Biochemistry: Carbohydrates Metabolism MD1251

Questions and Answers

Which of the following describes the role of GLUT-4 in skeletal muscle and adipose tissue?

Decreases glucose transport when insulin levels rise.

Functions independently of insulin action.

Is only present in the liver for glucose transport.

Increases both the number and activity in response to insulin. (correct)

What is the mechanism of transport for glucose into enterocytes?

Primarily facilitated diffusion through GLUT transporters.

Only passive and active transport systems.

Only passive diffusion.

Carrier-mediated Na+-dependent active transport and diffusion. (correct)

In the context of type 2 diabetes mellitus, what is primarily responsible for insulin resistance in skeletal muscle and adipose tissue?

Enhanced glucose metabolism in cells.

Inadequate insulin secretion from the pancreas.

Increased GLUT-1 levels.

Reduction in GLUT-4 quantity due to insulin deficiency. (correct)

What characterizes GLUT1 deficiency syndrome?

Diverse neurological symptoms and genetic autosomal dominant pattern. Signup and view all the answers

What is the source of energy for the transport of Na+ ions during glucose absorption in enterocytes?

Secondary active transport via electrochemical gradient. Signup and view all the answers

How is glucose transported from enterocytes to the bloodstream?

Through serosal carriers or diffusion, or both. Signup and view all the answers

Which glucose transporter is associated with transporting glucose across the blood-brain barrier?

GLUT-1. Signup and view all the answers

What type of transport does not directly use ATP?

Secondary active transport of glucose with Na+. Signup and view all the answers

What type of reactions are primarily responsible for breaking down complex molecules to release energy?

Catabolic reactions Signup and view all the answers

Which metabolic pathway is characterized by a series of reactions that can be circular in nature?

Cyclic pathway Signup and view all the answers

Which biomolecule plays a vital role in the construction of larger molecules using energy from ATP?

Carbohydrates Signup and view all the answers

What is the primary objective of glycolysis in carbohydrate metabolism?

To convert glucose to pyruvate Signup and view all the answers

What does a spiral pathway in metabolic pathways typically refer to?

Fatty acid biosynthesis Signup and view all the answers

What part of metabolism requires the use of ATP to synthesize larger molecules?

Anabolic reactions Signup and view all the answers

Which of the following roles does metabolism NOT directly support?

Gene expression Signup and view all the answers

What is the main role of isomaltase in carbohydrate digestion?

Hydrolyzes α-1→6 glycosidic linkages Signup and view all the answers

What are the products of glycolysis from one molecule of glucose?

Two molecules of pyruvate and two molecules of ATP Signup and view all the answers

Which statement about maltase is accurate?

It liberates equal amounts of two glucose molecules from maltose. Signup and view all the answers

Why can humans not digest cellulose?

Humans cannot produce enzymes to break β-1→4 glycosidic bonds. Signup and view all the answers

In what order are monosaccharides absorbed in the small intestine?

Glucose, Fructose, Galactose, Mannose Signup and view all the answers

What characterizes glucose transporters (GLUT)?

They are integral membrane proteins that facilitate passive transport. Signup and view all the answers

Which enzyme also displays activity against sucrose besides maltase?

Sucrase Signup and view all the answers

Which monosaccharide is absorbed most quickly by the small intestine?

Glucose Signup and view all the answers

Which of the following statements about dietary fiber is incorrect?

It is primarily made up of sugars. Signup and view all the answers

What condition is characterized by deceleration of head growth and is known as microcephaly?

Glucose Transporter Type 1 Deficiency Syndrome Signup and view all the answers

What is a hallmark symptom of Fanconi-Bickel syndrome?

Severe short stature Signup and view all the answers

In the patient case presented, what was indicated by the significant midepigastric and right upper-quadrant tenderness?

Gallbladder inflammation Signup and view all the answers

What was the most likely diagnosis for the patient with increasing abdominal pain and gallstones?

Gallstone pancreatitis Signup and view all the answers

Which type of enzyme is amylase and what is its primary function?

Amylase; to metabolize carbohydrates Signup and view all the answers

Which symptom is least likely associated with Fanconi-Bickel syndrome?

Chronic diarrhea Signup and view all the answers

What complication arises as a result of glucose transporter dysfunction in Fanconi-Bickel syndrome?

Hepatomegaly Signup and view all the answers

What laboratory findings would likely support the diagnosis of gallstone pancreatitis?

Increased liver function tests Signup and view all the answers

What is the end product of glycolysis under aerobic conditions?

Pyruvate Signup and view all the answers

Which cells primarily rely on glycolysis for their energy needs?

Erythrocytes Signup and view all the answers

How many ATP molecules are consumed during the initial phase of the Embden–Meyerhof–Parnas pathway?

2 ATP Signup and view all the answers

What is lactate's role during intense exercise?

It is converted to glucose in the liver. Signup and view all the answers

In which conditions is glycolysis considered an emergency energy pathway?

In the absence of oxygen Signup and view all the answers

What does increased metabolism during exercise lead to?

Increased lactate production Signup and view all the answers

Which of the following statements about glycolysis is NOT correct?

It is a significant source of ATP in tissues with mitochondria. Signup and view all the answers

Which of the following is a product of the complete oxidation of pyruvate after glycolysis?

CO₂ and H₂O Signup and view all the answers

Study Notes

Course Overview

Delivered by Dr. Samson Awotunde and Dr. Elizabeth Gori
Module Code: MD1251, Title: Biochemistry
Key Objectives: Understand carbohydrate digestion, glycolysis, pyruvate fates, and associated conditions/diseases.

Metabolism

Encompasses biochemical reactions that release energy for biological activities (thermoregulation, reproduction, coordination).
Requires biomolecules: proteins, fats, carbohydrates, nucleic acids.

Metabolic Pathways

Sequences of reactions with specific purposes (e.g., glucose degradation, fatty acid synthesis).
Types of pathways: linear, cyclic, spiral (e.g., fatty acid biosynthesis).

Metabolic Reactions

Catabolic Reactions: Breakdown of complex molecules to produce energy and smaller molecules.
Anabolic Reactions: Utilize ATP energy to synthesize larger molecules.

Key Enzymes in Carbohydrate Digestion

Isomaltase: Hydrolyzes α-1→6 glycosidic bond, producing maltose and glucose.
Maltase: Hydrolyzes α-1→4 glycosidic bond in maltose, releasing two glucose molecules.
Sucrase: Hydrolyzes sucrose into glucose and fructose.

Absorption of Carbohydrates

Digestion completes in the small intestine converting complex carbohydrates to monosaccharides.
Monosaccharides absorbed quickly: glucose and galactose are absorbed faster than fructose and pentoses.

Cellulose and Digestion

Cellulose, found in plants, is indigestible due to the lack of the enzyme needed to break β-1→4 bonds.
Provides dietary fiber, aiding in intestinal motility.

Glucose Transporters (GLUT)

Integral membrane proteins facilitating glucose transport across membranes.
GLUT transporters (1-7) identified across various tissues; critical for glucose metabolism.
Insulin increases GLUT-4 activity in muscle and adipose tissue; insulin resistance leads to type 2 diabetes mellitus.

Transport Mechanisms

Monosaccharides enter enterocytes via passive diffusion or active transport (Na+-dependent).
Glucose transported out of cells into intercellular space via serosal carriers or diffusion.

Notable Syndromes

GLUT1 Deficiency Syndrome: Autosomal dominant disorder leading to neurological symptoms due to glucose transport failure.
Fanconi-Bickel Syndrome: Associated with GLUT2 dysfunction, resulting in glycogen accumulation and metabolic disturbances.

Case Discussion

Diagnosis of gallstone pancreatitis based on presenting symptoms and lab results.
Role of amylase: Critical enzyme for carbohydrate metabolism, aiding digestion of glycogen and starch.

Embden-Meyerhof-Parnas Pathway

Consists of five reactions involving phosphorylation and cleavage of hexose into triose phosphates.
Energy-consuming process requiring ATP, particularly during lactate production in exercise.

Significance of Glycolysis

Universal pathway occurring in all cells; essential for energy production in erythrocytes.
Functions anaerobically (producing lactate) or aerobically (producing pyruvate, further oxidized).
Emergency energy source under low oxygen conditions.
Provides carbon skeletons for non-essential amino acids and glycerol for fats.
Reversible reactions linked to gluconeogenesis, serving as a preliminary step for complete oxidation of carbohydrates.

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Explore the metabolic pathways associated with carbohydrates in this biochemistry quiz tailored for medical students. Gain a solid understanding of the digestion process and the significance of carbohydrates in human health. This quiz will cover key concepts and stages of carbohydrate metabolism.