MED 302: Carbohydrate Metabolism Quiz

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Questions and Answers

What is the purpose of metabolism in living cells?

To facilitate only the absorption of electrolytes.

To generate energy without chemical reactions.

To acquire and utilize free energy for cellular functions. (correct)

To only break down large molecules without creating any.

Which of the following best describes catabolism?

The conversion of energy from sunlight into chemical energy.

The process of energy storage within cells.

The breakdown of large molecules into smaller ones. (correct)

The buildup of complex molecules from simpler ones.

What is the role of anabolism in metabolism?

It facilitates the digestive process exclusively.

It breaks down molecules to release energy.

It is solely responsible for energy regulation.

It combines small molecules to form larger ones, consuming energy. (correct)

What are metabolites in the context of metabolism?

Products generated from metabolic pathways. Signup and view all the answers

Which pathway is referred to as amphibolism?

Pathways that are involved in both breakdown and buildup of molecules. Signup and view all the answers

What is produced during the citric acid cycle (CAC) that is essential for the electron transport chain?

NADH and FADH2 Signup and view all the answers

What is the end result of catabolism?

Production of ATP for energy storage. Signup and view all the answers

During which process are macromolecules converted into small units?

Digestion in the GIT. Signup and view all the answers

What enzyme in saliva initiates the digestion of carbohydrates?

Salivary amylase (ptyalin) Signup and view all the answers

Which part of the digestive system does not contribute to carbohydrate digestion?

Stomach Signup and view all the answers

How is energy captured during the degradation of foodstuffs?

As ATP during catabolic reactions. Signup and view all the answers

Which enzyme is responsible for hydrolyzing lactate into glucose and galactose?

Lactase Signup and view all the answers

What role does GluT 2 play in glucose metabolism?

Glucose uptake in liver and acting as a glucose sensor Signup and view all the answers

Which of the following enzymes in the intestinal juice hydrolyzes terminal α-1→4 glycosidic linkages?

Intestinal amylase Signup and view all the answers

What type of metabolism is characterized by the entry of reducing equivalents into the electron transport chain?

Tertiary metabolism Signup and view all the answers

What are carbohydrates primarily broken down into during digestion?

Monosaccharides Signup and view all the answers

Which hormone is primarily responsible for lowering blood glucose levels?

Insulin Signup and view all the answers

What is the predominant glucocorticoid in humans that raises blood glucose levels?

Cortisol Signup and view all the answers

Which hormone secreted by the anterior pituitary gland opposes the action of insulin?

Growth Hormone Signup and view all the answers

What effect do catecholamines have on blood glucose levels?

They increase blood glucose levels. Signup and view all the answers

Which condition is NOT a cause of hyperglycemia?

Hypothyroidism Signup and view all the answers

What is a common cause of hypoglycemia related to insulin administration?

Insulinoma Signup and view all the answers

Which metabolic process does glucagon enhance in the liver during hypoglycemia?

Glycogenolysis Signup and view all the answers

What is the normal fasting blood glucose range in mg%?

60 to 100 mg% Signup and view all the answers

What is the renal threshold for glucose excretion in normal individuals?

170 to 180 mg/100 ml Signup and view all the answers

Which condition describes the presence of sugar in urine?

Glycosuria Signup and view all the answers

Which type of diabetes is characterized by absolute insulin deficiency?

Type I Diabetes Mellitus Signup and view all the answers

What is the primary cause of Type II Diabetes Mellitus?

Relative insulin deficiency and obesity Signup and view all the answers

Under normal dietary conditions, what sugar is primarily present in blood plasma?

Glucose Signup and view all the answers

Which of the following describes melituria?

Excretion of any type of sugar in urine Signup and view all the answers

When does glycosuria typically occur?

When blood glucose exceeds the renal threshold of 170 to 180 mg/100 ml Signup and view all the answers

Which condition is a secondary cause of diabetes?

Obesity Signup and view all the answers

What type of glucose transporter is GluT 4 and where is it found?

Insulin-dependent and found in skeletal muscle Signup and view all the answers

Which monosaccharide has the maximum absorption rate in the intestine?

Galactose Signup and view all the answers

How is glucose absorbed using GluT 1 transporter?

By co-transport with sodium Signup and view all the answers

What is the main function of GluT 5?

To absorb fructose in the small intestine Signup and view all the answers

What mechanism is involved in the absorption of both glucose and galactose?

Co-transport with sodium via GluT-1 Signup and view all the answers

Which glucose transporter is involved in the uniport system for glucose absorption into the bloodstream?

GluT 2 Signup and view all the answers

What characterizes the absorption process of fructose compared to glucose?

Fructose absorption is significantly lower Signup and view all the answers

What role does insulin play in glucose absorption?

Stimulates the expression of GluT 4 transporters Signup and view all the answers

Study Notes

Overview of Carbohydrate Metabolism

Metabolism encompasses all chemical reactions within living cells, acquiring and utilizing free energy.
Metabolism is categorized as intermediary, involving enzyme-catalyzed reactions that transform metabolites.
Metabolic pathways can be classified into catabolic, anabolic, and amphibolic paths.

Metabolic Pathways

Catabolism: Breakdown of large molecules into smaller ones, releasing energy.
Anabolism: Formation of large molecules from smaller ones, consuming energy.
Amphibolism: Involves both breakdown and synthesis processes, acting as a crossroad between catabolic and anabolic pathways.

Stages of Metabolism

Primary Metabolism: Digestion in the gastrointestinal tract (GIT) reduces macromolecules to smaller units (e.g., proteins to amino acids).
Secondary Metabolism: Absorption and catabolism occur, with the citric acid cycle generating reducing equivalents like NADH and FADH2.
Tertiary Metabolism: Reduced equivalents enter the electron transport chain for energy release, referred to as cellular respiration.

Digestion of Carbohydrates

Carbohydrates include polysaccharides (starch, glycogen) and disaccharides (sucrose, lactose) converting to monosaccharides (glucose, galactose, fructose) via hydrolysis.
Mouth: Salivary amylase begins carbohydrate digestion.
Stomach: Limited carbohydrate activity; no carbohydrate-splitting enzymes.
Duodenum: Pancreatic amylase continues breakdown of polysaccharides.
Small Intestine: Several enzymes (amylase, lactase, maltase, etc.) liberate free glucose and other monosaccharides.

Transport of Glucose

GluT 1: Present in numerous tissues, facilitates glucose uptake into most cells.
GluT 2: Found in intestinal cells and liver, acts as glucose sensor but has low affinity for glucose.
GluT 3: High-affinity glucose transporter in neurons and brain cells.
GluT 4: Insulin-mediated transporter in skeletal muscle and adipose tissue.
GluT 5: Mainly transports fructose in the small intestine.

Absorption Mechanisms

Only monosaccharides are absorbed; absorption rates: galactose (max), glucose (moderate), fructose (min).
Passive Diffusion: Dependent on concentration gradients.
Facilitated Diffusion: Rapid glucose and galactose absorption via sodium-dependent glucose transporter (S GluT-1).

Hormonal Regulation of Carbohydrate Metabolism

Insulin: Reduces blood glucose levels, promoting uptake in tissues.
Cortisol: Increases blood glucose levels through gluconeogenesis.
Growth Hormone and ACTH: Elevate blood glucose, acting against insulin.
Catecholamines (Epinephrine, Norepinephrine): Stimulate glycogenolysis, increasing blood glucose.
Glucagon: Released during hypoglycemia, promotes glycogenolysis and gluconeogenesis in the liver.

Blood Sugar Levels

Normal Fasting Glucose: 60 to 100 mg/dL.
Hyperglycemia: Elevated blood glucose, causes include diabetes and stress.
Hypoglycemia: Low blood glucose, causes include insulin overdose and severe exercise.

Glycosuria

Glucose is typically absent in urine; its presence indicates renal threshold exceeded (170-180 mg/dL).
Glycosuria occurs when blood glucose exceeds reabsorptive capacity of renal tubules.

Diabetes Mellitus (DM)

DM is characterized by chronic high blood glucose due to insulin deficiency or insensitivity.
Types of DM:
- Type I (Juvenile-Onset): Insulin-dependent.
- Type II (Maturity-Onset): Non-insulin dependent, often associated with obesity.
Causes: Hereditary factors, autoimmune responses (Type I), obesity, and dietary influences.

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Description

Test your understanding of carbohydrate metabolism as taught in MED 302. This quiz covers the normal responses during fed and fasting states, as well as the effects of exercise and diabetes on carbohydrate metabolism. Prepare to assess your knowledge on these critical aspects of medical biochemistry.