Lecture 4.1 - Energy storage - glycogen and lipids

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the primary function of carbohydrates, lipids, and proteins in the human body?

To provide structural support to organs

To synthesize hormones

To serve as fuel molecules (correct)

To regulate body temperature

What is the primary fate of glucose in the brain during initial physical activity?

It is converted to ketone bodies

It is used as an energy source for the nervous system (correct)

It is stored as glycogen

It is excreted through the kidneys

What is the function of GLUT molecules in glucose transport?

To activate glucose transport in the presence of insulin (correct)

To regulate glucose metabolism

To facilitate glucose storage

To inhibit glucose transport

What is the primary advantage of storing glucose as glycogen?

It is a more efficient storage form Signup and view all the answers

What is the primary hormone that initiates glycogenesis?

Insulin Signup and view all the answers

What is the primary function of hexokinase in glycogen synthesis?

To phosphorylate glucose Signup and view all the answers

What is the primary regulator of glycogenolysis during short periods of fasting?

Glucagon Signup and view all the answers

What is the primary difference between glycogen synthesis and glycogen degradation pathways?

One is anabolic and the other is catabolic Signup and view all the answers

During lipolysis, what is the primary source of fatty acids released from adipocytes?

Triacylglycerol Signup and view all the answers

What is the primary function of beta-oxidation in the mitochondria?

Releasing energy from fatty acids during fasting and exercise Signup and view all the answers

What is the role of AMPK in lipid metabolism?

Allosteric regulator of FA synthesis/lipid storage Signup and view all the answers

What is the site of lipogenesis in liver cells?

Cytoplasm Signup and view all the answers

What is the primary energy source during periods of fasting and starvation?

Fatty acids Signup and view all the answers

What is the effect of insulin on lipolysis?

Inhibits HSL Signup and view all the answers

Which of the following enzymes is responsible for the synthesis of glycogen?

Glycogen synthase Signup and view all the answers

What is the outcome of glycogen storage disorders?

Excess glycogen storage leading to tissue damage Signup and view all the answers

Which of the following hormones plays a role in the allosteric control of glycogen metabolism?

Adrenaline Signup and view all the answers

What is the incidence of glycogen storage disorders?

1 in 20,000 - 1 in 40,000 Signup and view all the answers

Which of the following is a characteristic of glycogen storage disorders?

Abnormal glycogen structure Signup and view all the answers

What is the consequence of a deficiency of glucose 6-phosphate in Von Gierke disease?

Accumulation of glucose-6-phosphate intracellularly Signup and view all the answers

What is the purpose of glycolysis?

To generate energy during physical activity or in low oxygen conditions Signup and view all the answers

What is the role of phosphofructokinase in glycolysis?

Rate-limiting enzyme Signup and view all the answers

Study Notes

Nutrients of Human Metabolism

Carbohydrates, lipids, and proteins serve as fuel molecules for the human body
Absorbed end products of carbohydrates are monosaccharides, lipids are monoacylglycerol and long-chain fatty acids, and proteins are peptides

Carbohydrates

Contain carbon, hydrogen, and oxygen atoms
Primary source of energy is glucose, which has different fates depending on the body's needs
Includes sugars, fruits, vegetables, fibers, and legumes

Glucose

Most important fuel source for life
Preferred energy source for the nervous system during initial physical activity
Lack of glucose in the brain can lead to neurological issues
Essential building block found in cell membranes, with small quantities stored
Cannot enter cells by simple diffusion, requires GLUT molecules and insulin presence
Glucose homeostasis requires a balance between glucose diffusion, storage, and metabolism

Storage of Glucose - Glycogen

Glucose can be stored as glycogen, a polymer of glucose
Efficient storage with minimal osmotic effect
Liver can supply approximately 16 hours of glucose
- Muscle stores approximately 400g of glycogen
- Liver stores approximately 75g of glycogen

Glycogen Synthesis - Glycogenesis

Initiated by the anabolic hormone insulin
Hexokinase is an important enzyme

Glycogen Degradation - Glycogenolysis

Provides glucose during short periods of fasting, between meals, and during sleep
Regulated by glucagon and adrenal catecholamines epinephrine and norepinephrine
Pathway is not a reversal of the synthetic pathway

Regulation of Glycogen Metabolism

Synthesis: insulin activates glycogen synthase
Degradation: regulated by glycogen phosphorylase
Allosteric control from adrenaline, insulin, and glucagon hormones

Disorders of Glycogen Metabolism

Incidence: 1 in 20,000 to 1 in 40,000
Arise from deficiency or dysfunction of enzymes in glycogen metabolism
Affects liver and/or muscle, leading to abnormal glycogen structure and excess glycogen storage

Glycogen Metabolism in Clinical Context

Von Gierke disease: deficiency of glucose 6-phosphate enzyme, leading to accumulation of glucose-6-phosphate intracellularly
- 1 in 100,000 births, inherited as autosomal recessive traits
- Signs and symptoms: hypoglycemia, lactic acidosis, enlarged liver, and cerebral damage

Glycolysis

Enzymatic catabolism of glucose into two pyruvate molecules and 2 ATPs
Anaerobic metabolism of glucose, important during initial physical activity or limited oxygen availability
Ten-step reaction, with rate-limiting enzyme phosphofructokinase
Energy-requiring phase: two ATPs spent
Energy-releasing phase: four ATPs produced

Gluconeogenesis

Synthesis of new glucose from non-carbohydrate substrates such as lactate, pyruvate, glycerol, and alanine
Occurs in the liver and kidney cortex
Response to stress situations (e.g., fasting, starvation, prolonged exercise) under hormonal control

Lipid Storage

Fatty acids stored primarily in adipocytes as triacylglycerol
Triacylglycerol must be hydrolyzed to release fatty acids
Triacylglycerols are highly calorific and efficient in producing energy
Hormonal control:
- Insulin promotes storage
- Glucagon, adrenaline, cortisol, and GH promote mobilization

Lipolysis - Mobilization of Fatty Acids

Adipocytes release triacylglycerol, which is broken down into glycerol and non-esterified fatty acids
Regulation:
- Insulin inhibits HSL
- Epinephrine, norepinephrine, ACTH, and glucagon activate HSL

Fatty Acid Oxidation

Beta-oxidation source of energy during periods of fasting and exercise
Supply energy when glycogen and gluconeogenic precursors become scarce
FA activates as FA-CoA derivative
Occurs in the mitochondria
4 ATP per round - beta-oxidation is very efficient

Lipogenesis - Fatty Acid Synthesis

Fatty acids synthesized from acetyl-CoA
Requires ATP and NADPH
Occurs in the cytoplasm of liver cells
Acetyl-CoA comes from mitochondria via transport mechanism across mitochondrial membrane

Fatty Acid Synthesis/Lipid Storage

AMPK is an allosteric regulator

Lipogenesis vs Lipolysis

Opposite processes, with lipogenesis promoting fatty acid synthesis and lipolysis promoting fatty acid mobilization

Studying That Suits You

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

Description

This quiz covers the role of carbohydrates, lipids, and proteins in human metabolism, including their absorption and utilization as fuel molecules.