Glucose Transport Systems Quiz

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187 Questions

Which glucose transporter is responsible for basal glucose uptake in almost all mammalian cells?

GLUT1

In what type of cells is GLUT-3 the primary glucose transporter?

Neurons

Which glucose transporter is present in the liver and pancreatic β cells and allows glucose to rapidly enter liver cells only in times of plenty glucose levels?

GLUT2

Which glucose transporter is insulin-dependent and transports glucose into muscle and fat cells?

GLUT4

Which glucose transporter functions primarily as a fructose transporter and is present in the small intestine?

GLUT5

Which glucose transporter in the GLUT family has a Km of around 15-20 mM and plays a role in sensing glucose levels in the pancreas?

GLUT2

Which term best describes the breakdown of 1 molecule of glucose to 2 molecules of pyruvate in the glycolysis pathway?

Glycolysis

In which cellular compartment does glycolysis take place?

Cytosol

Which tissues rely primarily on glycolytic breakdown of glucose as their main source of metabolic energy?

Brain tissue

What is the main purpose of the Pentose Phosphate Pathway in glucose metabolism?

Generate NADPH for reductive biosynthetic processes

Under aerobic conditions, what is the fate of pyruvate produced from glycolysis?

Converted to CO2 for more ATP production

What are the characteristics of the preparatory phase of glycolysis?

Requires priming steps that demand energy

What are the three enzymes in glycolysis that are potential regulation sites due to catalyzing virtually irreversible reactions?

Hexokinase, pyruvate kinase, and phosphofructokinase

In glycolysis, what initiates an increase in the amount of glucokinase, phosphofructokinase, and pyruvate kinase in the liver?

Meals rich in carbohydrates

What effect does glucagon have on the activity of enzymes like glucokinase, phosphofructokinase, and pyruvate kinase?

Diminishes their activity

Which enzyme is inhibited by high levels of glucose 6-phosphate (G6P), indicating that the cell doesn't require glucose for energy or glycogen synthesis?

Hexokinase

What initiates an increase in the synthesis of glucokinase by the liver?

Elevation of blood glucose levels after a meal

What is the primary function of glycolysis in muscle?

To provide ATP for muscle contraction

What is the main control site in the mammalian glycolytic pathway?

Phosphofructokinase (PFK)

In muscle functioning anaerobically, why is the inhibitory effect of phosphofructokinase important?

To protect the muscle from damage

How is pyruvate kinase affected by high levels of ATP?

Inhibited

What is the role of glucokinase in the liver?

Converts glucose to glycogen

How is glucokinase activity regulated in the liver?

Indirectly inhibited by fructose 6-phosphate

What activates phosphofructokinase (PFK) in the liver?

[F-2,6-BP] increase

What is the rationale behind the cleavage of F-1,6-Bisphosphate in glycolysis?

To convert a six-carbon sugar into two three-carbon sugars.

Why is Phosphofructokinase-1 in glycolysis considered highly regulated?

It catalyzes an irreversible reaction.

What is the purpose of the oxidation of Glyceraldehyde 3-Phosphate to 1,3Bisphosphoglycerate in glycolysis?

To create a high-energy phosphate compound.

Why is the migration of the phosphate important in glycolysis?

To form high-energy phosphate compounds.

Which process in glycolysis involves dehydration of 2-PG to PEP?

Conversion of Fructose 6-Phosphate to Fructose 1,6 bis-Phosphate.

What is the primary reason for keeping the concentration of Glyceraldehyde-3-Phosphate low during glycolysis?

To pull reactions forward.

Which pathway regenerates NAD+ for further glycolysis under anaerobic conditions?

Lactic acid fermentation

In what type of cells does the reduction of pyruvate to ethanol occur?

Muscle cells

Which pathway involves the reduction of pyruvate to lactate?

Lactic Acid Fermentation

What is the fate of pyruvate under aerobic conditions?

Oxidized to acetate for the citric acid cycle

Which tissues rely primarily on anaerobic glycolysis for energy production?

Muscle

Under hypoxic conditions, how is NAD regenerated?

Lactic acid fermentation

What happens to lactate released from cells undergoing anaerobic glycolysis in the liver?

It is used to synthesize glucose which is then returned to the blood

What is the primary function of the Cori Cycle?

Metabolic cooperation between skeletal muscle and the liver

In glycolysis, why is there a need for shuttles like the Glycerol 3-phosphate shuttle?

To transport NADH across the mitochondrial inner membrane

What is the major function of the Malate–aspartate shuttle in glycolysis?

Transport NADH across the mitochondrial inner membrane

Which statement accurately describes the fate of lactate in many tissues?

It is oxidized to pyruvate and then to CO2 in the TCA cycle

What role does oxygen supply play in determining the fate of lactate in tissues?

It enhances the conversion of lactate to pyruvate

Where do glycolytic NADH molecules undergo reoxidation to keep the glycolytic pathway functional?

Inner mitochondrial membrane

Which enzyme is responsible for the conversion of malate to oxaloacetate in the malate-aspartate shuttle?

Malate dehydrogenase

What is the main reason for using the malate-aspartate shuttle for NADH reoxidation in liver, heart, and kidney cells?

Prevention of NADH accumulation in the cytoplasm

Which molecule is not involved in the feeder pathways for glycolysis?

Pyruvate

What is the primary function of the glycerol phosphate shuttle in oxidative phosphorylation?

Formation of mitochondrial FADH2

What is the role of glycogen phosphorylase in the feeder pathways for glycolysis?

Converting glycogen to glucose-1-phosphate

What is the role of Succinate Dehydrogenase in the TCA cycle?

Catalyzes the conversion of succinate to fumarate

Where does the citric acid cycle (TCA cycle) primarily occur in eukaryotic cells?

Mitochondrial matrix

Which stage of cellular respiration involves the generation of GTP?

Stage 2: Acetyl-CoA Oxidation

What is the function of the Pyruvate Dehydrogenase Complex in cellular respiration?

Converts pyruvate to acetyl-CoA

Which enzyme is responsible for the conversion of pyruvate to acetyl-CoA in the mitochondria?

Pyruvate Dehydrogenase Complex

What is the main function of the Citric Acid Cycle (TCA cycle) in cellular metabolism?

Produce reducing equivalents NADH and FADH2

What is the role of arsenite in inhibiting the pyruvate dehydrogenase complex?

It affects lipoic acid in the complex

Which of the following is NOT an advantage of multienzyme complexes like the pyruvate dehydrogenase complex (PDC)?

Increases the complexity of regulation

What is the prosthetic group involved in the inhibition of aconitase by fluorocitrate?

FAD

How is Succinate Dehydrogenase different from Isocitrate Dehydrogenase and α-Ketoglutarate Dehydrogenase?

Have different active sites for substrates

Which enzyme catalyzes the conversion of Succinyl-CoA to Succinate in the TCA cycle?

Succinate Thio kinase

Why is the hydration of Fumarate to Malate considered a stereospecific trans addition by Fumarase?

Only one side of fumarate receives an OH- group

What happens in tissues capable of fatty acid synthesis when there is an inhibition of isocitrate dehydrogenase?

Buildup of citrate leading to the cessation of glycolysis.

What is the consequence of inhibiting α-ketoglutarate dehydrogenase?

Buildup of α-ketoglutarate used for the synthesis of many amino acids and purine bases.

What does a rise in mitochondrial Ca2+ levels lead to in terms of pyruvate dehydrogenase activity?

Enhances the phosphatase activity for acetyl CoA production.

In tissues capable of fatty acid synthesis, what role does insulin play in relation to pyruvate?

Stimulates the phosphatase for the conversion of pyruvate into acetyl CoA.

What is the significance of a buildup of citrate due to isocitrate dehydrogenase inhibition?

Signals glycolysis to stop.

Which enzyme catalyzes the step in the citric acid cycle that involves substrate-level phosphorylation to give GTP?

Succinyl-CoA synthetase

Which vitamin is required for the citric acid cycle as a precursor to Coenzyme A (CoA)?

Pantothenic Acid (B5)

What is the net result of the citric acid cycle on a per Acetyl-CoA basis?

2 NADH, 1 FADH2, 1 GTP

Which enzyme is primarily responsible for the regulation of Pyruvate Dehydrogenase Complex through reversible phosphorylation?

Pyruvate dehydrogenase kinase

Which statement accurately describes the regulation of the Citric Acid Cycle?

Activated by substrate availability, inhibited by product accumulation

Which vitamin functions as a precursor to FAD, an essential cofactor in the citric acid cycle for electron transfer reactions?

Riboflavin (B2)

What is the main purpose of PEP carboxykinase in gluconeogenesis?

Converts pyruvate to phosphoenolpyruvate

Which enzyme is the first regulatory enzyme in the gluconeogenic pathway?

Pyruvate carboxylase

What source of energy does GTP provide in the conversion of oxaloacetate to phosphoenolpyruvate?

Phosphate group

Where does phosphoenolpyruvate carboxykinase (PEPCK) primarily convert oxaloacetate to phosphoenolpyruvate?

Cytosol

What factor determines the relative importance of the two pathways from pyruvate to phosphoenolpyruvate?

Presence of lactate or pyruvate

What effect does glucagon have on fructose 1,6-bisphosphatase activity in response to low glucose levels?

Activates it

Which enzyme does glucagon inhibit to decrease the concentration of fructose 2,6-bisphosphate in the liver?

PFK-2

Where is glucagon primarily produced in the body?

Pancreas

What effect does glucagon have on glucose export into the bloodstream from muscle and adipose tissue?

Halts it completely

What is the transcriptional effect of glucagon on PEP-carboxykinase?

Induction

What is the exception to the rule that glucose cannot be synthesized from fatty acids?

Propionate

Which molecule can be converted to glucose through the generation of dihydroxyacetone phosphate?

Fructose

Where does pyruvate carboxylase convert pyruvate into oxaloacetate?

Mitochondria

Which enzyme is involved in the first energy-consuming step to convert pyruvate into oxaloacetate?

Pyruvate carboxylase

Which location does glucose 6-phosphatase primarily occupy?

Endoplasmic reticulum

What is the importance of UDPglucose in the conversion of galactose into glucose?

Recycling intermediate

What enzyme catalyzes the reverse reaction of the opposing step in glycolysis during gluconeogenesis?

Fructose bisphosphatase-1

Which enzyme is responsible for converting Fructose 1,6-bisphosphate to Fructose 6-phosphate in gluconeogenesis?

Fructose bisphosphatase-1

Where is Glucose 6-phosphatase found in hepatocytes and renal cells?

Endoplasmic reticulum

What is the cost in terms of ATP, GTP, and NADH for producing one molecule of glucose through gluconeogenesis?

4 ATP, 2 GTP, 2 NADH

Which cells rely ONLY on glucose for ATP generation?

Brain, nervous system, and red blood cells

When do the bypasses of fructose bisphosphatase-1 and glucose 6-phosphatase occur in gluconeogenesis?

During starvation

What effect does increased concentration of acetyl-CoA have on pyruvate carboxylase and the pyruvate dehydrogenase complex in the context of gluconeogenesis?

Inhibits pyruvate carboxylase and activates the pyruvate dehydrogenase complex

Under which conditions is pyruvate carboxylase active?

Elevated levels of Acetyl CoA

What is the role of Fructose 2,6-Bisphosphate in the liver in terms of glycolysis and gluconeogenesis?

It is a positive allosteric effector of PFK-1 and an inhibitor of fructose-1,6-bisphosphatase

What induces Phosphoenolpyruvate carboxykinase, an enzyme involved in gluconeogenesis?

Glucagon

What is the impact of high ATP and citrate levels on cellular metabolism?

Indicate high energy charge and abundant biosynthetic intermediates

How do glucagon and insulin influence the regulation of gluconeogenesis?

Glucagon promotes gluconeogenesis while insulin inhibits it

Which enzyme is required for the synthesis of glycogen from UDP-glucose?

UDP-glucose pyrophosphorylase

What is the high-energy carrier involved in glycogen synthesis?

UDP-glucose

In glycogen synthesis, what is the function of branching enzyme?

Catalyzes formation of branch points in glycogen molecules

Which enzyme is necessary for the de novo synthesis of a new glycogen molecule in addition to the regular glycogen synthesis enzymes?

Glycogenin

What is the activated form of glucose used in glycogen synthesis?

UDP-glucose

Where does de novo synthesis of glycogen predominantly occur?

Cytosol

Why is glycogen considered a good source of fuel for anaerobic activity?

Glycogen can be used as an energy source even in the absence of oxygen.

Where is glycogen principally stored in the body?

Cytosol granules of liver and muscle cells

What is the significance of the large number of nonreducing ends in glycogen structure?

They allow for rapid mobilization of glycogen stores.

What is the average distance between branch points in glycogen structure?

8-10 residues

How does the regulation of glycogen synthesis and breakdown differ between skeletal muscle and liver cells?

Skeletal muscle cells break down glycogen for immediate use while liver cells maintain blood glucose levels.

What role does the large number of nonreducing ends play in glycogen metabolism?

They are required for the regulation of enzymes involved in glycogen metabolism.

What is the primary function of glycogen phosphorylase?

Catalyzes the removal of glucosyl residues from glycogen

What is the purpose of the debranching enzyme in glycogenolysis?

To cleave a-1,6 linkages in glycogen

What is the outcome of the phosphorolysis reaction catalyzed by glycogen phosphorylase?

Removal of glucosyl residues from glycogen

What is the role of transferase in glycogen breakdown activities?

Moves a-1,4 linkages to a-1,6 linkages

What is the role of glycogenin in glycogen synthesis?

Catalyzes the addition of the initial glucosyl unit to tyrosine

Which enzyme catalyzes the conversion of Glucose 6-phosphate into Glucose?

Glucose 6-phosphatase

What serves as the primer for glycogen synthesis before glycogen synthase takes over?

Glycogenin

What is the significance of branching in glycogen regarding its solubility?

Branching increases solubility of glycogen

Which enzyme forms α-1,6 linkages to facilitate branching in glycogen synthesis?

Branching enzyme

What is the minimum length of the a-1,4 chain required for branching by glucosyl α-4:6 transferase?

~9-11 residues

What activates branching enzyme to facilitate branching in glycogen synthesis?

High levels of ATP

Which enzyme breaks the α-1,4 link and forms α-1,6 linkages in the process of remodeling during glycogen synthesis?

Branching enzyme

What is the role of transferase in glycogen metabolism?

Transfers a block of three residues to the non-reducing end of the chain

What is the function of α-1,6-Glucosidase in glycogen metabolism?

Cleaves alpha-1,6-linked glucose residues

What is the fate of glucose 6-phosphate in the liver?

Converted to glucose by dephosphorylation

Where are the transferase and α-1,6-Glucosidase activities located in eukaryotes?

Within one bifunctional protein

In prokaryotes, how is glucose 1-phosphate converted to glucose 6-phosphate?

By phosphoglucomutase

What enables glucose to leave the liver?

Glucose 6-phosphatase enzyme

What is the significance of having a large number of nonreducing ends in glycogen structure?

They are required as substrates for the enzymes of glycogen metabolism.

Why is glycogen considered a good source of fuel for anaerobic activity?

It is quickly mobilized in muscle.

In which organelle is glycogen principally stored in the cytosol granules?

Mitochondria

How are the branch points structured in glycogen?

Every 8-10 residues

What is the main reason for storing glucose as glycogen?

To maintain blood glucose levels during fasting

What is the role of glycogen in liver cells?

Maintains blood glucose levels

What enzyme catalyzes the formation of UDP-glucose from Glucose-1-phosphate and UTP during glycogen synthesis?

UDP-glucose pyrophosphorylase

Which enzyme is essential for catalyzing the attachment of glucose residues in the autoglucosylation process during glycogen synthesis?

Glycogenin

In what form is glucose primarily transported during glycogen synthesis?

UDP-glucose

Which enzyme is responsible for catalyzing the addition of glucose to the nonreducing end during glycogen synthesis?

Glycogen synthase

What is the role of branching enzyme (glucosyl transferase) in glycogen synthesis?

Forms α-1,6 linkages to create glycogen branches

What is the activated form of glucose used in the synthesis of glycogen?

UDP-glucose

What is the role of glycogenin in glycogen synthesis?

Catalyzes the transfer of glucose molecules from UDP-glucose to form a primer

What is the function of branching enzyme in glycogen synthesis?

Cleaves α-1,4 linkages and forms α-1,6 linkages to create branches

How does glycogen synthase contribute to glycogen synthesis?

Adds glucose residues to the existing glycogen chain

What is the consequence of inhibiting the activity of glycogenin in glycogen synthesis?

Inability to elongate the glycogen chain beyond a few glucose molecules

How does glycogen branching facilitate both degradation and synthesis processes?

Provides substrate sites at non-reducing ends for enzyme action

What is the significance of glycogenin remaining permanently attached to the reducing end of the glycogen molecule?

Allows for continuous addition of new glucose residues to the chain

What is the main function of the debranching enzyme in glycogenolysis?

Cleave a-1,6 linkages

What is the primary role of the phosphorylase enzyme in glycogen metabolism?

Cleave a-1,4 linkages

What is the significance of branching in glycogen structure?

Increases solubility of glycogen

Which enzyme is responsible for remodeling glycogen to ensure it remains a substrate for degradation?

Transferase

What process involves the removal of glucosyl residues from the nonreducing ends of the glycogen molecule?

Phosphorolysis

What is the final step in the glycogen breakdown process?

Cleavage by glucosidase

What enzyme works on non-reducing ends until it reaches four residues from an (a1→ 6) branch point in glycogen metabolism?

Glycogen phosphorylase

In eukaryotes, where are the transferase and α-1,6-Glucosidase activities located?

Within one bifunctional protein

Which enzyme is responsible for converting glucose 1-phosphate to glucose 6-phosphate in prokaryotes?

Phosphoglucomutase

What enzyme dephosphorylates glucose-6-phosphate in the liver for transport out of the liver?

Glucose 6-phosphatase

In which organ can glucose leave due to the presence of glucose 6-phosphatase?

Liver

Which enzyme enables glucose to leave the liver by hydrolyzing glucose 6-phosphate?

Glucose 6-phosphatase

What is the principal building block of fatty acids?

Acetyl CoA

Which molecule acts as a feedback inhibitor of the enzyme involved in fatty acid synthesis?

Acetyl CoA

What is the source of NADPH in fatty acid synthesis?

Malate

Which process is considered the rate-limiting step in the biosynthesis of fatty acids?

Acetyl-CoA carboxylase reaction

Which molecule plays a central role in diverting cellular metabolism towards storage as fatty acids instead of consumption?

Citrate

What cellular compartment does fatty acid synthesis primarily occur in?

Cytosol

What is the primary function of phosphatidic acid phosphatase in the pathway to TAGs?

Hydrolyzing phosphatidic acid to form 1,2-diacylglycerol

In which tissue does glyceroneogenesis coupled with reesterification of FFA control the rate of FA release to the blood?

Adipose tissue

What is the role of glyceroneogenesis in brown adipose tissue in relation to mitochondria?

Control delivery of FFA to mitochondria for thermogenesis

During fasting in humans, what percentage of fatty acids reesterified to triacylglycerol is supported by glyceroneogenesis in the liver?

65%

What is the final product formed by transesterification with a third fatty acyl–CoA in the conversion of diacylglycerols to TAGs?

TAGs

What is the principal form of stored energy in most organisms?

Triacylglycerols

What is the reducing agent in the fatty acid synthetic sequence?

NADPH

Which enzyme catalyzes the formation of malonyl-CoA from acetyl-CoA?

Acetyl-CoA carboxylase

What specialized lipids serve as pigments and cofactors?

Retinal and carotene

In fatty acid synthesis, what activates the groups on the enzyme-bound -SH groups?

ATP

What happens when the fatty acyl chain reaches a length of 16 in the synthesis cycle?

It leaves the cycle as palmitate

Which fatty acids are essential for mammals and must be obtained from dietary plant material?

Linoleate

What is the precursor of regulatory lipids, the eicosanoids?

Arachidonate

Which enzyme is responsible for the formation of fatty acyl esters of glycerol?

Fatty Acyl–CoA Synthetases

What is the central intermediate in lipid biosynthesis that can be converted to either triacylglycerols or glycerophospholipids?

Phosphatidic Acid

What is the precursor of eicosatrienoate and arachidonate, which can only be made from this specific fatty acid?

Linoleate

What effect does phosphorylation have on acetyl-CoA carboxylase activity?

Inhibits the enzyme

Where does fatty acid elongation primarily take place?

Endoplasmic reticulum

Which enzyme catalyzes the introduction of double bonds into fatty acid chains?

Desaturase

What is the role of NADPH in fatty acid elongation?

Donates reducing equivalents

Which fatty acids serve as precursors for the synthesis of palmitoleate and oleate?

Palmitate and stearate

What happens to acetyl-CoA carboxylase when it is in its active form?

Polymerizes into long filaments

Test your knowledge on glucose transport systems including Na+-independent facilitated diffusion (GLUT family) and Na+-monosaccharide cotransporter (SGLT family) found in epithelial cells of the intestine, renal tubules, and choroid plexus. Learn about GLUT1, GLUT3, and SGLT characteristics and functions.

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