Download Ch 9 Power Point - Cellular Respiration

Chapter 9~
Cellular
Respiration:
Harvesting
Chemical Energy
• All energy can be traced back to the sun.
• Energy flows in as sunlight and leaves as
heat. Chem elements are recycled.
Principles of Energy Harvest
• Catabolic pathway – releases energy
by oxidizing organic fuels
• Energy – stored in chem bonds –
released when bonds break
– Used for work and given off as
heat
• Fermentation – partial degradation of
sugars that occurs w/out O2
• Cellular Respiration – most efficient
– C6H12O6 + 6O2 ---> 6CO2 +
6H2O + E (ATP + heat)
Redox reactions
• Oxidation/reduction
– Aka redox
• Oxidation is e- loss;
reduction is e- gain
• Reducing agent:
e- donor
• Oxidizing agent:
e- acceptor
See board
Oxidizing agent in respiration
• NAD+ (nicotinamide adenine
dinucleotide) – coenzyme – eacceptor
• Removes electrons from food
(series of reactions)
• NAD+ is reduced to NADH
• Enzyme action: dehydrogenase
– Removes a pair of H atoms
from the substrate (sugar)
& delivers 2e- and 1 proton
(H+) to NAD+ - releases
other H+
• Oxygen is the eventual eacceptor
Electron transport chains
• Sequence of reactions that
prevents energy release in 1
explosive step
• Electron carrier molecules
(mitochondrial membrane
proteins)
• Shuttle electrons that release
energy used to make ATP
• Electron route: food-->
NADH-->electron transport
chain-->oxygen
– O2 is more
electronegative and pulls
e- down chain
Cellular respiration
• Glycolysis: cytosol;
degrades glucose into
pyruvate
• Kreb’s Cycle (Citric Acid
Cycle): mitochondrial
matrix; pyruvate into
carbon dioxide
• Electron Transport Chain
(ETC): inner membrane of
mitochondrion; electrons
passed to oxygen
Glycolysis I
•
•
•
•
“splitting sugar”
Occurs in cytosol
w/ or w/out oxygen
1 Glucose --->
2 pyruvate molecules
• Net energy yield per
glucose molecule: 2 ATP
plus 2 NADH; no CO2 is
released; occurs
aerobically or
anaerobically
Glycolysis II
• Energy investment phase: cell uses ATP to phosphorylate fuel
– Glucose is phosphorylated by 2 ATP molecules
– 2 Glyceraldehyde-3-phosphate molecules are produced
• Energy payoff phase: ATP is produced by substrate-level
phosphorylation and NAD+ is reduced to NADH by food
oxidation
• Every product is doubled because step 4 splits sugar in ½
– NADH, 2ATP, H20, and pyruvate (C3H3O3) are produced for
each glyceraldehyde-3-phosphate
Kreb’s Cycle I
•
•
•
•
In mitochondrial matrix
If molecular oxygen is present…
Junction steps
(1) Carboxyl group (-COO-)
removed from pyruvate &
released as CO2
• (2) Remaining fragment
oxidized → acetate; NAD+ is
reduced →NADH
• (3) Coenzyme A is attached to
acetate → acetyl CoA
Kreb’s Cycle II
• Citric Acid Cycle
– Acetyl group of acetyl CoA added to oxaloacetate → Citrate
– In several steps - CO2 is removed; NADH, FADH2, and ATP are
produced
– Oxaloacetate is regenerated (the “cycle”)
– For each pyruvate that enters:
• 3 NAD+ reduced to NADH
• 1 FAD+ reduced to FADH2
• 1 ATP molecule
• 2 CO2
– Remember: have 2 pyruvate from 1 glucose
• All of the numbers will be doubled
Electron transport chain
• Inner membrane of
mitochondria
• Multiprotein Complex (I, II, III,
IV)
• Many of the proteins are
cytochromes – have a heme
group (iron) which accepts
protons
• NADH and FADH2 enter and
release e• e- are passed down the
complexes until they reach
oxygen (which also picks up 2 H
atoms from surrounding solution
to form H2O)
ATP Synthase I
• Uses the energy of an existing ion gradient to
power ATP synthesis (chemiosmosis – energy
coupling mechanism)
• Driven by difference in H+ concen on either side
of inner membrane
• H+ difference is created when ETC breaks down
NADH and FADH2
• Synthase is the only place where H+ may flow
down gradient
ATP Synthase II
• 4 parts: stator, rotor,
rod, knob
• H+ flows down btw
stator and rotor
• Causes rotor and rod to
rotate
• Rotating rod causes
conformational changes
to knob
– Activiates catalytic
sites which combine
ADP and P forming
ATP
Review: Cellular Respiration
• Glycolysis:
– 2 ATP , 2 NADH,
2 Pyruvate
• Kreb’s Cycle:
– 2 ATP, 6 NADH,
2 FADH2, 4 CO2
• Electron transport & oxidative
phosphorylation:
– 2 NADH (glycolysis) =
6ATP
– 2 NADH (acetyl CoA) =
6ATP
– 6 NADH (Kreb’s) = 18 ATP
2 FADH2 (Kreb’s) = 4 ATP
• 38 TOTAL ATP/glucose
Related metabolic processes
• Fermentation: anaerobic
conditions – glycolysis still
occurs first – purpose to form
NAD+
• Alcohol~ pyruvate to ethanol,
CO2, & NAD+
• Lactic acid~ pyruvate to
lactate & NAD+
• Facultative anaerobes – can do
both (yeast/bacteria)
• Beta-oxidation – lipid
catabolism – breaks fatty acids
down to 2-C fragments which
entre Citric Acid Cycle
– 1g fat produces more than
2X ATP as carbs