Unit 3 Test

Question 1

enzymes

Answer 1

A macromolecule serving as a catalyst, a chemical agent that increases the rate of a reaction without being consumed by the reaction. Most enzymes are proteins.

Question 2

catalyst

Answer 2

A chemical agent that selectively increases the rate of a reaction without being consumed by the reaction.

Question 3

activation energy

Answer 3

The amount of energy that reactants must absorb before a chemical reaction will start; also called free energy of activation.

Question 4

substrate

Answer 4

The reactant on which an enzyme works.

Question 5

active site

Answer 5

The specific region of an enzyme that binds the substrate and that forms the pocket in which catalysis occurs.

Question 6

induced fit

Answer 6

Caused by entry of the substrate, the change in shape of the active site of an enzyme so that it binds more snugly to the substrate.

Question 7

cofactors

Answer 7

Any nonprotein molecule or ion that is required for the proper functioning of an enzyme. Cofactors can be permanently bound to the active site or may bind loosely and reversibly, along with the substrate, during catalysis.

Question 8

coenzyme

Answer 8

An organic molecule serving as a cofactor. Most vitamins function as coenzymes in metabolic reactions.

Question 9

competitive inhibitor

Answer 9

A substance that reduces the activity of an enzyme by entering the active site in place of the substrate, whose structure it mimics.

Question 10

noncompetitive inhibitor

Answer 10

A substance that reduces the activity of an enzyme by binding to a location remote from the active site, changing the enzyme’s shape so that the active site no longer effectively catalyzes the conversion of substrate to product.

Question 11

allosteric regulation

Answer 11

The binding of a regulatory molecule to a protein at one site that affects the function of the protein at a different site.

Question 12

cooperativity

Answer 12

A kind of allosteric regulation whereby a shape change in one subunit of a protein caused by substrate binding is transmitted to all the other subunits, facilitating binding of additional substrate molecules to those subunits.

Question 13

feedback inhibition

Answer 13

A method of metabolic control in which the end product of a metabolic pathway acts as an inhibitor of an enzyme within that pathway.

Question 14

metabolic pathways

Answer 14

A series of chemical reactions that either builds a complex molecule (anabolic pathway) or breaks down a complex molecule to simpler molecules (catabolic pathway).

Question 15

cellular respiration

Answer 15

The catabolic pathways of aerobic and anaerobic respiration, which break down organic molecules and use an electron transport chain for the production of ATP.

Question 16

aerobic respiration

Answer 16

A catabolic pathway for organic molecules, using oxygen (O2) as the final electron acceptor in an electron transport chain and ultimately producing ATP. This is the most efficient catabolic pathway and is carried out in most eukaryotic cells and many prokaryotic organisms.

Question 17

fermentation (anaerobic)

Answer 17

A catabolic pathway in which inorganic molecules other than oxygen accept electrons at the “downhill” end of electron transport chains. // A catabolic process that makes a limited amount of ATP from glucose (or other organic molecules) without an electron transport chain and that produces a characteristic end product, such as ethyl alcohol or lactic acid.

Question 18

redox reactions

Answer 18

A chemical reaction involving the complete or partial transfer of one or more electrons from one reactant to another; short for reduction-oxidation reaction.

Question 19

oxidation

Answer 19

The complete or partial loss of electrons from a substance involved in a redox reaction.

Question 20

reduction

Answer 20

The complete or partial addition of electrons to a substance involved in a redox reaction.

Question 21

NAD+/NADH

Answer 21

The oxidized form of nicotinamide adenine dinucleotide, a coenzyme that can accept electrons, becoming NADH. NADH temporarily stores electrons during cellular respiration. // The reduced form of nicotinamide adenine dinucleotide that temporarily stores electrons during cellular respiration. NADH acts as an electron donor to the electron transport chain.

Question 22

FADH/FADH2

Answer 22

a redox cofactor that is created during the Krebs cycle and utilized during the last part of respiration, the electron transport chain

Question 23

oxidative phosphorylation

Answer 23

The production of ATP using energy derived from the redox reactions of an electron transport chain; the third major stage of cellular respiration.

Question 24

substrate-level phosphorylation

Answer 24

The enzyme-catalyzed formation of ATP by direct transfer of a phosphate group to ADP from an intermediate substrate in catabolism.

Question 25

glycolysis

Answer 25

A series of reactions that ultimately splits glucose into pyruvate. Glycolysis occurs in almost all living cells, serving as the starting point for fermentation or cellular respiration.

Question 26

pyruvate (pyruvic acid)

Answer 26

nd product of glycolysis, which is converted into acetyl coA that enters the Krebs cycle when there is sufficient oxygen available. But when the oxygen is insufficient, pyruvate is broken down anaerobically, such as in fermentation that creates lactate or ethanol as an end-product

Question 27

acetyl CoA

Answer 27

Acetyl coenzyme A; the entry compound for the citric acid cycle in cellular respiration, formed from a two-carbon fragment of pyruvate attached to a coenzyme.

Question 28

citric acid (krebs) cycle

Answer 28

A chemical cycle involving eight steps that completes the metabolic breakdown of glucose molecules begun in glycolysis by oxidizing acetyl CoA (derived from pyruvate) to carbon dioxide; occurs within the mitochondrion in eukaryotic cells and in the cytosol of prokaryotes; together with pyruvate oxidation, the second major stage in cellular respiration.

Question 29

electron transport chain

Answer 29

A sequence of electron carrier molecules (membrane proteins) that shuttle electrons down a series of redox reactions that release energy used to make ATP.

Question 30

chemiosmosis

Answer 30

An energy-coupling mechanism that uses energy stored in the form of a hydrogen ion gradient across a membrane to drive cellular work, such as the synthesis of ATP. Under aerobic conditions, most ATP synthesis in cells occurs by chemiosmosis.

Question 31

ATP synthase

Answer 31

A complex of several membrane proteins that functions in chemiosmosis with adjacent electron transport chains, using the energy of a hydrogen ion (proton) concentration gradient to make ATP. ATP synthases are found in the inner mitochondrial membranes of eukaryotic cells and in the plasma membranes of prokaryotes.

Question 32

proton-motive force

Answer 32

The potential energy stored in the form of a proton electrochemical gradient, generated by the pumping of hydrogen ions (H+) across a biological membrane during chemiosmosis.

Question 33

alcohol fermentation

Answer 33

Glycolysis followed by the reduction of pyruvate to ethyl alcohol, regenerating NAD+ and releasing carbon dioxide.

Question 34

lactic acid fermentation

Answer 34

Glycolysis followed by the reduction of pyruvate to lactate, regenerating NAD+ with no release of carbon dioxide.

Question 35

obligate anaerobes

Answer 35

An organism that carries out only fermentation or anaerobic respiration. Such organisms cannot use oxygen and in fact may be poisoned by it.

Question 36

facultative anaerobes

Answer 36

An organism that makes ATP by aerobic respiration if oxygen is present but that switches to anaerobic respiration or fermentation if oxygen is not present.

Question 37

photosynthesis

Answer 37

The conversion of light energy to chemical energy that is stored in sugars or other organic compounds; occurs in plants, algae, and certain prokaryotes.

Question 38

autotroph

Answer 38

An organism that obtains organic food molecules without eating other organisms or substances derived from other organisms. Autotrophs use energy from the sun or from oxidation of inorganic substances to make organic molecules from inorganic ones.

Question 39

heterotroph

Answer 39

An organism that obtains organic food molecules by eating other organisms or substances derived from them.

Question 40

chlorophyll

Answer 40

A green pigment located in membranes within the chloroplasts of plants and algae and in the membranes of certain prokaryotes. Chlorophyll a participates directly in the light reactions, which convert solar energy to chemical energy.

Question 41

mesophyll

Answer 41

Leaf cells specialized for photosynthesis. In C3 and CAM plants, mesophyll cells are located between the upper and lower epidermis; in C4 plants, they are located between the bundle-sheath cells and the epidermis.

Question 42

stomata

Answer 42

pores created by the swelling of guard cells to allow CO2 to enter into the leaf. Water vapor and O2 are also allowed to escape via the pore.

Question 43

guard cells

Answer 43

The two cells that flank the stomatal pore and regulate the opening and closing of the pore.

Question 44

stroma

Answer 44

The dense fluid within the chloroplast surrounding the thylakoid membrane and containing ribosomes and DNA; involved in the synthesis of organic molecules from carbon dioxide and water.

Question 45

thylakoids

Answer 45

A flattened, membranous sac inside a chloroplast. Thylakoids often exist in stacks called grana that are interconnected; their membranes contain molecular “machinery” used to convert light energy to chemical energy.

Question 46

light reactions

Answer 46

The first of two major stages in photosynthesis (preceding the Calvin cycle). These reactions, which occur on the thylakoid membranes of the chloroplast or on membranes of certain prokaryotes, convert solar energy to the chemical energy of ATP and NADPH, releasing oxygen in the process.

Question 47

calvin cycle

Answer 47

The second of two major stages in photosynthesis (following the light reactions), involving fixation of atmospheric CO2 and reduction of the fixed carbon into carbohydrate.

Question 48

NADP+/NADPH

Answer 48

The oxidized form of nicotinamide adenine dinucleotide phosphate, an electron carrier that can accept electrons, becoming NADPH. NADPH temporarily stores energized electrons produced during the light reactions. // The reduced form of nicotinamide adenine dinucleotide phosphate; temporarily stores energized electrons produced during the light reactions. NADPH acts as “reducing power” that can be passed along to an electron acceptor, reducing it.

Question 49

photophosphorylation

Answer 49

The process of generating ATP from ADP and phosphate by means of chemiosmosis, using a proton-motive force generated across the thylakoid membrane of the chloroplast or the membrane of certain prokaryotes during the light reactions of photosynthesis.

Question 50

carbon fixation

Answer 50

The initial incorporation of carbon from CO2 into an organic compound by an autotrophic organism (a plant, another photosynthetic organism, or a chemoautotrophic prokaryote).

Question 51

electromagnetic spectrum

Answer 51

The entire spectrum of electromagnetic radiation, ranging in wavelength from less than a nanometer to more than a kilometer.

Question 52

wavelength

Answer 52

The distance between crests of waves, such as those of the electromagnetic spectrum.

Question 53

visible light

Answer 53

That portion of the electromagnetic spectrum that can be detected as various colors by the human eye, ranging in wavelength from about 380 nm to about 740 nm.

Question 54

photons

Answer 54

A quantum, or discrete quantity, of light energy that behaves as if it were a particle.

Question 55

absorption spectrum

Answer 55

The range of a pigment’s ability to absorb various wavelengths of light; also a graph of such a range.

Question 56

action spectrum

Answer 56

A graph that profiles the relative effectiveness of different wavelengths of radiation in driving a particular process.

Question 57

carotenoids

Answer 57

An accessory pigment, either yellow or orange, in the chloroplasts of plants and in some prokaryotes. By absorbing wavelengths of light that chlorophyll cannot, carotenoids broaden the spectrum of colors that can drive photosynthesis.

Question 58

photosystem I and II

Answer 58

A light-capturing unit in a chloroplast’s thylakoid membrane or in the membrane of some prokaryotes; it has two molecules of P700 chlorophyll a at its reaction center. // One of two light-capturing units in a chloroplast’s thylakoid membrane or in the membrane of some prokaryotes; it has two molecules of P680 chlorophyll a at its reaction center.

Question 59

reaction-center complex

Answer 59

A complex of proteins associated with a special pair of chlorophyll a molecules and a primary electron acceptor. Located centrally in a photosystem, this complex triggers the light reactions of photosynthesis. Excited by light energy, the pair of chlorophylls donates an electron to the primary electron acceptor, which passes an electron to an electron transport chain.

Question 60

light-harvesting complex

Answer 60

A complex of proteins associated with pigment molecules (including chlorophyll a, chlorophyll b, and carotenoids) that captures light energy and transfers it to reaction-center pigments in a photosystem.

Question 61

rubisco

Answer 61

Ribulose bisphosphate (RuBP) carboxylase-oxygenase, the enzyme that normally catalyzes the first step of the Calvin cycle (the addition of CO2 to RuBP). When excess O2 is present or CO2 levels are low, rubisco can bind oxygen, resulting in photorespiration.

Question 62

glyceralhehyde-3-phosphate (G3P)

Answer 62

A three-carbon carbohydrate that is the direct product of the Calvin cycle; it is also an intermediate in glycolysis.

Question 63

C3 and C4 plants

Answer 63

A plant that uses the Calvin cycle for the initial steps that incorporate CO2 into organic material, forming a three-carbon compound as the first stable intermediate. // A plant in which the Calvin cycle is preceded by reactions that incorporate CO2 into a four-carbon compound, the end product of which supplies CO2 for the Calvin cycle.

Question 64

CAM plants

Answer 64

A plant that uses crassulacean acid metabolism, an adaptation for photosynthesis in arid conditions. In this process, CO2 entering open stomata during the night is converted to organic acids, which release CO2 for the Calvin cycle during the day, when stomata are closed.