BB 16 Metabolic Energy (generation and storage) Flashcards
The overall free-energy change for a coupled series of reaction is the
sum of the free energy changes of the individual steps
A reaction can occur spontaneously only if
ΔG is negative
Three ways in which reactions can be coupled
- a shared chemical intermediate
• glycolysis and substrate level phosphorylation - An activated protein conformation
• molecular motors - Ionic (electrochemical) gradients across membranes
• oxidative phosphorylation
Energy is required for
- motion
- active transport of solutes across membranes against a gradient
- biosynthesis
- signal amplification
Energy is obtained from
- oxidation of foodstuffs (chemotrophs)
* trapping of light energy (phototrophs)
ATP is an energy carrier containing
2 phosphoanhydride bonds
ATP is an
activated carrier
• group carried is phosphoryl
Further examples of activated carriers
NADH
FADH2
• major electron carriers in the oxidation of food molecules
Chemotrophs derive free energy from
oxidation of fuel molecules such as
• glucose
• fatty acids
In aerobic organisms, the ultimate electron acceptor is
oxygen … BUT
not transferred directly to oxygen, but transferred to special electron carriers:
• pyridine nucleotides (NADH)
• flavins (FADH2)
Reduced electron carriers transfer their electrons to oxygen…
- via an electron transport chain in the inner mitochondrial matrix (IMM)
- the energy released is used to synthesize ATP (oxidative phosphorylation)
NAD+
Nicotinamide adenine dinucleotide
• major electron acceptor in the oxidation of fuel molecules
Formation of NADH
NAD+ accepts
• 1 H+
• 2 e-
NADH is used primarily for
the generation of ATP
NADPH
- reduced form of NADP+
- used for biosynthesis
- needs reducing power in addition to ATP
FAD
Flavin adenine dinucleotide
• other major electron carrier in the oxidation of fuel molecules
Reactive part of FAD
isoalloxazine ring accepts • 2 e- • 2 H+ to form FADH2
Enzymes speed the processes and
control the
• flow of free energy
.•reductive power
Activated carriers
- NADH
- NADPH
- FADH2
Most interchanges of activated groups in metabolism are accomplished by
a small set of carriers
Extraction of energy from foodstuffs
STAGE 1
large molecules of food are broken into smaller units
• proteins to amino acids
• polysaccharides to simple sugars
• fats to glycerol and fatty acids
NO USEFUL ENERGY IS GENERATED IN THIS STAGE
Extraction of energy from foodstuffs
STAGE 2
small molecules degraded to few simple units that play a central role in metabolism
• most are converted into Acetyl CoA
SOME ATP IS GENERATED IN THIS STAGE
Extraction of energy from foodstuffs
STAGE 3
citric acid cycle and oxidative phosphorylation
90% OF ATP IS GENERATED IN THIS LAST STAGE
3 ways metabolic pathways are regulated
- the amounts of enzymes
- the catalytic activities of these enzymes
- the accessibility of substrates
Metabolic pathways regulated by
amounts of enzymes
amount depends on rate of synthesis and breakdown
• amount of most enzymes regulated mostly by adjusting rate of transcription of genes encoding
them
Metabolic pathways regulated by
catalytic activity of enzymes
a) reversible allosteric control (feedback regulation)
b) reversible covalent modification (control amount of substrate capable of reaching enzyme)
Metabolic pathways regulated by
accessibility of substrates
eg controlling entry to cell
Biosynthetic and degradative pathways are
almost always DISTINCT (not the same)
• must be thermodynamically favorable = cant go back to substrates
Many reactions in metabolism are controlled by the
ENERGY STATUS of the cell
Energy charge
- one measure of the energy of the cell
* balance between the concentrations of ATP and AMP in the cell
energy charge =
[ATP] + ½ [ADP]
/
[ATP] + [ADP] + [AMP]
