ch 5. cori cycle and beta oxidation

What is glycogenesis?

gylcogen synthase

 mainly in liver and skeletal muscle.

What is glycogenolysis?

glycogen phosphorylase

the breakdown of glycogen into glucose

What is gluconegenesis

the production of glucose from noncarbohydrate molecules including lactic acid and amino acid primarily in the river

What is the cori cycle?

metabolic pathway where lactate produced by anaerobic glycolysis in muscles is transported to the liver, converted back to glucose via gluconeogenesis, and sent back to muscles

Exam logic: links muscle anaerobic metabolism to liver glucose homeostasis.

Main steps of cori cycle

1. Muscle: Glucose → Pyruvate → Lactate (anaerobic glycolysis, regenerates NAD⁺, 2 ATP net)

2. Blood transport: Lactate moves from muscle → liver

3. Liver: Lactate → Pyruvate → Glucose (gluconeogenesis, requires ATP)

4. Blood transport: Glucose returns to muscle → used for energy

Exam tip: energy flows from liver → muscle; liver “pays the ATP cost” to recycle lactate

Why is the Cori cycle important?

• Allows continued ATP production in muscles during anaerobic conditions

• Prevents lactate accumulation → acidosis

• Maintains blood glucose levels during intense exercise

What is the main function of lactate dehydrogenase (LDH)?

Catalyzes the interconversion of pyruvate and lactate, coupled with NADH ↔ NAD⁺.

Reaction:

Pyruvate + NADH + H⁺ ↔ Lactate + NAD⁺

Physiology focus: maintains NAD⁺ for glycolysis under anaerobic conditions.

What is lipogenesis? (lipid/fat matabolism)

the formation of triglycerides (fat), primarily in adipose tissue

What is liopolysis? (lipid/fat matabolism)

hydrolysis (break down) of triglycerides primarly in adipose tissue

What is ketogenesis? (lipid/fat matabolism)

the formation of ketone bodies which are four carbon long organic acids, from fatty acids occurs in the liver

 How are triglycerides broken down?

1. Lipolysis: Triglyceride → glycerol + 3 fatty acids (by hormone-sensitive lipase, HSL)

2. Glycerol: converted → G3P → glycolysis → pyruvate → TCA

3. Fatty acids: activated → transported into mitochondria via carnitine shuttle → β-oxidation

What happens if there is too much atp in lipid metabolism?

then acetyl - coA will produce cholesterol, ketone bodies, fatty acids

What is the main function of white adipose tissue?

• Energy storage: stores triglycerides for later use

 What is lipolysis?

The breakdown of triglycerides into glycerol and free fatty acids (FFAs) for energy production.

fatty acid liver enter blood stream as blood borne energy carriers - liver, skeletal muscles other organs

glycerol taken up by liver then converted into glucose via gluconeogenesis

what is B oxidation

enzymes remove acetic acid molecules from fatty acids to form acetyl CoA

Which of the following is TRUE about β-oxidation?

Produces Acetyl-CoA, NADH, and FADH

What is β-oxidation of fatty acids?

the mitochondrial breakdown of fatty acids into 2-carbon Acetyl-CoA units, producing NADH and FADH₂, which feed the TCA cycle and ETC to generate ATP.

for every 2c removed ur gonna make 1 acetyl CoA

What is brown adipose tissue (BAT)?

Specialized adipose tissue that generates heat (thermogenesis) instead of storing energy, rich in mitochondria and uncoupling protein 1 (UCP1).

• Found in infants, hibernating animals, and adults in neck and upper back

• Dark color due to high mitochondrial content

What happens when H⁺ leaks from the intermembrane space into the mitochondrial matrix?

• The proton-motive force across the inner mitochondrial membrane is dissipated.

• ATP synthase activity decreases → less ATP produced.

• Energy from electron transport is released as heat instead of ATP.

Exam logic: This is the basis of thermogenesis in brown adipose tissue.

What are ketone bodies?

Water-soluble molecules produced by the liver from acetyl-CoA during prolonged fasting, starvation, or uncontrolled diabetes.

• Main ketone bodies:

  • Acetoacetate

  • β-Hydroxybutyrate

  • Acetone (minor, excreted via lungs)

 How does lipolysis rate affect ketone body formation?

High lipolysis (fasting/starvation): ↑ free fatty acids (FFA) → liver uptake → ↑ acetyl-CoA → ketogenesis

What does the liver convert fatty acids into?

• Fatty acids → β-oxidation → Acetyl-CoA

• Excess Acetyl-CoA → ketone bodies (cannot enter TCA cycle fully due to low oxaloacetate during fasting)

Physiology focus: liver cannot use ketone bodies → they are exported to other tissue

 What is ketosis?

Elevated levels of ketone bodies in blood, occurs in:

• Fasting/starvation → physiological ketosis

• Uncontrolled diabetes (DKA) → pathological ketosis, can cause acidosis

What is the main purpose of amino acid metabolism?

 To extract energy, provide carbon skeletons for gluconeogenesis or ketogenesis, and safely remove nitrogen/ amino acids from proteins in body

Our body does not make all 20 meaning we get the rest from our diet

What is transamination?

keto acids can be converted to amino acids by adding an amine group (NH2)

What is the role of transaminases (aminotransferases) in amino acid metabolism?

• Transfer an amino group (-NH₂) from an amino acid to an α-keto acid, usually α-ketoglutarate → glutamate.

• Exam tip: transaminases do not remove nitrogen; they just transfer it.

 What is oxidative deamination?

The process by which an amino group (-NH₂) is removed from glutamate, forming α-ketoglutarate and ammonia (NH₄⁺), with NAD⁺ or NADP⁺ as electron acceptor.

How does oxidative deamination connect to the urea cycle?

1. Amino groups from glutamate → NH₄⁺ via GDH

2. NH₄⁺ enters carbamoyl phosphate → urea cycle in liver

3. Urea excreted in urine → safe removal of nitrogen