Lecture 12: Energy Metabolism

Question 1

What type of reactions do energy metabolism involve?

Answer 1

catabolic reactions

Question 2

What are catabolic pathways?

Answer 2

Breakdown of macromolecules from food or storage.

Question 3

What are two reasons why catabolic reactions are necessary in cells?

Answer 3

Reason 1: Produce building blocks to make other organic molecules.
Reason 2: Produce energy carriers to power cellular work.

Question 4

What are energy carriers?

Answer 4

nucleoside triphosphates (e.g., ATP)
and electron carriers (e.g., NAD)

Question 5

(review) What are three main type of work that a cell needs to carry out?

Answer 5

1. Synthesis
2. Movement
3. Transport

Question 6

How do energy carriers power cellular work?

Answer 6

by coupling endergonic processes to exergonic processes.

Question 7

Most energy coupling in cells is mediated by the hydrolysis of _____ .

Answer 7

ATP

Question 8

Can ATP be reused? How do you name this type of ressource?

Answer 8

Yes, ATP is a renewable resource.

Question 9

Illustrate the regeneration of ATP

Answer 9

Question 10

What are the three ways ATP can be made?

Answer 10

1. Substrate-Level Phosphorylation
2. Oxidative Phosphorylation (in cellular respiration)
3. Photophosphorylation (in photosynthesis ;covered later)

Question 11

What is substrate level phosphorylation?

Answer 11

Enzyme directly transfers a phosphate from a higher energy phosphorylated molecule (such as phosphoenolpyruvic acid) to ADP to form ATP.

Question 12

What is oxidative Phosphorylation?

Answer 12

H+ electrochemical gradient is used to make ATP from ADP and Pi by ATP synthase.

Question 13

What established the H+ electrochemical gradient necessary for ATP synthesis in oxydative phosphorylation?

Answer 13

by spontaneous redox reactions in an electron transport chain (ETC)

Question 14

Where do the electrons necessary for ATP synthesis in oxydative phosphorylation come from?

Answer 14

From Energy (electron) carriers NADH and FADH2 that act as electron donors to the chain.

Question 15

Where does oxidative phosphorylation happen?

Answer 15

during cellular respiration, in the mitochondrion’s mitochondrial matrix and intermembrane space

Question 16

What is phosphorylation potential?

Answer 16

likelihood to transfer their phosphate group to another molecule.

based on the ΔG of the hydrolysis reaction (release of inorganic phosphate).

Question 17

Where is ATP in the overall phosphorylation potential spectrum?

Answer 17

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

Question 18

How do you determine if a phosphorylated molecule can transfer a phosphate group to another molecule?

Answer 18

Phosphorylated molecules readily transfer a phosphate group to other molecules with a lower phosphorylation potential.

Question 19

Why is ATP’s standard free energies of hydrolysis not too high and not too low?

Answer 19

Because it can couple with low energy reactions to make them exergonic but is lower enough so it can be regenerated

Question 20

The more the standard free energy of hydrolysis for phosphorylated compounds is _________, the _______ is it’s phosphorylation potential.

Answer 20

exergonic (negative)

higher

Question 21

Is ΔG of hydrolysis positive or negative?

Answer 21

negative

Question 22

What are another type of energy carrier other than ATP in cells?

Answer 22

electron carriers

Question 23

Is transfer of electrons by electron carriers to other molecules endergonic or exergonic?

Answer 23

exergonic

Question 24

What type of reaction is transfer of electrons?

Answer 24

redox reaction

Question 25

Why do we call electron carriers "energy carriers"?

Answer 25

The energy released by electron transfer is used to power cellular work.

Question 26

What is a redox reaction?

Answer 26

Reduction–oxidation reactions (redox reactions) are chemical reactions that involve **electron transfers**.

Question 27

In redox reactions, can electrons get *lost*?

Answer 27

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.

Question 28

A molecule or an atom is _______ [reduced/oxidized] when it gains an electron.

Answer 28

reduced

Question 29

A molecule or an atom is _______ [reduced/oxidized] when it loses an electron.

Answer 29

oxidized

Question 30

What is a *complete* electron transfer?

Answer 30

When electrons are completely transferred from one atom to another during a redox reaction

Question 31

What is a *relative* electron transfer? What does this do to the reactants and products energy levels? (card to be verified)

Answer 31

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.

Question 32

Which metabolic process is this?

Answer 32

photosynthesis

Question 33

Is a reduced molecule higher or lower in energy than its unreduced form? Why?

Answer 33

The reduced molecule has **more C-H bonds** and **higher chemical energy**. Reducing carbon requires energy.

Question 34

What accompanies each electron when transferred, during redox reactions?

Answer 34

* Each electron transfer from one molecule to another during a redox reaction is usually accompanied by a proton (H+).

Question 35

What process is this?

Answer 35

cellular respiration

Question 36

Do electron carrier have high or low energy?

Answer 36

high

Question 37

What do transfer of electrons by electron carriers to acceptor molecules are used for?

Answer 37

to drive endergonic processes: A. Synthesis work B. Transport work

Question 38

What are the two most important electron carriers in energy metabolism?

Answer 38

the nucleotide coenzymes NAD and FAD.

Question 39

NADH is the ________ [reduced/oxidized] form while NAD+ is the ________ [reduced/oxidized] form of NAD.

Answer 39

reduced; oxidized

Question 40

Is NAD+ or NADH the electron carrier?

Answer 40

* NADH is an electron carrier. * NADH is the reduced form while NAD+ is the oxidized form of NAD.

Question 41

What does NAD stand for?

Answer 41

Nicotinamide adenine dinucleotide

Question 42

What does FAD stand for?

Answer 42

Flavin adenine dinucleotide

Question 43

FADH2 is the ________ [reduced/oxidized] form while FAD is the ________ [reduced/oxidized] form of FAD.

Answer 43

reduced; oxydized

Question 44

Where do NADH and FADH stand on the overall spectrum of reduction potential among molecules?

Answer 44

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.

Question 45

What is another name for *reduction potential*?

Answer 45

reducing power

Question 46

What is reduction potential?

Answer 46

likelihood to transfer their electron(s) to another molecule.

Question 47

What is reduction potential based on?

Answer 47

the ΔG of the redox reaction

Question 48

How do you tell if an electron carrier will transfer its electrons to another molecule?

Answer 48

Electron carriers readily transfer electrons to other molecules with a lower reduction potential.

Question 49

What is non-biological oxidation?

Answer 49

Oxidation of glucose by combustion would release energy but that energy would be lost as heat and light.

Question 50

What is biological reduction?

Answer 50

reduced organic molecules are oxidized in a **series of steps** of redox reactions

Question 51

How are high energy electrons controlled in biological oxidation?

Answer 51

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

Question 52

In what process does stored energy by each reduced electron carrier is used?

Answer 52

oxidative phosphorylation

Question 53

How efficient is the capture of total energy from glucose in cellular respiration?

Answer 53

in cellular respiration is about **30-40% efficient**