The Working Cell: Energy from Food

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Transcript The Working Cell: Energy from Food

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
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
ATP Structure
ATP consists of:
– adenine
– ribose (a 5-carbon sugar)
– 3 phosphate groups (TP = tri phosphate)
Copyright Pearson Prentice Hall
3 Phosphate groups
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.
Adenosine Diphosphate
(ADP) + Phosphate
Copyright Pearson Prentice Hall
Adenosine Triphosphate (ATP)
Chemical Energy and ATP
Releasing Energy
Energy stored in ATP is released by breaking
the chemical bond between the second and
third phosphates.
2 Phosphate groups
Copyright Pearson Prentice Hall
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
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
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
ATP Synthase
ATP per
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
• NADH reacts with the pyruvic acid, making
NAD+ available to carry electrons so
glycolysis can continue making ATP
Two Types of Fermentation
Pyruvic Acid → CO2 +
ethyl alcohol
Pyruvic Acid → Lactic Acid
• Occurs in yeast
• CO2 makes dough
rise and bubbles in
beer & champagne
• Ethyl alcohol makes
alcoholic beverages
• Occurs in muscles
during vigorous
exercise (can feel
• Occurs in prokaryotes
used to make cheese,
yogurt, sour cream,
and sauerkraut