Chapter 15 Flashcards
(34 cards)
First Stage of the Generation of Energy from Food
large molecules in food are broken down into smaller molecules in the process of digestion
Second Stage of the Generation of Energy from Food
the many small molecules are processed into key molecules of metabolism, most notably acetyl CoA
Third Stage of the Generation of Energy from Food
ATP is produced from the complete oxidation of acetyl CoA
Energy is needed for:
- Movement: muscle contraction, cells
- Active transport: molecules and ions
- Biosynthesis: building complex molecules
Ultimate energy source
phototrophs: capture and transform sunlight energy
chemotrophs: get energy from oxidizing carbon fuel
Energy currency
- all “LIFE” uses ATP to link energy release and energy use
- carbon fuel oxidation generates ATP
Metabolic Pathways
- Stepwise reactions breaking down or synthesizing molecules
- Reaction types actually limited
- Often common intermediates
- Reaction types actually limited
- Typically defined by a specific substrate getting converted to a specific end point
Example: glucose into: pyruvate or acetyl-CoA or CO2, water and ATP
Intermediary Metabolism
- Pathways interact with other pathways
- All reactions within a cell considered “Intermediary Metabolism” - Traditionally studied as isolated pathways
- Then linked by defining key interaction points
- “Systems biology” is an emerging field that attempts
to study the pathways all at once
Catabolic
metabolic pathway: converts energy from fuel to ATP
ex: glycolysis
Anabolic
metabolic pathway: requires energy for synthesis
ex: gluconeogenesis
Catabolic and anabolic pathways
- share reactions (enzymes)
- but there will be key, regulated, irreversible reactions for distinct pathways
Amphibolic Pathways
- Pathways that can be catabolic or anabolic
depending on situation
- TCA Cycle convert Acetyl-CoA to energy
- TCA cycle providing carbon backbones for
synthesis
Thermodynamics of Pathways
- Each reaction must be specific in the pathway
- Overall pathway must be thermodynamically favourable
ATP: High-Energy Phosphates
- Phosphoryl groups in cellular compounds
- The hydrolysis of ATP is exergonic because the triphosphate
unit contains two phosphoanhydride bonds that are unstable - The energy released on ATP hydrolysis is used to power a host of cellular functions
ATP: Energy yield
Phosphoanhydrides have more energy than phosphoesters
- High phosphoryl-transfer potential
Four Factors that contribute to phosphoryl transfer potential
- Electrostatic repulsion
- Resonance stabilization
- Increase in entropy
- Stabilization due to hydration
Electrostatic Repulsion
- At pH 7.4, phosphates have negative charges
- Triphosphate of ATP carries 4 negative charges
- Negative charges repel each other
- Anhydride (ADP and ATP) have more repulsion
- Ester (AMP) bond has less repulsion
Resonance stabilization
- Ability to share electrons across the molecule
- More sharing = Lower energy state - Orthophosphate (Pi): Individual phosphate allows more sharing of electrons
- ATP: When phosphates have anhydride bond, the electron sharing is
reduced compared with individual phosphates
- One oxygen not able to form O=O
Increase in Entropy
- Hydrolysis of ATP generates 2 molecules instead of one molecule, which increases entropy
- A water molecule is lost?
- But the system already has a high concentration of water (55.5M)
- Losing one water molecule has essentially no effect
Stabilization due to Hydration
- Ability of water to hydrogen bond to molecule
- More hydrogen bonds possible with ADP and Pi versus ATP
- More stabilization
- Inhibits reverse reaction to form ATP
ATP: Energy yield
High phosphoryl-transfer potential
- Ability to transfer phosphate groups
- ATP has phosphoryl-transfer potential that is intermediate
- Act as a carrier of phosphoryl groups
Clinical Insight: Exercise and Energy
Resting muscle [ATP] = 4mM
[Creatine phosphate] = 25mM
- Amount of muscle ATP used rapidly
- Higher amount of creatine phosphate
- Creatine phosphate has high phosphoryl-transfer potential
- Buffers (regenerates) ATP; eventually creatine phosphate depleted
- Anaerobic support
- Followed by increasing need for aerobic support
Carbon Oxidation is Paired with
- Oxidation reactions involve loss of electrons; must be paired with reactions that gain electrons, reduction reactions
- carbon atoms in fuels are oxidized to yield CO2, and the electrons are ultimately
accepted by oxygen to form H2O. - more reduced a carbon atom is, the more free energy is released upon oxidation.
What is a more efficient food source
- Fats are a more efficient food source than glucose because fats are more reduced
