Bioenergetics pt 2

Formation of ATP

• Insufficient Oxygen:

  • Phosphocreatine provides an immediate source of ATP.

  • Glucose undergoes partial oxidation to provide a small amount of ATP through glycolysis.

• Anaerobic ATP Synthesis:

  • Sufficient Oxygen: Glucose and fat undergo full oxidation to maximize ATP production through oxidative phosphorylation (aerobic ATP synthesis is optimal).

Anaerobic ATP Synthesis

• Refers to the ability to generate ATP in the absence of sufficient oxygen at the cellular level.

• There is often a mismatch between O2 delivery and the immediate need for energy in muscle activity.

Energy Sources Under Anaerobic Conditions

• Phosphocreatine:

  • Present in muscles and primed to donate its phosphate group.

• Glucose:

  • Can be oxidized by glycolysis in the absence of oxygen.

  • ATP can only be stored in small amounts (10-15 seconds worth).

  • Anaerobic work lasts around 15-20 seconds, producing little ATP in exercise.

Phosphagen System (ATP-PCr)

• Fastest way to create ATP, involving two components:

  • ATP molecules

  • Larger quantity of phosphocreatine (PCr)

• Limited amount within skeletal muscle.

• This system is effective for the first 5 seconds of intense work when no oxygen is available.

Glycolysis Overview

• A 10-step process that breaks down glucose into two pyruvate or lactate molecules.

• Two Phases:

  1. Energy investment phase

  2. Energy generation phase

Phases of Glycolysis

• Energy Investment Phase:

  • Requires ATP input.

  • Net ATP: 2 ATP used (4 produced, 2 net).

  • Produces 2 NADH and 2 pyruvate or lactate.

• Energy Generation Phase:

  • Involves oxidation and phosphorylation processes.

Energy Investment Phase Steps

1. Glucose phosphorylated by ATP to form glucose-6-phosphate (G6P) using hexokinase (requires 1 ATP).

2. Fructose-6-phosphate formation through rearrangement.

3. Fructose-1,6-bisphosphate produced from a second phosphorylation (requires another ATP).

Glycolysis Details

• Phosphofructokinase (PFK) is crucial for regulating glycolysis.

• Why two ATPs are needed: one for initial phosphorylation and another to ensure equal splitting of the molecule.

Oxidation Processes in Glycolysis

• Occurs during the breakdown of glyceraldehyde-3-phosphate (G-3-P), resulting in the reduction of NAD+ to NADH.

Energy-Harvesting Steps in Glycolysis

• 8 steps that ultimately lead to pyruvate formation if oxygen is present.

• Pyruvate ions can then enter the mitochondria for further breakdown.

Role of NAD and FAD in Glycolysis

• NAD (Nicotinamide adenine dinucleotide):

  • Acts as an oxidizing agent, accepting electrons to form NADH (reducing agent).

• FAD (Flavin adenine dinucleotide):

  • Functions similarly in electron transport, allowing ongoing biochemical processes.

Final Step: Creation of Lactate

• When oxygen is absent, pyruvic acid is converted to lactic acid/lactate via Lactate Dehydrogenase (LDH).

• Important for energy production in absence of oxygen.

Glycogen vs. Blood Glucose in ATP Synthesis

• Use of muscle glycogen bypasses hexokinase step, resulting in a net gain of 3 ATP from glycogen (4-1).

Blood Glucose Pathway

• Glucose entering muscles from blood; may either be fully oxidized (with oxygen) or converted to lactate (without oxygen).

• Production of additional ATP occurs when glucose is fully metabolized in aerobic conditions.