Transcript Cellular Respiration

Conversion of glucose to ATP
Outline of what you will be learning…
 1. Overview
 2. Purpose: To Get ATP!
 3. Electron Carrier Molecules
 4. Mitochondria
 5. The Basics of Cell Respiration
 6. Glycolysis
 7.Pyruvate chemical “grooming”
 8. Kreb’s Cycle
 9. Electron Transport Chain (Oxidative
Phosphorylation)
 10. Cell Respiration Summary
 11. Fermentation- Anaerobic Respiration
1. Overview
 Who does it?
 All living things: both autotrophs and heterotrophs
 What is it?
 Carbohydrates and O2 are used to make ATP (energy).
CO2 and H20 are waste products.
 The opposite of photosynthesis.
 Involves three steps: glycolysis, kreb’s cycle, and
electron transport chain.
 Where does it occur?
 The cytoplasm and the mitochondria of the cell
1. Overview
 Equation:
 C6H12O6 + 6O2 6CO2 + 6H20 + ATP
 Glucose+ oxygen carbon dioxide + water + energy
2. Purpose: To Get ATP!
 ATP: A modified nucleotide molecule that powers all
cellular work directly.
 Its structure: adenine, ribose and three phosphates are
combined by dehydration synthesis
2. Purpose: To Get ATP!
 Phosphorylation
 ATP molecules release phosphate groups to various
other molecules. These molecules take in the phosphate
by phosphorylation and get excess energy to perform
various processes.
 When ATP releases a phosphate + energy it produces
ADP (adenosine diphosphate)
 ADP can turn back to ATP by taking in a phosphate
and energy by phosphorylation
 Similar to recharging a battery
2. Purpose: To Get ATP!
3. Electron Carrier Molecules
 There are two different molecules that are used to
carry electrons and hydrogen ions to the last step
cellular respiration.
 NAD+ carries 2 electrons and a hydrogen ion at a time –
NADH
 FAD+ carries 2 electrons and two hydrogen ions at a
time – FADH2
4. Mitochondria
5. The Basics of Cell Respiration
 Redox reaction
 Cellular respiration is a collection of enzyme catalyzed
reactions of:
 oxidation (the loss of electrons from an element)
 reduction (the gaining of an electron by an element)
5. The Basics of Cell Respiration
 Cellular respiration releases energy by breaking down glucose
and other food molecules in the presence of oxygen.
 6 O2 + C6H12O6 → 6 CO2 + 6 H2O + ATP (energy)
 Cellular respiration takes place in small steps to minimize
the loss of energy in the form of heat or light.
 Processes that require oxygen to take place are called
aerobic.
 Processes that do not require oxygen to take place are
anaerobic.
5. The Basics of Cell Respiration
 Aerobic Cellular respiration consists of three major
steps (when oxygen is present):
 Glycolysis – occurs in the cytoplasm
 The Krebs cycle – occurs in the mitochondrion
 Electron transport chain – occurs in the mitochondrion
5. The Basics of Cell Respiration
6. Glycolysis
 Means “splitting sugar”
 Begins with a single molecule of glucose (6-C) and
concludes with two molecules of another organic
compound, called pyruvate (3-C).
 A net gain of 2 NADH molecules and 2 ATP
molecules
 ATP can be used by cell immediately; NADH must
pass down the ETC in mitochondria
 Substrate-level phophorylation occurs
 An enzyme transfers a phosphate group from a substrate
molecule directly to ADP, forming ATP
6. Glycolysis
 9 Steps (Figure 6.7C)
 Steps 1-3: A sequence of three chemical reactions converts
glucose to a molecule of fructose using 2 ATP.
 Step 4: Fructose splits into two G3P molecules
 Step 5: G3P gets oxidized and NAD+ is reduced to NADH
 Steps 6-9: specific enzymes make four molecules of ATP by
substrate-level phosphorylation. Water gets produced as a
by-product
6. Glycolysis
 2 ATP produced account only for 5% of the energy that
a cell can harvest from a glucose molecule.
 2 NADH account for another 16%, but there stored
energy is not available for use in the absence of O2.
6. Glycolysis
7. Pyruvate chemical
“grooming”
 As pyruvate forms at the end of glycolysis, it is
transported from the cytoplasm into the mitochondria
 Pyruvate does not enter the Kreb’s Cycle as itself.
 It undergoes major chemical “grooming”
7.Pyruvate chemical “grooming”
 A large, multienzyme complex catalyzes three reactions:
1. A carbon atom is removed from pyruvate and released
in CO2
2. The two-carbon compound remaining is oxidized while
a molecule of NAD+ is reduced to NADH
3. A compound called coenzyme A, derived from a B
vitamin, joins with the two-carbon group to form a
molecule called acetyl coenzyme A:
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Abbreviated acetyl CoA, is a high-energy fuel molecule for the
Kreb’s Cycle
For each molecule of glucose that enters glycolysis, two
molecules of acetyl CoA are produced and enter the Kreb’s
cycle.
7. Pyruvate chemical
“grooming”
8. Kreb’s Cycle
 Overview:
 Called Krebs in honor of Hans Krebs, German-British researcher who
worked out much of this cyclic phase of cellular respiration in the
1930s.
 Only the two-carbon acetyl part of the acetyl CoA molecule actually
participates in the citric acid cycle.
 Coenzyme A helps the acetyl group enter the cycle and then splits off
and is recycled.
8. Kreb’s Cycle
 Overview (continued):
 Occurs in the matrix of the mitochondria
 Compared with glycolysis, Kreb’s Cycle pays big energy dividends to
the cell
 This makes 1 ATP, 3 NADH and 1 FADH2, per acetyl coA
(double that for each glucose molecule)
 Releases CO2 as waste
 is aerobic (requires oxygen)
8. Kreb’s Cycle
8. Kreb’s Cycle
 Details of the citric acid cycle: Figure 6.9B:
 Step 1
Acetyl coA is stripped via enzymes: coA is recycle and the
remaining acetyl (2-C) is combined with oxaloacetate already
present in the mitochondria forming citrate (6-C)
 Step 2 and 3
 Redox reactions take place stripping hydrogen atoms from organic
intermediates producing NADH molecules and dispose of 2-C that
came from oxaloacetate, which are released as CO2.
 Substrate-level phos. of ADP occurs to form ATP.
 A 4-C molecule called succinate forms.
 Step 4 and 5
 Oxaloacetate gets regenerated from maltate, and FAD and NAD+ are
reduced to FADH2 and NADH, respectively.
 Oxaloacetate is ready for another turn of the cycle by accepting
another acetyl group
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9. Electron Traansport Chain
 Involves oxidative phosphorylation
 A clear illustration of structure fitting function:
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the spatial arrangement of electron carriers built into a
membrane makes it possible for the mitochondrion to use the
chemical energy released by redox reactions to create an H+
gradient and then use the energy stored in the gradient to
drive ATP synthesis
 Chemiosmosis also occurs
 The potential energy of the concentration gradient is
used to make ATP.
9. Electron Transport Chain
 Built into the inner membrane of the mitochondrion,
or in the cristae folds, providing space for thousands of
copies of the electron transport chain and many ATP
synthase complexes
 With all these ATP-making “machines,” a
mitochondrion can produce many ATP molecules
simultaneously
9. Electron Transport Chain
9. Electron Transport Chain
 Figure 6.10:
 Path of electron flow from the shuttle molecules NADH
and FADH2 to O2, the final electron acceptor.
 Each oxygen atom (1/2 O2) accepts two electrons from
the chain and picks up two hydrogen ions from the
surrounding solution to form H2O, one of the final
products of cellular respiration.
 Most of the carrier molecules reside in the three main
protein complexes, while two mobile carriers transport
electrons between the complexes.
9. Electron Transport Chain
 Figure 6.10 (continued):
 All of the carriers bind and release electrons in redox
reactions, passing electrons down the “energy staircase.”
 Protein complexes shown in the diagram use the energy
released from the electron transfers to actively transport
H+ across the membrane, from where they are less
concentrated to where they are more concentrated.
 Hydrogen ions are transported from the matrix of the
mitochondrion (its innermost compartment) into the
mitochondrion’s intermembrane space.
9. Electron Transport Chain
 Figure 6.10 (continued):
 The resulting H+ gradient stores potential energy, similar
to a dam storing energy by holding back elevated water.
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Dams can be harnessed to generate electricity when the water is
allowed to rush downhill, turning giant wheels called turbines.
Similarly, ATP synthases built into the inner mitochondrial
membrane act like minature turbines. H+ can only cross through
ATP synthases bc they are not permeable to the membrane.
Hydrogen ions rush back “downhill” through an ATP synthase,
spinning a component of the complex, just as water turns the
turbine in a dam.
Rotation activates catalytic sites in the synthase that attach
phosphate groups to ADP molecules to generate ATP.
9. Electron Transport Chain
 Why is this process called oxidative phosphorylation?
 The energy derived from the oxidation-reduction
reactions of the electron transport chain that transfer
electrons from organic molecules to oxygen is used to
phosphorylate ADP.
 By chemosmosis, the exergonic reactions of electron
transport produce an H+ gradient that drives the
endergonic synthesis of ATP.
10. Cell Respiration Summary
 TOTAL= 38 ATP (theoretical)
 Glycolysis
Occurs in cytoplasm
2 ATP
2 NADH
2 H20 get released
 2 pyruvate
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 Kreb’s Cycle (including pyruvate grooming)
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2 ATP
8 NADH
2 FADH2
6 CO2 get released
 Electron Transport Chain
 H20 gets released
 10 NADH get converted to 3ATP= 30 ATP
 2 FADH2 get converted to 2 ATP= 4 ATP
11. Fermentation- Anaerobic
Respiration
 Glycolysis is the metabolic pathway that generates
ATP during fermentation.
 No O2 is required; it generates a net gain of 2 ATP
while oxidizing glucose to two molecules of
pyruvate and reducing NAD+ to NADH.
 Significantly less ATP is generated, but it is enough
to keep your muscles contracting for a short while
when the need for ATP outpaces the delivery of O2
via the blood stream
 Many microorganisms supply all their energy needs
with the 2 ATP yield of glycolysis.
11. Fermentation- Anaerobic
Respiration
Strict Anaerobes
require anaerobic conditions and are poisoned by
oxygen
Facultative Anaerobes
can make ATP either by fermentation or by oxidative
phosphorylation, depending on whether O2 is
available.
11. Fermentation- Anaerobic
Respiration
 Fermentation provides an anaerobic step that recycles
NADH back to NAD+; essential to harvest food energy
by glycolysis.
 Two types of fermentation:
 Lactic acid
 Alcohol
11. Fermentation- Anaerobic
Respiration
 Lactic acid fermentation
 Figure 6.13A
 NADH is oxidized to NAD+ as pyruvate is reduced to
lactate (the ionized form of lactic acid)
 Lactate builds up in muscle cells during strenuous
exercise is carried in the blood to the liver, where it is
converted back to pyruvate
 Dairy industry use this to with bacteria to make cheese
and yogurt
11. Fermentation- Anaerobic
Respiration
 Alcohol fermentation
 Figure 6.13A
 Used in brewing, winemaking, and baking
 Used by yeasts and bacteria (facultative anaerobes)
 Recycle their NADH to NAD+ while converting pyruvate
to CO2 and ethanol (ethyl alcohol).
 CO2 provides bubbles in beer and champagne, and
bread dough to rise
 Ethanol is toxic to organisms that produce it; must
release it to their surroundings