Ch. 13 Thermodynamics Flashcards
What attributes must reactions have to occur during metabolism? (2)
Reactions must be possible.
Reactions must be useful.
What are the five (but really 6) main types of metabolic reactions?
Reactions that make or break C-C bonds, Internal rearrangements and isomerizations, free radical reactions, group transfers, redox reactions, and phosphoryl group transfers.
What is a reaction that makes or breaks C-C bonds?
The carbon in a carbonyl carbon bond is partially positive and electrophilic, therefore it will pull electrons from its neighboring carbon creating a double bond.
What are C-C bonds all about?
All about electrophilic attack!
What are internal rearrangements and isomerizations?
When functional groups move within a molecule.
What are examples of an internal rearrangement/isomerization?
glucose-6-phosphate being converted to fructose-6-phosphate, movement of double bonds, and cis-trans isomerizations
What are free radical reactions?
A reaction where a free radical is somewhere in the reaction.
Where is the radical typically found?
Free radical can be in the intermediate, and biochemists don’t draw intermediates, so you may not see the free radical.
What are group transfers?
When a function group is leaving one molecule and being attached to another.
Why are group transfers done?
Often done to put a good leaving group on a molecule. An investment of energy to be harvested later.
What is an example of a group transfer?
Phosphorylation, methylation, acetylation, etc.
What is a redox reaction?
Oxidation-reduction reaction. Carbon is frequently being oxidized or reduced in metabolic reactions.
How do we track electrons in a redox reaction?
Electrons are always accompanied by hydrogen ions. Count hydrogen and if it is gaining hydrogen it is reduced, if it is losing hydrogen it is oxidized.
What is the main electron acceptor in redox reactions?
Nicotinamide adenine dinucleotide (NAD) accepts electrons and protons (hydrogen ion).
What is the reduced form of nicotinamide adenine dinucleotide? Oxidized form?
NAD is oxidized and NADH is reduced.
( NAD + 2e⁻ + 2H⁺ ↔ NADH⁺ + H⁺ )
What is a telltale sign that a reaction is redox?
If NAD/H or dehydrogenase are present, the reaction is a redox.
What are phosphoryl group transfers?
When a phosphate group is transferred from ATP to another molecule.
( ATP + H₂O → ADP + Pᵢ with a ΔG = -30.5 kJ/mol )
Why is phosphorylation commonly seen in metabolism reactions?
Phosphate is a good leaving group, so when it leaves the molecule it has been attached to it allows the molecule to become the intended product.
What is the phosphorylated compound considered in a phosphoryl group transfer?
Intermediate.
Why does hydrolysis of ATP occur?
The products (ADP and inorganic phosphate*) are more stable, so products are favored. This gives ATP hydrolysis a “﹣” ΔG
What is standard Gibbs free energy (ΔG°).
It is ΔG at standard conditions (1M, 1 atm, 25℃).
Why does ΔG not always match ΔG°?
All cells have different concentrations of ATP, ADP, and inorganic phosphate, so the true ΔG will different in each cell. Cells also have different internal conditions (pH, temp, etc.) which contributes to this also.
Why does the ΔG of ATP hydrolysis in erythrocytes become more positive while excersising?
Cells become acidic during exercise, as pH decreases, ATP becomes less and less energetic leading to a more positive ΔG.
(Real ΔG of erythrocytes is ⋍ -52 kJ/mol)
Can only ATP be the molecule used in/for phosphorylation?
No! Lots of molecules have a phosphate group attached to them, and there is an energy associated with cleaving the phosphate off for all of them.
