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Cellular Respiration
H.B.3A.4 Develop models of the major inputs and outputs of cellular respiration
(aerobic and anaerobic) to exemplify the chemical process in which the bonds of
food molecules are broken, the bonds of new compounds are formed and a net
transfer of energy results. Use the models to explain common exercise phenomena
(such as lactic acid buildup, changes in breathing during and after exercise, and cool
down after exercise).
Why Do We Need to Breathe?
• Why you need oxygen?
You need oxygen in order for your body to USE the food that you
eat!
© 2013 Vanessa Jason “Biology Roots”)
Harvesting Chemical Energy
• The food you eat cannot be used by cells directly.
• Cells have only one usable energy form, ATP (adenosine
triphosphate).
• Cellular Respiration is the complex process in which cells
make ATP by breaking down organic compounds.
• Any food (organic) molecule, or nutrient, including
carbohydrates, fats/lipids, and proteins can be processed
and broken down as a source of energy to produce ATP
molecules.
What is the ATP produced during
cellular respiration used for?
• ATP can then release the energy for cellular
metabolic processes:
– Active Transport
– Protein synthesis
– Muscle contraction.
What type of organism carry out cellular
respiration?
• Autotrophs
– Use the glucose created during photosynthesis
• Heterotrophs
– Use organic compounds that are harvested from
digestion
Cellular Respiration Occurs in Two
Stages
• Step 1:Glycolysis
– Glyco= Sugar
If Oxygen is Available
-Lysis- To Break Apart
• Step 2: Aerobic Respiration
• Aerobic = Requires Oxygen
– The two steps of aerobic respiration are:
1. Citric acid cycle or Krebs cycle
2. Electron Transport Chain
Where Does Cellular Respiration Occur?
• Occurs in two different locations
• Glycolysis occurs in the cytoplasm.
• The Krebs cycle occurs in the Mitochondria
Review of Mitochondria Structure
• Smooth outer
Membrane
• Folded inner
membrane
• Folds called Cristae
• Space inside cristae
called the Matrix
Many Reactions in Cellular Respiration
are REDOX reaction
• A chemical reaction in which there is the
transfer of one or more electrons from one
reactant to another.
• Oxidation is the loss of electrons
• Reduction is the gain of electrons.
• Because the electron transfer requires a donor
and an acceptor, oxidation and reduction
always go together
Glycolysis
• Breaks down glucose into 2 pyruvate molecules
(aka pyruvic acid), a 3 carbon compound.
• Anaerobic = Does not require Oxygen
• Carbon Dioxide is released.
• As the bonds in C6H12O6 are broken, energy is
released.
• Net of 2 ATP molecules are made
• Occurs in a series of reactions that are catalyzed
by specific enzymes
Chemical Reactions in Glycolysis
- Glycolysis is often referred
to as the “energy investment”
phase because it requires 2 ATP
to begin.
-Four Electrons are removed from glucose
and are now in a high energy state and
passed on to the electron carrier NAD+
(nicotinamide adenine dinucleotide) which
will carry 1 pair (two total) of electrons
Which is transformed into NADH
- 2 molecules of pyruvic acid are formed
Summary and Advantages of Glycolysis
• Although the energy created from glycolysis is minimal
( 2 ATP required + 4 ATP made = 2 ATP net gain) the
process occurs very rapidly.
• Another advantages is that the process does not
require oxygen, which means glycolysis can quickly
supply the cell with energy even when oxygen is not
available to the cell.
Location
ATP USED
ATP created
Net ATP
Product
Cytoplasm
2
4
2
2 Pyruvates
The Kreb’s Cycle: A Little History
• Discovered by Hans
Krebs in 1937
• He received the Nobel
Prize in physiology or
medicine in 1953 for his
discovery
• Forced to leave
Germany prior to WWII
because he was Jewish
The Krebs Cycle
• Sometimes called the Citric Acid Cycle
• Requires oxygen = Aerobic
• Takes place in the mitochondria
• Has a seconds step: Electron Transport Chain
Step 1: Pyruvic Acid passes
through the two
membranes of the
mitochondrion into the
matrix.
Step 2: 1 carbon from
Pyruvic Acid is removed to
make CO2
Step 3: The remaining two
carbons rearrange to make
Acetyl-CoA which is made
of 2 carbons, 1 Oxygen
and 3 Hydrogen Atoms
Step 4:Acetyl-CoA adds
the 2-carbon acetyl group
to a 4-carbon molecule
already present,
producing a 6-carbon
molecule called citric acid.
The Krebs Cycle: Energy Extraction
Step 5:Citric acid is
broken down into a 4carbon molecule, more
carbon dioxide is
released, and electrons
are transferred to
energy carriers.
For each turn of the cycle, a molecule of ADP is converted
to a molecule of ATP.
At five places in the cycle, electron carriers accept
a pair of high-energy electrons, and NAD+ and
FAD are converted to NADH and FADH2.
Summary Krebs Cycle
Location
Reactants
Products
Mitochondrial Matrix
Pyruvic acid
4 CO2 molecules
6 NADH
2 FADH2
2 ATP
Electron Transport
• Electron transport uses the high-energy electrons from
glycolysis & the Krebs cycle to synthesize ATP from ADP.
• Where most of the ATP is made
• Series of chemical reactions that combine hydrogen +
oxygen to make water
• Electron transport chain is composed of a series of
electron carriers located in the inner membrane of
the mitochondrion.
• NADH and FADH2 pass electrons through these
electron carriers and at the end an enzyme combines
these electrons with Hydrogen ions and oxygen to
make water
Electron Transport: ATP Production
• The mitochondria membrane contains proteins called ATP
Synthases
• ATP is made through chemiosmosis:
the movement of ions across a semipermeable membrane,
down their electrochemical gradient
• The charge differences across the
membrane forces H+ ions through channels
in these enzymes, which causes the
synthase to spin
• With each rotation the enzyme
Grabs and ADP and attaches a phosphate
Making an ATP molecule
Total ATP from Cellular Respiration
Glycolysis, the Krebs cycle, and the electron transport chain release about 36
molecules of ATP per molecule of glucose.
2
2
CO2
32
Total ATP?
34-36
Cellular Respiration Equation
• Does not represent all of the steps that occur during the process of aerobic
respiration.
• C6H12O6 + 6O2 
6CO2 + 6H2O + energy
• One glucose molecule and six oxygen molecules are needed to produce six
carbon dioxide molecules and six water molecules.
• Each of the reactants (glucose and oxygen) is used during different stages of
aerobic respiration.
– Glucose used during glycolysis
– Oxygen used during Krebs Cycle and ETC
•
Each of the products (carbon dioxide and water) is formed during different
stages of the process
• The energy that is released is primarily used to produce approximately 34 to
36 molecules of ATP per glucose molecule.
What Do Cells Do When Oxygen is not available?
•
•
•
•
Cells can obtain energy through anaerobic respiration
An =Not, Without
If there is no O2 available fermentation takes place
Fermentation is not as efficient as aerobic respiration
– ATP is produced in minimal amounts (2 ATP)
• There are two types of fermentation depending on the organism:
– alcoholic fermentation & lactic acid fermentation
Why am I Sore? : Lactic Acid Fermentation
• Occurs in Animal cells
• Ex. Muscle Tissue during vigorous exercise
• The pyruvic acid formed during glycolysis is broken down to lactic
acid and energy is released
• Glucose  Pyruvic Acid Lactic Acid Energy
• Occurs so that the cell can have a continual source
of energy
Alcoholic Fermentation
• Occurs in plant cells, yeast and some bacteria
• Glucose Pyruvic acid  Alcohol + Co2 + Energy
• Sugars are converted into cellular energy and produce ethanol
(alcohol)and carbon dioxide as metabolic wastes.
•
This reaction occurs in the production of ethanol fuels, in the
rising of bread dough, production of yogurt, pickles and cheese.