cellular respiration
TRANSCRIPT
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Cellular Respiration
Releasing Chemical Energy
Chapter 6
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BIOCHEMICAL REACTIONS
• All living organisms require a constant supply of energy to sustain life.
• Cellular respiration - the chemical energy stored in glucose is converted into a more usable form – ATP – Requires the presence of oxygen and the correct enzymes – Carbon dioxide, water and heat are also released as by-products
of this reaction.
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy (ATP + heat)
glucose + oxygen → carbon + water + energy dioxide
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Why Cell “Respiration”?
1. This process requires oxygen, which is supplied by breathing
2. The mechanical movement of air or water through the lungs/gills is often referred to as ventilation to distinguish it from respiration.
3. What about plants?
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• Cellular respiration – slow, controlled release of energy (max. harvest of energy from food)
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Review of ATP
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Review of ATP• ATP is the “energy
currency/rechargeable batteries” of cells• When energy is harvested from a chemical
reaction or sunlight, it is stored when a phosphate group is attached to an ADP to form ATP.– Called phosphorylation
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• When the ATP is broken back down to ADP, stored chemical energy is released to do work in a cell – Called dephosphorylation– Some energy is lost as heat
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C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy (ATP + heat)
glucose + oxygen → carbon + water + energy
dioxide
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OXIDATION REACTIONS
• Oxidation begins in the cytoplasm and is completed in the mitochondria
• 3 parts to cellular respiration (each an enzyme-controlled pathway)
– Glycolysis – Krebs cycle – Electron transport
system
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Overview
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• Animation: http://www.qcc.cuny.edu/BiologicalSciences/Faculty/DMeyer/respiration.html
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1. Glycolysis - a 6C glucose molecule is broken into 2 3C molecules of pyruvate (pyruvic acid)
a. Occurs in the cytoplasm of the cell – near the mitochondria
b. Yields: + 2 ATP (4 ATP – 2ATP - used to phosphorylate glucose when it enters cell)
+ 2 NADH (NAD+ is reduced to NADH)
c. This process is anaerobic (without oxygen)…can happen even if there is an insufficient O2 level to carry out the rest of cellular respiration
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If there is O2 present, respiration continues. Each 3C pyruvate will…
1. Lose atoms of carbon and oxygen – CO2 released
(…it is now called an acetyl group)
2. Join to a molecule of coenzyme A (which is a B vitamin) – Acetyl CoA
- CoA acts as a shuttle, carrying acetyl groups
3. NAD+ (coenzyme that shuttles around hydrogen and electrons) is reduced to NADH.
4. These reactions are often called the ‘Intermediate Reactions’
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2. Kreb’s Cycle (Citric Acid Cycle)a. Acetyl CoA enters the mitochondrion and 2C
acetyl group bonds to a 4C compound (oxaloacetate) to form a 6C compound called Citric Acid (citrate)
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b. The 6C compound is broken down to a 5C compound
1 CO2 is produced
1 NAD+ is reduced to NADH
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c. 5C compound is broken down into a 4C compound1 CO2 is produced
1 NAD+ is reduced to NADH
d. Oxaloacetate is regenerated (4C 4C)
This yields:1 ATP (ADP ATP)
1 FADH2 (FAD FADH2)
1 NADH (NAD+ NADH)
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e. So, the total yield of just the Kreb’s cycle is:2 ATP
6 NADH
2 FADH2 per glucose
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3. Electron transport system (ETS) makes ATPa. Electrons from
reduced coenzymes NADH and FADH2 are transferred through a series of redox reactions until the electrons are accepted by oxygen to make water.
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b. Mitochondrial structure
1) Double membrane-bound organelle
2) Inner membrane folded into christae a) Increase surface
area for reactions
b) ETS located here• Intermembrane
space • Matrix - Kreb’s
cycle
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c. ATP synthesis 1. H atoms from coenzymes
dropped off at ETS (inner membrane)
2. H atoms split into a proton (H+) and an electron (e-)
- Electrons go through ETS
- Energy from electrons is used to pump the H+ out into the intermembrane space
3. H+ concentration in this space increases
4. The H+ RUSH back into the matrix (because of concentration gradient) through an H+ channel (ATP synthetase complex) making ATP
5. Called chemiosmosis
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• Animation:
http://vcell.ndsu.nodak.edu/animations/atpgradient/movie.htm
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d. Happy endings…1. H+ and e- (now low energy) are rejoined2. H atoms bond to available oxygen atoms and form water:
H+ + e- + O2 H2O
This is why you breathe!! The O2 is merely a hydrogen dump!
O2 allows the continual movement of H+ through the ATP synthetase
No O2, no rushing H+ movement, no ATP, no life!
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e. ETS produces: (per glucose)
2 NADH (from glycolysis)
2 NADH (from intermediate reactions) +
6 NADH (Krebs cycle)______________
10 NADH x 3 ATP/NADH = 30 ATP
2 FADH2 x 2 ATP/ FADH2 = 4 ATP____
for a total 34 ATP/glucose from ETS
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Cellular Respiration Energy Summary
34 ATP/glucose from ETS +2 ATP (glycolysis) +2 ATP (Krebs cycle)_______________
38 ATP per glucose!!!38 ATP per glucose!!!
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• Prisoners’ explanation
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• Current applications
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• Other nutrients can be used for energy– Lipids fatty acids,
enter Krebs Cycle– Proteins amino
acids• NH3 removed urea• Carbon portions enter
Krebs Cycle as oxaloacetate
– Carbon skeletons can be used for biosynthesis of amino acids, nucleic acids and fatty acids
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Alternatives to Aerobic Respiration
What if there’s not enough oxygen?
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Glycolysis still happens (since it’s anaerobic anyway…).
- Yield is 2 ATP + 2 NADH + 2 pyruvic acid (3 C molecule).
- Fate of the pyruvic acid depends on what type of organism you are…
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If you are a plant or yeast cell…Pyruvic acid will become ETHANOL in a process
called alcoholic fermentation.
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If you are a bacterial cell…Your pyruvic acid can be fermented to vinegar or to start the process of cheesemaking.
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If you are an animal cell…
Your pyruvic acid becomes LACTIC ACID in a process called lactic acid fermentation.
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Photosynthesis and Cellular Respiration
• Cellular respiration and photosynthesis share several features:– They are enzyme-controlled
biochemical pathways.– They make use of ATP for energy transfer– They use an Electron Transport
System to help make ATP.
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Photosynthesis and Cellular Respiration
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Photosynthesis and Cellular Respiration
Light + 6 CO2 + 6 H2O → C6H12O6 + 6
O2
CC66HH1212OO66 + 6 O + 6 O22 → 6 CO → 6 CO22 + 6 H + 6 H22O + O + energy energy (ATP + heat) (ATP + heat)
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• End of cellular respiration!
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Acetyl CoA
NADH
NADPH
FADH
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CELLULAR RESPIRATION
• Breakdown of glucose molecules in the presence of oxygen.
• The oxidation of glucose (by many enzymes) results in carbon dioxide and water.
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy (ATP + heat)
glucose + oxygen → carbon + water + energy
dioxide
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A Definition of Cellular Respiration
The energy stored in glucose (with the presence of oxygen and the correct enzymes) is converted into a more usable form – ATP. Carbon dioxide and water are also released as by-products of this reaction.
C6H12O6 + 6 O2 6 CO2 + 6 H2O + ATP
[Read the last paragraph on page 131]
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GLYCOLYSIS
• Glucose (6 carbons) is broken into two 3 carbon molecules called pyruvate (pyruvic acid).
• This makes enough energy to make 2 ATP molecules.
• In addition, an NADH molecule is also made and transferred to the electron transport chain.
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3. Electron transport system (ETS), located in the membranes of mitochondria (and chloroplasts) makes ATP.– High-energy electrons are
passed stepwise through a series of oxidation-reduction reactions from one carrier molecule to another.
• Every time the electron is passed, some of its energy is released and can be used to make ATP
• The rest of the energy is released as heat
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How much energy do you get from 1 molecule of glucose?
Glycolysis – 2ATP and 2 NADH (each x3)Intermediate – 2 NADH (each x3)Kreb’s Cycle – 2 ATP, 6 NADH (each x3),
and 2 FADH2 (each x2)The ETS yields 8 ATP from glycolysis, 6
ATP from the Intermediate Reactions, 24 ATP from the Kreb’s Cycle
For a total of…38 ATP per initial molecule of glucose
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Throughout the process, coenzymes are being reduced so, in the end, they
can all be oxidized (so ATP can be generated!) – sort of like POKER!
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CELLULAR RESPIRATION SUMMARY
• Glucose is broken down to carbon dioxide and water, making 4 ATPs directly and another 32 ATP via the electron transport system.