Cellular Respiration and Energy Use

Cellular Respiration Overview

• Cellular respiration uses electron power to build a concentration gradient.

• This gradient releases potential energy to generate kinetic energy.

• This energy is then captured in an ATP molecule.

Dietary Energy and Cellular Respiration

• Energy consumption varies with activity levels, measured in kcal consumed per hour for a 67.5-kg (150-lb) person.

• Examples:

  • Sitting: 61 kcal

  • Driving a car: 28 kcal

  • Slow dancing: 204 kcal

  • Walking (3 mph): 245 kcal

  • Bicycling (10 mph): 408 kcal

  • Fast dancing: 490 kcal

  • Swimming (2 mph): 510 kcal

  • Running (8-9 mph): 979 kcal

Key Questions

• How does the body use energy in food?

• How does aerobic respiration extract useful energy from food?

• When does fermentation occur, and why can’t humans survive solely on fermentation?

• What factors influence weight gain and weight loss?

Energy Availability

• Bacterial and eukaryotic cells use oxygen to harvest energy from food molecules.

• This energy is available to power cell work in the form of ATP molecules.

Energy Transfer

• Energy is transferred, but not created; it must come from an external source.

• Matter is neither created nor destroyed, adhering to the law of conservation.

Cellular Respiration Defined

• Transfers energy in organic molecules (food) to ATP.

• ATP is continuously used by our cells.

Chemical Equation for Cellular Respiration

• Inputs:

  • Glucose: $C<em>6H</em>{12}O_6$

  • Oxygen: $O_2$

• Outputs:

  • Carbon dioxide: $CO_2$

  • Water: $H_2O$

  • Energy (ATP)

Aerobic Respiration

• Converts stored food energy into ATP.

• Occurs in the presence of oxygen.

Stages of Cellular Respiration

• Glycolysis: occurs in the cytosol, produces ATP and pyruvate.

• Citric Acid Cycle: occurs in the mitochondrial matrix, extracts high-energy electrons, releases carbon dioxide, generates ATP, NADH, and FADH2.

• Electron Transport Chain: occurs in the inner mitochondrial membrane; uses electrons to produce a majority of ATP molecules.

Aerobic Respiration Process

• Blood transports glucose (from food) and oxygen (from lungs).

• Cells release energy from glucose and capture it in ATP.

• Blood transports excess carbon dioxide to the lungs and water to the kidneys.

Aerobic Respiration Stages

1. Glycolysis

2. Citric Acid Cycle

3. Electron Transport Chain

Glycolysis Details

• Occurs in the cytoplasm.

• Breaks down sugar into smaller units (pyruvate).

Citric Acid Cycle Details

• Extracts energy (high-energy electrons) from food.

• NAD+ picks up and transfers electrons.

• Releases carbon dioxide.

Electron Transport Chain Details

• NAD+ molecules bring electrons to folds on the inner membrane of the mitochondria.

• Electrons flow down a chain of molecules on the inner membrane.

• Oxygen accepts electrons and combines with hydrogen atoms to form water at the end of the chain.

• The flow of electrons powers the production of most ATP in aerobic respiration.

Mini Case: Interference with Electron Transport

• A molecule interferes with the capture of energy as ATP after the electron transport chain.

• Impact: Overall ATP production decreases.

• The energy that was not captured as ATP is released as heat, following the law of conservation of energy.

• Brown fat in human babies is thermogenic due to specialized mitochondria that release heat.

Fermentation

• Harvesting chemical energy without oxygen.

• Glycolysis occurs to produce ATP when oxygen is scarce

• Fermentation regenerates $NAD^+$.

• Products: lactic acid or alcohol, small amount of ATP.

Lactic Acid Fermentation

• Glucose undergoes glycolysis to produce 2 ATP and 2 pyruvate molecules.

• 2 NADH molecules recycle to 2 $NAD^+$.

• 2 Lactate molecules are formed.

• This process occurs in muscle cells and is also used in the production of cheese, soy, and sauerkraut.

• 1 glucose molecule yields 2 ATP molecules and 2 lactate molecules.

Alcohol Fermentation

• Glucose undergoes glycolysis to produce 2 ATP and 2 pyruvate molecules.

• 2 NADH molecules recycle to 2 $NAD^+$.

• Products: 2 ATP, 2 Ethanol and 2 $CO_2$

• Used to produce alcohol in beer and wine and to make bread rise.

• 1 glucose molecule yields 2 ATP molecules, ethanol, and $CO_2$.

Glycolysis Evolution

• Glycolysis evolved early in the history of life on Earth.

• It is the universal energy-harvesting process of living organisms.

• All cells use glycolysis, no oxygen is required, used in both fermentation & respiration, and takes place in the cytoplasm.

Early Earth

• Early Earth had no oxygen when life first arose.

• Early organisms made ATP through glycolysis pathways.

Pollution Crisis

• The first pollution crisis on earth occurred about 2.2 billion years ago.

• Cyanobacteria evolved photosynthesis, leading to the oxygenation of the atmosphere.

Metabolism Pathways Layout

• Glycolysis occurs in the cytosol.

• Pyruvate is oxidized.

• Citric Acid Cycle occurs in the mitochondrial matrix.

• Oxidative Phosphorylation (electron transport and chemiosmosis) occurs in the inner mitochondrial membrane.

Food Breakdown

• Proteins, fats, and carbohydrates are sources of dietary energy.

• Food is usually not pure glucose but is broken down into various components that feed into cellular respiration.

• Glycolysis breaks down carbohydrates into pyruvate, which is then converted to Acetyl CoA

• Lipids are broken down into glycerol and fatty acids that feed into glycolysis or the citric acid cycle

• Proteins are reduced to amino acids and amino groups and feed into glycolysis or the citric acid cycle

Obesity

• Defined as having an unhealthy amount of body fat.

• In 2019, nearly 40% of U.S. adults were obese.

Energy Expenditure

• Three ways we expend energy:

  1. Basal metabolism (60%)

  2. Digestion (10%)

  3. Physical activity or Thermogenesis

  • Deliberate exercise (exercise activity thermogenesis)

  • Nonexercise activities (NEAT)

• Excess glucose can be converted to ATP, glycogen, or triglycerides.

ATP and biosynthesis

• ATP drives biosynthesis of biomacromolecules.

• Intermediates in the citric acid cycle, such as pyruvate drive synthesis of glucose, amino acids, glycerol, sugars, fatty acids.

• Macromolecules, such as proteins, fats, and carbohydrates that form cells, tissues, organisms.

Energy Storage

• Animals store extra energy as:

  • Glycogen in muscle and liver cells (short-term).

  • Triglycerides in fat cells (long-term).

Glycogen

• Complex carbohydrate made up of linked chains of glucose molecules.

• Used as short-term energy storage.

Triglycerides

• Lipids found in fat cells.

• Cells convert fats, amino acids, and sugars into triglycerides.

• Used for long-term energy storage.

Sedentary Lifestyle

• Humans have adopted a sedentary lifestyle in the past 150 years.

• This has decreased their NEAT by ~1,500 Calories per day.

Body Mass Index (BMI)

• Estimates body fat based on height and weight.

• The percentage of overweight adults has remained relatively constant.

• The percentage of obese and extremely obese adults has grown.

Balancing Energy

• A healthy diet includes balancing calories from food with calories burned.

• An imbalance of energy in and out can lead to weight gain or weight loss.

Nonexercise Activity Thermogenesis (NEAT)

• Includes daily activities, such as yard work, shopping, and walking a dog.

• People who increase their NEAT do not gain as much fat when fed extra calories.

  • Lean participants stood and walked more = 350 cal per day more.

  • Obese participants sat 2.25 hours longer per day.

• Intentional exercise did not account for the differences between the groups.

Overfeeding Study Conclusion

• People resistant to weight gain can switch on their NEAT in response to overfeeding.

Summary Points

• Macronutrients (proteins, carbohydrates, and fats) are sources of dietary energy.

• Excess energy is stored in the bonds of glycogen and triglycerides.

• Cells carry out chemical reactions to break down food and obtain usable energy in the form of ATP.

• Aerobic respiration produces large amounts of ATP in the presence of oxygen.

• Fermentation follows glycolysis in the absence of oxygen, producing less ATP than aerobic respiration.

• Activity (exercise and NEAT) helps burn stored Calories.

• Glycogen is used first during exercise; stored fats are tapped when glycogen stores are depleted.

• Photosynthesis and respiration form a cycle: the carbon dioxide given off during aerobic respiration is used by photosynthesizers to make glucose and oxygen.

Data Interpretation: Marathon Runner

• A well-trained 130-pound female marathon runner loads up on a carbohydrate meal and has the maximum amount of stored glycogen (6.8 g of glycogen per pound of body weight).

  • a. How many grams of glycogen is she storing?

  • b. How many Calories does she have stored as glycogen?

  • c. If this same number of Calories were stored as fat, how much would it weigh?

  • d. Suppose this athlete decides to go for a run at a pace of 9 mph (she will be running 6.5-minute miles). Given her weight, she will burn 885 Calories per hour at this pace. How long will it take her to deplete her glycogen stores? How many miles can she run before her glycogen supplies run out? Will she be able to complete a 26.2-mile marathon?

  • e. Once her glycogen supplies run out, what has to happen if she wants to keep running?

Term 1: Cellular Respiration
Definition 1: Uses electron power to build a concentration gradient, releasing potential energy to generate kinetic energy. This energy is then captured in an ATP molecule.
Term 2: Aerobic Respiration
Definition 2: Converts stored food energy into ATP and occurs in the presence of oxygen.
Term 3: Glycolysis
Definition 3: Occurs in the cytosol and breaks down sugar into smaller units (pyruvate).
Term 4: Citric Acid Cycle
Definition 4: Occurs in the mitochondrial matrix, extracts high-energy electrons, releases carbon dioxide, and generates ATP, NADH, and FADH2.
Term 5: Electron Transport Chain
Definition 5: Occurs in the inner mitochondrial membrane and uses electrons to produce a majority of ATP molecules.
Term 6: Fermentation
Definition 6: Harvesting chemical energy without oxygen, regenerating $NAD^+$ and producing lactic acid or alcohol with a small amount of ATP.
Term 7: Lactic Acid Fermentation
Definition 7: Glucose undergoes glycolysis to produce 2 ATP and 2 pyruvate molecules, recycling 2 NADH molecules to 2 $NAD^+$ and forming 2 Lactate molecules.
Term 8: Alcohol Fermentation
Definition 8: Glucose undergoes glycolysis to produce 2 ATP and 2 pyruvate molecules, recycling 2 NADH molecules to 2 $NAD^+$, resulting in products: 2 ATP, 2 Ethanol and 2 $CO_2$.
Term 9: Nonexercise Activity Thermogenesis (NEAT)
Definition 9: Includes daily activities (yard work, shopping, walking a dog).
Term 10: Glycogen
Definition 10: Complex carbohydrate made up of linked chains of glucose molecules and used as short-term energy storage.
Term 11: Triglycerides
Definition 11: Lipids found in fat cells, used for long-term energy storage, and converted from fats, amino acids, and sugars.