Overview of Biochemical Pathways Flashcards Preview

DEMS: Unit II > Overview of Biochemical Pathways > Flashcards

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Basic concept of energy balance

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

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


Positive energy balance definition

normal state of nutrient excess that occurs after feeding

aka “fed state”

nutrients are distribute between tissues and stored for later use


Negative energy balance definition

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

aka “fasted state”

e.g. illness or exercise


Characteristics of energy imbalance vs. energy balance

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

gain = intake > expenditure 

loss = intake < expenditure


Components of Total Energy Expenditure (TEE)

Resting metabolic rate (RMR)

Thermic effect of food (TEF)

Energy expended in Physical Activity (EEPA)


Determinants of resting metabolic rate

Primary = fat free mass (lean body mass)

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


Measurement of RMR (Resting Metabolic Rate)

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)


Determinants of Thermic Effect of Food

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


Measurement of TEF (Thermic Effect of Food)

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


Determinants of energy expended in physical activity (EEPA)

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


Measurement of Total Energy Expenditure (TEE)

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


Measurement of energy expended in physical activity (EEPA)

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


Components of energy intake (EI)

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


Measurement of energy intake (EI)

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%


Main biomolecules that serve as nutrients

Glucose Fatty acids Amino acids


Glucose structure

Carbon ring


Fatty Acid structure

Hydrocarbon chain + methyl group + carboxylic acid group


Amino Acid structure

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


Approximate nutrient energy stores in body

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


Measurement of body composition

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


Hierarchy of nutrient oxidation

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


Consequences of hierarchy of nutrient oxidation

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


Broad categorizations of metabolic pathways

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


Characteristics of fed vs. fasted state

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


Anabolic vs. Catabolic processes

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


Main metabolic pathways

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


Glycolysis fxn/basic mechansim

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


TCA cycle fxn

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


Electron transport chain fxn

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


Gluconeogenesis fxn

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


Glycogen fxn

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


Pentose Phosphate Pathway

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


De Novo Lipogenesis (Triacylglycerol synthesis) fxn

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


Triacylglycerol degradation, beta-oxidation and ketogenesis pathway fxn

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


Urea cycle fxn

disposal of nitrogen derived from metabolism of amino acids