Microbiology Chapter 5 Terms

Front 1

metabolism

Back 1

the sum of complex biochemical reactions within an organism, including catabolic reactions which break down nutrient molecules and release energy stored in ATP molecules (exergonic) and anabolic reactions which synthesize macromolecules and use ATP energy (endergonic).

Front 2

precursor metabolites

Back 2

Enzymes catabolize nutrients into which are rearranged by polymerization reactions to form macromolecules.

Front 3

anabolic reactions

Back 3

synthesize macromolecules and use ATP energy (endergonic).

Front 4

catabolic reactions

Back 4

break down nutrient molecules and release energy stored in ATP molecules (exergonic)

Front 5

Oxidation-reduction (redox) reactions

Back 5

involve the transfer of electrons. These reactions always occur simultaneously because an electron gained by one molecule is donated by another molecule.The electron acceptor is said to be reduced. The molecule that loses an electron is oxidized. If the electron is part of a hydrogen atom, the reaction is called a dehydrogenation reaction.

Front 6

Three electron carrier molecules that are often required in metabolic pathways are

Back 6

nicotinamide adenine dinucleotide (NAD+), nicotinamide adenine dinucleotide phosphate (NADP+), and flavine adenine dinucleotide (FAD).

Front 7

Energy from the chemical bonds of nutrients is concentrated in the

Back 7

high-energy phosphate bonds of ATP.

Front 8

Substrate-level phosphorylation

Back 8

describes the transfer of phosphate from a phosphorylated organic nutrient to ADP to form ATP.

Front 9

Oxidative phosphorylation

Back 9

phosphorylates ADP using inorganic phosphate and energy from respiration.

Front 10

Photophosphorylation

Back 10

is the phosphorylation of ADP with inorganic phosphate using energy from light. There is a cyclical conversion of ATP from ADP and back with the gain and loss of phosphate.

Front 11

Catalysts

Back 11

increase reaction rates of chemical reactions but are not permanently changed in the process.

Front 12

Enzymes

Back 12

organic catalysts, are often named for their substrates, which are the chemicals they cause to react. Substrates fit onto the specifically shaped active sites of enzymes.

Front 13

Enzymes are classified into six categories based on their mode of action:

Back 13

hydrolases, lyases, isomerases, ligases or polymerases, oxidoreductases, transferases

Front 14

hydrolases

Back 14

add hydrogen and hydroxide from the hydrolysis of water to split larger molecules into smaller ones

Front 15

lyases

Back 15

split molecules without using water

Front 16

isomerases

Back 16

form isomeric compounds

Front 17

ligases or polymerases

Back 17

join molecules

Front 18

oxidoreductases

Back 18

oxidize or reduce

Front 19

transferases

Back 19

transfer functional groups.

Front 20

apoenzymes

Back 20

protein portion

Front 21

cofactors

Back 21

one or more nonprotein

Front 22

Inorganic cofactors

Back 22

ions such as iron, magnesium, zinc, or copper

Front 23

Organic cofactors

Back 23

are made from vitamins and include NAD+, NADP+, and FAD. Organic cofactors are also called coenzymes.

Front 24

holoenzyme

Back 24

The combination of both apoenzyme and its cofactors

Front 25

ribozymes

Back 25

RNA molecules functioning as enzymes Ribozymes process RNA molecules in eukaryotes. Ribosomal enzymes catalyze the actual protein synthesis reactions of ribosomes; thus, ribozymes make protein enzymes.

Front 26

Activation energy

Back 26

the amount of energy required to initiate a chemical reaction. Activation energy may be supplied by heat, but high temperatures are not compatible with life; therefore, enzymes are required to lower the activation energy needed. The complementary shapes of active sites of enzymes and their substrates determine enzyme-substrate specificity. In catabolism, an enzyme binds to a substrate, forming an enzyme-substrate complex, the bonds within the substrate are broken, the enzyme separates from the two new products, and the enzyme is released to act again.

Front 27

denatured

Back 27

by physical and chemical factors such as temperature and pH, which change their shape and thus their ability to bond. The change may be reversible or permanent.

Front 28

competitive inhibitors,

Back 28

block but do not denature active sites

Front 29

allosteric inhibition, noncompetitive inhibitors

Back 29

attach to an allosteric site on an enzyme distorting the active site and halting enzymatic activity. In excitatory allosteric control, the change in the shape of the active site activates an inactive enzyme.

Front 30

Feedback inhibition (negative feedback)

Back 30

occurs when the final product of a series of reactions is an allosteric inhibitor of some previous step in the series. Thus accumulation of the end product “feeds back” a stop signal to the process.

Front 31

Glycolysis (the Embden-Meyerhof pathway)

Back 31

involves the splitting of a glucose molecule in a series of ten steps which ultimately results in two molecules of pyruvic acid and a net gain of two ATP and two NADH molecules. The ten steps of glycolysis can be divided into three stages: energy-investment, lysis, and energy-conserving.

Front 32

pentose phosphate and Entner-Doudoroff pathways

Back 32

alternative pathways for the catabolism of glucose, but they yield fewer ATP molecules than does the Embden-Meyerhof pathway. However, they produce precursor metabolites not produced in glycolysis. The pentose phosphate pathway produces metabolites used in synthesis of nucleotides, amino acids, and glucose by photosynthesis. The Entner-Doudoroff pathway, used by only a few bacteria, uses different enzymes and yields precursor metabolites and NADPH, which is not produced by the Embden-Meyerhof or pentose phosphate pathways.

Front 33

Cellular respiration

Back 33

is a three-stage metabolic process that involves oxidation of substrate molecules and production of ATP. The stages of respiration are: synthesis of acetyl-CoA, Krebs cycle, and electron transport.

Front 34

electron transport chain

Back 34

series of redox reactions that passes electrons from one membrane-bound carrier to another and then to a final electron acceptor. The energy from these electrons is used to pump protons (H+) across the membrane. Ultimately ATP is synthesized

Front 35

The four categories of carrier molecules in the electron transport system

Back 35

flavoproteins, ubiquinones, proteins containing heavy metal, and cytochromes.

Front 36

Chemiosmosis

Back 36

a mechanism in which the flow of ions down an electrochemical gradient across a membrane is used to synthesize ATP. For example, energy released during the redox reactions of electron transport is used to pump protons across a membrane, creating a proton gradient.

Front 37

proton gradient

Back 37

is an electrochemical gradient of protons that has potential energy known as a proton motive force. When protons flow down their electrochemical gradient through protein channels called ATPases, ATP is synthesized.

Front 38

ATP synthases (ATPases)

Back 38

are enzymes that synthesize ATP by oxidative phosphorylation and photophosphorylation.

Front 39

Fermentation

Back 39

is the partial oxidation of sugar to release energy using an organic molecule from within the cell as electron acceptor. In lactic acid fermentation, NADH reduces pyruvic acid from glycolysis to form lactic acid. In alcohol fermentation, pyruvic acid undergoes decarboxylation (CO2 is given off) and reduction by NADH to form ethanol. Some fermentation products are useful to health and industry while some are harmful.

Front 40

Photosynthesis

Back 40

is a process in which light energy is captured by pigment molecules (called chlorophylls) and transferred to ATP and metabolites.

Front 41

Photosystems

Back 41

photosystem I (PS I) and photosystem II (PS II), are networks of chlorophyll molecules and other pigments held within a protein matrix in membranes called thylakoids.

Front 42

Stacks of thylakoids within chloroplasts are called

Back 42

grana.

Front 43

reaction center chlorophyll

Back 43

a special chlorophyll molecule of photosystem I, which is excited by transferred energy absorbed by pigment molecules elsewhere in the photosystem.

Front 44

Excited electrons from the reaction center are passed to an acceptor of an electron transport chain, protons are pumped across the membrane, a proton motive force is created, and ATP is generated in a process called

Back 44

photophosphorylation.

Front 45

cyclic photophosphorylation

Back 45

electrons return to the original reaction center chlorophyll after passing down the electron transport chain. The resulting proton gradient produces ATP by chemiosmosis.

Front 46

noncyclic photophosphorylation

Back 46

photosystem II works with photosystem I, and the electrons are used to reduce NADP+ to NADPH. Therefore, noncyclic photophosphorylation, a cell must constantly replenish electrons to PS II. In oxygenic organisms, the electrons come from H2O. In anoxygenic organisms, the electrons come from inorganic compounds such as H2S.

Front 47

Calvin-Benson cycle

Back 47

of the light-independent pathway occurs in three steps: carbon fixation in which CO2 is reduced; reduction by NADPH to form molecules of G3P, which join to form glucose; and regeneration of RuBP to continue the cycle.

Front 48

Amphibolic reactions

Back 48

are metabolic reactions that can proceed toward catabolism or toward anabolism depending on the needs of the cell. Examples are found in the biosynthesis of carbohydrates, lipids, amino acids, and nucleotides.

Front 49

Gluconeogenesis

Back 49

refers to metabolic pathways that produce sugars, starch, cellulose, glycogen, peptidoglycan, etc. from noncarbohydrate precursors such as amino acids, glycerol, and fatty acids.

Front 50

Amino acids are synthesized by

Back 50

amination

Front 51

by transamination

Back 51

a reversible reaction in which an amine group is transferred from one amino acid to another by the action of enzymes using coenzyme pyridoxal phosphate.

Front 52

Nucleotides are produced from

Back 52

precursor metabolites derived from glycolysis and the Krebs cycle: ribose and deoxyribose from ribose-5 phosphate, phosphate from ATP, and purines and pyrimidines from the amino acids glutamine and aspartic acid

Front 53

The pathways of cellular metabolism can be categorized into three groups

Back 53

pathways synthesizing macromolecules (proteins, nucleic acids, polysaccharides, and lipids), intermediate pathways, and pathways that produce ATP and precursor molecules (glycolysis, Krebs cycle, pentose phosphate pathway, and Entner-Doudoroff pathway).

Front 54

Cells use a variety of mechanisms to regulate metabolism. They are:

Back 54

control of gene expression, which controls enzyme production needed for metabolic pathways, and control of metabolic expression in which the cells control enzymes that have been produced