Biochemistry

Question 1

Ketone Bodies

Answer 1

Three water soluble molecules (acetoacetate, acetone, and ?-hydroxybutyrate) that are produced in the body during fasting.

The production of ketone bodies by ketogenesis can also occur in patients with type I diabetes.

Question 2

Gel Electrophoresis

Answer 2

A laboratory technique used to separate molecules by charge and size.

Gel electrophoresis separates amino acids primarily by charge as all amino acids are about the same size but separates DNA primarily by size as all DNA molecules are negatively charged.

Question 3

Gluconeogenesis

Answer 3

The biochemical pathway that produces glucose from non-carbohydrate precursors.

Gluconeogenesis and glycolysis are reverse pathways that are tightly regulated to prevent futile cycles (dissipation of energy to produce heat) from occuring.

Question 4

Primary Protein Structure

Answer 4

The linear sequence of covalently-linked amino acids in a protein.

The primary structure of a protein is determined by the mRNA that encodes for the protein.

Question 5

Catabolism

Answer 5

The metabolic pathways that breakdown larger molecules into smaller ones.

Catabolic pathways typically release energy and include glycolysis, the citric acid cyle, and fatty acid oxidation.

Question 6

Mixed Inhibitor

Answer 6

A molecule that can bind to both the enzyme and the enzyme-substrate complex to inhibit catalytic activity.

All mixed inhibitors decrease the maximum reaction velocity of the enzyme. The effect on the affinity of the enzyme for the substrate depends on whether the inhibitor has a greater affinity for the enzyme or the enzyme-substrate complex.

Question 7

Quaternary Protein Structure

Answer 7

The arrangement of multple polypeptide subunits to form a complex (not all proteins have quaternary structure).

Quaternary structure is determined by the same interactions as tertiary protein structure. Hemoglobin and myoglobin are both oxygen carriers but only hemoglobin has quaternary structure.

Question 8

Steroid

Answer 8

A type of lipid molecule characterized by three cyclohexane rings and one cyclopentane ring all fused together.

Steroid molecules include chloesterol, estrogen, and testosterone.

Question 9

Hexokinase

Answer 9

The first enzyme in the glycolytic pathway that catalyzes the reaction of glucose to glucose-6-phosphate.

Hexokinase is inhibited by glucose-6-phosphate, an example of feedback inhibition.

Question 10

Ion-Exchange Chromatography

Answer 10

A separation technique used to separate a mixture of molecules by charge.

In cation exchange chromatography, the mixture is passed through a column with a negatively charged resin that bind to the positively charged molecules, allowing neutral and negatively charged molecules to pass through.

Question 11

Coenzymes

Answer 11

Small organic molecules that assist in enzyme activity.

NADH and CoA are both examples of coenzymes.

Question 12

Uncompetitive Inhibitor

Answer 12

A molecule that can only bind to the enzyme-substrate complex to inhibit catalytic activity.

Uncompetitive inhibitors increase the apparent affinity of the enzyme for the substrate and decrease the maximum reaction velocity.

Question 13

ATP Synthase

Answer 13

The enzyme that uses the proton motive force to produce ATP.

As protons pass through the membrane, a molecular motor is rotated in ATP synthase to create ATP.

Question 14

Cofactors

Answer 14

Organic or inorganic compounds required for the catalytic activity of some enzymes.

Cofactors can be metals or coenzymes.

Question 15

Secondary Protein Structure

Answer 15

The local folding of the peptide chain due to backbone hydrogen bonding.

Two common secondary structures are the ?-helix and the ?-sheet.

Question 16

Fermentation

Answer 16

In both types of fermentation (lactic acid and ethanol), the first step is glycolysis, in which glucose is oxidized, and donates its electrons to NAD+ to form NADH. Pyruvate is reduced in fermentation. At any rate, pyruvate is not oxidized in either type of fermentation

Humans perform lactic acid fermentation that converts pyruvate to lactic acid. Bacteria and yeast can perform ethanol fermentation that converts pyruvate to ethanol.

Question 17

Glycolysis

Answer 17

The biochemical pathway in cells that converts glucose into two molecules of pyruvate.

The net products of glycolysis are two pyruvate, two NADH, and two ATP molecules.

Question 18

Active Site Model

Answer 18

Catalytic activity occurs at a specific region of the enzyme called the active site.

It is possible for a multi-subunit enzyme to contain multiple active sites.

Question 19

Disulfide Bond

Answer 19

A covalent linkage formed between two thiol groups (usually two cysteine residues).

Disulfide bonds are formed by oxidation and cleaved by reduction.

Question 20

Lipid

Answer 20

A group of biological molecules that are all hydrophobic.

Lipids include fats, waxes, steroids, fat-soluble vitamins, phospholipids, terpenes, and more.

Question 21

Glucagon

Answer 21

A peptide hormone released by the pancreatic islets when the blood glucose concentration is low.

Glucagon results in increased gluconeogenesis and glycogenolysis.

Question 22

Non-competitive Inhibitor

Answer 22

A type of mixed inhibitor that has equal affinity for the enzyme and enzyme-substrate complex.

Non-competitive inhibitors do not affect the affinity of the enzyme for the substrate but decrease the maximum reaction velocity.

Question 23

Tertiary Protein Structure

Answer 23

The folding of the secondary structures of the protein to form a 3D geometric shape.

Tertiary structure is determined by the interactions of the side chains of the residues and may include London dispersion forces, dipole-dipole forces, hydrogen bonds, ionic interactions, and disulfide bonds.

Question 24

Proton Motive Force

Answer 24

The proton gradient across the membrane generated by the electron transport chain.

ATP synthase uses the energy of the proton motive force to produce ATP.

Question 25

Denaturation

Answer 25

The loss of quaternary, tertiary, and secondary structure in proteins or nucleic acids

Denaturation can be induced by extreme pH, salt concentrations, and temperatures.

Question 26

Glycogen

Answer 26

A polysaccharide that serves as the primary storage form of glucose in animal cells.

Glycogen contains many branched chains to allow for efficient hydrolysis when glucose is needed by the cell or body.

Question 27

Pentose Phosphate Pathway

Answer 27

A parallel biochemical pathway to glycolysis that uses glucose to produce NADPH and ribose-5-phosphate.

NADPH is an important cofactor for anabolic reactions and ribose-5-phosphate is used in nucleotide synthesis.

Question 28

Terpene

Answer 28

A type of lipid molecule derived biosynthetically from one or more isoprene units.

A monoterpene, diterpene, and triterpene contain 2, 4, and 6 isoprene units, respectively.

Question 29

Affinity Chromatography

Answer 29

A separation technique used to separate a mixture of molecules using a specific interaction.

One example of affinity chromatography uses a column coated with a specific antibody. As the mixture passes through the column, molecules containing the epitope for the antibody are trapped and the rest of the mixture passes through.

Question 30

Electron Transport Chain

Answer 30

A series of proteins and protein complexes that facilitate the release of energy from NADH and FADH2 to generate a proton gradient across the membrane.

There are four protein complexes in the electron transport chain. NADH enters at complex I and FADH2 enters at complex II so NADH produces more energy than FADH2 per molecule.

Question 31

Enzyme

Answer 31

Biological catalysts that increase the rate of chemical reactions.

Enzymes can be made of proteins or RNA (ribozymes).

Question 32

Size-Exclusion Chromatography

Answer 32

A separation technique used to separate a mixture of molecules by size.

In size-exclusion chromatography, the mixture is passed through a column with adorbent materials that trap smaller molecules, allowing larger molecules to elute first.

Question 33

Anabolism

Answer 33

The metabolic pathways that build larger molecules from smaller ones.

Anabolic pathways typically require energy and include gluconeogenesis, glycogenesis, and fatty acid synthesis.

Question 34

Competitive Inhibitor

Answer 34

A molecule that can only bind to the enzyme at the active site to inhibit catalytic activity.

Competitive inhibitors decrease the affinity of the enzyme for the substrate but do not affect the maximum reaction velocity.

Question 35

Phosphofructokinase

Answer 35

A key enzyme in the glycolytic pathway that converts fructose-6-phosphate to fructose-1,6-bisphosphate.

Phosphofructokinase (PFK) is inhibited by ATP and citrate but activated by AMP.

Question 36

Citric Acid Cycle

Answer 36

The biochemical pathway that oxidizes acetyl-CoA into two molecules of carbon dioxide.

Each round of the citric acid cycle consumes one acetyl-CoA molecule and produces two CO2, one GTP, one FADH2, and three three NADH molecules.

Question 37

Hydrophobic Effect

Answer 37

The primary driving force for the folding of proteins in water.

The hydrophobic effects leads to nonpolar residues clustered in the center and polar/charged residues exposed on the surface.

Question 38

Zymogen

Answer 38

A catalytically inactive enzyme that can be activated by specific chemical processes.

The zymogen pepsinogen is converted into the active form, pepsin, by hydoochloric acid released by parietal cells in the stomach.

Question 39

Insulin

Answer 39

A peptide hormone released by the pancreatic islets when the blood glucose concentration is high.

Insulin results in increased cellular intake of glucose, increased glycolysis, increased glycogen synthesis, increased lipid synthesis, decreased lipolysis, and decreased gluconeogenesis.

Question 40

Induced-fit Model

Answer 40

When the subtrate enters the active site, the enzyme changes conformation to increase the binding strength for the substrate and catalytic activity.

The induced-fit model replaced the lock-and-key model, which stated that enzymes and their subtrates had complementary shapes that fit each other precisely.

Question 41

Allostery

Answer 41

The regulation of a protein’s activity by the binding of a molecule at a site other than the active site

The catalytic activity of phosphofructokinase (PFK) is inhibited when ATP binds at an allosteric site on the enzyme.