Download • In the cell, nutrients and oxygen, have different electron affinities.

• The flow of electrons is frequently coupled to accomplishment of work.
– We are most familiar with work accomplished by electric motor. – Other energy transformations are also possible, for example electron flow to light energy. • In a battery operated electric motor, the battery contains two chemicals that differ in affinity for electrons.
– The electrons flow spontaneously through an electron carrier
called a wire to the chemical with higher electron affinity. – Electron movement is driven by an force protional to the difference in electron affinity, measured in “volts”
– When coupled to a "transducer or motor", the flow of electrons is used to accomplished mechanical work. – A transducer transforms one form of energy into another... in this case potential electric energy of the battery to mechanical
energy + heat energy.
• In the cell, nutrients and oxygen, have different electron affinities. – Electrons flow spontaneously towards the chemical with higher electron affinity (oxygen) through a series of electron carrier molecules rather than a wire. • The flow is driven by a force proportional to difference in electron affinity. • The flow of electrons is used by organic molecules that are energy transducers.
– Enzymes (ATP Synthases)
– Transport proteins (ATPase Pumps)
– Motor Proteins (myosin ATPase) Energy Stored Within ATP
• Mechanical work
• Transport work
• Chemical work
Production and Use of ATP requires different enzymes
• ATP production requires ATP synthases
• ATP hydrolysis reactions are coupled to phosphorylation reactions by kinases or ATPases. Phosphate group from ATP is transferred to some other molecule, energizing that molecule by altering its electron configuration.
Phosphorylation
Via ATP synthase
enzymes
Hydrolysis via
ATPases or
Kinases
ATP
enz
Energy from
catabolism of
nutrients like CHO
enz
Energy for cellular work
(energy- consuming
processes)
ADP + P
protein
How Does ATP power cellular work?
• ATP hydrolysis reactions are coupled to phosphorylation
reactions:
• Phosphate group from ATP is transferred to some other molecule, “energizing” that molecule.
• Presence or absence of Phosphate group alters shape and activity of protein
• In the mitochondria, multiple membrane bound molecules allow spontaneous flow of electrons from different nutrients to oxygen.
• They couple the electron flow to production of a proton concentration difference across the inner mitochondrial membrane. • The proton concentration difference created across the membrane has potential energy. – This potenial energy is used to do chemical work:
• Synthsis of ATP from ADP + Pi by an enzyme ATP SYNTHASE. – ATP synthase is a transducer
– It links the spontaneous flow of protons from high to low concentration gradient across the membrane to synthesis of ATP from ADP + Pi.
Fig. 2-12, p. 31
ATP Production
•
Sequence of steps involved in generation of ATP from CARBOHYDRATE within the cell
1.
2.
3.
Glycolysis
Citric acid cycle (Krebs Cycle)
Electron transport chain
In AIR: C6H12O6 + 6 O2  6 CO2 + 6H2O + 686 kcals HEAT
In CELL: C6H12O6 + 6 O2  6 CO2 + 6H2O + HEAT + 32 ATP
ALL molecules are in moles:
6 O2 means 6 moles of O2; one mole of O2 has a volume of 22.4 liters
32 ATP means 32 moles of ATP; one mole of ATP = 507 grams
In a person 134.4 liters of O2 are used to produce 16224 grams of ATP from the potential energy locked in the covalent bonds of 180 grams of glucose
Each liter of O2 consumed is equivalent to production of 120 grams of ATP
The typical human ATP and ADP content is < 100 grams
Each gram of ADP has to be recycled times 400‐500 times per day
1 gram of ATP has 1,187,968,441,814,600,000,000 molecules of ATP (1/507 gram/mole ATP x 6.023 x 1023 molecules/mole)
C6H12O6
6 O2
Uncontrolled oxidation
of food outside the
body (burning)
Explosive release
of energy as heat
and carbon dioxide
C6H12O6
Controlled oxidation
food inside the body
accomplished by the
small steps of CHO
Metabolic pathways
Energy harnessed as ATP,
the common energy
currency for the body
Partly used to maintain
body temperature
MODIFIED Fig. 2-14, p. 32
6 O2
Energy released
as heat + CO2
Heat + CO2
to the environment
Cytosol
Glycolysis
Glucose
(GLYCOGEN)
2 ATP
Pyruvate
Mitochondrial
inner membrane
Mitochondrial matrix
Pyruvate to acetate
Acetyl-CoA
Citric acid
cycle
2 ATP
Electrons carried by
NADH and FADH2
Oxidative
phosphorylation
(electron transport system
and chemiosmosis)
28
ATP
Fig. 2-9, p. 29
Carbohydrate Catabolism
Glycolysis in Non‐aerobic as opposed to anerobic
• Non‐aerobic: no oxygen required
• Anaerobic: no oxygen available
Anaerobic conditions cannot be demonstrated in living mammals
Fig. 2-15, p. 33
Glycolysis produces 4 ATP and 2 Lactate from 1 glucose molecule
• OLD VIEWPOINT
– occurs in cytoplasm
– requires 2 NAD, produces 2 NADH2 and 2 Pyruvate under “aerobic” conditions
– requires 2 NAD and produces 2 lactate under anaerobic conditions
• Cellular handling of NADH2 formed in glycolysis
– Oxidative phosphorylation in mitochondria requires O2 to proceed, NADH2
NAD (aerobic = oxygen required)
– In cytoplasm
2 Pyruvate + 2 NADH2  2Lactate + 2 NAD (non‐aerobic = no oxygen required)
– What happens to lactate ?
Old Viewpoint from Pre‐1990’s: accumulates and causes fatigue
New Viewpoint from 2000’s • Lactate is shuttled to mitochondria of cell producing and oxidized either as lactate or pyruvate (intracellular shuttle is controversial)
• Lactate is shuttled to mitochondria of some other cell and oxidized as either lactate or pyruvate (intercellular shuttle is widely accepted)
Intracellular shuttle?
Intercellular shuttle
Glycolysis occurs in cells regardless of O2 content; O2 is never required for glycolysis; fate is lactate is dependent on what cell produces it and how fast it is produced
Blood transport to
Cytoplasm
O2 NEVER REQUIRED
Glycolysis
2 Pyruvate
2 Lactate
Glucose
2
Intracellular
Lactate shuttle
Mitochondria
Mitochondrion
Glycolysis
Glucose
2 Pyruvate
2
O22 required
Citric acid cycle/Oxidative
phosphorylation
Lactate using cells
such as heart and
slow twitch skeletal
Muscle (intercellular)
Mitochondrial
membranes
30 ATP + CO2+H2O
Cytosol
Lactate is the natural end product of glycolysis, is not a waste
product, and is the link between glycolytic and oxidative
metabolism
Fig. 2-15, p. 33
Lactic Acid Dehydrogenase
Pyruvic Acid Dehydrogenase Complex