Lecture 12: Energy Metabolism Flashcards
What type of reactions do energy metabolism involve?
catabolic reactions
What are catabolic pathways?
Breakdown of macromolecules from food or storage.
What are two reasons why catabolic reactions are necessary in cells?
Reason 1: Produce building blocks to make other organic molecules.
Reason 2: Produce energy carriers to power cellular work.
What are energy carriers?
nucleoside triphosphates (e.g., ATP)
and electron carriers (e.g., NAD)
(review) What are three main type of work that a cell needs to carry out?
- Synthesis
- Movement
- Transport
How do energy carriers power cellular work?
by coupling endergonic processes to exergonic processes.
Most energy coupling in cells is mediated by the hydrolysis of _____ .
ATP
Can ATP be reused? How do you name this type of ressource?
Yes, ATP is a renewable resource.
Illustrate the regeneration of ATP
What are the three ways ATP can be made?
- Substrate-Level Phosphorylation
- Oxidative Phosphorylation (in cellular respiration)
- Photophosphorylation (in photosynthesis ;covered later)
What is substrate level phosphorylation?
Enzyme directly transfers a phosphate from a higher energy phosphorylated molecule (such as phosphoenolpyruvic acid) to ADP to form ATP.
What is oxidative Phosphorylation?
H+ electrochemical gradient is used to make ATP from ADP and Pi by ATP synthase.
What established the H+ electrochemical gradient necessary for ATP synthesis in oxydative phosphorylation?
by spontaneous redox reactions in an electron transport chain (ETC)
Where do the electrons necessary for ATP synthesis in oxydative phosphorylation come from?
From Energy (electron) carriers NADH and FADH2 that act as electron donors to the chain.
Where does oxidative phosphorylation happen?
during cellular respiration, in the mitochondrion’s mitochondrial matrix and intermembrane space
What is phosphorylation potential?
likelihood to transfer their phosphate group to another molecule.
based on the ΔG of the hydrolysis reaction (release of inorganic phosphate).
Where is ATP in the overall phosphorylation potential spectrum?
ATP occupies an intermediate position in the overall spectrum
ATP can serve as a phosphate donor in some biological reactions and its dephosphorylated form, ADP, can serve as a phosphate acceptor in other reactions
How do you determine if a phosphorylated molecule can transfer a phosphate group to another molecule?
Phosphorylated molecules readily transfer a phosphate group to other molecules with a lower phosphorylation potential.
Why is ATP’s standard free energies of hydrolysis not too high and not too low?
Because it can couple with low energy reactions to make them exergonic but is lower enough so it can be regenerated
The more the standard free energy of hydrolysis for phosphorylated compounds is _________, the _______ is it’s phosphorylation potential.
exergonic (negative)
higher
Is ΔG of hydrolysis positive or negative?
negative
What are another type of energy carrier other than ATP in cells?
electron carriers
Is transfer of electrons by electron carriers to other molecules endergonic or exergonic?
exergonic
What type of reaction is transfer of electrons?
redox reaction
Why do we call electron carriers “energy carriers”?
The energy released by electron transfer is used to power cellular work.
What is a redox reaction?
Reduction–oxidation reactions (redox reactions) are chemical reactions that involve electron transfers.
In redox reactions, can electrons get lost?
no since oxidation and reduction events are always coupled—if one atom loses an electron, another atom has to gain it.
Electron donors are always paired with electron acceptors.
A molecule or an atom is _______ [reduced/oxidized] when it gains an electron.
reduced
A molecule or an atom is _______ [reduced/oxidized] when it loses an electron.
oxidized
What is a complete electron transfer?
When electrons are completely transferred from one atom to another during a redox reaction
What is a relative electron transfer? What does this do to the reactants and products energy levels? (card to be verified)
During a redox reaction, electrons can simply shift their position in covalent bonds.
These shifts in electron position change the amount of chemical energy in products and reactants.
Which metabolic process is this?
photosynthesis
Is a reduced molecule higher or lower in energy than its unreduced form? Why?
The reduced molecule has more C-H bonds and higher chemical energy.
Reducing carbon requires energy.
What accompanies each electron when transferred, during redox reactions?
- Each electron transfer from one molecule to another during
a redox reaction is usually accompanied by a proton (H+).
What process is this?
cellular respiration
Do electron carrier have high or low energy?
high
What do transfer of electrons by electron carriers to
acceptor molecules are used for?
to drive endergonic
processes:
A. Synthesis work
B. Transport work
What are the two most important electron carriers in energy metabolism?
the nucleotide coenzymes NAD and FAD.
NADH is the ________ [reduced/oxidized] form while NAD+ is the ________ [reduced/oxidized] form of NAD.
reduced; oxidized
Is NAD+ or NADH the electron carrier?
- NADH is an electron carrier.
- NADH is the reduced form while NAD+ is the oxidized form of NAD.
What does NAD stand for?
Nicotinamide adenine dinucleotide
What does FAD stand for?
Flavin adenine dinucleotide
FADH2 is the ________ [reduced/oxidized] form while FAD is the ________ [reduced/oxidized] form of FAD.
reduced; oxydized
Where do NADH and FADH stand on the overall spectrum of reduction potential among molecules?
intermediate position:
The reduced forms can serve as an electron donors in some biological reactions and the oxidized forms can serve as an electron acceptors in other reactions.
What is another name for reduction potential?
reducing power
What is reduction potential?
likelihood to transfer their electron(s) to another molecule.
What is reduction potential based on?
the ΔG of the redox reaction
How do you tell if an electron carrier will transfer its electrons to another molecule?
Electron carriers readily transfer electrons to other molecules with a lower reduction potential.
What is non-biological oxidation?
Oxidation of glucose by combustion would release energy but that energy would be lost as heat and light.
What is biological reduction?
reduced organic molecules are oxidized in a series of steps of redox reactions
How are high energy electrons controlled in biological oxidation?
High energy electrons from the series of redox reactions are transferred to NAD+ to produce NADH or FAD to produce FADH2.
There is controlled release of energy “by the electrons” for the synthesis of ATP
In what process does stored energy by each reduced electron carrier is used?
oxidative phosphorylation
How efficient is the capture of total energy from glucose in cellular respiration?
in cellular respiration is about 30-40% efficient
