Cellular Respiration
Chapter 9 in the textbook
Chemical Energy and Food
The equation for cellular respiration is catabolic.
• Catabolic Reactions: a chemical reaction that breaks
down larger molecules into smaller units.
– Catabolic reactions are exergonic: energy is released.
• Anabolic reaction: an endergonic reaction that builds
molecules from smaller units.
– Photosynthesis is an anabolic reaction.
Chemical Energy and Food
Oxidation: Glucose loses electrons (and hydrogens)
Reduction: Oxygen gains electrons (and hydrogens)
Cellular Respiration is an oxidation/reduction reaction
• Oxidation: The loss of electrons
• Reduction: The gain of electrons
In cellular respiration glucose is oxidize and oxygen is reduced
• Hydrogen is a source of electrons
Chemical Energy and Food
Heterotrophic organisms get the glucose from the food they
consume.
• Calorie: a unit to measure the amount of energy in food.
– 1 Calorie = the amount of energy needed to raise the
temperature of kilogram (or liter) of water 1oC
– 1 calorie = the amount of energy needed to raise the
temperature of gram (or milliliter) of water 1oC
– 1 Calorie = 1,000 calories
– Unit for measuring energy in food =
Calorie
Chemical Energy and Food
Carbohydrates, lipids and proteins can all be broken down to
release energy.
• 1 Gram of Carbohydrates = 4 Calories
– The bodies primary source of energy
– Only a small amount of carbohydrates can be stored in the
body.
– Glycogen is a polysaccharide that is created to store glucose
–Amylase: An enzyme
that breaks down
polysaccharides like
glycogen and starch into
glucose to begin cellular
respiration.
Chemical Energy and Food
• 1 Gram of Lipids = 9 Calories
– The bodies secondary source of energy
– Carbohydrates can be converted to lipids
for storage.
– Can body can store an unlimited amount
of lipids.
• 1 Gram of Proteins = 4 Calories
– Lipids and Proteins are broken down with processes other than
cellular respiration.
– Proteins in food are broken down into amino acids which are
used as building material.
– The body can break down proteins into energy as a last resort.
An Overall of Cellular Respiration
Cellular respiration occurs at the mitochondria:
Parts of the Mitochondria
• Outer Membrane: contains many pore proteins to
allow materials in and out of the mitochondria.
• Inner Membrane: contains enzymes essential for cell
respiration.
– Cristae: the folded sections of the inner
membrane.
– Inner membrane is about 5 times larger
than the outer membrane (increases
surface area and rate of respiration)
– The inner membrane must be folded to fit
inside
An Overall of Cellular Respiration
• Intermembrane Space:
space between the inner
and outer membrane of
the mitochondria.
• Matrix: the area inside of
the inner membrane.
– Contains proteins,
cytosol, and
mitochondrial DNA.
An Overall of Cellular Respiration
• Cellular respiration happens slowly and in many steps.
• If all the energy was release in one step . . . Most
would be lost as light and heat.
• Three steps of
cellular respiration
1. Glycolysis
2. Krebs Cycle
3. Electron
Transport
Chain
Step 1: Glycolysis
• Location: In the cytosol just
outside the mitochondria
• Purpose: Splits glucose into
two molecules of pyruvic acid.
– To begin glycolysis the cell
needs to invest two ATP
– Glycolysis produces 4 ATP
and 2 NADH
(NADH is similar to NADPH in
photosynthesis)
Step 2: Krebs Cycle
• Location: The mitochondrial
matrix
– Pyruvic acid from glycolysis
enters the mitochondria.
• Purpose: To break down the
pyruvic acid into CO2.
• Every turn of the Krebs Cycle
produces:
– 3 CO2
– 1 ATP
– 1 FADH2 (similar to NADH)
– 4 NADH
Step 2: Krebs Cycle
What happens to the products of the Krebs cycle?
Carbon dioxide is lost to the
atmosphere
ATP can be used directly to
supply energy for the cell
High energy electron carriers
move into the electron
transport chain.
Step 3: Electron Transport Chain
• Location: The inner membrane of the mitochondria
• Purpose: Use the energy from NADH and FADH2 to
convert ADP into ATP.
– NADH and FADH2 were produced during glycolysis and
the Kred’s cycle.
– NADH → 3 ATP’s
– FADH2 → 2 ATP’s
Step 3: Electron Transport Chain
The Process
1. NADH and FADH2 give high energy elections to
protein pumps in the inner mitochondria membrane.
2. Energy from the electrons is used to pump H+ ions
from to matrix to the intermembrane space.
3. There is now a higher concentration of H+ in the
intermembrane space compared to the matrix.
4. Chemiosmosis: H+ ions flow back to the matrix
through an enzyme called ATP Synthase
5. ATP Synthase: using the kinetic energy from H+
moving down a concentration gradient to convert ADP
into ATP
Step 3: Electron Transport Chain
Cell Respiration Summary
The totals:
• 1 glucose = 36 ATP
Importance of Oxygen:
• Oxygen is the final electron
acceptor after the electron
transport chain.
• Oxygen combines with
electrons and H+ to form H2O
Fermentation
Fermentation: an anaerobic process that produces ATP from
glucose.
• Anaerobic: it occurs in the absence of oxygen.
• Cell Respiration is an aerobic process (it requires) oxygen.
– Glycolysis occurs with or
without oxygen.
– Krebs Cycle and Electron
Transport Chain do not
occur in the absence of
oxygen.
Fermentation
• Location: In the cytosol
• Purpose: Converts NADH back into NAD+ so that
glycolysis can continue.
– During fermentation all
of the ATP is produced
during glycolysis.
– Glycolysis would not be
able to occur if there
was no NAD+
Fermentation
• There are two different types of fermentation:
1. Lactic Acid Fermentation
2. Alcoholic Fermentation
Lactic Acid Fermentation
• Happens in muscle cells during exercise when body can’t
get oxygen to tissues fast enough.
– Lactic acid builds up in muscles causing soreness.
• Bacteria use lactic acid fermentation to several foods:
yogurt, cheese, sour cream, pickles, sauerkraut, kimchi.
Alcoholic Fermentation
• Occurs in yeast cells
– Yeast is added to bread recipes because the CO2
produced by fermentation make the bread rise.
– Alcohol is toxic to cells, if too much fermentation
occurs and the alcohol is allow to build up it will kill
the yeast cells.
Comparing Respiration and
Fermentation
Advantages
Fastest way to
produce ATP
Fermentation
Cellular
Respiration
Occurs without
oxygen
Can generate
enough ATP for
long periods of
activity
Disadvantages
Only provides enough
energy for a few
seconds of activity.
Efficiency
2 ATP per
Glucose
Produces Lactic acid
Releases energy more
slowly
Needs oxygen
36 ATP per
Glucose