Fat storage

Question 1

What is the primary function of adipose (fat) cells?

Answer 1

To store energy in the form of triglycerides

Question 2

What are the primary substrates for triglyceride storage in adipocytes?

Answer 2

Glucose, triacylglycerol (TAG), and non-esterified fatty acids (NEFAs)

Question 3

What are the four key processes involved in fat storage?

Answer 3

Uptake of metabolic substrate, lipogenesis, lipolysis, and lipid export

Question 4

Besides storage, what other role do adipocytes play?

Answer 4

They sense and respond to changes in systemic energy balance

Question 5

What are the three types of adipocytes?

Answer 5

White, brown, and beige

Question 6

What is the main function of white fat?

Answer 6

Energy storage in the form of triglycerides

Question 7

How does white fat respond during fasting?

Answer 7

It releases fatty acids and glycerol via lipolysis

Question 8

Which hormones regulate white fat metabolism?

Answer 8

Insulin and catecholamines

Question 9

What hormone-like molecules are secreted by white fat?

Answer 9

Leptin, adiponectin, adipsin, TNF-α, and resistin

Question 10

What is the primary role of brown fat?

Answer 10

To dissipate energy as heat through thermogenesis

Question 11

What protein is key to brown fat’s thermogenic function?

Answer 11

Uncoupling protein 1 (UCP1)

Question 12

Why is brown fat brown in color?

Answer 12

Due to its high mitochondrial content

Question 13

What is lipogenesis?

Answer 13

The biological process of creating fat molecules from acetyl-CoA and other precursors

Question 14

Where does lipogenesis primarily occur?

Answer 14

In the liver and adipose tissue

Question 15

What are the two main biochemical pathways in lipogenesis?

Answer 15

De novo fatty acid synthesis and triglyceride formation

Question 16

What enzymes are involved in de novo fatty acid synthesis?

Answer 16

Fatty acid synthase (FAS) and acetyl-CoA carboxylase

Question 17

What is the role of perilipin in lipogenesis?

Answer 17

It stabilizes TAG droplets in adipocytes

Question 18

What is the function of triglyceride formation?

Answer 18

To store excess calories as fat for future energy use

Question 19

How does insulin affect lipogenesis?

Answer 19

It stimulates lipogenesis and inhibits lipolysis by reducing cAMP levels

Question 20

What enzyme does insulin activate to convert pyruvate to acetyl-CoA?

Answer 20

Pyruvate dehydrogenase (via pyruvate dehydrogenase phosphatase)

Question 21

What is the role of malonyl-CoA in lipogenesis?

Answer 21

It is used in the elongation of fatty acid chains

Question 22

How are triglycerides released from the liver?

Answer 22

As very-low-density lipoproteins (VLDL) into the bloodstream

Question 23

How does growth hormone (GH) affect lipogenesis?

Answer 23

It inhibits lipogenesis and stimulates lipolysis

Question 24

What enzymes does GH suppress to inhibit lipogenesis?

Answer 24

Fatty acid synthase (FAS) and acetyl-CoA carboxylase

Question 25

What conditions can result from excessive lipogenesis?

Answer 25

Obesity, hepatic insulin resistance, and type 2 diabetes

Question 26

How is lipogenesis linked to insulin sensitivity?

Answer 26

Imbalances in lipogenesis can impair insulin sensitivity, contributing to metabolic disorders

Question 27

What is lipolysis?

Answer 27

The breakdown of triacylglycerols (TAGs) into glycerol and free fatty acids via hydrolysis

Question 28

Which proteins regulate lipase access to lipid droplets?

Answer 28

Perilipin dissociation allows cytosolic lipases to act on TAGs

Question 29

What are the sequential breakdown products of TAGs?

Answer 29

Diacylglycerol → Monoacylglycerol → Glycerol + Free Fatty Acids

Question 30

What hormones stimulate lipolysis?

Answer 30

Epinephrine, norepinephrine, testosterone, and cortisol

Question 31

How do these hormones activate lipolysis?

Answer 31

By increasing cAMP via adenylate cyclase, activating protein kinase A, which activates lipases

Question 32

What does adipose triglyceride lipase (ATGL) do?

Answer 32

Hydrolyzes TAG into diacylglycerol

Question 33

What does hormone-sensitive lipase (HSL) do?

Answer 33

Hydrolyzes diacylglycerol into monoacylglycerol

Question 34

What does monoacylglycerol lipase (MGL) do?

Answer 34

Hydrolyzes monoacylglycerol into glycerol and free fatty acids

Question 35

What happens to free fatty acids after release?

Answer 35

They bind to albumin in the blood or are absorbed by tissues like muscle

Question 36

What happens to glycerol after lipolysis?

Answer 36

It is taken up by the liver for gluconeogenesis

Question 37

How does insulin affect lipolysis?

Answer 37

High insulin levels inhibit lipolysis by reducing cAMP levels

Question 38

What are the main ketone bodies?

Answer 38

Acetoacetate and β-hydroxybutyrate

Question 39

When does the brain use ketone bodies for energy?

Answer 39

After fasting for about three days

Question 40

What is the role of ketone bodies during fasting?

Answer 40

They preserve glucose for the brain and erythrocytes

Question 41

What condition can result from high ketone levels?

Answer 41

Ketoacidosis, especially in type I diabetes

Question 42

How do short and medium-chain fatty acids enter cells?

Answer 42

They diffuse freely into the cytosol and mitochondria

Question 43

How do long-chain fatty acids enter cells?

Answer 43

Via fatty acid translocase (FAT) or fatty acid-binding protein (FABP)

Question 44

What enzyme activates fatty acids in the cytosol?

Answer 44

Acyl-CoA synthase converts them to fatty acyl-CoA

Question 45

How is fatty acyl-CoA transported into mitochondria?

Answer 45

Via CPT-I → CAT → CPT-II, converting it to fatty acyl-carnitine and back

Question 46

What is beta oxidation?

Answer 46

The degradation of fatty acids by removing two-carbon units in the mitochondrial matrix

Question 47

What are the products of beta oxidation?

Answer 47

NADH, FADH₂, and Acetyl-CoA

Question 48

What happens to odd-chain fatty acids in beta oxidation?

Answer 48

They yield propionyl-CoA, which is converted to succinyl-CoA

Question 49

How does beta oxidation regulate PDH activity?

Answer 49

High fatty acid oxidation inhibits PDH, limiting glycolysis

Question 50

What happens in fatty acid oxidation deficiency?

Answer 50

Increased glucose oxidation and impaired gluconeogenesis