Week 9: Energy Metabolism

metabolism

1. after digestion, nutrients routed through metabolic pathways based on body’s needs → constant, dynamic

2. energy stored in bonds that make up macronutrients → energy released when these bonds are broken

metabolic pathway

linked series of chemical reactions

• each step involves reactants and products

• often facilitated by enzymes and coenzymes (ie; vitamins)

energy metabolism

• glucose → pyruvate → acetyl CoA → TCA cycle → ATP produced

• metabolic pathways involved in production of ATP

• body breaks down macronutrients into CO2 and water, capturing energy released as ATP in the process

ATP

high-energy molecule composed of adenine, ribose, and three phosphate molecules → used by cells to fuel all biological processes

• when phosphate bond broken, energy released

locations of metabolism within cells

1. mitochondria

2. cytoplasm

3. nucleus

mitochondria

organelles that generate most of the cell’s energy through aerobic metabolism

cytoplasm

fluid-portion of cell involved in anaerobic metabolism

nucleus

location of DNA

ribosomes

manufacture proteins

smooth ER

produce lipids used by organelles

red blood cells

produce energy anaerobically in their cytoplasms

anabolic reactions

require ATP to combine smaller molecules into larger compound

• glucose → glycogen

catabolic reactions

break down larger molecules into smaller compounds and release energy in form of ATP and heat

• glycogen → ATP → glucose

ATP and ADP

source of energy used by cells

• getting ATP from food components requires using ATP

• need source (pool of phosphates removed in creating ADP) of phosphate to regenerated ATP from ADP

creative phosphate (PCr)

high-energy compound formed in muscle cells

creation of ATP and ADP

1. need energy → body hydrolyzes one of P bonds; releases on P and a ton of energy

2. P group added back to ADP to reform ATP during anabolism (reaction requiring energy)

metabolic fate - sources of energy

1. ATP immediately available to cells (3-5 seconds)

2. PCr available up to 10s

3. anaerobic metabolism (1-1.5 min)

4. circulating BG (glucose → pyruvate → acetyl CoA → TCA) 

5. aerobic metabolism capacity = endless

6. glycogen in liver and muscle tissue hydrolyzed to yield glucose

7. conversion of substrates into glucose for circulation as needed

lipogenesis

forming glucose into triglycerides for storage

lipolysis

triglycerides broken down to glycerol and FFAs

gluconeogenesis

glucose synthesized from multiple precursors

glycologenolysis

glycogen breakdown to glucose

insulin

anabolic, protein and glycogen synthesis, no impact on fat metabolism

glucagon

catabolic, protein degradation, glycogenolysis, lipolysis

glucocortisoids (ie; cortisol)

catabolic, no impact on protein metabolism, glycogenolysis, lipolysis

role of enzymes in metabolism regulation

catalysts for metabolic reactions

role of coenzymes in metabolism regulation

assist enzymes in speeing up reactions

• important ones come from B vitamins (niacin = B3)

niacin (B3)

• oxidized form = NAD+ (accepts H ion to become NADH)

• reduced form = NADH

glycolysis

10-step process of breaking down 1 6-C molecule glucose into 2 3C molcules of pyruvate; key pathway for glucose oxidation

• 1st step leading to ETC

products of glycolysis

• 2 ATP

• 2 pyruvate

• 2 NADH from NAD⁺

• 2 H⁺ ions transported to ETC

• 2 H₂O molecules

substrates entrance, in order

1. fructose and galactose

2. glucogenic amino acids

3. glycerol

4. fatty acids and ketogenic amino acids

substrates entering glycolysis

glucogenic amino acids, glycerol, galactose and fructose (metabolized to glucose)

substrates converted into acetyl coA

ketogenic amino acids, fatty acids

glucogenic amino acids

histidine, methionine, threonine, valine

• transformed to pyruvate via anaerobic process

• amino acids broken down into pyruvate; can reverse through glycolysis leading to gluconeogenesis

• amino acids → deamination → pyruvate

pyruvate

• converted to acetyl coA and enter TCA cycle

• transformed into lactate (diffuses out of cell into blood) in absence of oxygen

• entry point for 6 amino acids (alanine, serine, glycine, threonine, tryptophan, cysteine)

• can enter gluconeogenesis to produce glucose if limited in diet

ketogenic amino acids

• aerobically converted into acetyl CoA

• cannot be used for gluconeogenesis

• leucine, lysine

• can be transformed to fatty acids (stored as TGs)

• can enter TCA cycle

• amino acids → transamination → acetyl CoA

gluco- and ketogenic amino acids

isoleucine, phenylalanine, tryptophan

triglycerides

• glycerol converted to glucose

• fatty acids enter energy production via beta-oxidation

• liver converts fatty acids → ketone bodies → enter circulation

beta oxidation

molecule of coenzyme A attached to end of fatty acid

• two end Cs and coA cleaved off → acetyl CoA, NAD+ → NAH + H and FAD → FADH2

glycerol

• enter in pyruvate

• glucogenic; can be converted to glucose in liver cells

• can be converted to pyruvate

• dietary sources of fat → ENERGY

fatty acids

• enter as acetyl CoA

• hydrolyzed from TGs via lipolysis

• need to be activated to cross mitochondria (beta-oxidation)

oxidation pathways of fatty acids

1. triglycerides (diet/adipose) undergo lipolysis → FFAs and glycerol (reaction stimulated by lipase)

2. glycerol converted to DHAP

3. beta oxidation

4. beta-oxidation repeats itself until all fatty acids converted to acetyl CoA

5. acetyl CoA enters TCA cycle

cori cycle

metabolic pathway between muscle and liver

• liver regenerates glucose from lactate released from muscle