Overview of Biochemical Pathways Flashcards
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
