Download Unit 3.2: Respiration

Unit 3.2: Cellular Respiration
Vocabulary:
• Glycolysis: glyco- = sweet, sugar; lysis = break apart;
process in which glucose is broken down into pyruvate,
releasing energy; occurs in the cytoplasm
• NAD+/NADH: a molecule that can carry energy, electrons
from one part of the mitochondria to another. (NAD+ is
“empty” bucket, NADH is “full”)
• Anaerobic Respiration: an- = without; aero- = air; process
that breaks down glucose in the absence of oxygen; also
called fermentation.
• Aerobic Respiration: process that breaks down glucose in
the presence of oxygen.
• Krebs Cycle: (also called the Citric Acid Cycle); a process in
aerobic respiration that breaks down acetyl coA into CO2.
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I. Structure of Mitochondria:
A. Contains cristae: highly infolded inner membrane
that increases surface area for more reactions.
B. Also contains matrix: fluid that fills mitochondria
1. Like cytoplasm for the mitochondria
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Overview of Respiration
C6H12O6 + 6O2  6CO2 + 6H2O + ATP
glucose + oxygen  carbon dioxide + water + energy
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C6H12O6 + 6O2  6CO2 + 6H2O + energy
Cellular Respiration
Glycolysis
If no oxygen
Anaerobic Respiration
(fermentation )
If oxygen present
Aerobic Respiration
Kreb’s Cycle
Lactic Acid
Alcoholic
Electron Transport Chain
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II. Glycolysis (occurs in cytoplasm in all organisms)
A. Process splits 6-carbon glucose into (2) 3-carbon pyruvate
molecules
B. Requires input of 2 ATP to get process started, but creates
4 ATP, so net gain of 2 ATP/glucose
1. **Inefficient for large organisms, but okay “in a pinch”
2. **Lots of energy still locked in C-C bonds of pyruvate
C. NAD+ (empty bucket) collects e-’s/H+, becomes NADH
(full bucket)
D. So far: C6H12O6  pyruvate + ATP + NADH
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III. Anaerobic Respiration/Fermentation
• “an-” = without; “aero” = air, oxygen
A. Purpose: anaerobic respiration regenerates NAD+
so it can be re-used in glycolysis
1. If NADH from glycolysis is not recycled, then respiration
stops.
B. Two different paths:
1. Lactic Acid fermentation
2. Alcoholic fermentation
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B.1. Lactic Acid Fermentation:
a. H from NADH and free H+ combine with
pyruvate to become lactic acid (aka: lactate)
1) In cultured dairy products, bacteria break down
lactose (milk sugar) into lactic acid using this
NADH + H+
process: yogurt, cottage cheese
2) Your muscles go through lactic acid fermentation
if there is not enough O2. Lactic acid buildup can NAD+
lead to cramping.
a) When you stop exercising, lactate is turned back
into pyruvate; goes into aerobic respiration
b. NAD+ is “regenerated”
1) Back to cytosol for glycolysis
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B.2. Alcoholic Fermentation
Pyruvate
Acetaldehyde
Ethanol
a. Pyruvate releases CO2, takes H+ from NADH to
become ethanol (a 2-Carbon molecule)
1) Yeast use alcoholic fermentation, make CO2 that makes
champagne bubbly, makes bread rise
b. NAD+ is “regenerated”
1) Back to cytosol for glycolysis
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IV. Aerobic Respiration: if O2 is present
A. Krebs Cycle: occurs in
mitochondrial matrix
1. 3-carbon pyruvate is
converted into 2-carbon
acetyl coA
a. Loses 1 CO2
b. Converts NAD+  NADH
2. Acetyl coA joins with 4carbon OAA to become 6carbon citric acid.
a. This is why Kreb’s is also
called Citric Acid cycle.
b. OAA: oxaloacetic acid
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3. As 6-carbon Citric Acid is
converted back to 4carbon OAA to continue
cycle, gives off:
• 2 CO2 (6-Carbon citric
acid – 4-Carbon OAA = 2
CO2)
4. This conversion also
transfers high-energy
electrons to:
• 3 NADH: now a full
bucket that goes to ETC
• 1 FADH2: now a full
bucket that goes to ETC
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B. Electron Transport Chain: (similar to photosynthesis)
1. NADH, FADH2 carry their stored energy/electrons to the
ETC located in the membranes of the cristae
•
Now NAD+ and FAD are empty buckets, can return to matrix
to pick up more electrons/energy
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2. As electrons are transferred from one carrier to another,
they lose energy, used to pump H+ across membrane
a. Creates lots of H+ in intermembrane space, low H+ in matrix
3. Oxygen is the final electron acceptor at the end of ETC
a. 4H+ + O2  2 H2O
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C. Chemiosmosis: (similar to photosynthesis)
1. High H+ in intermembrane space, low H+ in matrix
2. H+ travel down their gradient from intermembrane
space into matrix through ATP synthase
•
Combines ADP + P to make ATP
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D. Energy Tally:
1.
Glycolysis creates 2 ATP and 2 NADH
a. Converting pyruvate to acetyl coA creates 2 more NADH
2.
3.
Kreb’s Cycle creates 2 ATP, 6 NADH, and 2 FADH2
ETC converts NADH, FADH2 into ATP as follows:
a. Each NADH generates 3 ATP
b. Each FADH2 generates 2 ATP
•
•
•
•
Glycolysis:
2 ATP; 2 NADH
Conversion to acetyl coA:
2 NADH
Kreb’s Cycle:
2 ATP; 6 NADH; 2 FADH2
ETC conversion
10 NADH (3 ATP per NADH) 30 ATP
2 FADH2 (2 ATP per FADH2) + 4 ATP
• Total ATP per molecule glucose: 38 ATP
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A word about the elegance of the “paradox”
between photosynthesis and cellular respiration
Photosynthesis: 6H2O + 6CO2 + light energy  6O2 + C6H12O6
Respiration:
C6H12O6 + 6O2  6CO2 + 6H2O + energy
Photosynthesis: starts with breaking apart water to release
oxygen, sending electrons down the ETC (creating full
buckets), sending electron carriers to the Calvin cycle to
join CO2 molecules into glucose
Respiration: starts with breaking apart glucose to release CO2,
sending it through the Kreb’s cycle, sending electron
carriers to deliver electrons down the ETC, (creating empty
buckets), and combining them with oxygen to make water
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