Transcript The Kreb`s Cycle

Miss Tee
Monday, March 22nd
 Glycolysis
 in every living cell
 break down of one glucose molecule (6Carbon sugar) into (2) 3-Carbon sugar
(pyruvate)
 Yield of ATP low
 Takes place in cytosol
 Pyruvate Oxidation
 Pyruvate transported to matrix
 Modified into acetyl CoA
 Prepares molecule for further oxidation in
Kreb’s cycle (S-bond unstable)
 Sir Hans Krebs
 1937, awarded Nobel Prize for discovery of
cyclic series of enzymatic reactions in
mitochondria
 Def: cyclic series of enzymatic rxns that
transfers energy from organic molecules to
ATP, NADH, and FADH2 and removes
carbon atoms as CO2
 8 steps
 By the end:
 Original glucose molecule completely consumed
 6 carbon atoms leave as 6 CO2  waste
CCCCCC  CCC + CCC  CC + CC + CO2 + CO2 4
CO2
(glucose) (2 pyruvate)
(2 acetyl CoA + 2 CO2)
(4CO2)
 Energy stored in 2 ATP (1 ATP/acetyl CoA molecule)
 Where do you see substrate-level phosphorylation?
 Step 5
 Electron transport chain
 Consists of series of enzymes on IMM
 Electrons are released from NADH, FADH2
 Enzymes arranged in increasing
electronegativity
 Alternating redox, gaining and losing 2 e Electrons shuttle through ETC, occupying
more stable positions
 Oxygen: final electron acceptor
 Strips 2 e- from enzyme complex + 2 H+ from
matrix = H20
 Free energy released used to actively
transport protons (H+) through proton pumps
 By creating a simple chemical gradient,
specialized enzyme ATP Synthase is
powered to phosphorylate ADP = ATP
Miss Tee
Monday, March 22nd
 3 minutes of silent review
 Identify areas of weak understanding
 Consult your colleague
 Come up with a strategy (mnemonic,
acronym, simile) to help you remember
 Kids Prefer Cheese Over Fried Green
Spinach.
 Kingdom, Phylum, Class, Order, Family,
Genus, Species
 NADH and FADH2 slightly different:
 FADH2 skips 1st enzyme  transfers 2 e- directly to Q
 FADH2 contributes 2 protons  2 ATP
 NADH contributes 3 protons  3 ATP
 What about cytosolic NADH from glycolysis?
 Cannot access matrix (inner membrane impermeable)
 Electrons passed to FAD = FADH2
 Cytosolic NADH ATP yield different from matrix NADH
 Why are there many folds of the inner membrane?
 Limiting factor NAD+ and FAD molecules
 Converts chemical potential energy into
electrochemical potential energy
 Like a charged battery: accumulation of
charge on one side of an insulator
 Creates electrochemical potential (voltage)
 H+ unable to diffuse through phospholipid
bilayer
 Forced through specialized proton channels
coupled to ATP synthase
 Drives ADP + Pi  ATP
 Process for synthesizing ATP using the
energy of an electrochemical gradient and
the ATP synthase enzyme
 Continual production of ATP by this method
dependent upon maintenance of H+
reservoir
 ATP transported via facilitated diffusion into
cytosol, needed for active transport,
movement, synthesis reactions
 *Why do we need O2?
 To survive, we need ATP from
ETC/chemiosmosis
 We need a maintenance of H+ reservoir
 We need the flow of e We need O2 to “pull” electrons down the ETC
(in their “energy-yielding fall”…like a skydiver)
 Food
 Glucose
 (2) G3P molecules
 (2) pyruvate molecules
 Molecule prepped for Kreb’s cycle  Acetyl
CoA (ticket into Kreb’s)
 Kreb’s cycle (ATP; NADH, FADH2)
 Electrons dropped off at the ETC
 Electrons dropped off at the ETC
 NADH  3 protons (3 ATP)
 FADH2  2 protons (2 ATP)
 CAVEAT: cytosolic NADH ultimately contributes 2
ATP
 proton gradient established
 H+ will travel through specialized channel
coupled to ATP Synthase
 Shipped off to wherever it is needed
 Virtual Cell animation
 http://vcell.ndsu.edu/animations/atpgradient/m
ovie-flash.htm
 We breathe to acquire O2 to accept the final
electron in the ETC.
 The ETC serves to separate electrons of
hydrogen atoms from their protons.
 The protonmotive force (electrochemical
gradient) drives ATP synthesis.
 Amount of energy consumed by an organism
at a given time
 BMR: basal metabolic rate
 minimum amount of energy required for
organism survival
 Accounts for 60-70% energy consumed per
day
 When is an individual’s BMR greatest??
Ethanol Fermentation
Lactic Acid Fermentation
Organisms have evolved ways of recycling NAD+
and allowing glyoclysis to occur in the absence of
O2
Fermentation: transfer of hydrogen atoms from
NADH
to different molecules
instead of ETC
Hypoxic environment
 How do we make use of this?
 Wine, beer, liquor
 Bread, pastries
 Soy sauce
 How does yeast work??
 Single-celled fungi (Saccharomyces
cerevisiae)
 Live yeast cells + flour (starch)
 Ferment glucose, release CO2  bubbles
cause dough to rise
 Ethanol evaporates in high heat in oven
 Why is most wine 12% alcohol by volume??
 Yeast + grape juice (sugars)
 Ethanol produced
 Stops at 12%, point at which yeast die
 Strenuous exercise
 Muscle cells require >> O2 than provided
Hypoxic environment
 Lactate threshold:
 Point during exhaustive, all-out exercise at
which lactic acid builds up in the blood stream
faster than the body can remove it.
 Anaerobic metabolism produces energy for
short, high-intensity bursts of activity (lasting
no more than a few minutes)
 Lactic acid build-up reaches a threshold
 can no longer be absorbed and, therefore,
accumulates
 This is the lactate threshold
 What does this mean for athletes?
 Helps determine how to train, at what pace
they can maintain during endurance sports.
 Lactate threshold can be increased greatly
with training
 Athletes, coaches devise complicated training
plans to increase this value
 Train to endure increasingly higher intensity
exercise  increase # of mitochondria
 Convert more glucose potential energy to
usable energy (ATP)
 Having a higher lactate threshold means an
athlete can continue at a high-intensity effort
with a longer time to exhaustion.
 How do you accomplish this?
 Interval training and continuous training
 Nutrition