Ch. 3 Bioenergetics (pt. 2)

Monosaccs

fructose, glucose

Disaccs

Sucrose, maltose

Polysaccs

cellulose, starch, glycogen

Glycogen

polysacc that’s stored in animal tissues and synthesized by glycogen synthase.

muscle and liver cells.

Glycogen stores are depleted within a few hours of prolonged exercise, so glycogen synthesis is an ongoing process

Glycogenolysis

Glycogen —> glucose

In muscle cells, glucose serves as a source of energy for muscle contraction

On liver cells, glucose is released in blood stream and transported to body tissues

Fatty acids

free form of triglycerides

primary type of fat used in skeletal muscles

Triglycerides

storage form of fatty acids in muscle and adipose tissue

broken down into glycerol and fatty acids via lipolysis

Phospholipids

not used as an energy source

serve many biological roles: cell membrane integrity, sheath around nerve fibers

steroids

derived from cholesterol— not an energy source

needed to synthesize sex hormones

Protein

not a primary energy source during exercise

some can be converted to glucose in the liver

• alanine by gluconeogenesis and stored as glycogen

• liver glycogen broken to glucose and used by working muscles

others can be converted to metabolic intermediates in the muscle

ATP synthesis and breakdown

ATP= adenine, ribose, 3 phosphates (w/ high energy bond)

Synthesis: ADP + Pi —> ATP

Breakdown: ATP —ATPase—> ADP + Pi + Energy

3 metabolic pathways to form ATP

PC breakdown (anaerobic)

Glycolysis (anaerobic)

Oxidative phosphorylation (aerobic)

ATP-PC system

Immediate source of ATP (simplest, fastest)

PC + ADP —creatine kinase—> ATP + C

Production of ATP is limited bc muscles store limited amts of PC

Useful fro onset and short-term high intensity exercise

Glycolysis

Glucose —> 2 pyruvate (aka 2 lactic acid)

Occurs in sarcoplasm of muscle cell

Series of coupled rxns

System must be “primed” by the addition of ATP

Energy investment phase (1) of glycolysis

Requires 2 ATP for glucose; 1 ATP for glycogen

Endergonic

Energy generation phase. (2) of glycolysis

Produces 4 ATP, 2 NADH, and 2 pyruvate/lactate per molecule of glucose

Exergonic

Interaction btwn glucose and glycogen as fuel source

• Glycogen is only minimally stored in the sarcoplasm, so most glucose comes from liver glycogenolysis

• glucose always has to be phosphorylated to form glucose 6-phosphate no matter the source

• However, glucose obtained from glycogen stored in the cell doesn’t require ATP to form glucose 6- phosphate, but instead Pi located in the cell.

Glucose: -2 invested + 4 produced = 2 NET ATP

Glycogen: -1 invested + 4 produced = 3 NET ATP

Electron carrier molecules

Transport hydrogens and associated electrons

• to mitochondria for ATP generation (aerobic)

• to convert pyruvic acid to lactic acid (anaerobic)

NAD+ and FAD

transport H+ ions (and associated electrons) to bioenergetic pathways for ATP production

NAD in glycolysis

NAD+ accepts H+ atom

The NAD+ must be resorted, or glycolysis will stop

Two ways to regenerate NAD+

1. If sufficient O2, the hydrogens from NADH can be shuttled into the mitochondria, where they can contribute to the aerobic production of ATP

2. If insufficient O2, pyruvate can accept H+ ions to form lactate anaerobically

Aerobic ATP production

Aerobic ATP results from cooperation btwn the citric acid cycle and ETC (mitochondria)

Citric acid/Krebs cycle

Completes oxidation of fuels (e.g. fats, carbs, proteins) to provide electrons for the ETC

• Pyruvic acid (3C) —> acetyl coA (2C)

• CO2 formed

• Acetyl CoA forms citrate

• Citrate metabolized to oxaloacetate

• 2 CO2 molecules given off

• Produces 3 molecules of NADH and one FADH2

• one molecule of GTP is formed (= 1 ATP)

ETC

energy obtained from electron transport is used to produce ATP at the end of the ETC

Steps leading to oxidative phosphorylation

1. Products of catabolism shuttled from the cytoplasm into the mitochondrial matrix to be converted into acetyl-coA

2. Formation of acetyl-coA in glycolysis

3. Oxidation of acetyl-coA in Citric acid cycle

4. Oxidative phosphorylation (ATP formation) in the ETC

Fats in aerobic metabolism

• triglycerides —> glycerol and fatty acids

• fatty acids —> acetyl-coA

• glycerol not important muscle fuel during exercise

Protein in aerobic metabolism

Broken down —> amino acids

converted —> glucose, pyruvic acid, acetyl-CoA, and Krebs cycle intermediates

Beta oxidation

Occurs in mitochondria

triglycerides catabolized —> glycerol and fatty acids

fatty acids can be converted into acetyl-coA via beta oxidation

it chops fatty acids into 2 carbon molecules forming acetyl coA so it can enter krebs cycle

ETC