Exam 3 Study guide

Which of the following best describes the relationship among a subunit of the protein, metal cofactors, and ligands?

A metal ion and ligand interact with the protein in locations proximal to one another.

Which amino acid is NOT a target for kinases?

Asp

Which of the following is the balanced reaction for the catabolism of glucose to lactate?

Glucose + 2 ADP + 2 Pi → 2 Lactate + 2 ATP + 2 H2O

Which enzyme can be used in the production of HFCS to convert glucose to fructose in a single step?

Glucose isomerase

Which of the following is correct about the link between Ras and cancer?

Mutated Ras is an oncogene.

Which of the following is correct about the binding of epidermal growth factor to its receptor?

The cytoplasmic tail of EGFR2 is phosphorylated before EGFR1.

In which situation is glycolysis alone likely to be a major contributor to ATP generation?

erythrocytes

Which state of glycogen phosphorylase gives the enzyme its highest activity?

phosphorylated glycogen phosphorylase

Which of the following is least likely to affect the metabolic flux of a metabolic pathway?

steady-state substrate concentrations

Why does lactase deficiency lead to the retention of lactose within the small intestine and prevent transport across the intestinal lumen?

-Transport proteins in the intestinal lumen are specific for monosaccharides. -Lactose is a polar molecule and cannot cross the intestinal membrane without a transport protein

Phosphorylation of glucose to produce glucose-6-phosphate has ΔG˚'

13.8 kJ/mol without the use of ATP.

Consider the pathway A → B → C → D → E. Reactions A → B, B → C, and D → E have a ΔG near equilibrium, while C → D has a ΔG << 0. Which of the following is true about this pathway if it were operating within a cell?

Adding more A to the system will increase the amount of B and C in the system.

What step of insulin-initiated signaling is shown in B in the figure below?

Autophosphorylation of tyrosine

Determine the relative proportions of secondary and quaternary structure(s). What best describes these structures?

The major secondary structures are beta sheets, and there is no quaternary structure.

Which of the following ligands is most likely to bind the receptor shown in B?

Vit D

Cancer cells have many alterations in their metabolic pathways, including some that alter the way they metabolize and use glucose. This is known as the Warburg effect. One component of the Warburg effect is the inhibition of the enzyme that converts pyruvate to acetyl CoA. Under these conditions, what metabolite will be elevated in cancer cells as compared to noncancerous cells even under normal oxygen

lactate

Even in the presence of a properly signaling TNF receptor signaling pathway that involves FADD and TRADD, breast cancer cells do not undergo apoptosis in response to TNF -alpha allowing tumors to grow and metastasize... What is the most likely cause of resistance to cell death by TNF- alpha in breast cancer cells?

loss or mutational inactivation of caspase 8

Coupling phosphorylation with ATP hydrolysis gives ΔG˚'

-16.7 kJ/mol.

The net reaction would have ΔG˚= _____ kJ/mol

-6.7

A net yield of ___ ATP would be produced from the conversion of three molecules of glucose into pyruvate.

6

Consider the two metabolic reactions below: Reaction 1: A + B → C ΔG˚ = 8.8 kJ/mol Reaction 2: C → D ΔG˚ = -15.5 kJ/mol If reaction 1 and 2 are coupled, what would the net reaction be?

A + B --> D

Which of the following statements is true concerning the role of cGMP in vasodilation?

A cGMP is a secondary messenger that acts on protein kinase G.

Which of the following mutations would most impact PKA, leading to a constitutively active enzyme?

A mutation of the catalytic subunit where the kinase can still bind its target but no longer binds the regulatory subunit

If phosphofructokinase experienced a mutation that interfered with substrate binding, then what other enzyme is going to be most immediately impacted in terms of accessing substrate?

Aldolase

The structure of D-arabinose is shown below as a Fischer projection. Identify the correct structure of L-arabinose.

B

two disaccharides commonly found in nature. Which end is responsible for a positive result in Benedict's test?

B

Once insulin has bound the alpha subunit of the insulin receptor, the beta subunit of the receptor can bind to an insulin receptor substrate (IRS) protein, which acts as a membrane scaffold. What events happen next that enable the beta subunit and the IRS protein to bind together

Binding of insulin induces conformational changes in the beta subunits, which enables them to autophosphorylation tyrosine residues. These P-tyrosine residues are recognized by the phosphotyrosine binding sites (PTB domain) present in an IRS protein

Which of the following can enter glycolysis without additional reactions?

Both products from maltose after maltase treatment

Both epinephrine (a tyrosine derivative) and glucagon (a peptide hormone) increase glucose export from the liver into the bloodstream. Each ligand binds a different receptor, but both lead to an activation of PKA. How does this happen?

Both receptors bind and activate the same Gα subunit, Gsα, which indirectly leads to PKA activation.

Which of the following is NOT a primary mechanism for affecting catalytic efficiency?

Cellular compartmentalization

Which of the following relationships is correctly defined?

D-Ribose and D-Xylose are epimers

Which of the following activates a zymogen?

Enterokinase

Kinase enzymes phosphorylate other proteins and enzymes. This is a common mechanism of covalently modifying enzymes in order to control their catalytic efficiency. Which of the following amino acids is not targeted for phosphorylation by kinases?

Leucine

Which of the following is not a primary mechanism used to regulate the catalytic efficiency of enzymes?

RNA synthesis

Part 1 Observe the ribbon structure of pepsin. To do this, click the green-outlined box at the bottom of the player. Green x's will appear over your selection. Then go to the dropdown menu and on the "Display" line, click the "Toggle Ribbon for selection" icon. Then click the "Toggle CPK for selection" icon to remove the space-filling display. To remove the green x's, click "Clear Selection" on the "Misc" line of the dropdown menu. Determine the relative proportions of secondary and quaternary structure(s). What best describes these structures?

The major secondary structures are beta sheets, and there is no quaternary structure.

The reaction mechanism of glyceraldehyde-3-phosphate dehydrogenase is shown below. Glyceraldehyde-3-phosphate dehydrogenase catalyzes the phosphorylation of glyceraldehyde-3-phosphate, but unlike other glycolytic reactions, it does not require energy investment from ATP. This reaction occurs in two stages: oxidation/reduction and phosphorylation. Why is the oxidation/reduction reaction necessary to make phosphorylation favorable?

The oxidation/reduction reaction is necessary to form an intermediate with a large free energy of hydrolysis

Which of the following is not a biochemical process affecting the bioavailability of enzymes?

binding of a competitive inhibitor kinase

Determine the secondary structure(s) that is/are exhibited in this polypeptide.

both alpha helices and beta sheets

What molecule, labeled "A" in the figure below, is responsible for protein kinase A activation?

cAMP

The Lineweaver-Burk plot shown below is for a(n) __________ inhibitor.

competitive inhibitor

A _______ inhibitor is a type of irreversible inhibitor.

covalent

A consequence of skipping step 4 (adding yeast straight into anaerobic culture conditions) would cause the total amount of ethanol produced to

decrease

The flux of which of the following reactions would depend only on substrate availability?

dihydroxyacetonephosphate → glyceraldehyde-3-phosphate -glucose-6-phosphate → fructose-6-phosphate

does not bind directly to a membrane receptor?

estradiol

Glucagon binding to the glucagon receptor inhibits which of the following processes?

glycogen synthesis

In which step would the majority of pyruvate produced from glycolysis be converted to acetyl CoA?

step 4

Individuals with a deficiency in the aldolase B enzyme have a condition known as hereditary fructose intolerance. The metabolic intermediate that accumulates in the liver as a result of this deficiency can have an indirect, activating effect on hepatic glucokinase. The blood glucose levels in these individuals

would be lower than normal due to the increased reaction rate of glucokinase.

Label the graph below to show the effect of high ATP, ADP, or fructose-2,6-bisphosphate on phosphofructokinase-1 (PFK-1) activity

yellow C green A red B

The last reaction in glycolysis involves transfer of a phosphate group from phosphoenolpyruvate to ADP, yielding pyruvate and ATP. The coupled ΔG°' of this reaction is -31.4 kJ/mol. If ΔG°' of ATP hydrolysis is -30.5 kJ/mol, what is the ΔG°' of hydrolysis of phosphoenolpyruvate?

-61.9 kj/mol

Why would mutation of a tyrosine residue to glutamate in the intracellular portion of a growth factor receptor lead to increased tumor formation?

-A receptor with a glutamate in the place of a tyrosine is a "phosphomimetic." That is, the protein mimics the phosphorylated state of tyrosine. -Unlike tyrosine, a glutamate will leave the receptor "constitutively" active and no longer responsive to the phosphatases that shut off such signaling.

Again consider the pathway above. Under what conditions would adding more A to the system not lead to an increase in the flux of the pathway from A to E?

-An allosteric inhibitor of the enzyme that catalyzes C → D is also present in the system. -The enzyme that catalyzes C → D has already reached 100% of Vmax.

Which of the following statements correctly describe the properties of glucose and fructose?

-Glucose and fructose are both hexose sugars -Glucose can form furanose and pyranose ring structures, while fructose can only form a furanose ring -Glucose is found in at least three common disaccharides found in nature, while fructose is a component of only one

Along with other similar symptoms, both deficiencies can also result in reduced lactate levels during exercise. In order to distinguish between these two disorders, a physician could test the patient's lactate levels during exercise before and after administering glycerol. What would be the expected results if this test were performed?

-Lactate levels would be low after intense exercise and would not increase after glycerol was administered if the patient has a deficiency in lactate dehydrogenase. -Lactate levels would be low after intense exercise and would increase after glycerol was administered if the patient has a deficiency in muscle phosphofructokinase-1.

Cross talk is when one signaling pathway, such as a GPCR, can activate a different receptor's signaling pathway, such as a growth factor receptor (tyrosine kinase receptor) pathway. You have created a new drug X that you find activates cell growth in a dish of cultured cells. Remembering that ERK activation can lead to cell growth, you now wish to find out how your drug might be activating ERK. Using a special antibody that only recognizes activated phosphorylated extracellular signal regulated kinase (pERK), you find that your drug blocks the phosphorylated ERK (see the western blot figure). To test what pathway(s) your compound might inhibit, you incubate the drug without or with a combination of two inhibitors. PKA Inhibitor (PKA-I) blocks the activation of PKA. Raf Inhibitor (Raf-I) stops Raf from binding to its targets. Using the results of this experiment, select the correct answer or answers that describe the results of the experiment.

-Loss of activation of ERK when PKA-I is added prior to compound X indicates that the drug is activating via a GPCR. -Compound X activates ERK through a PKA phosphorylation-mediated event. -ERK phosphorylation is increased when compound X is added to the dish, indicating the activation of ERK.

Cortisone is a type of glucocorticoid mimic that binds to a nuclear receptor, activating the receptor's transcriptional regulatory function. The ligand-activated receptor binds coregulatory proteins, and the protein complex targets gene transcription involved with inflammation. Which of the following statements about these two drugs best describe their mechanism of action?

-Rosiglitazone will bind to its receptor (peroxisome proliferactor-activated receptor), and the receptor-ligand complex can bind to the RXR receptor in a head-to-tail fashion -Receptor dimers with bound cortisone bind to the DNA target using zinc finger to bind to an inverted repeat that must be at least partially palindromic to be recognized

Structure-based drug design strategies often devise competitive inhibitors that bind to certain enzyme active sites. For example, saquinavir and indinavir are designed HIV protease inhibitors that bind to the aspartate protease enzyme of HIV, which is required for the virus to produce functional proteins for further HIV infection. Which of the following statements are true about saquinavir and indinavir?

-Saquinavir and indinavir both have a component that mimics the natural Phe-Pro dipeptide substrate of aspartate protease. -Very high local concentrations of proteins with Phe-Pro or Tyr-Pro peptide bonds would reduce the effectiveness of saquinavir and indinavir in limiting HIV's infectivity of new cells. -The removal of the phenyl ring (six-membered carbon ring containing three double bonds and no attached functional groups) on indinavir and saquinavir would likely affect their inhibitory activity.

Tasting involves many different cell-signaling processes that ultimately generate nerve signals transduced by membrane depolarization. Sweet tastes result in PIP2 hydrolysis, while salty tastes allow sodium ions to directly alter the membrane potential. What can you deduce about the signaling mechanisms for sweet and salty?

-Sweet utilizes the GPCR signaling pathway, activating phospholipase C. -Sodium ions directly enter the cells, indicating the signal is transduced by an ion channel.

Glycolytic reactions can either be described as reversible or irreversible. Looking at all 10 reactions in glycolysis, what conclusions can you make about irreversible reactions in general?

-The enzymes that catalyze these reactions are not shared in opposing pathways (i.e., glycolysis and gluconeogenesis). -They operate far from equilibrium. -The activity of the enzymes that catalyze irreversible reactions can be increased or decreased.

Insulin is released by the beta islets of the pancreas after a meal when glucose levels are high. Released as a peptide, insulin binds to a unique class of receptors that lead to the reduction of blood sugar levels. The insulin receptor has a tyrosine kinase intracellular domain. However, unlike many other similar single transmembrane receptors with a tyrosine kinase activity (such as growth factor receptors), the insulin receptor is a crosslinked dimer in the resting state made of two alpha and two beta strands (heterotetramer). Which of the following statements describe how the insulin receptor is activated?

-The intracellular domain of the insulin receptor, specifically the tyrosines, must be phosphorylated to recruit the intracellular signaling partners. -Insulin binding to the insulin receptor induces a conformational change that stimulates tyrosine autophosphorylation of the beta subunits.

Retinoblastoma is a rare form of eye cancer where tumors grow in youth and young adults. For the most part, this cancer is due to one gene called the Rb1 gene. You have found that a father carries one of the genes with this mutation. He does not show symptoms of the disease. Genetic screening of the mother finds both copies of her genes are wild-type, not mutated. Of the four children, only one has retinoblastoma, but it did not show up until much later in the young man's life. Another family with both parents harboring one of the mutated copies had one of their four children with the disease, and the symptoms started much earlier. Which of the following are likely to explain these results

-The requirement for both genes to mutate indicates a loss-of-function tumor suppressor gene mutation. -The son whose father carried the mutated Rb1 gene likely developed a mutation in the Rb1 gene later in life, indicating this is a tumor suppressor gene.

Sucralose is a nonnutrative sweetener composed of a chlorinated molecule shown below. The IUPAC name of this molecule is 1,6-dicholoro-1,6-dideoxy-β-D-fructofuranosyl-4-chloro-4-deoxy-α-D-galactopyranoside. Although the majority of ingested sucralose is not hydrolyzed in the small intestine, a small amount can be hydrolyzed to produce equimolar amounts of 1,6-dichloro-1,6-dideoxyfructose and 4-chloro-4-deoxygalactose. Are either of the hydrolysis products reducing sugars?

1,6-Dichloro-1,6-dideoxyfructose is a nonreducing sugar, and 4-chloro-4-deoxygalactose is a reducing sugar.

Whether a G alpha subunit is active or inactive depends on which guanine nucleotide is bound to it. Binding of GDP or GTP results in the protein switching between two conformational states. Which of the following answers best describes the structural changes that occur in a G alpha subunit due to guanine nucleotide binding?

Dissociation of GDP for GTP with the G alpha subunit structurally shifts the switch II helix region, allowing for the association of G alpha with its effector proteins, such as adenylate cyclase.

Lysophosphatidic acid (LPA) is a water-soluble phospholipid derivative found in blood serum, where it binds to receptors throughout the body, inducing cell growth and other effects. This is an example of what kind of signaling system?

Endocrine

Which of the following first messengers is unique because it is not water soluble and does not bind directly to a membrane receptor?

Estradiol

Beta-adrenergic receptor signaling must be terminated quickly or an extended metabolic shift could cause serious problems for the organism. Which best explains how receptors are "desensitized"?

G protein-coupled receptor kinases (GRKs) are protein kinases that phosphorylate receptors for internalization.

You have a mystery hormone (agonist), and to test the nature of the agonist you add it to a dish of cultured liver cells. Shortly afterward you observe an increase in protein kinase activity. In a second experiment, you find the kinase is inhibited if you add an adenylate cyclase inhibitor to the cells prior to adding your mystery agonist. Which kind of receptor system is the agonist signaling through?

GPCR

Why is HFCS preferred over corn syrup for sweetening beverages and processed foods?

HFCS is sweeter than corn syrup

How would the oxygen saturation of hemoglobin in an individual with diphosphoglycerate mutase deficiency compare to that in an unaffected individual?

Hemoglobin oxygen saturation would be increased in the erythrocytes of individuals with diphosphoglycerate mutase deficiency as compared to a normal individual.

Which of the following statements best describes the effect of ADP on the activity of PFK-1?

High concentrations of ADP block the inhibitory effect of ATP by competing for the same allosteric site on PFK-1.

Which of the following is true regarding the roles of adenylylation and uridylylation in the control of glutamine synthetase?

High levels of ATP and α-ketoglutarate result in more deadenylylated glutamine synthetase.

Interaction of glucocorticoid receptors with which of the following prevents binding to glucocorticoid response elements (GREs)?

Hsp90

Lactose intolerance is a condition caused by a deficiency in the lactase enzyme. Individuals with this deficiency can experience unpleasant symptoms if they eat lactose-containing foods such as dairy products. The human gene for lactase is expressed at high levels in infants to aid in the digestion of lactose in breast milk; however, lactase expression normally declines in adults, with the notable exception of people of Scandinavian descent. What reaction is catalyzed by lactase?

Hydrolysis of lactose to produce glucose and galactose

Which of the following is the downstream signaling protein for the TRADD-associated complex in the cell survival path of TNF signaling?

IKK

Caffeine leads to a vasoconstriction, raises the epinephrine levels, and increases nervous signaling. A metabolite of caffeine blocks phosphodiesterase. What is the most likely impact of caffeine on cell signaling?

Inhibition of the phosphodiesterase results in an elevated cAMP levels and PKA activation, leading to increased glycogen breakdown and increased phosphorylation of events controlling the physiology of caffeine addiction.

Mike has lactose intolerance and has to ingest commercial lactase in pill form before consuming milk products in order to avoid the unpleasant symptoms associated with this disorder. One day he noticed a classmate refusing a free sample of the new milkshakes sold in the campus cafe. His classmate, Jamal, explains that he has to avoid all milk products in his diet because he has galactosemia. Mike offers Jamal one of his lactase pills. Because both of their disorders are caused by consumption of milk products, he thinks Jamal should try lactase to see if it will allow him to try the milkshake. Should Jamal try the lactase pill to see if it will work?

Jamal should not follow Mike's advice. If Jamal ingests lactase along with the milkshake, it could cause harmful side effects.

Long-term ( longterm ) activation by nuclear receptors differs from the more transient membrane receptor signaling for what reason?

Long-term activation occurs by nuclear receptors activating sets of genes, while membrane receptors involve small second messenger molecules responding quickly, as their signaling occurs by activation of kinases, phosphatases, and other enzymes already expressed in the cell.

One subtype of breast cancer involves the human epidermal growth factor receptor 2 gene (EGF receptor). One in every five breast cancers has a mutation in this gene. Understanding that this is a growth factor receptor gene, which of the answer choices best describes how this type of cancer develops?

Mutations that activate the kinase portion of the receptor result in a receptor that is constantly phosphorylated. This causes constitutive activation of downstream signaling and the resulting cell growth and proliferation.

Phosphorylation of glucose requires 1 ATP. Can the reverse reaction be used for substrate-level phosphorylation?

No, phosphate hydrolysis of glucose-6-phosphate is not spontaneous enough to couple to ATP synthesis.

A student on the cross country team wishes to improve her performance in an upcoming race. She has taken an introductory science course and knows that oxidation of glucose produces ATP for muscle contraction. The student normally eats small amounts of glucose gel for energy during a long run, and she decides that the best course of action is to triple the amount of glucose gel she eats each time so that her muscles can have access to more glucose. Will this strategy work?

No; ingesting additional glucose gel will raise the blood glucose level but will not increase the reaction rate of hexokinase. Instead, the increase in glucose will increase the reaction rate of glucokinase, which could have negative effects on the athlete's performance.

Which of the following is not a parameter that governs the cell-specific physiological responses controlled by nuclear receptors?

Organism-wide expression of coregulatory proteins

Choose the correct statements about the function and activity of arrestin.

PKA phosphorylation also modifies GPCR, leading to arrestin binding to the receptor for endosomal transport Arrestin facilitates protein transport, which prevents a receptor from reassociating with the G protein complex

Which enzyme is responsible for terminating the activity of membrane-bound PIP3?

Phosphatase and tensin homolog, PTEN

Which enzyme's activity is controlled by the levels of glucose-6-P and fructose-6-P in the cell?

Phosphoglucoisomerase

Phosphorylation of glucose requires 1 ATP. Can the reverse reaction be used for substrate-level phosphorylation?

Phosphorylation of glucose requires 1 ATP. Can the reverse reaction be used for substrate-level phosphorylation?

The catalytic activity and/or conformational stability of this protein is likely dependent upon _____ of peripheral amino acid side chains. These side chains are expected to have a _____ value.

Protonation Low pka

Erythrocytes with a deficiency in both _______ and biphosphoglycerate mutase would have 2,3-biphosphoglycerate levels similar to that of unaffected erythrocytes.

Pyruvate kinase

The spontaneous direction of a metabolic reaction is dictated by the ratio of substrate and products under equilibrium conditions (K) and under cellular conditions (Q). Compare the two reactions A→B and C→D. For A→B, ΔG˚ = -13 kJ/mol. For C→D, ΔG˚ = 3.5 kJ/mol. The cellular concentrations are as follows: [A] = 0.050 mM, [B] = 4.0 mM, [C] = 0.060 mM, and [D] = 0.010 mM. Which statement below correctly describes the relationship between Q and K for both reactions? Are these reactions spontaneous as written under cellular conditions?

Q < K for both reactions. Both are spontaneous at those concentrations of substrate and product.

Under cellular conditions, ΔG' = -26.8 kJ/mol for the coupled reaction, while phosphoenolpyruvate hydrolysis has ΔG' = -76.0 kJ/mol. How does coupling phosphoenolpyruvate hydrolysis with ATP synthesis change the relationship between Q and Keq?

Q < Keq for both reactions; Q/Keq uncoupled < Q/Keq coupled

Consider two reactions. Reaction 1 (P → Q) has ΔG = 2.3 kJ/mol. Reaction 2 (Q → R) has ΔG = 12.3 kJ/mol. Which reaction is more likely to require coupling to ATP or the equivalent in order to be spontaneous under cellular conditions?

Reaction 2 (Q → R). This reaction is nonspontaneous and operates far from equilibrium in the cell. It will not be able to proceed as written in the cell without coupling to a process with a large negative free energy change (such as ATP hydrolysis).

TNF-alpha activation can lead to a cell survival mechanism as well as cell death. In the survival portion of TNF receptor signaling, TRADD recruits two adaptor proteins that function to initiate a downstream phosphorylation cascade. What is the role for one of these adaptor proteins called TNF receptor-associated factor 2 (TRAF2)?

TRAF2 recruits and activates NIK (NFkB inducing kinase) to the TNF receptor complex where NIK phosphorylates IKK, leading to the active transcription of anti-apoptotic genes.

Glyceraldehyde-3-phosphate dehydrogenase catalyzes the phosphorylation of glyceraldehyde-3-phosphate, but unlike other glycolytic reactions, it does not require energy investment from ATP. This reaction occurs in two stages: oxidation/reduction and phosphorylation. Why is the oxidation/reduction reaction necessary to make phosphorylation favorable?

The oxidation/reduction reaction is necessary to form an intermediate with a large free energy of hydrolysis.

Which of the following correctly describes the biochemistry of the amino acids at the termini of pepsin?

Two nonpolar amino acids at the N-terminus and one polar amino acid at the C-terminus

You are culturing mammalian brain cells with standard growth media that includes 10% fetal bovine serum (FBS). FBS has a number of hormones and other components that stimulate cell growth. Over a busy weekend you made a mistake and left the cells in media without FBS. These cells have begun apoptosis while normally cultured cells are growing and surviving just fine. Which might be the reason for the dying cells?

Withdrawal of a positive growth signal induced the cell death pathway of TNF-alpha.

Using concentrations of intermediates found in a cell, the phosphorylation of glucose using inorganic phosphate has ΔG' = 19.7 kJ/mol, while phosphoryl transfer from ATP (ATP investment) results in ΔG' = -34.5 kJ/mol. What does this tell you about the values of Q and Keq for the phosphorylation of glucose with and without energy investment from ATP?

Without ATP investment, Q > Keq, and with ATP investment Q < Keq.

Which statement explains why glucose phosphorylation could not occur without ATP investment?

Without ATP investment, one or both of the substrates would need to exceed the solvent capacity of the cell for glucose phosphorylation to occur

Sucrose, maltose, and lactose are common dietary disaccharides. Their monosaccharide components are substrates for the glycolytic pathway, but some must participate in additional reactions before they can act as substrates for a glycolytic enzyme. As a result, all do not enter glycolysis at the same step. In muscle cells, which enzyme would act as the rate-limiting step to regulate entry of products from all three dietary disaccharides into glycolysis?

phosphofructokinase-1

The catalytic activity and/or conformational stability of this protein is likely dependent upon protonation of peripheral amino acid side chains. These side chains are expected to have a low pKa value.

protonation low pka

A hydrophobic environment is necessary for optimal activity of phosphoglycerate kinase

to prevent hydrolysis of 1,3-bisphosphoglycerate.

Glucokinase is important for the regulation of glycolysis because it

traps extra glucose in liver cells for glycogen production.

Part 2 Which of the following correctly describes the biochemistry of the amino acids at the termini of pepsin?

two nonpolar amino acids at the N-terminus and one polar amino acid at the C-terminus