Calories, Caloric Density, and ATP/ADP Vocabulary

Calorie is a unit of chemical energy used in the physical and biological sciences.
A calorie (c) is the amount of energy required to raise the temperature of one gram of water by one degree Celsius (OC).
The caloric content of food is measured by burning it completely to ashes under a container of water and measuring the increase in the water temperature.
Only a handful of peanuts has enough chemical energy to boil more than a quart of water if the peanuts could be completely converted to heat.
A bomb calorimeter is used by food scientists to measure the caloric content of foods.

The plates of kiwi fruit and M&Ms each contain about 200 food calories.
Although certain foods may have about equal caloric content, they can differ substantially in caloric densities.
Source links mentioned in the transcript (for reference):
- https://www.asymptotia.com

Caloric accounting is based on a person's food and beverage intake, basal metabolic rate (BMR) for body functions, and physical activity.
One pound of body weight equals approximately $1\ \,\text{lb} \approx 3500 \ \text{cal}$ .
Caloric imbalances among these three factors can lead to weight gain or weight loss; for example, if calories in exceed calories out, a person would gain weight.
Visual concept (from transcript): CALORIES IN vs CALORIES OUT (Food/Beverages vs Body Functions/Physical Activity)

ATP stands for adenosine triphosphate: components are adenine, adenosine, ribose, and three phosphate groups (triphosphate).
ATP contains a high-energy phosphate bond capable of doing work when broken.
ADP stands for adenosine diphosphate: components are adenine, adenosine, ribose, and two phosphate groups (diphosphate).
The release of the high-energy phosphate bond in ATP provides energy for cellular work.
The chemical equation and specifics of aerobic cellular respiration are referenced as a redox reaction; oxygen is required for aerobic respiration.
Note: Aerobic respiration is not the same as aerobic exercise.

The chemical equation for aerobic cellular respiration is shown on the next slide (not provided in the transcript).
A key product of cellular respiration is ATP.
The left- and right-hand sides of the equation relate to a chemical cycle in ecosystems.
The chemical equation represents a redox reaction.
Reminder: Aerobic respiration requires oxygen; it is distinct from aerobic exercise.

The crowding of negative charges in the molecular tail of ATP is similar to storing energy in a compressed spring.
When released, a spring can perform useful work.
The release of the third phosphate group from the molecular tail of ATP makes energy available for cellular work.
After the release, the molecule has two remaining phosphate groups and is called ADP (adenosine diphosphate).
Phosphate Transfer:
- The third phosphate group released from ATP is transferred to other molecules.
- This transfer enables cells to perform work—mechanical, chemical, or transport.

ATP is restored by adding a phosphate group to ADP using the chemical energy that cellular respiration harvests from food molecules (such as carbohydrates and fats).
The process is called the ATP cycle.
ATP Cycle (conceptual description):
- ATP stores energy from food molecules (potential energy from food molecules).
- The circle turns as chemical energy is used for cellular work, converting ATP back to ADP and Pi (inorganic phosphate).
- Cycle continues: ADP + Pi are reassembled into ATP using energy from food.
Diagrammatic notes from transcript (described):
- ATP → ADP + P_i + Energy (when energy is released for cellular work)
- ADP + P_i → ATP (energy from food) to replenish ATP stores
- Overall, ATP serves as the energy currency of the cell, cycling between ATP and ADP + Pi as energy is consumed and replenished.