Carbohydrate Metabolism

Turning Sugar into Energy

Outline

• What is Metabolism?

• Glycolysis

• TCA Cycle

• Electron Transport System

What is Metabolism?

• Sum of all chemical reactions in the body

What is Metabolism?

• Sum of all chemical reactions in the body

• Creates energy (ATP)

Why do we need to make ATP?

• Power muscular contraction

• Active Transport

• Homeostasis

• Synthesis of macromolecules

ATP is short-term energy storage

• ATP consumed < 1 minute from synthesis

Types of Metabolic Reactions

• Anabolic reactions– Building macromolecules in the body

Types of Metabolic Reactions

• Anabolic reactions– Building macromolecules in the body

• Catabolic reactions– Hydrolysis of foods in GI tract– Chemical breakdown releases energy

Types of Metabolic Reactions

• Anabolic reactions– Building macromolecules in the body

• Catabolic reactions– Hydrolysis of foods in GI tract– Chemical breakdown releases energy

• Where does the energy come from?

Fuel Up with Slyders!

Our Fuel Sources

• Carbohydrates– Sugars and starches– First choice of metabolic fuel

• Fats

• Protein

Glucose: Our Primary Fuel

C6H12O6

All carbohydrates we consume are eventually converted into glucose

Catabolism of Glucose

C6H12O6 + 6O2 6CO2 + 6H2O + energy

• Transfer energy from glucose to ATP

• Most energy lost as heat

Glucose

Catabolism of Glucose

• Occurs as a series of steps….

• Major Pathways

Glycolysis (does not require O2)- glucose split into 2 parts, generating 2 ATP

Aerobic Respiration (requires O2)

- catabolizes the products of glycolysis and generates more than 30 ATP

Where is Glucose Broken Down?

TCA

Glycolysis (Sugar Splitting)

• Occurs in presence and absence of O2

• Occurs in cytoplasm

• Provides energy during strenuous exerciseAll I need is

Glycolysis…And my Jenny.

1. Glucose enters cell by facilitated diffusion

Key Steps in Glycolysis

2. Glucose is Phosphorylated by ATP

Key Steps in Glycolysis

3. Glucose split into two 3-carbon molecules

Key Steps in Glycolysis

4. Coenzyme NAD+ collects hydrogen

Key Steps in Glycolysis

Coenzymes in Metabolism

• Collect electrons (hydrogen atoms) during catabolism of glucose

– Transfer 2H+ and 2 e- at a time to coenzymes NAD+ and FAD

– NAD+ (made from niacin) NAD+ + 2H NADH + H+

– FAD (made from vitamin B2) FAD + 2H FADH2

• Temporary carriers of energy

4. Coenzyme NAD+ collects hydrogen

Key Steps in Glycolysis

5. Create 4 ATP by substrate-level phosphorylation

Key Steps in Glycolysis

Substrate-level Phosphorylation

6. Create 2 Pyruvate molecules

Key Steps in Glycolysis

Final Products of Glycolysis

2 molecules of Pyruvate

2 molecules of NADH + H+

4 gross ATP molecules, but only 2 net ATP

Quick Energy….but, not very much ATP

Glycolysis Animation

Some Cells Stop at Glycolysis

• Red Blood Cells

• Skeletal Muscle

(during exercise)

Much Energy Remains in Pyruvate

2

TCA

ATP Produced

• Aerobic vs. Anaerobic Respiration

• Kreb’s Cycle

• Electron Transport Chain

So What Happens to Pyruvate?

Most ATP is Generated in Mitochondria

• Two principal steps:

Matrix Reactions (Krebs Cycle) • occurs in matrix of mitochondria• Pyruvate is oxidized and electrons are transferred to

NAD+ and FAD, forming NADH +H and FADH2

Membrane Reactions (Electron Transport Chain)• Occurs within the inner mitochondrial membrane• NADH & FADH2 are oxidized, transferring energy to ATP

and regenerating NAD+ and FAD

Mitochondria: The Cell Powerhouse

The Krebs Cycle

Also known as….Tricarboxylic Acid Cycle

TCA CycleCitric Acid Cycle

Major Steps of the TCA Cycle

1. CO2 removed from Pyruvate and several intermediate molecules

C6H12O6 + 6O2 6CO2 + 6H2O + energy

• CO2 is a metabolic waste product

Glucose

2. Hydrogen removed from intermediate molecules

Picked up by NAD+ and FAD coenzymes

Major Steps of the TCA Cycle

Summary of Krebs Cycle

2 pyruvate + 6 H2O 6 CO2

2 ADP + 2 Pi 2 ATP

8 NAD+ + 8 H2 8 NADH + 8 H+

2 FAD + 2 H2 2 FADH2

• Carbon from Pyruvate converted to CO2 and exhaled

• Energy has been lost (as heat) or stored in 2 ATP, 8 NADH, and 2 FADH2.

Kreb’s Cycle Animation

Do not worry about the following: Names of Intermediate carbon molecules What GTP is (it is an ATP precursor)

Focus on the following: CO2 production Action of coenzymes NAD & FAD Creation of ATP

Animation

To the Inner Mitochondrial Membrane!

2 2

TCA

So what happens to all of the NADH and FADH?

Most ATP is Generated in Mitochondria

• Two principal steps:

Matrix Reactions (Krebs Cycle) • occurs in matrix of mitochondria• Pyruvate is oxidized and electrons are transferred to

NAD+ and FAD, forming NADH +H and FADH2

Membrane Reactions (Electron Transport Chain)• Occurs within the inner mitochondrial membrane• NADH & FADH2 are oxidized, transferring energy to ATP

and regenerating NAD+ and FAD

Electron Transport System (ETS)

• Occurs on Inner mitochondrial membrane

• Requires oxygen

ETS Makes Lots of ATP

Electron Transport System

1) NADH and FADH2 release hydrogen atoms

Splitting of Hydrogen

2) Electrons passed along electron transport system

Protons (H+) pumped out of mitochondrial matrix

Flow of electrons powers active transport of H+

ATP Synthase Creates ATP

3) H+ diffuse into matrix through ATP Synthase

Flow of H+ powers anabolism of ATP

Electron Transport System Payoff

• Produce ~34 ATP

• Efficiency of 40%

• Rest is body heat

Electron Transport System

Electron Transport Animation

Summary of Glucose Catabolism

TCA