The Working Cell:Energy from Food

(and Sunlight)Chapters 7 & 8

Sunlight Powers Life, Materials Cycle

Energy is the ability to do work

Photosynthesis is a chemical process that coverts solar energy into chemical energy that both autotrophs and heterotrophs can use to do cellular work

Cellular (Aerobic) Respiration is one way that cells break down complex organic molecules into smaller molecules with less chemical energy in the presence of oxygen

Energy Transfers

When you slide down a slide into a swimming pool, you convert potential energy into kinetic energy.

As your body collides with air and water molecules, you transfer energy to the molecules in random directions. That random molecular motion is thermal energy or HEAT.

The Energy to Move Again

The thermal energy created CANNOT be retrieved and put back to work inside the body.

So to move again, you must use a fresh supply of energy.

That energy is the chemical energy stored in FOOD (organic molecules).

Measuring Energy

Energy is measured in units called calories

A calorie is the amount of energy needed to raise the temperature of 1 gram of water 1◦C

1000 calories = 1 kcal or Calorie (a nutritional calorie)

However, food is not used directly by cells to do work, it must be converted into another usable form called ATP.

What is ATP?

ATP is called the "currency" of the cell– ATP is a small packet of Energy that can be

used a little at a time, like coins– ATP is constantly reused and recycled– You can’t buy things without $$, cells can’t

Work without Energy from ATP

Copyright Pearson Prentice Hall

ATP Structure

ATP consists of:

– adenine

– ribose (a 5-carbon sugar)

– 3 phosphate groups (TP = tri phosphate)

Adenine

ATP

Ribose 3 Phosphate groups

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Chemical Energy and ATP– Storing Energy

• ADP has two phosphate groups instead of three.• A cell can store small amounts of energy by adding a

phosphate group to ADP.

ADPATP

Energy

Energy

Partiallycharged battery

Fullycharged battery

+

Adenosine Diphosphate (ADP) + Phosphate

Adenosine Triphosphate (ATP)

Copyright Pearson Prentice Hall

Chemical Energy and ATP

P

ADP

2 Phosphate groups

– Releasing EnergyEnergy stored in ATP is released by breaking the chemical bond between the second and third phosphates.

The ATP Cycle

ATP → ADP + phosphate + energy for Work

ADP + Energy (from food) + phosphate → ATP

Why does the process of cellular respiration release energy?

• In an atom the positive nucleus attracts negative electrons

• When electron “fall” towards the nucleus, potential energy is released

• OXYGEN attracts electrons very strongly compared to carbon and hydrogen

• During respiration, the carbon-hydrogen bonds in sugar are rearranged to bond with oxygen instead (CO2 + H2O)

Electron Transport Chains

• Instead of releasing all the energy stored in food at once (like burning), cellular respiration releases the energy in controlled “steps”

• Glucose gets broken down in several steps, transferring electrons to molecules called electron carriers

• The electron carriers accept high-energy electrons from glucose and pass them along a chain of electron carriers (ETC) releasing ATP

• Oxygen comes in at the end to accept 2 low energy electrons, bond with hydrogen, and form water

ETC Animation

The Difference Between Aerobic and Anaerobic Respiration is in the Electron Acceptor

Aerobic respiration - final electron acceptor is oxygen

Anaerobic respiration - final electron acceptor is a molecule other than oxygen (NAD+)

Aerobic Respiration

Occurs in 3 Stages:1. Glycolysis

2. The Kreb’s Cycle

3. Electron Transport Chain and ATP Synthase

Adding up the ATP from Cellular Respiration

Mitochondrion

Glycolysis

Glucose2

Pyruvicacid

2Acetyl-

CoA

KrebsCycle

ElectronTransport

MaximumATP perglucose:

ATP Synthase

Harvesting Energy WITHOUT Oxygen

• If oxygen is not available to capture the 2 low energy electrons at the end of the ETC, the Kreb’s cycle and the ETC will stop producing ATP

• Glycolysis will continue to generate 2 ATP molecules, 2 NADH, and 2 Pyruvic Acid molecules

• NADH reacts with the pyruvic acid, making NAD+ available to carry electrons so glycolysis can continue making ATP

Two Types of Fermentation

ALCOHOLICPyruvic Acid → CO2 +

ethyl alcohol

• Occurs in yeast• CO2 makes dough

rise and bubbles in beer & champagne

• Ethyl alcohol makes alcoholic beverages

LACTIC ACIDPyruvic Acid → Lactic Acid

• Occurs in muscles during vigorous exercise (can feel “burn”)

• Occurs in prokaryotes used to make cheese, yogurt, sour cream, and sauerkraut