1
Q
C-H bonds and Red-Ox
A
- Increase in C-H bonds = reduction
- Decrease in C-H bonds = oxidation
2
Q
Reduction and Oxidation
A
- Also applies to partial shift of electrons (formation of polar covalent bonds)
- Oxidation (loss of electrons, dehydrogenation)
- Reduction (gain of electron and H atom, hydrogenation)
3
Q
What is Free Energy Change (delta G)
A
- Gibbs free energy: amount of energy in a system available to ‘do work’ (energy contained in bonds of molecule)
- Delta G: change in free energy in transition from one molecule to another
4
Q
Exergonic reactions
A
- -ve Delta G
- Energetically favourable (increase disorder)
- Decrease free energy of system
- Net release of energy
- Reactants contain more energy than products
5
Q
Endergonic reactions
A
- +ve delta G
- Requires input of energy
- Since cells must carry out anabolic rxns: by coupling (consecutive rxns) to exergonic rxns)
- Products contain more energy than reactants
6
Q
What compounds have high energy bonds?
A
- Phosphorylated carbon compounds and ATP
- Have large -ve delta G when hydrolyzed
7
Q
Activation of energy carriers
A
- Transfer of H and an electron (H-, hydride ion) to carrier results in reduction
- High energy electron can now be transferred when needed
8
Q
Activated carrier molecules
A
- Small molecules that temporarily store energy in form that can be transferred to metabolic rxns
- Readily transferable chemical groups/high energy electrons
- Provide energy for biosynthetic (+ve delta G) rxn
- e.g. ATP, acetyl CoA, NADH
9
Q
Enzymes + activation energy
A
- Enzymes can greatly accelerate an energetically favourable rxn but cannot force an energetically unfavourable rxn (without coupling)
- Bind reactants (substrates) and accelerate their conversion to products
10
Q
How do cells avoid rxn equilibrium (delta G = 0)
A
- Exchange of materials w/ environment
- Products of one reaction being substrates in another
11
Q
How do enzymes catalyze a rxn?
A
- Substrates bind to the active site
- Interactions btw substrates + amino acids at active sites facilitate conversion of substrates to products (AE lowered, enzyme changes shape)
- Products have low affinity at active site so they are released + enzyme returns to original shape
12
Q
Enzyme cofactors
A
- Help enzymes carry out some chemistry required for cell f(x)
- Inorganic –> metal ions (e.g. zinc, manganese)
- Organic –> coenzymes: shuttling of electrons + protons (NADH) (many vitamins are a part of coenzymes)
- Coenzymes are chemically changed during rxn –> must be regenerated to complete catalytic cycle
13
Q
Regulatory molecules (enzyme)
A
- Bind to enzyme + change its reactivity
- 2 types of regulation: allosteric + competitive
14
Q
Competitive inhibition
A
- Inhibitor competes w/ substrate to bind to active site; substrate cannot bind
- Can be overcome by increasing [substrate]
15
Q
Allosteric (non-competitive inhibition)
A
- Inhibitor may bind to site away from active site, changing enzyme’s conformation so substrate can no longer bind
- Non-competitive inhibitor binds to allosteric site
- Can’t be overcome by excess substrate
16
Q
Covalent modification (enzyme regulation)
A
- Covalent modification of enzyme by functional groups
- Enzyme changes shape –> changes activity
- Most often phosphorylation at -OH containing side chains
17
Q
What is a hydride ion (H-)?
A
- Compound transferred to NAD+ in a reduction rxn
- H atom with extra electron
- Anion of hydrogen
18
Q
After TCA cycle and before ETC + oxidative phosphorylation, in what form is most of the energy from glucose?
A
NADH molecules (“loaded” energy carriers)
19
Q
Substrate level phosphorylation
A
- Formation of ATP (endergonic) coupled to exergonic rxns
- Immediate production of a few ATP during glycolysis
20
Q
Oxidative phosphorylation
A
- (aerobic respiration)
- Series of redox rxns leading to transfer of electrons into activated carriers
- energy from activated carriers used to pump H+ across a membrane
- protons allowed back across (diffusing down gradient) and run ATP synthase
21
Q
Where does glycolysis occur?
A
Cytosol
22
Q
Where does TCA cycle occur?
A
Mitochondrial matrix
23
Q
Where does oxidative phosphorylation occur?
A
Mitochondrial matrix/intermembrane space (H+ pumped there)
24
Q
Where does pyruvate oxidation occur?
A
Mitochondrial matrix
25
Main events of glycolysis
- Energy investment (2 ATP spent to make glucose more reactive)
- Cleavage (doubly phosphorylated sugar is split)
- Energy generation (each 3C sugar joins with free phosphate --> more reactive)
- 2 phosphate groups on each sugar transferred to ATP
- Results in 2 pyruvate per glucose
26
Fermentation
- Goal: to reduce (regenerate) NAD+ for glycolysis to continue
- In absence of oxygen/anaerobic conditions
27
Pyruvate oxidation
- Decarboxylation rxn (taking off a C from pyruvate)
- NAD+ reduced to NADH
- Activating 2-carbon acyl groups using coenzyme A
28
TCA Cycle
- 2 carbon acyl unit (from acetyl CoA) binds to oxaloacetate to form 6 carbon unit (citrate)
- NAD+ and FAD reduced to NADH and FADH2
- Oxaloacetate must be regenerated through cycle to start again
29
ETC
- Series of molecules imbedded in inner mitochondrial membrane (protein complexes)
- NADH reduce protein complexes (hydride ion, H-)
- Protein complexes pump H+ into intermembrane space (forming electrochemical gradient)
- Oxygen is final electron acceptor at last complex, binds with H to form water
30
Proton Motive Force
- Storage of energy as a combo of voltage + proton gradients across membrane
31
ATP Synthase
- Protons pass through to matrix (due to gradient), causing ATP synthase to spin --> catalyze conversion of ADP to ATP
- ATP synthase phosphorylates ADP to form ATP
32
Why regulate phosphofructokinase?
- Conversion of fructose 6-PO4 --> fructose 1,6-bisPO4 is so energetically favourable, it cannot be reversed (commitment to glycolysis)
33
What inhibits phosphofructokinase?
High levels of ATP
- Two ATP binding sites (active site, allosteric site)
- High [ATP] --> binds at regulatory site --> enzyme changes shape (reduced activity)
34
Regulation in TCA cycle
- Feedback inhibition by products of TCA cycle (NADH, ATP, acetyl CoA)
35
Roles of Acetyl CoA
- High [ATP] = oxidative pathway inhibited (cells make fatty acids --> store fat), synthesis of energy storage molecules (carbs, fats)
- Low [ATP] = oxidative pathway predominates (production of ATP)
