Overview of Biochemical Pathways

Question 2

Basic concept of energy balance

Answer 2

Intake of energy/nutrients (ingestion) vs. energy expended via metabolic processes

“nutrients” = macronutrients = carbohydrates, fat, and protein

Question 3

Positive energy balance definition

Answer 3

normal state of nutrient excess that occurs after feeding

aka “fed state”

nutrients are distribute between tissues and stored for later use

Question 4

Negative energy balance definition

Answer 4

previously stored nutrients mobilized to provide energy/substrates for metabolic processes

aka “fasted state”

e.g. illness or exercise

Question 5

Characteristics of energy imbalance vs. energy balance

Answer 5

energy balance stable weight intake = expenditure energy imbalance weight gain or loss

gain = intake > expenditure

loss = intake < expenditure

Question 6

Components of Total Energy Expenditure (TEE)

Answer 6

Resting metabolic rate (RMR)

Thermic effect of food (TEF)

Energy expended in Physical Activity (EEPA)

Question 7

Determinants of resting metabolic rate

Answer 7

Primary = fat free mass (lean body mass)

RMR = energy cost of maintaining basic body fxns E.g. Na+/K+ balance, heart, body temp

Question 8

Measurement of RMR (Resting Metabolic Rate)

Answer 8

Indirect calorimetry

Measures O2 consumption vs. CO2 production O2 consumption correlates to energy expenditure (b/c oxidation is main method of gaining cellular energy)

Estimate with age, sex, height, weight (+/- lean body mass)

Question 9

Determinants of Thermic Effect of Food

Answer 9

Energy cost of digesting and distributing nutrients from diet to body tissues TEF varies by nutrient: Protein TEF > Carb TEF > Fat TEF

Question 10

Measurement of TEF (Thermic Effect of Food)

Answer 10

Indirect calorimetry: Measure amount of extra energy expended above RMR after ingestion of defined test meal

Question 11

Determinants of energy expended in physical activity (EEPA)

Answer 11

NEAT = non-exercise activity thermogenesis Unplanned/unconscious activity, e.g. fidgeting Exercise Some energy physical work Some energy lost as heat

Question 12

Measurement of Total Energy Expenditure (TEE)

Answer 12

“double labeled water” test measures O2 consumption over several weeks

Question 13

Measurement of energy expended in physical activity (EEPA)

Answer 13

calculation EEPA = TEE – TEF – RMR Questionnaires Devices: pedometers, GPS, etc.

Question 14

Components of energy intake (EI)

Answer 14

Brain determines meal frequency and size based on assessment of stored energy and circulating nutrients/hormones

Question 15

Measurement of energy intake (EI)

Answer 15

Few methods to directly measure energy intake in free-living individuals If weight is stable then EI = TEE and doubly labeled water test will predict EI Self-reported food intake is commonly used, however most people under-report food intake by 20-40%

Question 16

Main biomolecules that serve as nutrients

Answer 16

Glucose Fatty acids Amino acids

Question 17

Glucose structure

Answer 17

Carbon ring

Question 18

Fatty Acid structure

Answer 18

Hydrocarbon chain + methyl group + carboxylic acid group

Question 19

Amino Acid structure

Answer 19

Central alpha carbon Hydrogen Carboxylic acid group Amino group Side chain (R group)

Question 20

Approximate nutrient energy stores in body

Answer 20

Fat = ~120,000 kcal 9 kcal/g 13 kg in a 70kg person Carbohydrates = ~2,000 kcal 4 kcal/g 500g stored as glycogen @ muscle (400g) and liver (100g) Protein No storage site

Question 21

Measurement of body composition

Answer 21

BMI Skin fold thickness Bioelectrical impedance Body density measures Dual energy x-ray absorptiometry (DEXA) Most accurate form of measure

Question 22

Hierarchy of nutrient oxidation

Answer 22

Protein Oxidized first if in excess because body lacks a storage site Carbohydrates If protein is balanced, then carbs oxidized before fats due to limited storage capacity vs. fats Fat

Question 23

Consequences of hierarchy of nutrient oxidation

Answer 23

Fat is last to be oxidized and most likely to be stored if in excess individuals in positive energy balance will tend to accumulate body fat

Question 24

Broad categorizations of metabolic pathways

Answer 24

fed vs. fasted state anabolic vs. catabolic state positive vs. negative energy balance

Question 25

Characteristics of fed vs. fasted state

Answer 25

fed goal: assimilate ingested nutrients insulin high glucagon low fasted goal: use stored nutrients to maintain body processes insulin low glucagon high

Question 26

Anabolic vs. Catabolic processes

Answer 26

anabolic = building polymers from monomers catabolic = breaking down polymers to monomers

Question 27

Main metabolic pathways

Answer 27

Carbohydrates Glycolysis Tricarboxylic acid cycle (TCA cycle) Electron transport Gluconeogenesis Glycogen Pentose phosphate pathway Fat Triacylglycerol synthesis Triacylglyceral degradation, beta-oxidation and ketogenesis Protein Urea cycle

Question 28

Glycolysis fxn/basic mechansim

Answer 28

Fxn = cytoplasmic breakdown of glucose to generate ATP and pyruvate @ cytoplasm: glucose 2 pyruvate ( lactate if no oxygen) pyruvate TCA cycle

Question 29

TCA cycle fxn

Answer 29

fxn = pyruvate enters pathway to extract energy molecule CO2, NADH, and FADH2

Question 30

Electron transport chain fxn

Answer 30

series of proteins in the inner membrane of the mitochondria NADH and FADH2 deliver electrons to help produce ATP from ADP. Rxns of ET consume oxygen and produce water in a process known as oxidative phosphorylation

Question 31

Gluconeogenesis fxn

Answer 31

Generate glucose (from lactate or muscle-derived amino acids) for use by the brain during periods of fasting

Question 32

Glycogen fxn

Answer 32

Storage of excess glucose Mostly stored @ skeletal muscle (400g) Some stored @ liver (100g)

Question 33

Pentose Phosphate Pathway

Answer 33

Aka Hexose Monophosphate Shunt Glycolysis pathway detour Occurs during glucose excess or need for pentose pathway products NADPH and ribose (5 carbon) sugars

Question 34

De Novo Lipogenesis (Triacylglycerol synthesis) fxn

Answer 34

generate fatty acids for storage from glucose + acetyl-CoA (i.e. glucose fat) 3 fatty acids + glycerol triglyceride stored as triglyceride rich lipoproteins (VLDL)

Question 35

Triacylglycerol degradation, beta-oxidation and ketogenesis pathway fxn

Answer 35

use stored fat as energy to oxidizing tissues (e.g. skeletal muscle and liver) during negative energy balance @ fat storage: triglycerides FA + glycerol circulation @ liver/muscle: FA broken down via beta-oxidation acetyl-CoA (OR) ketone bodies

Question 36

Urea cycle fxn

Answer 36

disposal of nitrogen derived from metabolism of amino acids