GLUT Transporters in Metabolism Quiz

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Questions and Answers

What role does GLUT1 play in glucose metabolism?

It supplies glucose primarily to erythrocytes and brain endothelial cells. (correct)

It transports fructose in the intestine.

It facilitates glucose transport in muscle and adipose tissue.

It regulates insulin levels in the pancreas.

Which statement is true regarding GLUT2?

It transports monosaccharides from enterocytes into the bloodstream. (correct)

It is expressed predominantly in muscle and adipose tissue.

It has a high affinity for glucose.

It does not respond to changes in blood glucose concentration.

The primary action of insulin on GLUT4 involves which process?

Degradation of GLUT4 in muscle cells.

Translocation of GLUT4 to the plasma membrane. (correct)

Synthesis of GLUT4 from amino acids.

Inhibition of GLUT4 activity in liver cells.

Which GLUT transporter is primarily responsible for fructose transport?

GLUT5 Signup and view all the answers

GLUT3 has a predominant expression in which types of tissues?

Brain and neurons. Signup and view all the answers

Which condition is associated with GLUT1 deficiency syndrome?

Insufficient supply of glucose to the brain. Signup and view all the answers

What is the primary physiological function of GLUT4?

Regulating blood glucose levels by insulin signaling. Signup and view all the answers

Which organs are primarily involved in maintaining blood glucose concentration?

Small intestine, liver, kidneys, skeletal muscle, and adipose tissue. Signup and view all the answers

What are carbohydrates primarily constructed from?

Carbon, oxygen, and hydrogen Signup and view all the answers

Which type of carbohydrates contains more than 10 saccharide units?

Polysaccharides Signup and view all the answers

What role do oligosaccharides play when conjugated to proteins and lipids on cell surfaces?

They are important modulators of cell function Signup and view all the answers

What is the most abundant saccharide found in complex carbohydrates?

Glucose Signup and view all the answers

Which of the following structures increases the surface area of the small intestine?

Villi, large circular folds, and microvilli Signup and view all the answers

What is the primary function of carbohydrates in the human diet?

To serve as the main energy source Signup and view all the answers

Which component of the small intestine is responsible for nutrient transport from enterocytes?

Lacteal (lymphatic vessel) Signup and view all the answers

How are carbohydrates classified based on their structure?

Simple and complex carbohydrates Signup and view all the answers

What distinguishes liver glucokinase from muscle hexokinase in terms of feedback inhibition?

Liver glucokinase is not inhibited by glucose-6-phosphate. Signup and view all the answers

In what metabolic state does muscle hexokinase typically operate at maximum velocity?

At normal (fasting) blood glucose levels. Signup and view all the answers

How does glucose phosphorylation contribute to glucose entry into liver cells?

It decreases free glucose concentration, enhancing blood glucose influx. Signup and view all the answers

What is the effect of insulin on glucokinase activity?

Insulin induces glucokinase activity. Signup and view all the answers

What role does phosphoglucomutase play in glycogenesis?

It moves the phosphate group from C-6 to C-1 of glucose. Signup and view all the answers

What is the primary role of SGLT1 in enterocytes?

Active transport of dietary glucose and galactose Signup and view all the answers

Which glucose transporter is primarily involved in glucose uptake in the liver?

GLUT2 Signup and view all the answers

What is a significant factor contributing to low glucokinase activity in individuals with type 1 diabetes?

Very low insulin levels. Signup and view all the answers

Which of the following accurately describes the glucose transport mechanism of GLUT transporters?

It utilizes facilitated diffusion to move glucose across membranes Signup and view all the answers

What differentiates the Km values of muscle hexokinase and liver glucokinase?

Muscle hexokinase has a lower Km than liver glucokinase. Signup and view all the answers

What characterizes the distribution of SGLTs and GLUTs in the human body?

They exhibit tissue-specific expression with different substrate specificities Signup and view all the answers

What facilitates the initial entry of monosaccharides into the enterocytes?

Facilitated diffusion at the brush border membrane Signup and view all the answers

Which GLUT transporter is known for allowing glucose to cross the blood-brain barrier?

GLUT1 Signup and view all the answers

What role does uridine triphosphate (UTP) play in glycogenesis?

It provides energy through hydrolysis to form UDP-glucose. Signup and view all the answers

How do SGLTs achieve transport of monosaccharides into cells?

By coupling monosaccharide transport with sodium influx Signup and view all the answers

Which enzyme is responsible for attaching UDP-glucose to the growing glycogen chain?

Glycogen synthase Signup and view all the answers

What is the function of the branching enzyme in glycogenesis?

To form a(1-6) bonds at branch points in glycogen. Signup and view all the answers

Which statement best describes the cellular membrane's property in relation to molecule transport?

Cellular membranes are selectively permeable, allowing controlled transport of molecules. Signup and view all the answers

What is the significance of the hepatic portal vein in relation to monosaccharide absorption?

It directs absorbed monosaccharides straight to the liver for metabolism. Signup and view all the answers

What initiates the process of glycogenesis by forming a primer?

Glycogenin Signup and view all the answers

What is the primary role of insulin in regulating blood glucose levels?

Lowers blood glucose levels by promoting cellular uptake Signup and view all the answers

How does insulin affect glycogen synthase?

It stimulates its dephosphorylation to activate the enzyme. Signup and view all the answers

What happens to glucagon secretion when blood glucose levels rise after a carbohydrate-rich meal?

It decreases Signup and view all the answers

What happens when glucose molecules are added to the glycogen chain?

They eventually form nonreducing ends for rapid glucose release. Signup and view all the answers

What is a significant purpose of branching in glycogen structure?

To enhance the molecule’s solubility and compactness. Signup and view all the answers

How does insulin affect GLUT4?

It stimulates the translocation of GLUT4 to the cell surface Signup and view all the answers

Which pathway provides additional glucose for glycogen synthesis in the liver?

Gluconeogenesis Signup and view all the answers

Which process is primarily initiated by glucagon to increase blood glucose levels?

Glycogenolysis Signup and view all the answers

What is the effect of glucocorticoid hormones on blood glucose levels?

They stimulate hepatic gluconeogenesis Signup and view all the answers

In the case of insulin resistance, what typically happens to GLUT4 levels on the cell membrane?

They remain low despite high insulin levels Signup and view all the answers

Which of the following pathways does insulin primarily promote?

Synthesis of glycogen Signup and view all the answers

The storage form of glucose in the body is primarily in the form of which molecule?

Glycogen Signup and view all the answers

Study Notes

Carbohydrate Metabolism

Carbohydrates are the most abundant organic molecules on Earth.
They are the primary structural component of plants and a major source of food energy, often in the form of starch and sugars.
Carbohydrates supply half or more of the world's food energy intake.
Carbohydrates serve as metabolic intermediates, components of RNA and DNA, structural elements of cells and tissues, and energy storage molecules.
Carbohydrate diversity arises from structural diversity.
Chemically, carbohydrates approximate a “hydrate of carbon” (C-H₂O)ₙ.

Carbohydrate Structure

Carbohydrates are categorized into simple and complex carbohydrates.
Simple carbohydrates include monosaccharides (one sugar unit) and disaccharides (two sugar units).
Complex carbohydrates include oligosaccharides (three to ten sugar units) and polysaccharides (more than ten sugar units, often thousands).
Monosaccharides include glucose, fructose, and galactose.
Disaccharides include sucrose, lactose, and maltose.
Oligosaccharides include raffinose, stachyose, and verbascose.
Polysaccharides include starch, glycogen, and dietary fiber.

Complex Carbohydrates

Complex carbohydrates are polymers of saccharide units linked by glycosidic bonds.
Oligosaccharides contain 3–10 saccharide units, while polysaccharides contain more than 10 (often thousands).
Glucose is the most common type of saccharide in complex carbohydrates.
Complex carbohydrates are a significant component of the human diet.
Oligosaccharides are frequently conjugated to proteins and lipids in cells, acting as modulators of cell function.

Components of the Small Intestine

The small intestine has several structural components that increase its surface area.
Circular folds (folds of Kerckring), villi, and microvilli greatly increase the absorptive surface area.
Villi are finger-like projections containing enterocytes (absorptive cells), blood capillaries, and lacteals (lymphatic vessels).
Microvilli are hair-like extensions of the plasma membrane of enterocytes.
The enterocyte membrane facing the lumen is called the brush border (or apical membrane).

Carbohydrate Absorption

Dietary monosaccharides must cross the plasma membrane of enterocytes twice to enter the bloodstream.
Monosaccharides first enter the cell on the brush border side and exit on the basolateral side.
The basolateral side connects to capillaries of the hepatic portal vein; delivering the absorbed sugars to the liver for metabolic processes.
The transport of molecules across cell membranes is closely regulated.
Sodium-dependent glucose cotransporters (SGLTs) and facilitated diffusion glucose transporters (GLUTs) facilitate carbohydrate transport across membranes.
Several GLUT types (GLUT1-7) have different regulatory properties and substrate specificities.

Blood Glucose Regulation

Maintaining blood glucose levels is a vital homeostatic process that requires the concerted efforts of multiple organs (small intestine, liver, kidneys, etc.).
Insulin and glucagon are important antagonistic pancreatic hormones that influence the control of blood glucose.
Insulin lowers blood glucose levels, while glucagon raises them.
Glucocorticoid hormones from the adrenal cortex also influence blood glucose levels.
After eating, a rise in blood glucose triggers insulin release, causing GLUT4 translocation to the cell surface enabling glucose removal from the blood.

Glycogenesis

Glycogenesis is the process of synthesizing glycogen.
Glycogen is the storage form of glucose in muscle and liver, etc.
Glucokinase in the liver and glucose-6-phosphate in the muscle are key enzymes in controlling glucose entry and metabolism.
Glycogenesis needs ATP and UTP, consuming energy, but aids in blood glucose homeostasis.
Glucose entering the liver is rapidly phosphorylated to glucose-6-phosphate, increasing glucose uptake.

Glycogenolysis

Glycogenolysis is the breakdown of glycogen to glucose.
Glycogen phosphorylase is the enzyme responsible for breaking down glycogen by cleaving alpha-1,4 glycosidic bonds.
When glucose levels are high, glycogen synthase is inhibited for homeostasis.
Additional enzymes remove glucose from branch points, called debranching enzyme, for later energy use.
In muscle, glucose release is used as energy, while in liver it's for maintaining blood glucose levels.

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Description

Test your knowledge on GLUT transporters and their roles in glucose metabolism. This quiz covers various aspects, including the functions of GLUT1, GLUT2, GLUT3, and GLUT4, as well as their involvement in different tissues and conditions. Challenge yourself to understand how insulin interacts with these glucose transporters.