Glucose Transport and Metabolism Quiz

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

Which glucose transporter is responsible for transporting glucose across the blood-brain barrier?

GLUT-3

GLUT-1 (correct)

GLUT-2

GLUT-4

What is the primary function of GLUT-5?

Transport glucose in muscle and adipose tissue

Transport glucose in the liver and kidney

Transport fructose in the small intestine (correct)

Transport glucose in neurons

How does GLUT-2 function when blood glucose levels are low?

Transport glucose into the cells

Transport glucose into the bloodstream (correct)

Inhibit glucose transport

Store glucose as glycogen

What characterizes facilitated diffusion in glucose transport?

It is mediated by transporter proteins. Signup and view all the answers

Which glucose transporter is insulin dependent?

GLUT-4 Signup and view all the answers

What happens during the energy-generation phase of glycolysis?

A net of 2 ATP molecules is produced per glucose molecule. Signup and view all the answers

Which of the following statements about sodium-dependent glucose transport is true?

It occurs in epithelial cells. Signup and view all the answers

Why do phosphorylated sugars not easily penetrate membranes?

They are negatively charged. Signup and view all the answers

What is the main function of catabolic pathways?

To convert molecules into building blocks for other components Signup and view all the answers

Which statement accurately describes the difference between catabolism and anabolism?

Catabolism involves breaking down complex molecules, while anabolism involves synthesizing complex molecules. Signup and view all the answers

What is the end product of anaerobic glycolysis?

Lactate Signup and view all the answers

Which metabolic feature is often needed for anabolic reactions?

NADPH Signup and view all the answers

What role does glycolysis play in glucose metabolism?

It oxidizes glucose to provide energy in the form of ATP. Signup and view all the answers

What is an essential consequence of a blockage in metabolic pathways?

Potential accumulation of substrates Signup and view all the answers

Which process describes aerobic glycolysis?

Occurs in the presence of oxygen producing pyruvate Signup and view all the answers

What term describes the pathways that synthesize complex molecules from simpler ones?

Anabolic pathways Signup and view all the answers

What is the primary role of glyceraldehyde 3-phosphate dehydrogenase in glycolysis?

Facilitating the oxidation of glyceraldehyde 3-phosphate Signup and view all the answers

What condition results from pentavalent arsenic poisoning in terms of glycolysis?

Inhibition of the GPDH reaction Signup and view all the answers

What activates pyruvate kinase in glycolysis?

Fructose 1,6 bisphosphate Signup and view all the answers

What is the major fate of pyruvate in poorly vascularized tissues?

Formation of lactate Signup and view all the answers

Why do individuals heterozygous for PK deficiency have resistance to severe malaria?

They have altered RBC metabolism Signup and view all the answers

What mechanism maintains glycolysis in the cell when NAD+ levels are low?

Respiratory chain oxidation of NADH Signup and view all the answers

What is the final product of anaerobic glycolysis in eukaryotes?

Lactate Signup and view all the answers

What condition may result from an elevated concentration of lactate in plasma?

Lactic acidosis Signup and view all the answers

What is the primary role of hexokinase in glycolysis?

To phosphorylate glucose, trapping it inside the cell Signup and view all the answers

How does hexokinase IV (glucokinase) differ from hexokinase 1-III?

Glucokinase has a higher Km, leading to decreased efficiency. Signup and view all the answers

What regulates the activity of glucokinase in the liver?

Reversible binding with glucokinase regulatory protein (GKRP) Signup and view all the answers

What is the primary function of phosphofructokinase-1 (PFK-1) in glycolysis?

It acts as a control point for fructose 6-phosphate. Signup and view all the answers

What is the effect of high levels of ATP on phosphofructokinase-1 activity?

Inhibits PFK-1 Signup and view all the answers

Which of the following statements about the isomerization of glucose 6-phosphate is true?

It is catalyzed by phosphoglucose isomerase. Signup and view all the answers

What immediate products result from the cleavage of fructose 1,6-bisphosphate by aldolase?

DHAP and Glyceraldehyde 3-P Signup and view all the answers

What is the role of fructose 2,6-bisphosphate in the regulation of glycolysis?

It activates phosphofructokinase-1 regardless of ATP levels. Signup and view all the answers

What is the energy yield from anaerobic glycolysis per molecule of glucose?

2 molecules of ATP Signup and view all the answers

Which enzyme regulation is directly influenced by insulin in glycolysis?

Transcriptional upregulation of major regulatory enzymes Signup and view all the answers

What is one of the three major types of regulation in glycolysis?

Hormonal regulation Signup and view all the answers

Which component is not involved in the regulation of glycolysis?

Temperature Signup and view all the answers

Under what condition is anaerobic glycolysis particularly useful?

Lack of oxygen Signup and view all the answers

Which of the following statements about aerobic and anaerobic glycolysis is correct?

Aerobic glycolysis yields more NADH than anaerobic Signup and view all the answers

What is the primary role of glucose transporters in cells?

To transport glucose into the cell Signup and view all the answers

Which of the following best explains why aerobic glycolysis is considered more efficient than anaerobic?

It produces more ATP overall Signup and view all the answers

Study Notes

Introduction to Metabolism & Glycolysis

Metabolism is the collection of enzymatic reactions occurring in pathways.
Enzmatic reactions are not isolated; they occur in pathways with each product becoming a substrate for the next reaction, acting like an assembly line.
Different pathways intersect; collectively, these reactions are called metabolism.
Catabolic pathways break down complex molecules into simpler ones.
Anabolic pathways synthesize complex molecules from simpler ones.
Nutrients (carbohydrates, fats, proteins) are the energy sources for metabolism.
Complex molecules (proteins, polysaccharides, lipids, nucleic acids) are broken down to precursor molecules (amino acids, sugars, fatty acids, nitrogenous bases).

Metabolic Map

Each pathway in metabolism is composed of multienzyme sequences.
Each enzyme may have catalytic or regulatory features.
Blockages in metabolic pathways can cause disorders.

Catabolic Pathways

Functions of catabolic pathways:
- To capture ATP from energy-rich molecules.
- To convert molecules into building blocks for other components.

Stages of Catabolism

Stage 1: Hydrolysis of complex molecules into component building blocks (proteins, carbohydrates, & fats).
Stage 2: Conversion of building blocks into acetyl-CoA (or simple intermediates).
Stage 3: Oxidation of acetyl-CoA and oxidative phosphorylation.

Anabolic Pathways

Combine simple components into complex ones. For example, amino acids combine to form proteins.
Require energy (endergonic) – often ATP, where the ATP is converted into ADP and Pi
Often requires reducing power NADPH.
Catabolism is a convergent process, anabolism is a divergent process.

Regulation of Metabolism

Intracellular communication
Intercellular communication
Second messenger systems
Adenylyl cyclase
- GTP-dependent regulatory proteins
- Protein kinases
- Dephosphorylation of proteins
- Hydrolysis of cAMP
Direct contact
- Signaling cell
- Target cells

Overview of Glycolysis

All tissues use glycolysis.
Functions:
- Oxidize glucose to provide energy in the form of ATP.
- Provides intermediates for other metabolic pathways.
Glycolysis is at the hub of CHO metabolism.
- Virtually all sugars are converted into glucose prior to entering glycolysis.

Aerobic and Anaerobic Glycolysis

Aerobic glycolysis occurs in cells with mitochondria and a sufficient oxygen supply and produces pyruvate as its end product.
Anaerobic glycolysis occurs in the absence of oxygen and converts pyruvate to lactate by oxidizing NADH to NAD+. It occurs in tissues lacking mitochondria (e.g., red blood cells) and during anoxia.

Transport of Glucose into Cells

Facilitated diffusion (sodium-independent) is mediated by a family of glucose transporters (GLUTs) in the cell membrane (GLUT1-GLUT14).
GLUTs have tissue specificity determined by gene expression.
Examples of GLUTs include GLUT-1(erythrocytes, blood barrier), GLUT-2 (liver, kidney, β-cells), GLUT-3 (neurons), GLUT-4 (muscle & adipose, insulin dependent), and GLUT-5 (fructose transporter in small intestine & testes).

Sodium-Monosaccharide Cotransport

Energy-requiring process (against concentration gradient):
Transporter-mediated process where glucose movement is coupled to the sodium (Na+) concentration gradient.
Called sodium-dependent glucose transporter (SGLT).
Occurs in epithelial cells of the intestine, renal tubules, & choroid plexus.

Glucose Transport in Intestinal Epithelial Cells

Glucose movement occurs through the different compartments of the cell.
Active transport of Na+ coupled to glucose
Facilitated diffusion of glucose out of the cell

Reactions of Glycolysis

Phase 1: Energy investment phase (first 5 reactions)
Phosphorylated intermediates formed using ATP molecules
Phase 2: Energy generation phase (subsequent reactions)
Net of 2 ATP formed during the substrate-level phosphorylation step.

Phosphorylation of Glucose

Phosphorylated sugars cannot easily penetrate cellular membranes.
Phosphorylation of glucose traps it inside the cell.
Glucose-6-phosphate is the first step in glycolysis which is irreversible.
Hexokinase and glucokinase are two enzymes that catalyze the phosphorylation of glucose.
Hexokinase has broad substrate specificity, low Km, and is inhibited by its product.
Glucokinase is found in the liver & β-cells of the pancreas. It is a glucose sensor that regulates insulin secretion.

Regulation of Glucokinase Activity by Glucokinase Regulatory Protein

GKRP regulates the activity of glucokinase.
In the presence of fructose-6-phosphate, GKRP binds tightly to glucokinase and inactivates it.
When glucose concentrations increase, glucokinase is released from GKRP, permitting phosphorylation of glucose.
Glucokinase functions as a glucose sensor in glucose homeostasis.

Isomerization of Glucose 6-Phosphate

Catalyzed by phosphoglucose isomerase.
Reaction is reversible
Not a rate-limiting or regulated step

Phosphorylation of Fructose 6-phosphate

Catalyzed by phosphofructokinase-1 (PFK-1).
Important control point in glycolysis.
Regulation by energy levels within the cell (inhibited by high ATP & citrate, activated by high AMP).
Regulation by fructose 2,6-bisphosphate (potent activator of PFK-1, can override ATP inhibition).

Cleavage of Fructose 1,6-bisphosphate

Aldolase cleaves fructose 1,6-bisphosphate into dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate.
Reaction is reversible and not regulated

Isomerization of Dihydroxyacetone Phosphate (DHAP)

Triose phosphate isomerase interconverts DHAP and glyceraldehyde 3-phosphate.

Oxidation of Glyceraldehyde 3-phosphate

First oxidation-reduction reaction in glycolysis, catalyzed by glyceraldehyde-3-phosphate dehydrogenase (GPDH).
NAD+ is regenerated in the cell for glycolysis through either lactate production (anaerobic glycolysis) or by respiration (aerobic glycolysis).

Synthesis of 3-phosphoglycerate, ATP Production, and Shift of Phosphate Group

Steps in glycolysis producing ATP & phosphorylated intermediates

Dehydration of 2-phosphoglycerate

Processes to form phosphoenolpyruvate

Formation of Pyruvate

Catalyzed by pyruvate kinase (PK), the third irreversible step in glycolysis.
Feedforward regulation by fructose-1,6-bisphosphate.
Regulation by phosphorylation - the protein kinase leads to inactivation. Dephosphorylation reactivates it.
PK deficiency relates to RBC maturation and lack of mitochondrial function.

Reduction of Pyruvate to Lactate

Lactate dehydrogenase (LDH) catalzyes the conversion of pyruvate to lactate by reducing NAD+ to NADH

Energy Yield from Glycolysis

Anaerobic glycolysis: 2 molecules of ATP/glucose; no net change in NADH.
Aerobic glycolysis: 2 molecules of ATP/glucose; 2 molecules of NADH.

Hormonal Regulation of Glycolysis

Insulin and glucagon reciprocally regulate glycolysis at 3 major control points.
The regulatory enzymes involved are transcriptionally upregulated (insulin) or downregulated (glucagon).
Hormonal regulation is coupled with the quick allosteric inhibition and activation, and covalent (phosphorylation/dephosphorylation) regulation.

Summary

Key elements of glycolysis: 3 irreversible reaction steps, importance of ATP and NAD+.

Why is CHO Metabolism of Interest to You?

Changes in cancer cells:
- Cancer cells often preferentially use anaerobic glycolysis (Warburg effect)
- Changes in glucose metabolism are implicated.

Changes in Glucose Metabolism in Cancer Cells

Detailed molecular mechanisms involved in the change in glucose metabolism in cancer cells.

Aldolase B-Mediated Fructose Metabolism Drives Metabolic Reprogramming of Colon Cancer Liver Metastasis

Summary of article about fructose metabolism in colon cancer.

What You Should Know at the End of This Lecture

Summary of key points for glycolysis in metabolism and related topics.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz explores various aspects of glucose transporters and their functions, including GLUT-2, GLUT-5, and facilitated diffusion. It also examines key metabolic pathways like glycolysis, catabolism, and anabolism. Test your knowledge on how these processes contribute to glucose metabolism and energy production.