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Cell Respiration part 3
Respiration
• Process in which organic molecules act as a fuel
– Main fuel molecule: Glucose
– Secondary sources of fuel: fatty acids, glycerol, amino
acids
• Organic molecules broken don in a series of
stages
• Release chemical potential energy
– Used to synthesize ATP
• Four stages of glucose break down:
1.
2.
3.
4.
Glycolysis
Link Reaction
Krebs Cycle
Oxidative Phosphorylation
Review
• Phosphorylation
– Conversion of an energyrich, but not very reactive,
molecule into one that is
MUCH more reactive
AND whose chemical
potential energy can be
released and trapped more
efficiently
CoEnzymes
• a nonprotein compound
• required for an enzyme to be able to catalyze
a reaction
– NOT a substrate
– Do not become part of the reaction
• bind with the protein molecule (apoenzyme)
to form the active enzyme (holoenzyme)
• bind to the active site of the enzyme
and participate in catalysis but are not
considered substrates of the reaction
• function as intermediate carriers of
electrons, specific atoms or functional
groups that are transferred in the overall
reaction
• Examples: NAD, NADP, FAD, CoEnzymeA
NAD (Nicotinamide adenine dinucleotide)
• Co-enzyme
• Carrier molecule
• 2 linked nucleotides, each with a ribose
– One nucleotide has adenine
– One had nictinamide ring (this accepts hydrogen ion and 2 electrons
• Becomes “reduced” because it carries hydrogen ions and
electrons
– “reduced NAD” aka NADH
• Removal of hydrogens is called an oxidation reaction
• Molecule that picks up the hydrogens is “REDUCED”
Other important coenzymes:
FAD and NADP
• NADP (nicotinamide adenine dinucleotide
phosphate)
– Slightly different form of NAD in photosynthesis
– Has a phosphate group instead of a hydrogen on
carbon 1 of the ribose rings
– Called NADP (reduced NADP is NADPH)
• FAD (flavin adenine dinucleotide)
– Similar in function of NAD
– Used in Krebs
– Made of two nucleotides
– one nucleotide containing ribose and adenine
– One nucleotide containing unusual structure involving a
linear molecule ribitol (instead of ribose)
Glycolysis
• Means “splitting glucose”
• Starting point for respiration in aerobic
AND anaerobic conditions
– Aerobic with oxygen
– Anaerobic no oxygen present
• Location: cytoplasm (cytosol) of cell
• Multi-step process
– Each step is catalyzed by a specific enzyme
(IMPORTANT!!!)
• ONE six carbon molecule splits into
TWO three carbon molecules called
PYRUVATE
• Energy required to begin (2 ATPs)
• Energy released at end (4 ATPs)
• Net total: 2 ATPs
• In order for Glycolysis to
continue, we MUST have
steady supply of NAD
Glucose (Hexose) (6C)
ATP
Fructose phosphate (6C)
ATP
2 ATP
2H
2 NAD
2
Reduced
NAD
2 ATP
Glycolysis
• First stage Phosphorylation with ATP (substrate level phosphorylation)
– 1st ATP to glucose glucose phosphate  fructose phosphate
– 2nd ATP to fructose phosphate  Fructose bisphosphate
– Fructose bisphosphate immediately breaks up into TWO molecules of triose phosphate
– Inorganic phosphate added to each triose phosphate creates triose bisphosphates
• Second Stage Dehydrogenation
– A phosphate is removed from each triose bisphosphate--. Back to 2 triose phosphates
– Hydrogen is removed from each triose phosphate by NAD  2 reduced NAD molecules
– Reduced NAD travels to mitochondria to be used in oxidative phosphorylation
• Third Stage Dephosphorylation
– Phosphate from triose intermediates removed to yield TWO more ATP molecules
• Product: 2 molecules of pyruvate (contains A LOT of chemical potential energy)
– When oxygen available, some of energy will be released via Krebs cycle and oxidative phosphorylation
Pyruvate + CoA + NAD   acetyl CoA + CO2 + reduced NAD
• Pyruvate enters mitochondria via ACTIVE
transport
– Through outer AND inner membranes of
mitochondria into MATRIX
• In the matrix, pyruvate is:
– DECARBOXYLATED
– Carbon dioxide molecule removed
– Diffuses out of mitochondria
– DEHYDROGENATED
– Hydrogen is removed (via NAD)
– Combined with Coenzyme A
– Makes a molecule called ACETYL Coenzyme A
CoEnzyme A
• Complex molecule
• Composed of:
– nucleoside
– Adenine + Ribose
– Vitamin
– Pantothenic acid
• Acts as a carrier of acetyl groups to
the Krebs cycle
• Proteins
– Amino acids
• Fatty Acids
– Broken down in mitochondria in a cycle of
reactions in which each turn of cycle
shortens the fatty acid chain by a two-carbon
acetyl group
– Each acetyl group can react with CoEnzyme
A  Acetyl CoEnzyme A
– Acetyl CoEnzyme A can now enter Krebs
Cycle
– Oxygen MUST be present
• In order to BURN fat (break of those
acetyl groups in a fatty acid) you must
conduct AEROBIC types of exercise
Krebs Cycle
• Citric Acid Cycle
• Tricarboxylic Acid Cycle (TCA)
• 1937, Hans Krebs
• Closed pathway of enzyme controlled reactions
• Location : Matrix of Mitochondria
• Most important aspect: the release of hydrogens (that go
onto oxidative phosphorylation to make ATP)
• In:
– Acetyl CoEnzyme A Enters
• Out:
–
–
–
–
Carbon Dioxide released
Reduced NAD released
Reduced FAD released
ATP is made
Steps of Krebs Cycle
• Acetyl CoEnzyme A combines with fourcarbon compound (OXALOACETATE) 
six- carbon compound (CITRATE)
• Citrate is DECARBOXYLATED (carbon
dioxide removed) then
DEHYDROGENATED (hydrogen
removed by NAD and FAD)
• OXALOACETATE regenerated at the end
of the cycle so it can happen all over again
• Products:
– ONE turn of Krebs yields:
–
–
–
–
TWO carbon dioxide molecules
ONE reduced FAD
THREE reduced NAD
ONE molecule of ATP (via intermediate)