Overview of Biochemical Pathways

Question 1

1. List the components of the energy balance equation including components of energy expenditure.

Answer 1

Total Energy Expenditure (TEE) = RMR + TEF + EEPA

1. Resting Metabolic Rate (RMR): 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.
2. Thermic Effect of Food (TEF): 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 fat. TEF accounts for about 8% of TEE.

3. Energy Expenditure of Physical Activity (EEPA):  is the energy expended on 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.
Non-exercise activity thermogenesis (NEAT) is the energy expended on “unconscious” or unplanned movements. It can be thought of as the unintentional exercise portion of activity (i.e. fidgeting in your chair during class is something you do, but you probably wouldn’t call it exercise).
Voluntary activity, such as activities of daily living (walking around at work, cleaning the house, etc.) or intentional exercise make up the other component of EEPA.

Question 2

Comment on the accuracy of methods for estimating and measuring energy expenditure and energy intake.

Answer 2

energy intake there are few and they all have poor accuracy

1. Indirect calorimetry—measures respiratory composition and flow to estimate oxygen consumption and CO2 production. RMR correlates with oxygen consumption.
2. RMR estimation based on age, sex, height, and weight.”

calorimetry is more accurate

1. TEF Indirect calorimetry Accurate
2. EEPA is estimated by determining TEE with “doubly labeled water” measurements and subtracting RMR and TEF.
3. EEPA can also be “measured” with pedometers or GPS devices.” Neither are super accurate, since they both rely on estimations.

Energy Intake (EI) Few available methods for measuring—most rely on self-reported food intake. Poor accuracy

Question 3

3. Estimate the pool sizes of stored fat, carbohydrate and protein in the body.

Answer 3

Fat—120,00 kcal or 13kg

Carbohydrates—2,000 kcal or 500g

400g in muscle and 100g in liver

Protein—no readily accessible storage form
During persistent negative energy balance, protein may be broken down to make glucose

Question 4

4. List the hierarchy of fuels for oxidation. Discuss how this affects weight gain.

Answer 4

Individuals in positive energy balance will tend to accumulate fat, meaning that weight gain is mostly fat gain. This is because we have such a large storage capacity for fat. When we are overfed, we burn protein first, followed by carbohydrates. This is a direct consequence of the fact that if we don’t use these nutrients, they have no place to go (their storage pools are much smaller or, in the case of protein, nonexistent). Unused fat, on the other hand, can be readily stored in a very large storage pool.

Question 5

5. Identify the structures of glucose, fatty acids, and amino acids.

Answer 5

Glucose is a 6-carbon monosaccharide.
Fatty acids are carboxylic acids with long hydrocarbon chains.
Amino acids consist of an amino group, a carboxylic acid and a variable R-group side chain.

Question 6

Glycolysis-

Answer 6

Glucose—>Pyruvate

Modest ATP production.

Question 7

TCA Cycle-

Answer 7

Energy extracted from pyruvate for use by the cell. Cycle produces CO2 and NADH/FADH2 that are used to generate ATP.

Question 8

Electron Transport chain (oxidative phosphorylation)

Answer 8

Electron Transport Produces ATP from ADP using NADH and FADH2. Oxygen is consumed and water is produced.

Question 9

Gluconeogenesis-

Answer 9

Generation of glucose from lactate and amino acid carbon skeletons in the liver and kidney. Roughly follows the reverse pathway of glycolysis.

Question 10

Glycogen synthesis/breakdown

Answer 10

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.

Question 11

Pentose Phosphate Pathway (Hexose Monophosphate Shunt)

Answer 11

Excess glucose is used to generate NADPH and ribose sugars. NADPH is used for fatty acid and steroid hormone synthesis. Ribose is important for nucleotide synthesis.

Question 12

Triacylglycerol Synthesis

Answer 12

Formation of fatty acids from acetyl-CoA. Fatty acids are then linked with glycerol to form triglycerides that are stored in adipose tissue or secreted from the liver in VLDL.

Question 13

Beta oxidation

Answer 13

Breakdown of triglycerides to form acetyl-CoA. Acetyl-CoA enters the TCA cycle to generate NADH and FADH2 for ATP synthesis.
Urea cycle Disposal of nitrogen derived from amino acid metabolism. Produces urea that is excreted by the kidneys.