Bioenergetics

Chapter 3

Bioenergetics

Converting foodstuffs (fats, proteins, carbohydrates) into energy

Chapter 3

Metabolism

Total of all chemical reactions that occur in the body– Anabolic reactions

• Synthesis of molecules

– Catabolic reactions• Breakdown of molecules

Cellular Level

Look back……

Cell Structure

Cell membrane– Protective barrier between interior of cell and

extracellular fluid Nucleus

– Contains genes that regulate protein synthesis Cytoplasm

– Fluid portion of cell– Contains organelles (***mitochondria***)

Structure of a Typical Cell

Even the Smallest Cells…

…are huge compared to the “bits and pieces” and chemicals in them.

If you had to wait for random action, you’d wait forever!

Cellular Chemical Reactions

Endergonic reactions– Require energy to be added

Exergonic reactions– Release energy

Coupled reactions– Liberation of energy in an exergonic

reaction drives an endergonic reaction• “Harnessed energy to accomplish a task”

Example:– “Combustion” of Carbohydrate

C6H12O6 reacts with 6O2 to become

6CO2 and 6H20 and Energy

C6H12O6 + 6O2 6CO2 + 6H20 + Energy

The Breakdown of Glucose: An Exergonic Reaction

Can we regulate reactions?

Make sure the reactions occur.

Make the reactions occur in a timely manner (speed up the reaction).

Prevent the reaction from occurring or slow it down – Rate Limiting

Enzymes

Catalysts that regulate the speed of reactions– Lower the energy of activation– Create specific conditions for reactions

Enzymes

Factors that regulate enzyme activity– Temperature– pH

• work in a narrow range – large gain

Enzymes

Interact with specific substrates– Lock and key model

Enzyme-Substrate Interaction

Action of Rate-Limiting Enzymes

How is energy converted?

Energy Systems Overview

Currency System

Money– Gold, $100’s, $50’s, $20’s, $10’s, $5’s,

$2’s, $1’s• Dollar coin, fifty cent, quarters, dimes, nickels,

pennies.

– Exchanged but not destroyed

– Recycled?

U.S. Currency System

A dollar has potential to do work for you.

Spend some, but still has potential left

Recycle it and it’s ready to go again

Only so much in circulation

Human Energy Currency System

Adenosine Triphosphate – ATP

Structure of ATP

High-Energy Phosphates

Adenosine triphosphate (ATP)– Consists of adenine, ribose, and three

linked phosphates Formation

Breakdown

ADP + Pi ATP

ADP + Pi + EnergyATP ATPase

Where Does ATP Come From?

Is it in our food?

Can you buy some at the store? – GNC?

Does grandma have some in the attic?

Where Does ATP Come From?

Stored in cells (muscle**)

Store limited amounts (heavy molecule)– Use 50 – 100 x body weight in ATP / 24 hrs.

Make it from ADP– Recycle “used” ATP

Bioenergetics

How to make (recycle) ATP -

“Phosphorylation”

- adding a phosphate

Bioenergetics

Anaerobic pathways (non-aerobic)– Do not require or involve O2

– Called direct phosphorylation

Bioenergetics

Aerobic pathways– Require O2 molecules

– Called oxidative phosphorylation

Anaerobic ATP Production

Stored ATP– Immediate (1st) source of ATP– Amount depends on muscle size– Runs low on substrate almost immediately

- ~ 1 sec.

– Used during initiation of movement

Anaerobic ATP Production

ATP-PC system (PC= phosphocreatine)– Stored in skeletal muscle– Source of phosphates– Rapid response but…– Runs low on substrate quickly ~ 1-5 sec

PC + ADP ATP + CCreatine kinase

Anaerobic ATP Production

Glycolysis– Occurs in cytoplasm– Fairly rapid response (small lag) ~ 3+ sec– High energy response– High energy because of it’s speed of action– Expensive in terms of energy required– Lasts as long as substrates available ~ 30+ sec– Makes product that can limit its action

Anaerobic ATP Production

Glycolysis– Energy investment phase

• Requires 2 ATP

– Energy generation phase• Produces 4 ATP• Produces NADH (carrier molecule)• Produces pyruvate or lactate

Glycolysis: Energy Investment Phase

Glycolysis: Energy Generation Phase

The Two Phases of Glycolysis

Glycolysis

Net ATP production =

4 ATP produced

- 2 ATP used

2 ATP available for muscle contraction

from each glucose molecule

Is That All That Happens?

No

Oxidation-Reduction Reactions

Oxidation– Molecule accepts electrons (along with H+)

Reduction– Molecule donates electrons

Nicotinomide adenine dinucleotide (NAD)

Flavin adenine dinucleotide (FAD)

FAD + 2H+ FADH2

NAD + 2H+ NADH + H+

Conversion of Pyruvic Acid to Lactic Acid Normally, O2 is available in the mitochondria

to accept H+ (and electrons) from NADH produced in glycolysis

In anaerobic pathways, O2 is not available

H+ and electrons from NADH are accepted by pyruvic acid to form lactic acid

Conversion of Pyruvic Acid to Lactic Acid

So glycolysis is…..

1 x 6 carbon molecule split into2 x 3 carbon molecules (costs 2 ATP)

2 x 3C molecule rearranged to make

2 x 3C pyruvic acids (makes 2 ATP each)

and 4 H+ are shuttled by 2NAD to

2 x 3C pyruvic acids to make

2 x 3C lactic acids

(if H+ s removed from lactic acid = pyruvic acid)

A fast method of providing energy for movement without the need for O2

A self-limiting method *Also a potential provider of H+ for

aerobic energy production

So glycolysis is…..

Aerobic ATP Production

Part 1 Krebs cycle (citric acid cycle)

– Completes the oxidation of substrates– Uses NAD and FAD to shuttle H+ s to the

Electron Transport System

The Krebs Cycle

So the Krebs Cycle is….

A 2C molecule added to a 4C molecule (6C)– rearranged to a 5C and then 4C (version)

– 2 x CO2 are made

– 3 x NADH are made– 1 x FADH is made– 1 x GTP (ATP) is made

Aerobic ATP Production

Part 2 Electron Transport System “ETS”

– Oxidative Phosphorylation

Aerobic ATP Production

ETS – Electrons removed from NADH and FADH

are passed along a series of carriers to drive phosphorylation of ADP to ATP

– H+ from NADH and FADH are accepted by O2 to form water – H2O (neutral)

Formation of ATP in the Electron Transport Chain

So for each……

1 NADH through the ETS = 3 ATP made

1 FADH through the ETS = 2 ATP made

The Three Stages of Oxidative Phosphorylation

Metabolic Process High-EnergyProducts

ATP from OxidativePhosphorylation

ATP Subtotal

Glycolysis 2 ATP2 NADH

—6

2 (if anaerobic)8 (if aerobic)

Pyruvic acid to acetyl-CoA 2 NADH 6 14

Krebs cycle 2 GTP6 NADH2 FADH

—184

163438

Grand Total 38

Aerobic ATP Tally – For Glucose

Efficiency of Oxidative Phosphorylation Aerobic metabolism of one molecule of

glucose– Yields 38 ATP

Aerobic metabolism of one molecule of glycogen– Yields 39 ATP

Overall efficiency of aerobic respiration is 40%– 60% of energy released as heat!!!!!

Is Glucose the Only Fuel Source?

No

Fuels for Phosphorylation

Carbohydrates – Glucose (6 carbon molecule)– Glycogen (branched carbon molecules)

• Glucose stored in muscle cells and liver• Glycogenolysis - makes carbons available for

metabolism– Occurring in muscle cells - glucose stays in muscle cells– Occurring in liver – glucose put into circulation

Fuels for Phosphorylation

Fats (18+ carbon molecule)– Primarily fatty acids (FA)

• Stored as triglycerides• Stored in muscle cells and in adipose cells• Beta oxidation makes FAs available for Krebs

Cycle– Release of FAs from adipose to blood stream– Hormone initiated– All working muscles have access to FAs via cellular

storage or via blood stream

Fuels for Phosphorylation

Proteins– Amino Acids (AA)– Storage is structural (no extra depot)– Carbons are available– Not a primary energy source during

exercise (too expensive)– But usable – long duration exercise (up to

15%)

What is common between all these fuel sources?

- A 2 carbon molecule called…..

Acetyl Co-A

Fuels for Phosphorylation

Relationship Between the Metabolism of Proteins, Fats, and Carbohydrates

There’s one other potential fuel source.

The Cori Cycle: Lactate As a Fuel Source

What’s it all about?

Does anybody know?

Here’s how I found out.

Can You See the “Big Picture” Regarding Aerobic ATP Production?

How is control maintained?

Control of Bioenergetics

Rate-limiting enzymes– An enzyme that regulates the rate of a metabolic

pathway

Levels of ATP and ADP+Pi

– High levels of ATP inhibit ATP production

– Low levels of ATP and high levels of ADP+Pi stimulate ATP production

Control of Bioenergetics

Rate-limiting enzymes– An enzyme that regulates the rate of a metabolic

pathway

Levels of ATP and ADP+Pi

– High levels of ATP inhibit ATP production

– Low levels of ATP and high levels of ADP+Pi stimulate ATP production

Calcium may stimulate aerobic ATP production

Action of Rate-Limiting Enzymes

Control of Metabolic Pathways

Pathway Rate-LimitingEnzyme

Stimulators Inhibitors

ATP-PC system Creatine kinase ADP ATP

Glycolysis Phosphofructokinase AMP, ADP, Pi, pH ATP, CP, citrate, pH

Krebs cycle Isocitratedehydrogenase

ADP, Ca++, NAD ATP, NADH

Electron transportchain

Cytochrome Oxidase ADP, Pi ATP

Remember…..

1 cell = absolute

Whole body = not absolute

Where is there interaction between energy systems?

Interaction Between Aerobic and Anaerobic ATP Production

Energy to perform exercise comes from an interaction between aerobic and anaerobic pathways

Interaction Between Aerobic and Anaerobic ATP Production

Effect of duration and intensity– Immediate movement

• Stored ATP

– Short-term, high-intensity activities• Greater contribution of anaerobic energy systems

– ATP-PC and Glycolysis

– Long-term, low to moderate-intensity exercise• Majority of ATP produced from aerobic sources

– Aerobic glycolysis, beta oxidation, protein

Questions?

End