THE WORKING CELL
ENERGY FROM FOOD
SUNLIGHT POWERS LIFE
• Obtaining Food
• All organisms require food for energy and building
materials.
• Autotrophs
• Organisms that make their own food, such as
plants, are autotrophs.
• They start with inorganic molecules and make
organic molecules, such as photosynthesis.
• Autotrophs are also called producers.
• On land, plants are the major producers.
• In oceans, lakes, and streams, algae and photosynthetic
bacteria are the major producers.
SUNLIGHT POWERS LIFE
• Heterotrophs
• These are organisms that cannot make their own
food and rely on other sources for it.
• They are also called consumers, and obtain their
food by eating producers or other consumers.
• Harvesting the Energy in Food
• Many organisms harvest the energy in foods
by cellular respiration.
• This is a chemical process that uses oxygen
to convert energy stored in organic molecules
to another form of chemical energy , ATP
(adenosine triphosphate).
SUNLIGHT POWERS LIFE
• The cells then use this ATP as their main
energy supply.
• Photosynthesis and cellular respiration are
opposites of one another.
• They both use water, carbon dioxide, oxygen, and
glucose, an organic compound.
• In photosynthesis:
• 6CO₂ + 6H₂O → 6O₂ + C₆H₁₂O₆
• In cellular respiration:
• 6O₂ + C₆H₁₂O₆ → 6CO₂ + 6H₂O + energy
REVIEW: CONCEPT CHECK 7.1,
page 137
1. Define autotroph and heterotroph, and
give an example of each.
2. Explain the role of food (glucose) in both
photosynthesis and cellular respiration.
3. Explain how life on Earth depends on the
sun.
FOOD STORES CHEMICAL ENERGY
• Introduction to Energy
• Energy is the ability to do work and work is
performed whenever an object is moved
against an opposing force.
• Potential and kinetic energy are the two basic
forms.
• Kinetic energy is the energy of motion.
• Potential energy is stored energy.
• Thermal energy is random molecular motion
or the sum of all the kinetic energy of all the
particles.
THERMAL ENERGY
FOOD STORES CHEMICAL ENERGY
• Chemical Energy
• How do organic compounds in food provide
energy for use?
• These organic compounds have a form of
potential energy called chemical energy.
• In this case, the potential to perform work is
due to the arrangement of the atoms within
the molecules.
• Chemical energy depends on the structure of
molecules.
• Potential energy is converted to kinetic energy
by motion, chemical energy is released to
CHEMICAL ENERGY
KINETIC vs. POTENTIAL ENERGY
FOOD STORES CHEMICAL ENERGY
potential energy after the rearrangement of
atoms during chemical reactions.
• This energy is then available for work in the
body.
• Putting Chemical Energy to Work
• Complex molecules are broken down into
smaller molecules that possess less chemical
energy than the original.
• We can compare organic molecules in food to
those in gasoline.
FOOD STORES CHEMICAL ENERGY
• Gasoline
• gasoline+oxygen→combustion→carbon dioxide+water
• The reaction of mixing oxygen with gasoline results in the
breakdown of gasoline releasing thermal energy as heat, which is
then used to power the car.
• Only 25% of this potential energy is converted to kinetic energy
with the rest lost as heat.
• Food energy
• sugar+oxygen→cellular respiration→carbon dioxide+water
• The reaction in our cells is slower than in a gas engine.
• Our cells are more efficient, converting 40% of the energy from
the food to kinetic energy.
• 60% is converted to thermal energy and lost as heat.
FOOD STORES CHEMICAL ENERGY
• Not all the heat generated by cellular
respiration is wasted.
• It is used to maintain a constant body temperature.
• Calories: Units of Energy
• A calorie is the amount of energy required to
raise the temperature of 1 gram (g) of water
by 1 degree Celsius (C⁰).
• Since this measure is so small, most scientists use
the kilocalorie (kcal) instead.
• Food labels usually show kilocalories and not
calories.
ENERGY CONSUMED BY
VARIOUS ACTIVITIES
FOOD STORES CHEMICAL ENERGY
• Measurement of energy content can be
done in the lab.
• Take a peanut, dry it, and burn it under an
insulated layer of water.
• The stored chemical energy is converted to
thermal energy, releasing heat.
• The increased temperature of the water is
then measured and knowing the definition of a
calorie, the total can be calculated.
• The peanut has about 5000 calories, or 5 kcal, or
enough chemical energy to raise the temperature
of 1 kg (1000 g) of water by 5⁰C.
FOOD STORES CHEMICAL ENERGY
• Cells use enzymes to break down organic
molecules by the process of cellular
respiration, and the released energy is more
manageable for work.
REVIEW: CONCEPT CHECK 7.2,
page 141
1. Identify the types of energy you have at
the top of a staircase and as you go down
the stairs.
2. Explain how your body uses chemical
energy during exercise.
3. If a food has 10 kcal of energy, how much
could it increase the temperature of 100g
of water?
ATP PROVIDES ENERGY FOR
CELLULAR WORK
• How ATP Packs energy
• ATP, as you remember, contains a
nitrogen containing compound called
adenine and a five carbon sugar called
ribose; and a triphosphate tail of three
phosphate groups.
• The phosphate groups are negatively
charged and are trying to repel each other.
• This is the potential energy stored in ATP.
ADENOSINE TRIPHOSPHATE
ADENOSINE TRIPHOSPHATE
CELL RESPIRATION
ATP PROVIDES ENERGY FOR
CELLULAR WORK
• Overall Equation for Cellular Respiration
C₆H₁₂O₆ + 6O₂→6CO₂ + 6H₂O + 38 ATP
• Cell respiration’s main job is to generate ATP for
cellular work.
• “Falling” Electrons as an Energy Source
• Remember a roller coaster with the greatest
potential energy at the top and its change to
kinetic energy as gravity pulls it down the tracks.
• An atom’s positively charged nucleus exerts a pull
on the negatively charged electrons.
ATP PROVIDES ENERGY FOR
CELLULAR WORK
• Potential energy is released as the electron
“falls” toward the nucleus.
• Oxygen attracts electrons as gravity pull
objects downward.
• Carbon and hydrogen exert much less pull on
electrons.
• Sugar molecules have carbon-hydrogen
bonds which during cellular respiration, the
carbon and hydrogen change partners and
bond with oxygen.
OXIDATION OF SUGAR
ATP PROVIDES ENERGY FOR
CELLULAR WORK
• C-H bonds are replaced by C-O and H-O
bonds.
• The energy is released as the electrons of
these bonds ‘fall’ toward the oxygen.
• Performing this in the lab is much quicker
than in the cells as ATP is made in the cells
rather than the heat and light in the lab.
• Electron Transport Chains
• Cellular respiration releases energy in small
amounts that are put to good use in the
formation of ATP molecules.
ELECTRON TRANSPORT
ATP PROVIDES ENERGY FOR
CELLULAR WORK
• Cellular respiration breaks down glucose in
several steps.
• Oxygen only enters as an electron acceptor in the
final electron transfer.
• In the breakdown of glucose, electron carriers
accept the high-energy electrons from the glucose.
• These carriers pass these electrons to other
carriers in a series of transfers called an
electron transport chain.
• Each subsequent carrier holds the electrons more
strongly than those before.
ATP PROVIDES ENERGY FOR
CELLULAR WORK
• At the end of the chain, oxygen-the electron
grabber-pulls electrons from the final carrier
molecule and joins them with hydrogen ions,
forming water.
• Each transfer of electrons in the chain
releases a little energy.
• The cell traps this released energy to make
ATP.
REVIEW: CONCEPT CHECK 7.4,
page 147
1. Compare and contrast breathing and
cellular respiration.
2. List the reactants and products in cellular
respiration.
3. What is meant by the “falling” of electrons
to oxygen? How does this process
release energy?
4. How does an electron transport result in
the gradual release of energy stored in
glucose?
CELLULAR RESPIRATION CONVERTS
ENERGY IN FOOD TO ENERGY IN ATP
• Structure of Mitochondria
• These organelles are found in almost all
eukaryotes and their structure is key to its role
in cellular respiration.
• Two membranes enclose the mitochondria.
• There are many folds of the inner membrane
to increase surface area with a thick fluid
contained within called the matrix.
• The enzymes needed to break down the food
for energy are contained within the inner
membrane.
MITOCHONDRIA
CELL RESPIRATION
CELL RESPIRATION
CELLULAR RESPIRATION CONVERTS
ENERGY IN FOOD TO ENERGY IN ATP
• A Road Map for Cellular Respiration
• The chemical processes that take place in the cell
make up it’s metabolism.
• Cellular respiration is a series of reactions, and,
therefore, is a metabolic pathway.
• Enzymes speed up or facilitate each of these
processes.
• There are three main stages to cellular
respiration:
• Glycolysis
• Krebs cycle
• Electron transport and ATP synthase
GLYCOLYSIS
GLYCOLYSIS
Glycolysis is one of the metabolic process for generating ATP from
glucose. ATP is the form of energy used by every cell. ATP inhibits the
enzyme phosphofructokinase to stop ATP production. The negative feed
back loop helps to regulate the amount of ATP produced.
CELLULAR RESPIRATION CONVERTS
ENERGY IN FOOD TO ENERGY IN ATP
• Stage I: Glycolysis
• This is the first step in breaking down a
glucose molecule (means splitting of sugar).
• It takes place in the cytoplasm, outside the
mitochondria.
• Two ATP molecules are the initial source of
energy, splitting the 6 carbon glucose in half,
resulting in 2 three carbon molecules, each
with one phosphate group.
• Each of these three carbon molecules
transfers electrons and hydrogen ions to a
CELLULAR RESPIRATION CONVERTS
ENERGY IN FOOD TO ENERGY IN ATP
carrier molecule, NAD⁺.
• With the acceptance of the two electrons and one
hydrogen ion converts the NAD⁺ to a compound
called NADH.
• The initial energy, 2 ATP molecules, needs to be
paid back, and four new ATP molecules are made,
netting two additional ATP molecules.
• In summary, the original glucose has been
converted to 2 molecules of pyruvic acid, with 2
ATP molecules used initially for energy but
resulting in four ATP molecules being produced,
KREBS CYCLE
KREBS CYCLE
CELLULAR RESPIRATION CONVERTS
ENERGY IN FOOD TO ENERGY IN ATP
and the pyruvic acid retaining most of the
energy of the original glucose molecule.
• Stage 2: The Krebs Cycle
• This stage complete the breakdown of pyruvic
acid molecules to carbon dioxide.
• Remember glycolysis takes place outside the
mitochondria with the production of two
pyruvic acid molecules.
• The pyruvic acid molecules do not take part in
the Krebs cycle, but in the mitochondria, each
molecule of pyruvic acid loses a molecule of
CELLULAR RESPIRATION CONVERTS
ENERGY IN FOOD TO ENERGY IN ATP
•
•
•
•
carbon dioxide.
What is left is converted to a two carbon
compound called acetyl coenzyme A, or
acetyl CoA.
The acetyl CoA enters the Krebs cycle and
joins a four carbon acceptor molecule.
Two more CO₂ molecules are produced and one
ATP molecule per acetyl CoA molecule.
The NADH with another electron carrier, FADH₂,
trap most of the energy.
CELLULAR RESPIRATION CONVERTS
ENERGY IN FOOD TO ENERGY IN ATP
• At the end of the Krebs cycle, the four carbon
acceptor molecule is regenerated and the
process continues.
• The Krebs cycle, turning twice for each
glucose molecule, produces 4 CO₂ molecules
and 2 ATP molecules.
• Stage 3: Electron Transport Chain and ATP
Synthase Action
• This stage occurs in the inner membranes of the
mitochondria.
ELECTRON TRANSPORT CHAIN
ELECTRON TRANSPORT CHAIN
ATP SYNTASE ACTION
CELLULAR RESPIRATION CONVERTS
ENERGY IN FOOD TO ENERGY IN ATP
• There are two parts: electron transport chain and
ATP production by ATP synthase.
• First, NADH transfers electrons from the
original glucose molecule to an electron
transport chain.
• Remember, electrons move to carriers that
attract them more strongly.
• Thus, the electrons move within the inner
membrane from carrier to carrier, being pulled
to the oxygen at the end of the chain.
• There, the oxygen and electrons combine with
hydrogen producing water.
CELLULAR RESPIRATION CONVERTS
ENERGY IN FOOD TO ENERGY IN ATP
• With each transfer, a small amount of energy
is released, which is used to pump H⁺ ions
across the membrane from less concentrated to
more concentrated.
• With this pumping action, potential energy is
stored similar to a dam holding back water.
• In the mitochondria there are protein structures
called ATP synthases.
• These are similar to the turbines in a dam.
• Hydrogen ions pumped by electrons proceed
through the ATP synthase.
CELLULAR RESPIRATION CONVERTS
ENERGY IN FOOD TO ENERGY IN ATP
• Then the ATP synthase uses the energy from
the flow of H⁺ ions to convert ADP to ATP,
generating up to 34 ATP molecules per original
glucose molecule.
• Adding Up the ATP Molecules
• A cell can convert one glucose molecule to as
much as 38 ATP molecules.
• Glycolysis = 4 ATP-2 ATP = 2 ATP
• Krebs cycle = 2 ATP
• ATP synthase = 34 ATP
• After glycolysis, most ATP production requires O₂.
ADDING UP THE ATP MOLECULES
REVIEW: CONCEPT CHECK 7.5,
page 152
1. How is the mitochondrion’s structure
suited to its function?
2. Identify the three steps of cellular
respiration, where in the cell each takes
place, and how many ATP molecules it
produces.
3. Summarize the use and production of
ATP in one cycle of cellular respiration.
SOME CELLS CAN HARVEST
ENERGY WITHOUT OXYGEN
• Fermentation in Human Muscle Cells
• Exercising depletes ATP, so it must be
replenished.
• Under normal circumstances, through cellular
respiration, the cells can produce enough
ATP.
• Increasing the exercise load requires more
oxygen to meet the muscles’ need for ATP.
• Another process is then used called
fermentation, that makes ATP without using
oxygen.
SOME CELLS CAN HARVEST
ENERGY WITHOUT OXYGEN
• ATP and fermentation work together to
produce the ATP but the main source when
both are working comes from fermentation.
• This process involves glycolysis only.
• No oxygen is used.
• Glycolysis produces a net gain of 2 ATP
molecules for each molecule of glucose.,
which is enough for those short bursts of
energy required.
• The waste product from fermentation is lactic
acid.
GLYCOLYSIS
FERMENTATION
SOME CELLS CAN HARVEST
ENERGY WITHOUT OXYGEN
• With the temporary buildup of lactic acid in the
muscles, one feels fatigue or cramping.
• Oxygen is consumed by the body as the lactic
acid is converted back to pyruvic acid.
• The heavy breathing after these short bursts
of speed or exercise restores the oxygen
supply.
• Fermentation in Microorganisms
• Yeast, a microscopic fungus, is capable of
both cellular respiration and fermentation.
• If they are kept in an anaerobic environment,
FERMENTATION
SOME CELLS CAN HARVEST
ENERGY WITHOUT OXYGEN
they will ferment sugar and other foods,
producing alcohol and not lactic acid.
• This is alcoholic fermentation, and CO₂ is
released.
• The CO₂ produces the bubbles in beer and champagne,
and makes bread rise.
• Some fungi and bacteria do produce lactic acid
during fermentation, and these are used to make
cheese and yogurt from milk, soy sauce from soy
beans, and sauerkraut from cabbage.
REVIEW: CONCEPT CHECK 7.6,
page 155
1. How is fermentation different from cellular
respiration?
2. Describe one example of how
fermentation in microorganisms produces
human food.
3. What is the waste product of fermentation
in your muscle cells?