [AMP] stimulates PFK‑1 activity low [O2][O2] inhibits the citric acid cycle Long‑term, continuous muscular activity acetyl-CoA inhibits pyruvate kinase. high [ATP] inhibits pyruvate kinase
Biological membranes are selectively permeable, allowing certain molecules to cross the membrane, but not others. Classify the molecules or ions depending on how they cross a biological membrane. Note that some of these examples may also utilize active transport to traverse a membrane. However, this question is limited to passive transport processes only.
Simple Diffusion steroid hormones CO2 Facilitated Diffusion lactose amino acids Ca2+
Protein X is an unknown membrane protein found in erythrocytes that can be extracted primarily from plasma membranes using a concentrated salt solution. What type of membrane protein is protein X? What do these observations suggest about the location of protein X in the plasma membrane?
Since protein X is extracted from the membrane by altering the ionic strength of the extraction solution, it is a peripheral membrane protein. Since proteolytic enzymes cannot fragment protein X in intact erythrocytes, protein X is located inside the cell and interacts with the inner surface of the membrane.
The succinyl CoA to citrate pathway of the citric acid cycle is shown. Identify the missing intermediates by placing the molecules to the appropriate position.
Succinyl CoA to Citrate ch 16 q 10
Consider the reaction of pyruvate with NADH and the standard reduction potentials, 𝐸′°, of pyruvate and NAD+. Redox pair. E'°, V pyruvate/lactate. -0.19 NAD+/NADH. -0.32 pyruvate+NADH↽−−⇀lactate+NAD+
The NAD+/NADH pair has the greater tendency to lose electrons because the NAD+/NADH 𝐸′°NAD+/NADH E′° value is the most negative.
Identify true statements about the propagation of a nerve impulse.
The action potential triggers the opening of sodium channels further down the axon. The influx of sodium ions makes the membrane potential more positive. When voltage‑gated potassium channels open, potassium ions move out of the cell restoring the resting membrane potential. The action potential can only travel in one direction along the axon. The action potential triggers the opening of voltage‑gated potassium channels. The propagation of a nerve impulse relies on changes in membrane potential along the length of a nerve.
Consider a general reaction A(aq)⥫⥬===enzymeB(aq)A(aq)⇌enzymeB(aq) The Δ𝐺°′ΔG°′ of the reaction is −6.090 kJ·mol−1−6.090 kJ·mol−1. Calculate the equilibrium constant for the reaction at 25 °C. What is Δ𝐺ΔG for the reaction at body temperature (37.0 °C) if the concentration of A is 1.5 M1.5 M and the concentration of B is 0.85 M0.85 M?
The equation that relates Δ𝐺°′ΔG°′ to 𝐾′eqKeq′ is Δ𝐺°′=−𝑅𝑇ln(𝐾′eq)ΔG°′=−RTln(Keq′) The value of the gas constant, 𝑅R, is 8.3145 J·mol−1·K−18.3145 J·mol−1·K−1. 𝑇T is the temperature in kelvins. 𝑇=25+273=298KT=25+273=298K Rearranging the equation to solve for 𝐾′eqKeq′ and inserting the appropriate values gives 𝐾′eq=𝑒−Δ𝐺∘′𝑅𝑇=𝑒−(−6.090×103 J/mol)(8.3145 J/mol⋅ K)(298K)=𝑒2.458=11.7Keq′=e−ΔG°′RT=e−(−6.090×103 J/mol)(8.3145 J/mol⋅ K)(298K)=e2.458=11.7 11.7 The relationship between Δ𝐺ΔG and Δ𝐺°′ΔG°′ can be represented as Δ𝐺=Δ𝐺°′+𝑅𝑇ln([B][A])ΔG=ΔG°′+RTln([B][A]) where 𝑇T is the temperature in kelvins. In this case, 𝑇=310KT=310K. Inserting the appropriate values into the equation gives Δ𝐺=−6.090kJmol+(8.3145Jmol⋅ K)(310K)ln(0.85 M1.5 M)=−6.090kJmol+−1.46kJmol=−7.55 kJmol -7.55
When a sample of purified phospholipids is mixed with water, spherical structures called liposomes form. Which of the characteristics of phospholipids enable liposomes to form in water?
The hydrophobic effect drives aggregation of phospholipids in an aqueous solution. The cross‑sectional area of the headgroups and acyl chains in the phospholipids are similar. The edges of lipid bilayers sheets fold back on themselves, forming a hollow sphere which releases the ordered waters at the edges.
Tetrodotoxin acts by blocking sodium channels. How does it lead to a loss of excitatory conduction in neurons?
The membrane cannot depolarize.
Predict the effects on the net reaction catalyzed by glyceraldehyde 3‑phosphate dehydrogenase and other reactions of glycolysis if phosphate were replaced by arsenate.
There would be no net conversion of ADP to ATP from the conversion of glucose to pyruvate during glycolysis. The 1‑arseno‑3‑phosphoglycerate intermediate would decompose nonenzymatically, so no ATP would be formed in the phosphoglycerate kinase reaction.
Na+/K+ATPaseNa+/K+ATPase (sodium potassum adenosine triphosphatase) is found in the plasma membrane and catalyzes the exchange of sodium and potassium ions across the membrane. Classify the statements about the transport system as either true or false. CH 11 Q 17
True: - Pumps Na+Na+ ions out of the cell. - Pumps K+K+ ions into the cell. - Exchanges 3Na+3Na+ ions for 2K+2K+ ions. - Creates a membrane potential that is negative on the inside. False: - Pumps Na+Na+ ions into the cell. - Pumps K+K+ ions out of the cell. - Exchanges 3K+3K+ ions for 2Na+2Na+ ions. - The transport protein becomes adenylated by ATPATP during the transport cycle.
Calculate the distance olive oil (a lipid) could move in a membrane in 11 seconds11 seconds assuming the diffusion coefficient is 1 𝜇m2/s1 μm2/s . Use the equation S=(4Dt)1/2S=(4Dt)1/2 where 𝑆S is distance traveled, 𝑡t is time, and 𝐷D is the diffusion coefficient. CH 11 Q 9
Use the following equation S=(4Dt)1/2S=(4Dt)1/2 S=(4×1𝜇m2s×11 s)1/2S=(4×1μm2s×11 s)1/2 S=6.6 𝜇mS=6.6 μm Note that 𝑥1/2=𝑥‾‾√ Distance: 6.63
Classify the chemical reactions as an oxidation‑reduction, elimination, isomerization, or nucleophilic substitution. CH 13 Q 1
View
Label the compounds.
View Ch 13 Q 3
Label the compounds. 2
View Ch 13 Q 4
The reactions of the citric acid cycle are shown in the image. As labeled in the diagram, reactions 1, 3, and 4 are regulation points in the citric acid cycle. Which molecules inhibit reaction 1? Which molecule inhibits reaction 3? Which molecules inhibit reaction 4? Which molecule or ion activates reaction 4? CH 16 Q 12
Which molecules inhibit reaction 1? succinyl‑CoA NADH citrate Which molecule inhibits reaction 3? NADH Which molecules or ions activate reaction 3? ADP CA2+ Which molecules inhibit reaction 4? succinyl‑CoA NADH Which molecule or ion activates reaction 4? Ca2+
Biological membranes are present in all cells, and they make up the endomembrane system of eukaryotic cells. Among other functions, they act as barriers that selectively allow the transport of small molecules and ions into and out of the cell or organelle. Which of the choices best describes a biological membrane? Which of the choices are components of biological membranes? Select all that apply.
Which of the choices best describes a biological membrane? a bilayer containing lipids with hydrophilic head groups oriented toward the solvent (extracellular fluid and cytosol) and hydrophobic tail groups pointing inward Which of the choices are components of biological membranes? Select all that apply. lipids proteins
Some G protein‑coupled receptors are sensitive to hormones such as angiotensin II and oxytocin and act through compounds such as phospholipase C and IP3IP3 . Complete the flowchart showing the cleavage of a membrane lipid to form compounds that ultimately cause the phosphorylation of specific proteins. The abbreviations used are phosphatidylinositol 4,5‑bisphosphate, PIP2PIP2 ; protein kinase C, PKCPKC ; diacylglycerol, DAGDAG ; inositol 1,4,5‑triphosphate, IP3IP3 ; and phospholipase C, PLCPLC . CH 12 Q 6
Which of the compounds can be considered second messengers? IP3 DAG Ca2+
Glycolysis is the process by which energy is harvested from glucose by living things. Several of the reactions of glycolysis are thermodynamically unfavorable, nonspontaneous, but proceed when they are coupled with other reactions. A. Pi+glucose⟶glucose−6−phosphate+H2OΔ𝐺=3.30 kcal/molA. Pi+glucose⟶glucose−6−phosphate+H2OΔG=3.30 kcal/mol B. Pi+fructose−6−phosphate⟶fructose−1,6−bisphosphate+H2OΔ𝐺=3.90 kcal/molB. Pi+fructose−6−phosphate⟶fructose−1,6−bisphosphate+H2OΔG=3.90 kcal/mol C. ATP+H2O⟶ADP+PiΔ𝐺=−7.30 kcal/mol
Which of the reactions are unfavorable? A B Which of the reactions can be coupled so that the overall reaction is favorable? A and C B and C What is the net change in free energy if one set of reactions from the previous question is coupled so that the overall reaction is favorable? If you selected more than one pair of reactions in the previous question, enter the net change for any one of your selected sets. Δ𝐺=−3.40 kcal/mol
Adenosine triphosphate (ATP) is considered the energy currency for the cell. This molecule is energy-rich, in part, due to its two phosphoanhydride bonds. Resonance structures for ATP are given, where X represents adenosine monophosphate (AMP).
Which of the structures are appropriate resonance forms of ATP? A C D Which molecule is more stable and has more resonance forms: ATP or orthophosphate (Pi)(Pi)? PiPi
The path of carbon through the glycolytic pathway is shown in the figure. Answer four questions about the steps in this pathway.
Which step of the pathway is the main control point? 3 What negative effector inhibits the enzyme in this step? ATP What positive effector activates the enzyme in this step? AMP Some of these steps are reversible and catalyzed by the same enzyme acting in either direction, glycolysis or gluconeogenesis. Which reaction steps are irreversible and require a different enzyme in gluconeogenesis than in glycolysis? Select every irreversible reaction step. 1 3 10
The original fluid mosaic model stated that membrane proteins move freely in the plane of the lipid bilayer via lateral diffusion "like protein icebergs in a sea of lipids." Since its initial description in 1927, the fluid mosaic model has been refined. Complete the statements that describe some of the refinements of the fluid mosaic model as it relates to protein mobility.
Within the fluid lipid matrix, (protein-protein interactions) may form a locally rigid, non‑lipid matrix. Membrane domains that are rich in sphingolipids and cholesterol are called (membrane or lipid rafts.) These regions have reduced lipid and protein mobility. (Cytoskeletal elements) reduce protein mobility by attaching to proteins or fencing in proteins.
Which of the molecules are used as second messengers in signal transduction pathways?
calcium ions cAMP IP3
Pyruvate is the end product of glycolysis. Its further metabolism depends on the organism and on the presence or absence of oxygen. Draw the structure of the product from each reaction as it would exist at pH 7. Include the appropriate hydrogen atoms. Draw the structure of the group attached to −SCoA. Reaction A: aerobic conditions in humans or yeast Reaction B: anaerobic conditions in humans Reaction C: anaerobic conditions in yeast (fermentation)Reaction C: anaerobic conditions in yeast (fermentation)
ch 14 q 14
Determine the direction that each of the reactions will progress. Assume that the reactants and products are present in equimolar amounts. The standard free energy of hydrolysis of ATP is -30.5 kJ/mol. CH 13 Q 9
fructose+ATPfructose+ATP → fructose 6‑phosphate+ADPfructose 6‑phosphate+ADP The standard free energy of hydrolysis for fructose 6‑phosphate is −15.9 kJ/mol.−15.9 kJ/mol. 3‑phosphoglycerate+ATP3‑phosphoglycerate+ATP ← 1,3‑bisphosphoglycerate+ADP1,3‑bisphosphoglycerate+ADP The standard free energy of hydrolysis for 1,3‑bisphosphoglycerate is −49.3 kJ/mol.−49.3 kJ/mol. pyruvate+ATPpyruvate+ATP ← phosphoenolpyruvate+ADPphosphoenolpyruvate+ADP The standard free energy of hydrolysis for phosphoenolpyruvate is -61.9 kJ/mol.
The passage describes some glycolysis reactions. Select the appropriate term for each blank to complete the passage. In the first reaction of glycolysis, glucose is converted to glucose 6‑phosphate. The phosphate comes from ATP. A kinase is an enzyme that transfers the terminal phosphate of ATP to a substrate. The product of this reaction is then isomerized to fructose‑6‑phosphate. Fructose‑6‑phosphate is then phosphorylated by a second kinase reaction, giving fructose 1,6‑bisphosphate .
glucose 6‑phosphate ATP Kinase ATP Isomerized Kinas Fructose 1,6-biphosphate
Q 10 Q2 Monosaccharides other than glucose can be modified to derivatives that can enter glycolysis. What is galactose converted to so that it enters the glycolytic pathway?
glucose-6-phosphate
Which of these is the galactose derivative that enters the glycolytic pathway? Which of these is the mannose derivative that enters the glycolytic pathway?
glucose-6-phosphate fructose-6-phosphate
How does fructose 2,6‑bisphosphate (F26BP) affect the activity of the enzymes phosphofructokinase‑1 (PFK) and fructose 1,6‑bisphosphatase (FBPase)?
increases PFK activity, decreases FBPase activity
Which molecules bind to receptors that have intracellular tyrosine kinase domains?
insulin epidermal growth factor (EGF)
Sodium and potassium ion channels have several negatively charged residues at the entry to the channel. Identify the bases on which K+K+ channels specifically select for K+K+ ions, in other words, why do K+K+ channels not enable Na+Na+ ions to cross the membrane?
ionic radius, Na+Na+ is too small energy cost it is too energetically costly to dehydrate Na+
Assume that the binding of one molecule of epinephrine to a seven‑transmembrane helix (7TM) receptor (also called the G protein‑coupled receptor, or GPCR) results in the activation of 380 Gα380 Gα subunits. In addition, suppose that each activated adenylyl cyclase catalyzes the conversion of 40 ATP40 ATP molecules to cAMP per second. Assume that each G protein activates a single unique adenylyl cyclase. Calculate the number of moles of cAMP that are produced per second. Enter your answer to two significant figures.
moles produced: 2.5 x 10^-20 The total number of cAMP molecules synthesized per second is 380 x 40 = 15000 cAMP Then, convert molecules to moles. 15000 x (1/6.022x10^23) = 2.5 x 10^−20
The plasma membrane of E. coli is approximately 75% protein and 25% phospholipid by weight. It is known that the average membrane protein molecular weight is 50,000 Da and an average membrane phospholipid molecular weight is 750 Da. Calculate the number of membrane phospholipid molecules present per molecule of membrane protein. CH 11 Q 10
number of membrane phospholipid molecules: 22.22 The ratio of moles of phospholipid to moles of protein can then be calculated. 0.000333 moles of phospholipid1. _______________________ / 5×10−5 moles of protein =22 Select the additional information that one would need to calculate the fraction of membrane surface covered by phospholipids. the average cross‑sectional areas of a 50,000 Da protein and a 750 Da phospholipid in a bilayer
Separate the redox reaction into its component half‑reactions. O2+2Mg⟶2MgOO2+2Mg⟶2MgO Use the symbol e−e− for an electron.
oxidation half-reaction: Mg⟶Mg2++2e− reduction half-reaction: O2+4e−⟶2O2−
Separate this redox reaction into its balanced component half‑reactions. Use the symbol e− for an electron. Cl2+2Na⟶2NaCl CH 13 Q 1 (bioenergetics)
oxidation half-reaction: Na⟶Na++e− reduction half-reaction: Cl2+2e−⟶2Cl−
Complete the overall reaction catalyzed by the pyruvate dehydrogenase complex. Move the compounds and cofactors to the correct answer blanks. Two terms will not be used. Ch 16 Q 1
pyruvate + CoA + NAD+ -> acetyl-CoA +NADH H+CO2
Select the redox pair that is the stronger oxidizing agent.
pyruvate/lactate
Which of the molecules could align side by side to form a lipid bilayer? CH 11 Q 1
sphingomyelins (sphingolipids) glycerophospholipids
Refer to the glycolytic pathway to answer the question. Identify the oxidation-reduction reactions of glycolysis. Use the step numbers from the glycolytic pathway shown.
step 6
What would be the limiting factor for ATP production by glycolysis in a strenuously exercising muscle that lacks lactate dehydrogenase? Ch 14 Q15
the supply of NAD+
Assuming that the concentrations of each reactant and product are 1 M and that the reaction is performed at pH 7 and 25 °C, determine the Δ𝐸′°ΔE′° for the reaction. Based on the Δ𝐸′°ΔE′° value, select the direction in which the reaction proceeds.
Δ𝐸′°=0.13 Δ𝐸′°=𝐸′°cathode−𝐸′°anode=(−0.19 V)−(−0.32 V)=0.13 V The reaction proceeds to the right.
Consider the malate dehydrogenase reaction from the citric acid cycle. Given the listed concentrations, calculate the free energy change for this reaction at energy change for this reaction at 37.0 ∘C37.0 ∘C (310 K). Δ𝐺∘′ΔG∘′ for the reaction is +29.7 kJ/mol+29.7 kJ/mol . Assume that the reaction occurs at pH 7. [malate]=1.37 mM[malate]=1.37 mM [oxaloacetate]=0.150 mM[oxaloacetate]=0.150 mM [NAD+]=350 mM[NAD+]=350 mM [NADH]=140 mM
Δ𝐺=Δ𝐺∘′+𝑅𝑇ln( [oxaloacetate][NADH] [malate][NAD+] ) Δ𝐺= 29.7 kJ⋅mol−1+(8.3145×10−3kJmol⋅K)(310K) x ln((0.000150 M)(0.14 M) (0.00137 M)(0.35 M)) =29.7 kJ⋅mol−1+(−8.06 kJ⋅mol−1) =21.64 kJ⋅mol−1
Synthesis of the activated form of acetate (acetyl‑CoA) is carried out in an ATP‑dependent process. Acetate+CoA+ATP⟶Acetyl−CoA+AMP+PPiAcetate+CoA+ATP⟶Acetyl−CoA+AMP+PPi The Δ𝐺′∘ for the hydrolysis of acetyl‑CoA to acetate and CoA is −32.2 kJ/mol−32.2 kJ/mol, and that for hydrolysis of ATP to AMP and PPiPPi is −30.5 kJ/mol−30.5 kJ/mol . Calculate Δ𝐺′∘ΔG′∘ for the ATP‑dependent synthesis of acetyl‑CoA shown in the equation. Almost all cells contain the enzyme inorganic pyrophosphatase, which catalyzes the hydrolysis of PPiPPi to PiPi . What effect does the presence of this enzyme have on the synthesis of acetyl‑CoA?
Δ𝐺′∘ = 32.2 kJ/mol Δ𝐺′∘ = −30.5 kJ/mo ________________________ Δ𝐺′∘ = 1.7 kJ/mol Δ𝐺′∘=1.7 kJ/mol Δ𝐺′∘=−19.2 kJ/mol _________________________ Δ𝐺′∘=−17.5 kJ/molΔG′∘=−17.5 kJ/mol Final Ans -17.5 Hydrolysis of pyrophosphate shifts the equilibrium of the reaction to the right, making the formation of acetyl‑CoA energetically more favorabl
Many metabolites are maintained at steady‑state concentrations that are far from equilibrium. A comparison of 𝐾′eqKeq′ and 𝑄Q , the mass‑action ratio, can determine whether a metabolic reaction is far from equilibrium. The equation for this equilibrium is, fructose 6-phosphate+ATP↽−−⇀fructose 1,6-bisphosphate+ADPfructose 6-phosphate+ATP↽−−⇀fructose 1,6-bisphosphate+ADP Calculate 𝐾′eqKeq′ for this reaction at 𝑇=25.0 ∘CT=25.0 ∘C . Δ𝐺∘′=−14.2 kJ/mol
𝐾′eq=Keq′= 308.4 Calculate the mass‑action ratio, 𝑄Q , from the approximate physiological concentrations for rat heart tissue shown in the table. Δ𝐺=𝑅𝑇ln(𝑄𝐾′eq)=8.3415Jmol⋅K×1 kJ1000 J×298 K ln(0.00016)=−21.8kJmol 𝑄=0.047 (35 X 1340) / (84 X11800)
