Midterm III

Question 1

What is a coenzyme?

Answer 1

A small molecule that helps an enzyme work

Question 2

Coenzyme A

Answer 2

Acetyl groups that are attached by a thioester bond (which has a very negative ∆G of hydrolysis); structure H-S-CoA

Question 3

NAD+/NADH

Answer 3

Reducing power packets; many oxidation/reduction reactions in metabolism because it can transfer electrons from glucose (oxidized) to oxygen (reduced); it oxidizes other molecules and carries the electrons released; NAD+ can accept two electrons from compounds that have a higher electron transfer potential in the form of a “hydride” ion

Question 4

ATP/ADP/AMP

Answer 4

All energy packets; hydrolyze with water to break phosphoanhydride bond of the phosphate group

Question 5

Pi/PPi

Answer 5

Inorganic phosphate and inorganic pyrophosphate respectively - what is cleaved off in the hydrolysis of ATP

Question 6

Vitamin

Answer 6

A small molecule needed for life that WE CANNOT SYNTHESIZE and thus require in our diet - often coenzymes or components of coenzymes

Question 7

pathway

Answer 7

a set of enzymatic reactions in series

Question 8

thioester bond

Answer 8

single bond from a carbonyl carbon to a sulfur atom; has relatively high ∆G of hydrolysis (~7.5 kcal/mol)

Question 9

phosphoanhydride bond

Answer 9

the chemical bond between two adjacent phosphate groups; also relatively high standard free energy of hydrolysis (~7.3 kcal/mol or greater)

Question 10

group transfer potential

Answer 10

the amount of energy released when a bond to a chemical group is hydrolyzed; a chemical group can be transferred from molec. with higher group transfer potential to one with lower group transfer potential to get ∆G < 0

Question 11

electron transfer potential

Answer 11

energy released when a molecule is oxidized (transferring of electrons to another molecule)

Question 12

coupled reactions

Answer 12

reactions that are forced by the enzymatic mechanisms of metabolism to occur together - one cannot occur without the other one also occurring

Question 13

catabolic

Answer 13

metabolic reactions that break larger molecules into smaller ones

Question 14

anabolic

Answer 14

metabolic reactions that build larger molecules from smaller ones

Question 15

futile cycle

Answer 15

set of metabolic reactions that send molecules through series of intermediates and back to the original molecules without making anything useful - bulldozing through the energy source

Question 16

regulation/integration

Answer 16

regulation to refer to mechanisms that control individual metabolic pathway; integration to refer to mechanisms that coordinate the regulation of different metabolic pathways

Question 17

glycolysis

Answer 17

conversion of glucose to pyruvate

Question 18

fermentation

Answer 18

anaerobic conversion of glucose to ethanol + CO2 (yeast) or lactate (humans)

Question 19

kinase

Answer 19

an enzyme that catalyzes transfer of a phosphoryl group between ATP and another molecule

Question 20

isomerase

Answer 20

an enzyme that rearranges a molecule without adding or removing any atoms

Question 21

dehydrogenase

Answer 21

an enzyme that catalyzes transfer of a phosphoryl group between ATP and another molecule

Question 22

aldol cleavage

Answer 22

a common reaction type in metabolism that breaks a carbon-carbon bond to generate alcohol and aldehyde groups at the two new ends generated from the cleaved bond

Question 23

metabolic flux

Answer 23

the rate at which metabolites flow through a pathway

Question 24

homeostasis

Answer 24

living organisms tend to maintain themselves in a constant state. In metabolism, this means that metabolites tend to be maintained at a constant concentration despite large changes in metabolic flux

Question 25

energy charge

Answer 25

a measure of current ability of the cell to supply ATP - decrease in energy charge is typically sensed by an increase of [ADP] and/or [AMP], as these quantities increase substantially before large decreases in [ATP] occur

Question 26

first committed step

Answer 26

the first non-equilibrium reaction unique to the metabolic pathway - think PFK! It is also usually used as the control point to regulate flux through the pathway

Question 27

feedback inhibition

Answer 27

a regulatory strategy in which a metabolite inhibits activity of non-equilibrium enzyme that acts somewhere upstream - helps hold the concentration of the metabolite at a constant homeostatic concentration

Question 28

feedforward activation

Answer 28

a regulatory strategy in which a metabolite activates the activity of a non-equilibrium enzyme that acts somewhere downstream in a pathway that consumes that metabolite

Question 29

biotin

Answer 29

a coenzyme that carries activated carboxyl groups, often used by carboxylase enzymes

Question 30

substrate cycle

Answer 30

a set of reactions that use one set of enzymes to convert metabolite A to B and different enzymes to convert B back to A

Question 31

The Cori Cycle

Answer 31

Allows muscles in an animal to carry out a sprint for longer; gluconeogenesis in the liver recycles the lactate from anaerobic homolactic fermentation int he muscle back to glucose that is then returned to the muscle

Question 32

Citric Acid Cycle

Answer 32

the pathway that oxidizes the acetyl group of acetyl CoA to 2 carbon dioxides, conserving the liberated free energy for ATP production

Question 33

amphibolic

Answer 33

this describes a pathway that is used for both catabolic and anabolic purposes (such as the citric acid cycle)

Question 34

prochiral

Answer 34

describes the asymmetry of a carbon atom that makes single bonds to four substituent chemical groups, two of which are identical. Enzymes have the ability to distinguish between the two identical substituents by recognizing the subtle asymmetry - think of citrate!

Question 35

pyruvate dehydrogenase

Answer 35

a multi-enzyme complex found in mitochondria that catalyzes a 5-step reaction that bridges between glycolysis and the citric acid cycle

Question 36

thiamine

Answer 36

a coenzyme used to decarboxylate a molecule and then transfer the remainder of the molecule onto an acceptor

Question 37

lipoamide

Answer 37

a coenzyme in pyruvate dehydrogenase that accepts an acetyl group, and then transfers it to coenzyme A

Question 38

FAD

Answer 38

Flavin adenine dinucleotide: an electron carrier that functions similarly to NAD+

Question 39

glyoxylate cycle

Answer 39

a modified citric acid cycle that can occur in plants and bacteria that allows them to carry out the conversion of FATTY ACIDS to CARBOHYDRATES, something humans cannot do

Question 40

oxidative phosphorylation

Answer 40

the process in which ATP is formed as a result of the transfer of electrons from NADH or FADH2 to O2 via a series of electron carriers

Question 41

substrate level phosphorylation

Answer 41

the process in which enzymes directly transfer phosphoryl groups from substrates with high phosphoryl group transfer potential to ADP to generate ATP

Question 42

mitochondrion

Answer 42

an organelle found in eukaryotic cells that carries the machinery of oxidative phosphorylation in a series of multienzyme complexes embedded in the inner of its two membranes

Question 43

electron transport chain/respiratory chain

Answer 43

reactions carried out by complexes I through IV of oxidative phosphorylation in which electrons from NADH and succinate pass through a series of electron carriers to ultimately reduce O2 to H2O, with the free energy released by these oxidation/reduction reactions used to pump protons out of the mitochondrial matrix

Question 44

electrochemical gradient

Answer 44

a proton gradient across the inner mitochondrial membrane that stores energy in both an electrical voltage across the membrane and in a chemical concentration gradient of protons across the membrane

Question 45

proton motive force

Answer 45

the force pushing protons down their electrochemical gradient

Question 46

reduction potential

Answer 46

a measure (in V) of the affinity of various molecules for electrons.. Oxidation/reduction reactions have a negative free energy when electrons pass from a molecule with a more negative reduction potential to one with a more positive reduction potential

Question 47

Coenzyme Q

Answer 47

a lipid-soluble small molecule dissolved in they hydrophobic core of the inner mitochondrial membrane that ferries electrons from complexes I and II to complex III

Question 48

Iron Sulfur Clusters

Answer 48

found in electron transport complexes; can accept and then give up one electron at a time

Question 49

cytochromes

Answer 49

small proteins found in electron transport complexes, or existing as a separate protein (e.g., cytochrome c) that carry a heme group. The cytochrome can carry one electron by reducing the iron ion at the center of the heme, and can then give up the electron when the iron is reoxidized

Question 50

The Q cycle

Answer 50

name of the mechanism used by complex III to transfer electrons from coenzyme Q to cytochrome c while using the free energy liberated to pump protons out of the mitochondrial matrix

Question 51

phosphatase

Answer 51

enzyme that hydrolyzes inorganic phosphate group off essentially