Biochemical Basics

Question 11

A chemical substance that cannot be broken down further using standard chemical techniques is known as:

Answer 11

An element

For example, carbon (C) is an element. Atoms of a particular element always have the same number of protons. For example, all carbon atoms have 6 protons!

Question 13

What is the difference between an atom, a molecule, and a compound?

Answer 13

• An atom is the fundamental unit of matter. Atoms contain protons, neutrons, and electrons.
• A molecule is a group of two or more atoms, connected by chemical bonds (for example, O₂).
• A compound is a molecule that contains atoms of more than one element (for example, H₂O).

Question 14

Which of the following are contained within the nucleus of a typical atom?

• Protons
• Neutrons
• Electrons

Answer 14

A typical atomic nucleus contains protons and neutrons. Electrons are not found in the nucleus; instead, they are located in regions (“shells”) surrounding the nucleus.

Question 15

Isotopes are atoms with the same number of:

Answer 15

protons

Isotopes are atoms with the same number of protons, meaning that they must represent the same element. Isotopes differ in their number of neutrons.

Question 16

Define:

ionic bond

Answer 16

A chemical bond that forms due to the transfer of specific electrons from one atom to another, with one atom losing an electron and the other gaining it.

The atom that gains electrons is given a negative charge, while the atom that gives up electrons is given a positive charge.

Question 17

Define:

covalent bond

Answer 17

A chemical bond that forms via the sharing (not complete transfer) of electrons.

When the electrons are shared unequally, the bond is polar covalent. For example, H₂O contains two polar covalent bonds between H and O, because these atoms have different electronegativities (attraction to electrons in a bond).

When the electrons are shared equally, the bond is nonpolar covalent. For example, O₂ contains a nonpolar covalent bond between the two O atoms, which have the same electronegativity.

Question 18

What is the chemical formula for water, and is the water molecule polar or nonpolar?

Answer 18

Water has a formula of H₂O, and it is polar.

The water molecule (shown here) is bent due to the presence of two lone pairs on the central oxygen atom. Oxygen is more electronegative than hydrogen, so the oxygen atom will carry a partial negative charge, while the hydrogen atoms will be partially positive. Molecules with asymmetrical charge distributions like this one are polar.

Question 19

How do hydrogen bonds differ from ionic or covalent bonds?

Answer 19

Hydrogen bonds are intermolecular, which means they occur between two or more different molecules. Ionic and covalent bonds are intramolecular, meaning they connect atoms within a single molecule.

Hydrogen bonds are attractive forces.

Question 21

Define:

a hydrophilic compound

Answer 21

One that is attracted to water.

Since water is polar, it tends to attract other polar compounds.

Question 22

Define:

a hydrophobic compound

Answer 22

One that is repelled by water.

Since water is polar, it tends to repel nonpolar compounds. A classic example is an oil slick on the top of the ocean. Oil is nonpolar, so it is not attracted to the ocean water, and the two liquids do not mix.

Question 23

Define:

macromolecule

Answer 23

A molecule that contains an extremely large number of atoms.

Question 24

Name the four main types of organic macromolecules that are found in living organisms.

Answer 24

1. Carbohydrates
2. Lipids
3. Proteins
4. Nucleic acids

Carbohydrates are commonly known as sugars, and lipids are commonly known as fats.

Question 25

What is the general chemical formula for a typical carbohydrate?

Answer 25

(CH₂O)_n

Where n is an integer.

This can be easily remembered, since H₂O represents water. Carbohydrates are simply “hydrated carbons.” Note that a few rare carbohydrates, like deoxyribose, have formulas that differ from this rule.

Question 27

Define a monosaccharide and give two common examples.

Answer 27

• A carbohydrate that contains only a single sugar subunit.
• Classic examples: glucose and fructose.

Question 28

Define a disaccharide and give three common examples.

Answer 28

• A carbohydrate that consists of two sugar subunits, joined by a bond called a glycosidic linkage.
• Classic examples: maltose, lactose, and sucrose.

Question 29

Define a polysaccharide and give three common examples.

Answer 29

• A carbohydrate that consists of a polymer (or long chain) of many sugar subunits.
• Classic examples: glycogen, starch, and cellulose.

Question 31

What type of reaction occurs when two carbohydrate subunits combine to form a disaccharide?

Answer 31

A dehydration reaction.

Dehydration reactions involve the combination (or condensation) of smaller reactants to form a larger product. This occurs along with the loss of a water molecule.

Question 32

What is the molecular formula for glucose?

Answer 32

C₆H₁₂O₆

Glucose is a six-carbon monosaccharide (meaning that it contains only one sugar subunit).

Question 33

What is the molecular formula for sucrose?

Answer 33

C₁₂H₂₂O₁₁

_{Sucrose is a disaccharide, meaning that it consists of two sugar subunits. Specifically, these subunits are glucose and fructose.}

Question 34

The main component of plant cell walls is classified as which of the four main types of organic macromolecule?

Answer 34

Carbohydrates

Plant cell walls are composed of cellulose, which is a polysaccharide, or carbohydrate polymer.

Question 35

Protein molecules are composed of smaller subunits known as:

Answer 35

Amino acids

Amino acids are the monomers, or individual subunits, that make up protein molecules. Adjacent amino acids are held together by peptide bonds.

Question 36

Which two functional groups are found in all amino acids?

Answer 36

1. amine
2. carboxylic acid

Each amino acid also contains a specific side chain.

Question 37

A laboratory technician is analyzing the composition of a plasma protein. Which elements could he expect to find in this protein’s structure?

Answer 37

• carbon
• hydrogen
• oxygen
• nitrogen

Sulfur also may be present, depending on the particular amino acids in the structure. Some proteins also contain trace amounts of selenium.

Question 38

Which would be expected to have a higher molecular weight: a dipeptide or a polypeptide?

Answer 38

polypeptide

A dipeptide is the smallest form of peptide and contains only two amino acids bound together. Polypeptides typically consist of long strings of amino acids, making them significantly heavier; a polypeptide can include up to around 50 amino acids in total.

Question 40

Name the four levels of protein structure.

Answer 40

• Primary structure
• Secondary structure
• Tertiary structure
• Quaternary structure

Question 41

Define:

the primary structure of a protein

Answer 41

It is simply its linear amino acid sequence.

Primary structure is often written using either a one- or a three-letter abbreviation for each amino acid (for example, “Gly-Pro-Ile-Cys…” or “GPIC…”).

Question 43

Define:

the secondary structure of a protein

Answer 43

Refers to the folding of the amino acid chain into repetitive structures due to hydrogen bonding between backbone groups.

Question 44

What functional group is present in all peptide bonds?

Answer 44

amides

In fact, they are sometimes alternatively known as amide linkages.

A peptide bond forms when the amine group of one amino acid attacks the carbonyl carbon of another.

Question 45

Define:

the tertiary structure of a protein

Answer 45

Refers to its large-scale three-dimensional shape.

Tertiary structure is determined by interactions between side chains and by hydrophobic interactions (the tendency for nonpolar groups to avoid facing the watery environment).

Question 46

Define:

the quaternary structure of a protein

Answer 46

It is present only in proteins that are composed of multiple subunits. This level of structure refers to interactions between subunits.

For example, hemoglobin (shown here) consists of four separate subunits, held together by various interactions and attractive forces.

Question 47

Define:

lipids

Answer 47

A class of organic macromolecule characterized by their nonpolar (non-water-soluble) nature.

Most notably, lipids include triglycerides (fats), oils, steroids, waxes, and phospholipids.

Question 48

What type of lipid is pictured here?

Answer 48

triglyceride

A triglyceride is commonly known simply as a fat. It consists of three fatty acid molecules attached to a three-carbon glycerol backbone.

Question 49

The diagram below depicts a fatty acid. Is this fatty acid saturated, monounsaturated, or polyunsaturated?

Answer 49

polyunsaturated

Saturated fatty acids have carbon chains that include only single bonds, while unsaturated fatty acids include one or more double bonds in their chains. Since this fatty acid contains three carbon-carbon double bonds, it is polyunsaturated. (To be monounsaturated, a fatty acid must include only one double bond in its carbon chain.)

Question 50

What functional groups are present in a typical fatty acid?

Answer 50

A carboxylic acid (COOH) group attached to a hydrocarbon chain.

Fatty acids can combine with glycerol to form triglycerides, or fat. Fatty acids can also be broken down to provide cells with energy.

Question 51

What type of lipid would be expected to be most predominant in a eukaryotic cell membrane?

Answer 51

phospholipids

The cell membrane (in both eukaryotes and prokaryotes) is composed mainly of phospholipids in the form of a “bilayer,” or double layer.

Question 52

A typical phospholipid includes both a polar “head” region and two nonpolar “tails.” What term describes this property of having both polar and nonpolar regions?

Answer 52

amphipathic

Specifically, the polar “head” region includes phosphate, which is charged; this charge is what gives the head group its polarity. The two “tails” consist of fatty acids, which are largely nonpolar due to their long hydrocarbon chains.

Question 53

What class of lipid is derived from the molecule below and plays a vital role in the endocrine system?

Answer 53

steroid hormones

Steroid hormones are derived from cholesterol (shown here). These lipid molecules can be easily spotted due to their structures, which include four fused rings.

Question 54

Structures like that shown below are found in which of the four major classes of organic macromolecules?

Answer 54

Nucleic acids

The structure pictured here is a nucleotide, as is evident from its nitrogenous base, sugar, and phosphate group. Nucleotides are the monomers (“building blocks”) that form nucleic acids, including DNA and RNA.

Question 55

A student is analyzing an unknown biomolecule. He knows that the molecule includes covalent bonds and that it is not a lipid. He is also certain that the molecule contains carbon, hydrogen, and phosphorus, although it may also include other elements. This biomolecule is most likely a:

Answer 55

Nucleic acid

All four of the main classes of organic macromolecule include covalent bonds, so that piece of information is unhelpful. However, only nucleic acids and (some) lipids can contain phosphorus. Since we are told that this molecule is not a lipid, it must be a nucleic acid.

Question 56

Define:

nucleic acids

Answer 56

A class of organic macromolecule, which consists of long chains of nucleotide monomers and are involved in the storage and transmission of genetic material.

Question 57

Define:

metabolism

Answer 57

It collectively refers to the biological processes that occur within cells. Specifically, these processes either generate energy through the breakdown of molecules or use energy to build molecules.

Metabolism is also known as “cellular respiration.”

Question 58

Define:

catabolism

Answer 58

It is the biological breakdown of molecules into smaller units. Catabolic processes are accompanied by the generation of energy.

The opposite of this class of metabolic reactions is anabolism.

Question 59

Define:

anabolism

Answer 59

It is the creation of larger biomolecules from smaller units. Anabolic processes require energy input.

The opposite of this class of metabolic reactions is catabolism.

Question 60

What broad distinction separates aerobic and anaerobic respiration?

Answer 60

Aerobic respiration requires oxygen, while anaerobic respiration does not require oxygen.

As part of metabolism, both processes involve the breakdown of biological molecules and the eventual release of energy.

Question 61

Which metabolic process occurs in the cytosol regardless of the presence or absence of oxygen?

Answer 61

Glycolysis

Glycolysis is a biochemical process that forms pyruvate from the breakdown of glucose. The pathway produces 2 NADH and a net total of 2 ATP per glucose molecule.

Question 62

Describe the net reaction of glycolysis.

Answer 62

C₆H₁₂O₆ + 2NAD⁺ + 2 P_i + 2 ADP ⇒ 2 pyruvate + 2 ATP + 2 NADH + 2 H₂O + 2 H⁺

While glycolysis only produces a net of two ATP molecules, it generates a total of four. However, two molecules of ATP are used as reactants in early glycolytic steps.

Question 63

Which metabolic process immediately follows glycolysis in oxygen-poor conditions?

Answer 63

Fermentation

This process takes place when O₂ is too scarce to facilitate the entry of glycolytic products into the Krebs cycle.

Fermentation can produce either ethanol or lactic acid, depending on the species.

Question 64

The conversion of pyruvate to lactic acid, often referred to simply as “fermentation,” produces no ATP. However, it is still necessary in anaerobic conditions. What purpose does this process serve?

Answer 64

Fermentation regenerates NAD⁺ by oxidizing NADH and reducing pyruvate.

NAD⁺ is necessary for glycolysis, but cannot be regenerated by the electron transport chain under anaerobic conditions. Fermentation serves to produce NAD⁺, reducing buildup of NADH and allowing glycolysis to continue.

Question 65

What are the substrates and products of pyruvate decarboxylation?

Answer 65

Pyruvate, a three-carbon molecule, is the substrate. CO₂, NADH, and acetyl-CoA are the ultimate products.

Question 66

Two glucose molecules undergo glycolysis, producing pyruvate. How many molecules of NADH will be produced simply from the decarboxylation of these pyruvate products?

Answer 66

4 NADH molecules

During glycolysis, the initial two glucose molecules will be converted into four molecules of pyruvate. For every molecule of pyruvate that is decarboxylated by pyruvate dehydrogenase, one molecule of NADH is formed.

Question 67

Which metabolic process generates both NADH and FADH₂?

Answer 67

The Krebs cycle produces the electron carriers NADH and FADH₂, as well as an ATP equivalent (either ATP or GTP).

The Krebs cycle, also known as the citric acid cycle, involves the cyclic transformation of organic molecules. It occurs in the mitochondrial matrix.

Question 68

How many molecules of NADH and FADH₂, respectively, are produced during one turn of the Krebs cycle?

Answer 68

One full cycle produces 3 NADH molecules and 1 FADH₂.

Other products include carbon dioxide, which is released as waste, and one molecule of GTP.

Question 69

Which metabolic process takes place along the inner mitochondrial membrane?

Answer 69

The electron transport chain (ETC) uses a series of complexes along the inner mitochondrial membrane. These molecules support a chain of oxidation-reduction reactions, ultimately resulting in the oxidization of NADH and FADH₂ and the reduction of O₂.

The transport of electrons through the chain creates a proton gradient that provides the energy to convert ADP to ATP.

Question 70

Which metabolic process is facilitated by the proton gradient within the mitochondria?

Answer 70

ATP synthesis

After establishment of the gradient, proton concentration in the intermembrane space is high. When possible, these protons will move down their gradient and reenter the matrix; this can only occur if they pass through ATP synthase, an enzyme. As this process occurs, ATP synthase uses this energy to convert ADP to ATP.

Question 71

Which of the following molecules are necessary substrates for the electron transport chain?

• glucose
• O₂
• NADH
• pyruvate
• CO₂

Answer 71

NADH is a required substrate, and O₂ must be present as the final electron acceptor in the chain.

Glucose and pyruvate, though linked to NADH production, are not directly necessary for the electron transport chain. CO₂ is a waste product of cellular respiration.

Question 72

Which of the following molecules are necessary substrates for fermentation?

• ethanol
• lactate
• pyruvate
• NADH
• NAD⁺

Answer 72

• Pyruvate
• NADH

Ethanol, lactate, and NAD⁺ are all products of fermentation.

Question 73

Which of the following molecules are products of glycolysis?

• glucose
• ATP
• NAD⁺
• pyruvate
• O₂

Answer 73

• ATP
• pyruvate

NADH, though not listed here, is another glycolytic product. Glucose and NAD⁺ are consumed in glycolysis, while O₂ is not involved. Remember that glycolysis is an anaerobic process.

Question 74

Which of the following molecules are products of the Krebs cycle?

• NADH
• acetyl-CoA
• pyruvate
• FADH₂
• NAD⁺

Answer 74

The Krebs cycle produces NADH and FADH₂, which are electron carriers that are later used.

Acetyl-CoA and NAD⁺ are consumed in the Krebs cycle, while pyruvate is not directly involved.

Question 75

Which two processes of cellular metabolism take place in the cytoplasm?

Answer 75

1. Glycolysis
2. Fermentation

Note that fermentation only takes place in anaerobic conditions.

All other processes take place in the mitochondria.

Question 76

Which two processes of cellular metabolism take place in the mitochondrial matrix?

Answer 76

1. The Krebs cycle
2. Pyruvate decarboxylation

The electron transport chain is also a mitochondrial process, but occurs along the inner membrane, not within the matrix itself.

Question 77

Which enzymes are responsible for the metabolism of proteins?

Answer 77

Proteases

also called peptidases

Proteins are cleaved into amino acids. Depending on their identity, these amino acids can be converted to acetyl-CoA, pyruvate, or other metabolic intermediates.

Question 78

What homeostatic change occurs in the blood when the cells are in oxygen debt?

Answer 78

Acidosis

or low pH

This is the result of excess CO₂ and the buildup of lactic acid in muscles during anaerobic respiration.

Note that normal plasma pH is 7.4.

Question 79

The majority of glucose molecules enter the cell via which transport method?

Answer 79

facilitated diffusion

This occurs with the assistance of a family of transport proteins.

This process is promoted by high plasma glucose levels, which creates a concentration gradient that drives glucose into the cells. It is also promoted by the activity of insulin, which increases the number of glucose transporters on the membranes of certain cell types.

Question 80

Which reaction is the rate-limiting step of glycolysis?

Answer 80

The phosphorylation of fructose 6-phosphate.

This reaction is catalyzed by the enzyme phosphofructokinase-1 (PFK-1). For this reason, PFK-1 is sometimes called the rate-limiting enzyme of glycolysis.

Question 81

Of AMP, ATP, and citrate, which is most likely to serve as an allosteric activator of PFK-1?

Answer 81

AMP

The other two molecules are inhibitors.

You can figure this out logically: “activate” means “stimulate.” Glycolysis should be stimulated when available energy is low (to make more) and inhibited when it is high. High AMP concentrations imply that cellular ATP is low.

Question 82

What is the chemical formula of glucose?

Answer 82

C₆H₁₂O₆

Broadly, glucose is a carbohydrate; specifically, it is a monosaccharide.

Question 83

Which two molecules can be created by the fermentation of pyruvate?

Answer 83

• ethanol
• lactate

Alcohol fermentation, which takes place in yeast and certain bacteria, involves the reduction of pyruvate to ethanol. Lactic acid fermentation, which takes place in human muscle cells as part of anaerobic respiration, involves the reduction of pyruvate to lactate.

Question 84

Which metabolic process immediately follows glycolysis and produces acetyl-CoA?

Answer 84

Pyruvate decarboxylation

Under aerobic conditions, pyruvate (a three-carbon molecule) is converted to a two-carbon acetyl group. This group then attaches to coenzyme A.

Question 85

What is the initial substrate of the Krebs cycle, and with which molecule does it first react?

Answer 85

Acetyl-CoA, a two-carbon compound, is the substrate entering the cycle. It immediately reacts with oxaloacetate to form a six-carbon compound (citrate).

Coenzyme A is released in this process and can be used again.

Question 86

The electron transport chain functions to produce a proton gradient. Into which mitochondrial region are these protons pumped?

Answer 86

Protons are pumped from the mitochondrial matrix to the intermembrane space.

Question 87

Define:

catalyst

Answer 87

A molecule that increases the rate of a reaction without being consumed itself.

Catalysts change the kinetics of a reaction, not the thermodynamics. In other words, they lower the activation energy without altering the equilibrium or free energy change of a reaction.

Question 88

Define:

enzyme

Answer 88

A biological catalyst that structurally facilitates a chemical reaction. Like all catalysts, enzymes increase the rate of a chemical reaction without being consumed.

Most enzymes are proteins, but RNA molecules called ribozymes also have enzymatic activity.

Question 89

Why are enzymes generally ineffective catalysts over a broad temperature range?

Answer 89

Enzymes must be at a certain optimal temperature to maintain their structure.

The structure of an enzyme, especially in relation to its active site, is essential to its function as a catalyst. Like other proteins, enzymes denature, or lose their original conformations, above a certain temperature. However, reactions generally progress more slowly at low temperatures, further narrowing the range of optimal activity.

Question 90

What effect does a reduced activation energy have on reaction kinetics?

Answer 90

A lowered activation energy increases the reaction rate.

Each reaction must overcome an activation energy barrier to progress from reactants to products. When this barrier is lower, reactants are more likely to collide with sufficient energy, speeding up the reaction.

Question 91

Why are enzymes generally ineffective catalysts over a broad pH range?

Answer 91

Enzymes can only maintain their functional structure at a certain optimal pH.

The structure of an enzyme, especially in relation to its active site, is essential to its function as a catalyst. The active site often contains positively or negatively charged groups, which contribute to the specificity of the site. Changes in pH can affect these sites, reducing enzyme activity.

Question 92

At the molecular level, why are prolonged, high fevers dangerous to human health?

Answer 92

At higher-than-optimal temperatures, most human enzymes lose function and cannot support necessary biological processes.

Most human enzymes function most efficiently at an optimal temperature of 37 ºC. While these enzymes can remain active at slightly higher temperatures, their function is impaired.

Question 93

Enzymes are usually limited to acting on a single substrate or class of substrate molecules. What term describes this quality?

Answer 93

Specificity

The substrate(s) that can be accommodated by an enzyme are determined by the shape of its active site. For example, proteases are specific to protein substrates, while lipases act on lipid-based substrates.

Question 94

What major limitation prevents the lock-and-key model from being fully accurate?

Answer 94

It wrongly portrays all enzymes as being rigid and inflexible.

In reality, the active site of an enzyme can change its conformation to facilitate binding to the substrate.

Question 95

What is the difference between cofactors and coenzymes?

Answer 95

• Cofactors are a broad group of compounds that are required for the proper functioning of enzymes.
• Coenzymes are a class of small, organic cofactors.

Cofactors can also be inorganic substances, such as ions.

Question 96

Many coenzymes are derived from molecules like niacin and riboflavin, which must be consumed as part of the diet. What category describes these molecules?

Answer 96

Vitamins

Vitamins are often used to synthesize coenzymes, which are non-protein organic compounds that are essential for proper enzyme function.

Question 97

Phosphofructokinase, a glycolytic enzyme, is allosterically inhibited by ATP. What common homeostatic process does this example demonstrate?

Answer 97

This is an example of negative feedback. In such processes, increased concentration of a product decreases the rate of the reaction that forms that product.

Glycolysis involves the breakdown of glucose to form ATP, among other products. If increased amounts of ATP are already present, glycolysis will slow.

Question 98

Define:

bioenergetics

Answer 98

This is the study of energy transformations within organisms. Specifically, it concerns the energy released and used during the formation and breaking of chemical bonds.

Bioenergetics is closely related to thermodynamics, especially Gibbs free energy.

Question 99

What single comparison between reactants and products can be made to determine whether a reaction will proceed?

Answer 99

The change in Gibbs free energy, or ΔG, determines reaction spontaneity.

A negative ΔG means the reaction will be spontaneous, while a positive ΔG denotes a nonspontaneous reaction.

Question 100

What term can be used to describe a thermodynamically favorable reaction?

Answer 100

exergonic

In such reactions, ΔG is always negative, meaning that free energy is released.

The opposite type of reactions are endergonic. In these processes, ΔG is positive and the reaction will not proceed spontaneously.

Question 101

How will the free energy diagram of a catalyzed reaction differ from that of an uncatalyzed reaction?

Answer 101

The catalyzed reaction will have a lower activation energy.

Note that the overall change in free energy will be the same for the catalyzed and uncatalyzed reactions.

Question 102

Define:

substrate

Answer 102

A specific molecule that an enzyme acts upon, usually via interactions with the enzyme’s active site.

For example, starch is the substrate of salivary amylase. This means that amylase, an enzyme, catalyzes a reaction involving starch as a reactant.

Question 103

What is the functional significance of the active site?

Answer 103

It is the structural component where enzyme-substrate interactions take place.

In other words, the active site is the catalytic region of an enzyme. It is structured to facilitate the binding of its substrate, often through the presence of certain amino acid residues.

Question 104

How does the lock-and-key model explain enzyme-substrate specificity?

Answer 104

it posits that a substrate will fit perfectly into the active site of its corresponding enzyme, without any conformational changes taking place.

In this model, the active site is the “lock” and its complementary substrate is the “key.”

Question 105

How does the induced fit model explain enzyme-substrate specificity?

Answer 105

It posits that active sites are flexible. When a substrate approaches the enzyme, the conformation of the active site will change to better fit the substrate.

The induced fit model is a more recent adaptation of the lock-and-key model.

Question 106

Define:

allosteric site

Answer 106

A region of an enzyme, separate from the active site, where molecules can bind and affect enzyme function.

Allosteric binding can either facilitate or inhibit the binding of substrate to the active site.

Question 107

How does a competitive inhibitor alter an enzyme-catalyzed reaction?

Answer 107

It binds to an enzyme on its active site, inhibiting the reaction.

Specifically, these inhibitors compete with the substrate and block it from binding the active site.

Question 108

How does a noncompetitive inhibitor alter an enzyme-catalyzed reaction?

Answer 108

It binds to an enzyme on a region outside of its active site, inhibiting the reaction.

Specifically, these inhibitors bind an allosteric site, inducing a structural change in the enzyme that decreases its efficiency. Substrates can still enter the enzyme’s active site.

Question 109

What class of substrate is common to maltase, sucrase and lactase?

Answer 109

disaccharides

Maltase breaks down maltose into two glucose molecules. Sucrase cleaves sucrose into glucose and fructose, and lactase breaks down lactose into glucose and galactose.

Question 110

What molecule is shown below, and what is its biological role?

Answer 110

This molecule is adenosine triphosphate (ATP), the major form of cellular energy.

ATP consists of three phosphate groups bound to the ribonucleoside adenosine. The cleavage of the third phosphate bond facilitates the release of energy, which the cell harnesses to drive biological processes.

Question 111

What name is given to the bonds circled in the structure below?

Answer 111

phosphoanhydride bonds

These phosphoanhydride bonds exist between phosphate groups on molecules like ATP (shown) and ADP.

The name of these bonds comes from the reaction that forms them: dehydration (removal of H₂O). Predictably, they can be broken by the reverse reaction, hydrolysis (addition of H₂O).