Bk2 Ch 3 Capturing Energy

Question 1

Metabolic pathways

Answer 1

A series of enzyme-catalysed reactions in which the product of one reaction becomes the substrate (reactant) for another reaction.

Question 2

Entropy

Answer 2

A measure of the degree of disorder within any system. The second law of thermodynamics describes the tendency of things to become disordered, and states that entropy can only increase in the Universe.

Question 3

Catabolism

Answer 3

The sum of enzymatic processes by which foodstuffs (organic molecules) are broken down into smaller molecules, yielding energy for the cell. Opposite of anabolism.

Question 4

Anabolism

Answer 4

The synthetic processes that build the molecules of which cells are comprised from smaller components. Opposite of catabolism.

Question 5

endergonic

Answer 5

Term used to describe a reaction or process which requires a net input of energy.

Question 6

Exergonic

Answer 6

Term used to describe a reaction or process which liberates energy.

Question 7

Free energy (G)

Answer 7

The total amount of energy in a system that can be used to do work; also referred to as Gibbs free energy (G) after Josiah Willard Gibbs, an American mathematical physicist, who defined the term in 1878.

Energetically favourable exergonic ^G negative

Energetically unfavourable endergonic ^G +ve

Question 8

Coupled

Answer 8

Term used to describe how an energetically unfavourable reaction can be paired with an energetically favourable one with a negative ΔG that is large enough to offset the positive ΔG of the unfavourable reaction. Thus, overall ΔG for the coupled reactions is negative.

Question 9

Phototrophy

Answer 9

Meaning ‘light-feeders’, this term describes organisms such as higher plants, algae, cyanobacteria and many other photosynthetic prokaryotes that are capable of photosynthesis (i.e. they can convert light energy from the Sun into chemical energy in the form of ATP and then use the ATP in anabolic reactions to synthesise organic molecules. The majority of phototrophs use carbon dioxide as a source of carbon from which they synthesise organic compounds (such organisms are called photoautotrophs); however others (called photoheterotrophs) get their carbon from organic molecules in their surroundings (e.g. some prokaryotes such as Rhodobacter).

Question 10

Anabolic reactions

Answer 10

Chemical reactions in which simpler substances are combined to build more complex molecules. Energy is required for these reactions.

Question 11

Organic molecules

Answer 11

Molecules which contain carbon atoms, typically linked together in rings or chains.

Question 12

Photosynthesis

Answer 12

The biochemical process by which plants, certain protists and some bacteria synthesise carbohydrates from carbon dioxide and water using light as an energy source. Oxygen is produced as a by-product.

Question 13

Carriers

Answer 13

Also called transporters, these multipass transmembrane proteins transfer small specific polar molecules and ions across membranes. The lipid impermeability to the transported substance is masked by combining it with the membrane-soluble carrier protein. They bind to a solute molecule (or ion) and release it on the other side of the membrane. Carrier-mediated transport can be either passive or active.

Question 14

Photoautotroph

Answer 14

Type of organism that obtains energy from the sun and is able to use the ATP that it makes by photosynthesis to fuel the synthesis of all its organic molecules from carbon dioxide; includes plants, algae, cyanobacteria and many other photosynthetic prokaryotes.

Question 15

Chemoautotroph

Answer 15

Type of organism that uses inorganic ions or inorganic molecules (such as hydrogen sulfide or hydrogen gas) as a source of energy, and uses carbon dioxide as a source of carbon; examples are prokaryotes such as Sulfolobus and the methanogens.

Question 16

Photoheterotroph

Answer 16

Type of organism that obtains energy from the sun and its carbon in the form of organic molecules from their surroundings; includes some prokaryotes such as Rhodobacter.

Question 17

Chemoheterotroph

Answer 17

Type of organism that uses organic molecules from other living or dead organic matter obtained in their diet as a source of both chemical energy and carbon; includes all animals, fungi, protists and many prokaryotes.

Question 18

Equilibrium

Answer 18

In a reversible reaction, chemical equilibrium is reached when the rate of the forward reaction equals the rate of the reverse reaction and hence there is no net change in the levels of the different components. Equilibrium is only achieved in an isolated system, where there is no input of reactants or removal of products.

Question 19

Oxidation

Answer 19

A reaction in which electrons are removed from the reactant. In biological systems, oxidation generally involves the removal of hydrogen atoms (i.e. a proton plus an electron) and the addition of oxygen atoms to the molecule; such reactions are exergonic (i.e. energy is released).

Oxidation is exergonic

Question 20

Reduction

Answer 20

A reaction in which electrons are added to the reactant; also usually involves addition of hydrogen atoms and loss of oxygen atoms. Reductions tend to be endergonic (i.e. energy is consumed).

Reduction is endergonic

Question 21

Redox

Answer 21

Term describing reactions that entail the oxidation of one substrate and the reduction of another.

Question 22

Aerobic respiration

Answer 22

The net effect of the reactions by which an organism uses oxygen to bring about the complete oxidation of simple organic compounds (such as carbohydrates) to carbon dioxide and water, thereby liberating the chemical energy needed to live and grow.

Question 23

Redox potential (E)

Answer 23

A measure of how attractive a reactant is to electrons; i.e. its electron affinity. Low redox potential indicates low electron affinity, so electrons will be readily transferred from a reactant with low redox potential to one with a higher redox potential. The transfer of electrons from a reactant with a low redox potential to one with a higher redox potential is exergonic and energetically favourable (ΔG is negative); conversely, transfer of electrons from a reactant with a high redox potential to one with lower redox potential is energetically unfavourable (ΔG is positive).

Question 24

Coenzymes

Answer 24

Small organic molecules that function as cofactors for enzymes that catalyse a variety of metabolic reactions; coenzymes are chemically altered (activated or inactivated) by these reactions. Activated coenzymes store energy and can transfer energy and atoms or groups of atoms between molecules, and are inactivated in the process. Examples are ATP, NAD and coenzyme A.

Question 25

Metabolites

Answer 25

The substrates, intermediates and products in metabolic pathways.

Question 26

Metabolic flux

Answer 26

The rate at which materials flow through a particular metabolic pathway, which depends on the activities of the enzymes that catalyse the various metabolic reactions in the pathway.

Question 27

Allosteric regulation

Answer 27

Mechanism by which the function of a protein is regulated by binding a specific ligand. The ligand, known as an allosteric effector, can be an activator or an inhibitor and binds to the protein at the allosteric site (from the Greek allos, meaning ‘other’ and steros, meaning ‘shape’). Binding of the effector causes the protein to change shape and thereby modifies its activity, usually by affecting its ability to interact with another ligand at another binding site, or, in the case of an enzyme, affecting its catalytic activity.

Question 28

Phosphorylation

Answer 28

The chemical addition of a phosphate group. In proteins, phosphorylation of the –OH group in the side chains of serine, threonine and tyrosine residues is catalysed by enzymes known as protein kinases; such phosphorylation is a particularly important reversible covalent modification of proteins.

Question 29

Feedback inhibition

Answer 29

Specific inhibition of an early reaction in a metabolic pathway by the product of a later reaction.

Question 30

Metabolites

Answer 30

The substrates, intermediates and products in metabolic pathways.

Question 31

Metabolic pathway

Answer 31

A series of enzyme-catalysed reactions in which the product of one reaction becomes the substrate (reactant) for another reaction.

Question 32

Metabolic flux

Answer 32

The rate at which materials flow through a particular metabolic pathway, which depends on the activities of the enzymes that catalyse the various metabolic reactions in the pathway.

Question 33

Feedback inhibition

Answer 33

Specific inhibition of an early reaction in a metabolic pathway by the product of a later reaction.

Question 34

Metabolic channelling

Answer 34

The passage of a metabolite or charged particle (such as an electron) directly from one protein complex or enzyme to another, thereby preventing its dispersion within the cell and enhancing the efficiency of the particular metabolic process.

Question 35

Oxidative phosphorylation

Answer 35

The final stage in the oxidation of glucose by aerobic respiration when the energy stored in the reduced coenzymes NADH and FADH2, which are produced during the earlier stages, is used to synthesise ATP.

Question 36

Aerobic respiration

Answer 36

The net effect of the reactions by which an organism uses oxygen to bring about the complete oxidation of simple organic compounds (such as carbohydrates) to carbon dioxide and water, thereby liberating the chemical energy needed to live and grow.

Question 37

OIL RIG

Answer 37

Oxidation is loss
Reduction is gain
(of electrons)

Question 38

Electron transport chain (ETC)

Answer 38

A series of protein complexes which act as electron carriers, passing electrons from one to another in a defined linear sequence. Such arrangements of electron carriers are involved in oxidative phosphorylation in mitochondria and in photophosphorylation in chloroplasts.

Question 39

Respiratory complexes

Answer 39

Each of the four large protein complexes of the mitochondrial electron transport chain (numbered I to IV) are referred to as respiratory complexes and consists of several proteins with associated prosthetic groups.

Question 40

Electrochemical proton gradient

Answer 40

Electrochemical gradient resulting from a difference in proton concentration across a membrane and the potential difference (membrane potential) across the membrane. Such a gradient is established across the inner mitochondrial membrane during oxidative phosphorylation in mitochondria, and across the thylakoid membrane during photophosphorylation in chloroplasts.

Question 41

Proton motive force

Answer 41

The free energy stored in an electrochemical proton gradient such as that which is established across the inner mitochondrial membrane or the thylakoid membrane in chloroplasts. It is this that drives synthesis of ATP in mitochondria and in chloroplasts.

Question 42

ATP synthase

Answer 42

A large multi-subunit enzyme that catalyses ATP synthesis from ADP and inorganic phosphate. Different forms of this enzyme are involved in oxidative phosphorylation in mitochondria (where it is situated in the inner mitochondrial membrane), and photophosphorylation in chloroplasts (where it is situated in the thylakoid membrane). In both cases, the synthesis of ATP is driven by energy released as protons move, via the synthase, down an electrochemical gradient.

Question 43

Chemiosmotic coupling

Answer 43

Coupling of electron transport and ATP synthesis by means of an electrochemical gradient.

Question 44

Fermentation

Answer 44

Metabolic pathway in which the electrons (or reducing power) extracted from the nutrient are transferred to the product of breakdown of the nutrient.

Question 45

ATP synthesis in eukaryotes by NADH and FADH2

Answer 45

When NADH passes its electrons to O2 via the ETC it is theoretically sufficient to drive the synthesis of 3 ATP. Whilst FADH2 yields 2 ATP.

Question 46

Photophosphorylation

Answer 46

Light-driven phosphorylation of ADP to make ATP. In photosynthesis, photophosphorylation is sometimes referred to as the light reactions, and, as well as producing ATP, it results in reduction of NADP+ to NADPH.

Question 47

Photosynthesis

Answer 47

The biochemical process by which plants, certain protists and some bacteria synthesise carbohydrates from carbon dioxide and water using light as an energy source. Oxygen is produced as a by-product.

Question 48

Light reactions

Answer 48

Those steps in photosynthesis that can take place only in the light (also known as photophosphorylation), in which energy from sunlight is used to synthesise ATP and reduce NADP+ to NADPH. The ATP and NADPH produced by the light reactions are used in the dark reactions of photosynthesis. Water acts as electron donor for the light reactions and is oxidised to release oxygen.

Question 49

Dark reactions

Answer 49

The steps of photosynthesis that convert carbon dioxide into carbohydrates using NADPH and ATP produced in the light reactions of photosynthesis.

Question 50

Photon

Answer 50

A discrete packet of light energy.

Question 51

Photosystem

Answer 51

Large pigment–protein complex where light harvesting and energy capture take place in the thylakoid membranes of chloroplasts. Photosystems contain a light harvesting complex (LHC) where light energy absorbed by pigments is converted into excitation energy, which is then funnelled towards a specific pair of chlorophyll molecules in a reaction centre. A high-energy electron is ejected from each of the reaction centre chlorophyll molecules and passes to an electron acceptor. There are two types of photosystem in the thylakoid membrane, termed PSI and PSII, with different electron acceptors.

Question 52

Light harvesting complex

Answer 52

Large complex of proteins and photosynthetic pigment molecules within a photosystem (a structure located in the thylakoid membranes of chloroplasts). Pigment molecules (chlorophyll) in the light harvesting complex absorb light energy (sunlight) and channel the energy towards a reaction centre in the photosystem where the photochemical reaction occurs.

Question 53

Reaction centre

Answer 53

Component of the photosystems that are found in the thylakoid membranes of chloroplasts and which are the site of the photochemical reactions. Excitation energy, derived from light energy captured by the light-harvesting complex (another component of the photosystem), is directed towards the reaction centre where it causes each of a specific pair of chlorophyll molecules to eject a high-energy electron which passes to an electron acceptor.

Question 54

Calvin cycle

Answer 54

The series of reactions in photosynthesis by which net carbon fixation is achieved in the light-independent dark reactions of photosynthesis. Also known as the C3 cycle, the Calvin cycle consumes ATP and NADPH and has three discrete stages: carboxylation, reduction and regeneration.

Question 55

Glycolysis

Answer 55

The first, anaerobic stage of glucose oxidation, in which glucose is converted into pyruvate or lactate, releasing small amounts of usable chemical energy in the form of high energy molecules like ATP. It takes place in the cytosol.

Question 56

Link reaction

Answer 56

The second stage in glucose oxidation by aerobic respiration is the link reaction, so-called because it links glycolysis and the tricarboxylic acid (TCA) cycle. It takes place in the mitochondrial matrix.

Question 57

Krebs cycle

Answer 57

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