Lecture 18: Fuels

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Questions and Answers

What is the difference between pyruvate and lactate molecules?

Lactate has more hydrogen than pyruvate (correct)

Pyruvate has more hydrogen than lactate

Lactate has more carbon than pyruvate

Pyruvate has more carbon than lactate

What is the direction of the reaction in lactic acid fermentation?

Lactate is oxidised to pyruvate

Lactate is reduced to pyruvate

Pyruvate is reduced to lactate (correct)

Pyruvate is oxidised to lactate

When does lactate production increase?

When oxygen is abundant

When the demand for ATP exceeds supply and oxygen is limiting (correct)

When ATP supply exceeds demand

When blood supply is increased

What is the byproduct of lactic acid fermentation?

NAD+ and ATP Signup and view all the answers

What percentage of nutrients are used to provide energy?

80-90% Signup and view all the answers

How long do nutrients absorbed from meals supply energy?

2-4 hours Signup and view all the answers

What do cells rely on for energy during a fasting state?

Energy stored as glycogen and fat Signup and view all the answers

What is the preferred metabolic substrate for the brain?

Glucose and ketone bodies Signup and view all the answers

What happens when the brain lacks glucose?

Diabetic hypoglycemia occurs Signup and view all the answers

What is the energy use of the liver per day?

1,063 kJ/day Signup and view all the answers

What is the function of 18F-2-deoxy-glucose (FDG) in imaging?

To measure cellular glucose uptake Signup and view all the answers

What is the preferred metabolic substrate for skeletal muscle?

Fatty acids, glucose, and ketone bodies Signup and view all the answers

What is the total energy use of a 30-year-old, 66 kg woman?

6,000 kJ/day Signup and view all the answers

Which of the following tissues prefers glucose as a metabolic substrate?

Red blood cells and many cancers Signup and view all the answers

What is the product of glycolysis in the presence of oxygen?

Pyruvate Signup and view all the answers

What is the energy yield from the electron transport chain?

32 ATP Signup and view all the answers

What is the product of fatty acid breakdown?

Acetyl CoA Signup and view all the answers

What is the role of the liver in amino acid oxidation?

To break down excess amino acids into urea and keto acids Signup and view all the answers

What is the byproduct of amino acid degradation?

Urea Signup and view all the answers

In what conditions does lactic acid fermentation occur?

In the absence of oxygen Signup and view all the answers

What is the energy yield from glycolysis?

2 ATP Signup and view all the answers

What is the product of the Krebs cycle?

NADH and FADH2 Signup and view all the answers

What is the role of CoA in fatty acid breakdown?

To combine with acetic acid molecules to form acetyl CoA Signup and view all the answers

What is the byproduct of glycolysis in the absence of oxygen?

Lactate Signup and view all the answers

What is the primary source of energy for skeletal muscle?

Fatty acids Signup and view all the answers

What is the approximate amount of ATP used by the heart per day?

6 kg Signup and view all the answers

Which of the following is NOT a source of energy in a starving person?

Blood Signup and view all the answers

What is the approximate amount of ATP produced per gram of fatty acid?

106 ATP Signup and view all the answers

What percentage of cellular activity is driven by ATP?

95% Signup and view all the answers

How long can the heart function without ATP production?

10 seconds Signup and view all the answers

Study Notes

Cellular Respiration

Glucose catabolism occurs in the presence of oxygen, producing ATP through glycolysis, intermediate reaction, Krebs cycle, and electron transport chain.
ATP production under anaerobic conditions involves lactic acid fermentation.

Oxidation of Fatty Acids

Fatty acid chains are broken into 2-carbon acetic acid molecules, which combine with enzyme CoA to form acetyl CoA.
Acetyl CoA enters the Krebs cycle and electron transport chain, producing ATP.

Oxidation of Amino Acids

Excess amino acids are transported to the liver, where they are degraded to produce sugars that can be converted to glucose or utilized in the Krebs cycle.
Amino acid degradation involves the removal of the amino group (NH2) and an extra H to form ammonia (NH3), and the non-nitrogenous portion becomes a keto acid (ketone body).

Lactic Acid Fermentation

Pyruvate is converted to lactate, which has more hydrogen compared to pyruvate, indicating that pyruvate is reduced to lactate.
Lactic acid fermentation occurs when the demand for ATP exceeds supply and oxygen is limiting, such as during strenuous exercise or inadequate blood supply.

Nutrient Preferences of Tissues

Brain: glucose, ketone bodies
Skeletal muscle: fatty acids, glucose, ketone bodies
Heart muscle: fatty acids, lactate, ketone bodies
Red blood cells: glucose
Many cancers: glucose (Warburg effect)

Cellular Energy Usage

Not all parts of the body use energy at the same rate, with the brain, skeletal muscle, liver, heart, and kidneys being major energy consumers.
Skeletal muscle can increase energy usage enormously, such as in woodchoppers who need 18,000 kJ a day.

ATP Production and Usage

Aerobic metabolism of glucose produces much more energy than anaerobic metabolism (34 ATP vs 2 ATP).
Fatty acids are not used to produce ATP in the absence of oxygen.
ATP is the energy source for >95% of cellular activity, including contractility, ion pumping, signaling, and biosynthesis.

Starving

Energy stores in a 70 kg person are depleted in the following order: glucose/glycogen, mobilizable proteins, and triglycerides.
The brain, liver, muscle, and adipose tissue have different energy stores and usage rates during starvation.

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Description

This quiz covers the different pathways of cellular respiration, including aerobic and anaerobic processes, and the production of ATP from various substrates. It also explores the importance of lactic acid fermentation in regenerating NADH for glycolysis.