Overview of Biochemical Pathways Flashcards

1
Q
A
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2
Q

Basic concept of energy balance

A

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

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

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3
Q

Positive energy balance definition

A

normal state of nutrient excess that occurs after feeding

aka “fed state”

nutrients are distribute between tissues and stored for later use

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4
Q

Negative energy balance definition

A

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

aka “fasted state”

e.g. illness or exercise

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5
Q

Characteristics of energy imbalance vs. energy balance

A

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

gain = intake > expenditure

loss = intake < expenditure

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6
Q

Components of Total Energy Expenditure (TEE)

A

Resting metabolic rate (RMR)

Thermic effect of food (TEF)

Energy expended in Physical Activity (EEPA)

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7
Q

Determinants of resting metabolic rate

A

Primary = fat free mass (lean body mass)

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

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8
Q

Measurement of RMR (Resting Metabolic Rate)

A

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)

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9
Q

Determinants of Thermic Effect of Food

A

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

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10
Q

Measurement of TEF (Thermic Effect of Food)

A

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

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11
Q

Determinants of energy expended in physical activity (EEPA)

A

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

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12
Q

Measurement of Total Energy Expenditure (TEE)

A

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

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13
Q

Measurement of energy expended in physical activity (EEPA)

A

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

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14
Q

Components of energy intake (EI)

A

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

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15
Q

Measurement of energy intake (EI)

A

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%

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16
Q

Main biomolecules that serve as nutrients

A

Glucose Fatty acids Amino acids

17
Q

Glucose structure

A

Carbon ring

18
Q

Fatty Acid structure

A

Hydrocarbon chain + methyl group + carboxylic acid group

19
Q

Amino Acid structure

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

20
Q

Approximate nutrient energy stores in body

A

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

21
Q

Measurement of body composition

A

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

22
Q

Hierarchy of nutrient oxidation

A

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

23
Q

Consequences of hierarchy of nutrient oxidation

A

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

24
Q

Broad categorizations of metabolic pathways

A

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

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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
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Anabolic vs. Catabolic processes
anabolic = building polymers from monomers catabolic = breaking down polymers to monomers
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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
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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
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TCA cycle fxn
fxn = pyruvate enters pathway to extract energy molecule CO2, NADH, and FADH2
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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
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Gluconeogenesis fxn
Generate glucose (from lactate or muscle-derived amino acids) for use by the brain during periods of fasting
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Glycogen fxn
Storage of excess glucose Mostly stored @ skeletal muscle (400g) Some stored @ liver (100g)
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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
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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)
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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
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Urea cycle fxn
disposal of nitrogen derived from metabolism of amino acids