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Cellular Respiration
Chemical Energy and Food
• Food is the energy source for cells. The energy in food is
measured in calories.
• A calorie is the amount of energy needed to raise the
temperature of 1 gram of water 1 degree Celsius. There are
3811 calories in one gram of sugar glucose.
• The cell doesn’t burn glucose directly but converts into an
energy source, ATP, through a process that begins with the
pathway called glycolysis.
Glycolysis
Glycolysis is the process in which one molecule of glucose is
broken in half, producing two molecules of pyruvic acid, a three
carbon compound.
• Glycolysis takes place in the cytoplasm of a cell.
• In the process of breaking glucose in half two molecules of ATP
are needed but four molecules of ATP are produced creating a
net gain of two molecules of ATP
• 4 high energy electrons are also removed and added to NAD+
(nicotinamide adenine dinucleotide) creating NADH, which
helps pass energy from glucose to other pathways in the cell.
•
Glycolysis
Glucose
2 Pyruvic acid
To the electron
transport chain
Chemical Pathways After Glycolysis
Glucose
Glycolysis
Krebs
cycle
Fermentation
(without oxygen)
Electron
transport
Alcohol or
lactic acid
Fermentation
• When oxygen is not present, fermentation follows glycolysis
• ● Fermentation releases energy from food molecules by producing ATP in
•
1)
2)
•
•
the absence of oxygen, this is an anaerobic process.
● There are two main types of fermentation:
Alcoholic fermentation
Lactic acid fermentation
● Alcoholic fermentation example is yeast which causes carbon dioxide to
form and make bread rise.
● pyruvic acid + NADH  alcohol + CO2 + NAD+
Fermentation
• ● Lactic acid fermentation:
• Pyruvic acid + NADH lactic acid + NAD+
• ● Lactic acid is produced in your muscles during rapid exercise
when the body cannot supply enough oxygen to the tissues.
• ● “FEEL THE BURN” is actually the result of a build up of lactic
acid in the muscles and can become painful and lead to
cramps.
Lactic Acid Fermentation
Glucose
Pyruvic acid
Lactic acid
Overview of Cellular Respiration
• If oxygen is present, The Krebs Cycle and electron transport chain
follow glycolysis
• Glycolysis, the Krebs Cycle, and the electron transport chain make
up the process called cellular respiration.
• Cellular respiration is the process that releases energy by breaking
down glucose and other food molecules in the presence of oxygen
(an aerobic process).
Cellular Respiration Chemical Equation
Cellular Respiration: An Overview
Mitochondrion
Electrons carried in NADH
Electrons
carried in NADH
and FADH2
Pyruvic acid
Glucose
Glycolysis
Krebs
Cycle
Electron
Transport Chain
Mitochondrion
Cytoplasm
The Krebs Cycle (Citric Acid Cycle)
• The Krebs cycle is the 2nd stage of cellular respiration.
(glycolysis is the 1st stage)
• During the Krebs cycle, pyruvic acid is broken down into
carbon dioxide in a series of energy-extracting reactions.
• The Krebs cycle is also known as the citric acid cycle, because
citric acid is one of its 1st products.
Stages Of The Krebs Cycle
1. The Krebs cycle starts when pyruvic acid formed by glycolysis enters the
mitochondrion.
2. The pyruvic acid is broken down into carbon dioxide and a 2-carbon acetyl
group.
3. The 2 carbons of the acetyl group join a 4-carbon compound to produce
citric acid. The Krebs cycle continues in a series of reactions. In these
reactions, two energy carriers accept high-energy electrons. NAD+ is
changed to NADH, and FAD is changed to FADH2. These molecules carry
high energy electrons to the electron transport chain. The carbon dioxide
is released as a waste product.
The Krebs Cycle
Citric Acid
Production
Mitochondrion
The Electron Transport Chain (ETC)
• The ETC is the 3rd and final stage of cellular respiration.
• The ETC uses the high energy electrons to change ADP into ATP.
• In the ETC, high energy electrons move from one carrier protein to the
next.
• At the end of the chain, oxygen pulls electrons from the final carrier
molecule. These electrons join with hydrogen ions, forming water.
• Each transfer along the chain releases a small amount of energy. ATP
synthase uses the energy to produce ATP.
Electron Transport Chain
Electron Transport
Hydrogen Ion Movement
Channel
Mitochondrion
mbrane
ATP synthase
Inner
Membrane
Matrix
ATP Production
Cellular Respiration Overview
Glucose
(C6H1206)
+
Oxygen
(02)
Glycolysis
Krebs
Cycle
Electron
Transport
Chain
Carbon
Dioxide
(CO2)
+
Water
(H2O)
ATP Totals For Cellular Respiration
•
•
•
•
•
● The totals for the cellular respiration cycle are as follows:
-Glycolysis: +4 ATP – 2 ATP = Net gain 2 ATP
-Krebs Cycle and ETC: +32 ATP
-Net gain for entire cycle is 34 ATP
Note: remember there are 2 ATP used in glycolysis, therefore
only 34 ATP are realized for the cell’s further needs.
• -The total number of ATP molecules formed during cellular
respiration is 36
The Partnership Between Photosynthesis And Cellular
Respiration
• The energy flows in photosynthesis and cellular respiration occur in
opposite directions.
• On a global level, photosynthesis removes carbon dioxide from the
atmosphere and puts back oxygen.
• Cellular respiration removes oxygen from the atmosphere and puts back
carbon dioxide.