Overview of Biochemical Pathways Flashcards
What are the four components of the energy balance equation?
Total Energy Expenditure: TEE Resting Metabolic Rate: RMR Thermic Effect of Food: TEF Energy Expenditure of Physical Activity: EEPA TEE = RMR + TEF + EEPA
Define the Resting Metabolic Rate
The RMR is the energy required to maintain basic bodily functions, such as keeping ion pumps pumping or maintaining body temperature. RMR increases with the amount of lean body mass a person has. RMR accounts for 75% of TEE in sedentary people.
Define the Thermic Effect of Food
The TEF is the energy cost associated with digesting and distributing nutrients in food. This energy requirement varies with different nutrients. Protein requires the most energy to digest/distribute, followed by carbohydrates and then fats. TEF accounts for about 8% of TEE.
Define the Energy Expenditure of Physical Activity
The EEPA is the energy expended in exercise. Part of the energy used in activity is used to do work and part is lost to the environment. The proportion of the TEE made up of the EEPA varies a great deal from person to person based on activity level. EEPA can be further divided into two subcomponents:
1 - Non-Exercise Activity Thermogenesis (NEAT) is the energy expended on “unconscious” or unplanned movements, i.e. fidgeting in a chair.
2 - Voluntary activity, such as activities of daily living (walking around work, cleaning house), or intentional exercise.
How is RMR tested and how accurate are these tests?
RMR is measured by:
Indirect calorimetry: measures respiratory composition and flow to estimate O2 consumption and CO2 production. This is fairly accurate
Estimation: based on age, sex, height, weight. This is not very accurate due to wide variation between similar individuals.
How is TEF tested and how accurate is this test?
TEF is measured vie indirect calorimetry (respiratory O2/CO2), which is fairly accurate.
How is EEPA tested and how accurate is this test?
EEPA is measured by:
Determining TEE with “doubly labeled water” measurements and subtracting RMR and TEF. This is not very accurate.
Also measured by pedometers or GPS devices. Also not very accurate.
What are the approximate storage pool sizes for fats, carbs, and proteins in the body?
Fats: 120,000 kcal (13kg)
Carbs: 2000 kcal (500g, 400 muscle/100liver)
Protein: No readily accessible storage form (during persistent negative energy balance, protein may be broken down to make glucose)
What is the hierarchy of oxidation of nutrients?
We burn protein first, then carbohydrates, because there is little to no excess storage capacity for these nutrients. Dietary fat is burned last because there is ample storage available for it.
What is the implication for weight gain due to the hierarchy of oxidation of nutrients?
Protein and carbs are preferentially burned first by the body. Dietary fat is the last resource used for energy and the easiest to store. Thus, the hierarchy of oxidation leads us towards increased fat storage and weight gain.
What is the general function of the glycolysis pathway?
Convert glucose into pyruvate, giving modest ATP production.
What is the general function of the TCA cycle?
Extracts energy from pyruvate for use by the cell. Cycle produces CO2, NADH, FADH2.
What is the general function of the Electron Transport Chain?
Produces ATP from ADP using NADH and FADH2. Oxygen is consumed and water is produced.
What is the general function of Gluconeogenesis?
Generation of glucose from lactate and amino acid carbon skeletons in the liver and kidney. Roughly follows the reverse pathway of glycolysis.
What is the general function of Glycogen synthesis/breakdown?
Glycogen is synthesized as a storage form of glucose in the liver and skeletal muscle. Glycogen is broken down when the body is in negative energy balance to provide glucose.
