nutrition: energy, metabolism, expenditure

What is energy?

The capacity to do work. The body uses energy for movement, growth, maintaining body temperature, and cellular processes.

What is metabolism?

The sum of all chemical reactions that occur in the body.

What is catabolism?

Breaking larger molecules into smaller molecules; often releases energy.

What is anabolism?

Building larger molecules from smaller molecules; requires energy.

What is ATP?

Adenosine triphosphate; the cell's immediate, usable energy source.

What are metabolic pathways?

A series of chemical reactions in which the product of one reaction becomes the starting material for the next.

How does food become usable energy?

Food is digested into smaller components, cells break nutrients down through metabolic pathways, some released energy is captured in ATP, and cells use ATP to perform work. Energy is also released as heat.

What unit is food energy measured in?

Kilocalories (kcal), commonly called calories on food labels.

How many kcal per gram do carbohydrates provide?

4 kcal/g.

How many kcal per gram does protein provide?

4 kcal/g.

How many kcal per gram does fat provide?

9 kcal/g.

How many kcal per gram does alcohol provide?

7 kcal/g.

What are the three energy-yielding nutrients?

Carbohydrates, fats, and proteins.

What are carbohydrates broken down into?

Simple sugars, especially glucose, which can enter energy-producing pathways.

What are fats broken down into?

Fatty acids and glycerol. Fatty acids can be used to produce large amounts of energy.

What are proteins broken down into?

Amino acids. They primarily build and maintain body tissues but can also supply energy.

What is glucose?

A 6-carbon sugar that serves as a major energy source.

What is glycolysis?

The first major pathway for breaking down glucose; it occurs in the cytoplasm and converts one glucose into two pyruvate molecules.

Where does glycolysis occur?

In the cytoplasm of the cell.

What is the energy result of glycolysis per glucose?

A net gain of 2 ATP and 2 NADH.

Does glycolysis directly require oxygen?

No. Glycolysis does not directly require oxygen.

What is pyruvate?

A 3-carbon molecule produced at the end of glycolysis.

What is NADH?

An electron carrier that transports high-energy electrons to later stages of energy metabolism.

What are the two main options for pyruvate?

It can be converted to acetyl CoA for aerobic energy metabolism, or converted to lactate to regenerate NAD+ so glycolysis can continue.

When can pyruvate be converted to lactate?

When the cell needs to regenerate NAD+ to keep glycolysis running.

What happens when pyruvate is converted to acetyl CoA?

Pyruvate loses one carbon as carbon dioxide, NADH is produced, and the remaining 2-carbon acetyl group attaches to coenzyme A.

What is acetyl CoA?

A 2-carbon compound formed from pyruvate; it enters the citric acid cycle. Class notes state acetyl CoA cannot be used to make glucose.

What is the pathway from glucose to acetyl CoA?

Glucose → glycolysis → pyruvate → acetyl CoA.

What is glycogenolysis?

Breaking down glycogen, the stored form of glucose, to release glucose or glucose-derived compounds.

What is gluconeogenesis?

Making new glucose from noncarbohydrate sources, including certain amino acids, lactate, and glycerol.

What organ plays a major role in maintaining blood glucose during fasting?

The liver.

What is beta-oxidation?

The process that breaks fatty acids into 2-carbon units, producing acetyl CoA, NADH, and FADH2.

Where does beta-oxidation usually occur?

Primarily in the mitochondria for fatty acids processed through the usual mitochondrial pathway.

Why does fat provide more energy per gram than carbohydrate?

Fat is more energy dense: about 9 kcal/g compared with 4 kcal/g for carbohydrate.

What is deamination?

Removal of the nitrogen-containing amino group from an amino acid.

What happens to nitrogen removed during deamination?

It can be converted into urea, which travels to the kidneys and is excreted in urine.

What happens to the carbon skeleton of an amino acid?

It can enter energy metabolism at different points; some amino acids can contribute to glucose production, while others contribute to acetyl CoA or related intermediates.

Does the body have a dedicated protein reserve for energy?

No. Using protein for energy can mean breaking down functional tissues.

What is the citric acid cycle also called?

The Krebs cycle or TCA cycle.

Where does the citric acid cycle occur?

In the mitochondrial matrix.

What enters the citric acid cycle?

Acetyl CoA.

What does the citric acid cycle produce?

Carbon dioxide, NADH, FADH2, and a small amount of ATP (or an equivalent energy-carrying molecule).

What is the major contribution of the citric acid cycle?

Generating NADH and FADH2 to carry high-energy electrons to the electron transport chain; it does not directly produce most ATP.

Where is the electron transport chain (ETC)?

In the inner mitochondrial membrane.

What do NADH and FADH2 do in the ETC?

They deliver high-energy electrons to the chain.

What happens as electrons move through the ETC?

Released energy helps pump hydrogen ions across the inner mitochondrial membrane, creating a gradient.

What is oxygen's role in aerobic respiration?

Oxygen is the final electron acceptor; it combines with electrons and hydrogen to form water.

What is chemiosmosis?

Hydrogen ions flow back across the inner mitochondrial membrane through ATP synthase, and that flow is used to make ATP.

What does ATP synthase do?

Uses the flow of hydrogen ions to make ATP from ADP and inorganic phosphate.

What is oxidative phosphorylation?

The process involving the electron transport chain and chemiosmosis that produces most ATP during aerobic glucose metabolism.

Where is most ATP from aerobic glucose metabolism produced?

Through oxidative phosphorylation.

Where is carbon dioxide released during aerobic glucose metabolism?

During pyruvate oxidation and the citric acid cycle.

Where is water formed during aerobic glucose metabolism?

At the end of the electron transport chain.

What is the overall aerobic pathway for glucose?

Glucose → glycolysis in the cytoplasm → pyruvate → acetyl CoA formation → citric acid cycle → electron transport chain and chemiosmosis → ATP and water; carbon dioxide is released earlier.

What is insulin?

A key hormone released by the pancreas in response to rising blood glucose.

What does insulin generally promote?

Glucose uptake into insulin-sensitive tissues, glycogen synthesis, fat storage when energy is abundant, and protein synthesis; it reduces breakdown of stored fuels.

What is feasting?

The period after eating, when nutrients enter the bloodstream and the body uses them for immediate needs or stores them for later.

What is glucagon?

A pancreatic hormone that helps raise blood glucose when it falls.

What happens during fasting?

The body shifts toward stored fuels to maintain energy supply and blood glucose.

What are the major processes used during fasting?

Glycogenolysis, gluconeogenesis, lipolysis, beta-oxidation, and ketogenesis.

What is lipolysis?

Breakdown of stored triglycerides into fatty acids and glycerol.

What is ketogenesis?

Production of ketone bodies, primarily in the liver, from fatty-acid-derived acetyl CoA.

What happens in early fasting?

Liver glycogen helps maintain blood glucose.

What becomes increasingly important as fasting continues?

Gluconeogenesis, as glycogen stores decline.

What happens during prolonged fasting?

The liver produces more ketone bodies from fatty-acid-derived acetyl CoA, and the brain uses ketones to meet part of its energy needs.

How does ketone use affect protein conservation?

Increased ketone use can reduce, but does not eliminate, the body's need to use amino acids for glucose production.

What is the Cori cycle?

A process through which lactate can be converted back to glucose.

What is the anaerobic pathway's role in exercise?

The anaerobic breakdown of glucose through pyruvate to lactate is a major energy source during short, intense exercise.

What is the aerobic pathway for pyruvate?

Pyruvate is converted to acetyl CoA, which enters the TCA/citric acid cycle.

What are glucogenic amino acids?

Amino acids that can be converted to pyruvate and contribute to glucose production.

What are ketogenic amino acids?

Amino acids that can be converted to acetyl CoA.

What happens to excess amino acids?

They cannot be stored as protein reserves; their components can be used for energy or converted to fat for storage.

What is ammonia's relationship to urea?

Deamination produces ammonia. Excess ammonia combines with carbon dioxide to form urea, which travels through the blood to the kidneys and is excreted in urine.

What is ketosis?

A state in which ketone production increases as the body relies more on fat-derived fuels when glucose availability is low.

What does the class material say about low-carbohydrate diets and metabolism?

They produce some changes similar to fasting: glycogen is used first, gluconeogenesis becomes more important as glycogen declines, and ketones can provide an alternative fuel for some brain cells.

What potential adverse effects of low-carbohydrate/ketogenic diets are listed in class?

Nausea, fatigue, constipation, low blood pressure, elevated uric acid, bad breath, and fetal harm or stillbirth during pregnancy.

How is alcohol processed?

Alcohol is absorbed into the bloodstream and processed primarily by the liver. Ethanol is converted to acetaldehyde and then acetate.

Why is acetaldehyde important?

It is toxic and contributes to alcohol-related harm.

How many kcal per gram does alcohol provide?

7 kcal/g.

How does alcohol metabolism affect fat metabolism?

It changes the liver's NADH-to-NAD+ balance, which can inhibit fatty-acid oxidation and promote fat accumulation in the liver.

How can alcohol affect gluconeogenesis?

Alcohol metabolism can interfere with gluconeogenesis, particularly when food intake is inadequate.

How does alcohol affect the brain and nervous system?

It impairs judgment, coordination, reaction time, and decision-making; it acts as a central nervous system depressant.

How does alcohol affect ADH?

Alcohol suppresses antidiuretic hormone (ADH), increasing urination and contributing to water and mineral loss.

Can food or coffee instantly sober someone up?

No. Food does not make alcohol disappear instantly, and coffee does not reverse alcohol impairment.

What does alcohol tolerance mean?

Increasing amounts of alcohol are needed to achieve the same effect; tolerance does not eliminate alcohol's effects.

What are the standard alcoholic drink amounts listed in class?

1.5 oz of 80-proof liquor, 5 oz of wine, 12 oz of beer, or 10 oz of wine cooler.

What are signs of alcohol use disorder listed in class?

Tolerance, withdrawal, impaired control, disinterest in important activities, substantial time obtaining/using/recovering from alcohol, impaired ability to meet responsibilities, and continued use despite problems.

What is energy balance?

When energy consumed from food and beverages is approximately equal to energy expended by the body.

What counts as energy in?

Energy supplied by foods and beverages.

What counts as energy out?

Energy used for basal metabolism, physical activity, digestion, and other physiological processes.

What is positive energy balance?

Energy intake is greater than energy expenditure. If it continues over time, the body generally stores some excess energy and weight tends to increase.

What is negative energy balance?

Energy expenditure is greater than energy intake, so the body uses stored energy to make up the difference; this results in weight loss.

What is energy balance/weight maintenance?

Energy intake approximately equals energy expenditure over time, and body weight tends to remain relatively stable.

Why can body weight fluctuate even when energy balance is stable?

Water balance, food in the digestive tract, and other factors can cause normal daily fluctuations.

What is the 3500-kcal rule?

A traditional estimate that 1 pound of fat corresponds to approximately 3,500 calories.

Why is body weight not the same as body fat?

Body weight includes fat, fluid, muscle, bone minerals, and other tissues.

What is direct calorimetry?

Measuring the heat released when food is burned.

What is a bomb calorimeter?

A device used to determine a food's gross energy value by burning it in a controlled chamber and measuring the heat released.

What is indirect calorimetry?

Estimating energy expenditure by measuring gas exchange, particularly oxygen consumption and carbon dioxide production.

What brain region is key in regulating hunger and food intake?

The hypothalamus.