Metabolism/Pathways intro Flashcards
Concept of energy balance
Energy in = Energy Out
Weight gain
Energy in > Energy Out
weight loss
Energy in
components of Total energy expenditure (TEE)
Resting metabolic rate, Thermic effect of food, energy expended in physical activity
Resting metabolic rate
- about 75% TEE in sedentary ppl
- primary determinant = free fat mass (lean body mass)
measure resting metabolic rate
indirect calorimetry – device measures respiratory gas composition and flow rates to estimate O2 consumption/CO2 production
Why is oxygen used in indirect calorimetry
energy mostly from oxidation of nutrients (oxygen final electron acceptor in oxidation of nutrients, so rate of oxygen consumed = indirect measure of energy expenditure)
Estimate RMR
formula based on age, sex, height, weight, and lean body mass if known fo rmore accuracy
Thermic effect of food (TEF)
- normally about 8% of TEE
- energy cost of digestion/distributing nutrients from diet to body tissues
- protein has highest energy cost, then carbs then fat
Measure Thermic effect of food
- indirect calorimetry - determine increment of energy expenditure above RMR following ingestion of defined test meal
Energy costs of nutrients
Protein > Carbs > Fat
Energy expended in physical activity
- most variable component of energy expenditure
- 30-40% for those exercising regularly
non-exercise activity thermogenesis (NEAT)
refers to energy consumed in movement that is unplanned/unconscious; i.e. fidgeting or other random movements
efficiency
ratio of work to total energy expenditure during activity (total includes that lost as heat/lost to environment)
measure total energy expenditure
doubly labeled water – measures O2 consumption in free living individuals over weeks then subtract RER and TEF
Energy intake regulated by
brain makes decisions about eating (how much, how often)
- get signals from senses, organs, internal signals (blood nutrient levels/hormones)— all regulated in brain pathways
3 key nutrient molecules
glucose, fatty acids, amino acids
Stores of which nutrient has largest energy
- Fat (about 9 kcal/g) – large storage pool
- Carbs: 4 kcal/g – stored as glycogen in muscle and liver
- Protein: 4 kcal/g but no true storage
what happens to excess protein
oxidized to carbohydrate or fat
- if in protein balance, carbs preferentially oxidized and fat stored
why do we accumulate body fat
- smaller capacity to store excess carbohydrates, so they will be preferentially oxidized while fat is stored
- can also convert carbs into fat for more efficient storage
What happens in fasting
- glycogen broken down, protein in muscle –> amino acids to convert to glucose
- eventually lack essential amino acids, essential fatty acids and micronutrients and get organ dysfunction/disease
what happens in positive energy balance
- assimilate ingested nutrients and fill storage pools
- may remake polymers from monomers –> anabolic
Forms of energy currency in cell
ATP, NADPH, GTP/UTP, NADH/FADH2
catabolic vs anabolic processes
catabolic = breakdown of complex molecules into simpler ones
anabolic - building complex molecules from simpler ones
Glycolysis
- in cytoplasm
- Breakdown of glucose (6C) to pyruvate (2 3-carbon molecules)
- pyruvate converted to lactate when no oxygen or cell doesn’t have mitochondria
TCA cycle
- Tricarboxylic acid cycle
- Pyruvate –> oxaloacetate
- produces CO2, GTP, NADH, FADH2
Electron transport
- series of protein in inner mitochondrial membrane
- take NADH/FADH2 –> produce ATP from ADP
- consume O2 and produce water – oxidative phosphorylation
Gluconeogenesis
produce glucose from other nutrients
- uses lactate, carbon skeletons of amino acids
Glycogen
storage of glucose; mostly in liver and skeletal muscle
Urea cycle
disposes of nitrogen left over from amino acid conversion to glucose
- produces urea that enters blood as BUN–excreted by kidneys as urea nitrogen
Main point of glycolysis
breakdown glucose to produce a little ATP and NADH
- ends with pyruvate in oxygen-containing tissues or converted to lactate if no oxygen/mitochondria
Purpose of TCA cycle
- requires O2 and mitochondria
- extract energy from pyruvate
- produce CO2, GTP, NADH, FADH2
Electron transport chain purpose
- oxidative phosphorylation– - consume oxygen to produce water
- takes all the NADH/FADH2 from TCA to produce ATP from ADP
- NEED OXYGEN and ADP!
purpose of gluconeogenesis
- when not enough glucose (negative energy balance)–> create glucose from lactate/amino acids
where does gluconeogenesis take place
liver, some kidney
what is glycogen
storage form of glucose
- liver - 100 g
- 400 g in skeletal muscle
Pentose Phosphate Pathway
- Hexose Monophosphate Shunt
- When excess glucose, generates NADPH and ribose
- NADPH used for fatty acidt/steroid hormones Ribose -5- phosphate is a key step in nucleotide synthesis
purpose of NADPH
- provides energy for synthesis of fatty acids and steroid hormones
- important in defending cells against oxidative stress and in pathogen killing by WBC
Triacylglycerol (triglyceride synthesis)
- De novo lipogenesis
- with excess glucose, rise in Acetyl-CoA that can be used to make fatty acids for storage
- chains of 3 fatty acids plus glycerol can make triglyceride to store in adipose tissue or secreted from liver
What is stored better, carbohydrate or fat?
Fat
Triacylglycerol degradation
if negative energy balance (fasting/exercise), stored fat can provide energy to oxidizing tissues (sk.muscle/liver)
can fat be converted to glucose
No, but its breakdown can provide energy for gluconeogenesis in the liver
Beta oxidation
breakdown of fatty acids 2 carbons at a time to get Acetyl-CoA
Ketogenesis
Process of breaking down fatty acids to ketone bodies when very low insulin and high counter regulatory hormones
Brain food
glucose; can use ketone bodies when fasting/uncontrolled type I diabetes
Functions of amino acids
- structural components of proteins
- precursors for other molecules (NT and hormones)
- substrate for gluconeogenesis
- nitrogen carriers
Urea cycle
disposal of Nitrogen from metabolism of amino acids
- produces urea (BUN in blood)
- BUN excreted by kidneys in form of urine area nitrogen
