Chapter 3 · 2020-03-17 · 3.1 Life’s molecular diversity is based on the properties of carbon...

PowerPoint Lectures Campbell Biology: Concepts & Connections, Eighth Edition REECE • TAYLOR • SIMON • DICKEY • HOGAN

Chapter 3

Lecture by Edward J. Zalisko

The Molecules of Cells

Introduction

• Most of the world’s population cannot digest milk-based foods.

• These people are lactose intolerant, because they lack the enzyme lactase.

• This illustrates the importance of biological molecules, such as lactase, in the daily functions of living organisms.

Figure 3.0-2

Chapter 3: Big Ideas

Introduction to Organic Compounds

Carbohydrates

Lipids Proteins Nucleic Acids

INTRODUCTION TO ORGANIC COMPOUNDS

3.1 Life’s molecular diversity is based on the properties of carbon

• Almost all the molecules a cell makes are composed of carbon bonded to

• other carbons and • atoms of other elements.

• Carbon-based molecules are called organic compounds.

• By sharing electrons, carbon can • bond to four other atoms and • branch in up to four directions.

• Methane (CH4) is one of the simplest organic compounds.

• Four covalent bonds link four hydrogen atoms to the carbon atom.

• Each of the four lines in the formula for methane represents a pair of shared electrons.

Figure 3.1a

The four single bonds of carbon point to the corners of a tetrahedron.

• Methane and other compounds composed of only carbon and hydrogen are called hydrocarbons.

• Carbon, with attached hydrogens, can form chains of various lengths.

• A carbon skeleton is a chain of carbon atoms that can differ in length and be

• straight, • branched, or • arranged in rings.

• Compounds with the same formula but different structural arrangements are called isomers.

Animation: L-Dopa

Animation: Carbon Skeletons

Animation: Isomers

Figure 3.1b-0

Butane

Length: Carbon skeletons vary in length.

Propane 1-Butene 2-Butene

Double bonds: Carbon skeletons may have double bonds, which can vary in location.

Double bond

Isobutane Cyclohexane Benzene

Branching: Carbon skeletons may be unbranched or branched.

Rings: Carbon skeletons may be arranged inrings. (In the abbreviated ring structures, eachcorner represents a carbon and its attachedhydrogens.)

Ethane

Figure 3.1b-1

Length: Carbon skeletons vary in length.

PropaneEthane

Figure 3.1b-2

Butane Isobutane

Branching: Carbon skeletons may be unbranched or branched.

Figure 3.1b-3

1-Butene 2-Butene

Double bonds: Carbon skeletons may have double bonds, which can vary in location.

Double bond

Figure 3.1b-4

Cyclohexane Benzene

Rings: Carbon skeletons may be arranged inrings. (In the abbreviated ring structures, eachcorner represents a carbon and its attachedhydrogens.)

3.2 A few chemical groups are key to the functioning of biological molecules

• The unique properties of an organic compound depend on

• the size and shape of its carbon skeleton and • the groups of atoms that are attached to that

skeleton. • The sex hormones testosterone and estradiol (a

type of estrogen) differ only in the groups of atoms highlighted in Figure 3.2.

Figure 3.2-0

Testosterone Estradiol

Figure 3.2-1

Testosterone Estradiol

Figure 3.2-2

Figure 3.2-3

• Table 3.2 illustrates six chemical groups important in the chemistry of life.

• The first five groups are called functional groups; they affect a molecule’s function in a characteristic way.

• These five groups are polar, so compounds containing them are typically hydrophilic (water-loving) and soluble in water.

• A sixth group, a methyl group, • consists of a carbon bonded to three hydrogen

atoms, • is nonpolar and not reactive, but • still affects molecular shape and thus function.

Table 3.2-0

Table 3.2-1

Table 3.2-2

• The functional groups are • hydroxyl group—a hydrogen bonded to an oxygen, • carbonyl group—a carbon linked by a double bond

to an oxygen atom, • carboxyl group—a carbon double-bonded to both

an oxygen and a hydroxyl group, • amino group—a nitrogen bonded to two hydrogen

atoms and the carbon skeleton, and • phosphate group—a phosphorus atom bonded to

four oxygen atoms.

3.3 Cells make large molecules from a limited set of small molecules

• There are four classes of molecules important to organisms:

1. carbohydrates, 2. lipids, 3. proteins, and 4. nucleic acids.

• The four classes of biological molecules contain very large molecules.

• They are often called macromolecules because of their large size.

• They are also called polymers because they are made from identical or similar building blocks strung together.

• The building blocks of polymers are called monomers.

• Monomers are linked together to form polymers through dehydration reactions, which remove water.

• Polymers are broken apart by hydrolysis, the addition of water.

• These reactions are mediated by enzymes, specialized macromolecules that speed up chemical reactions in cells.

Animation: Polymers

• A cell makes a large number of polymers from a small group of monomers. For example,

• proteins are made from only 20 different amino acids and

• DNA is built from just four kinds of monomers called nucleotides.

• The monomers used to make polymers are essentially universal.

Figure 3.3-0

Short polymer Unlinkedmonomer

Dehydration reactionforms a new bond

Longer polymer

Hydrolysisbreaks a bond

Figure 3.3-1-1

Figure 3.3-1-2

Dehydration reactionforms a new bond

Longer polymer

Figure 3.3-2-1

Figure 3.3-2-2

Hydrolysisbreaks a bond

CARBOHYDRATES

3.4 Monosaccharides are the simplest carbohydrates

• Carbohydrates range from small sugar molecules (monomers) to large polysaccharides.

• Sugar monomers are monosaccharides, such as those found in

• fructose, • glucose, and • honey.

Figure 3.4a

• Monosaccharides can be hooked together by dehydration reactions to form

• more complex sugars and • polysaccharides.

• The carbon skeletons of monosaccharides vary in length.

• Glucose and fructose are six carbons long. • Others have three to seven carbon atoms.

• Monosaccharides are • the main fuels for cellular work and • used as raw materials to manufacture other organic

molecules.

Figure 3.4b

Glucose Fructose

• Many monosaccharides form rings. • The ring diagram may be

• abbreviated by not showing the carbon atoms at the corners of the ring and

• drawn with different thicknesses for the bonds, to indicate that the ring is a relatively flat structure with attached atoms extending above and below it.

Figure 3.4c

Structuralformula

Abbreviatedstructure

Simplifiedstructure

3.5 Two monosaccharides are linked to form a disaccharide

• Two monosaccharides (monomers) can bond to form a disaccharide in a dehydration reaction.

• The disaccharide sucrose is formed by combining • a glucose monomer and • a fructose monomer.

• The disaccharide maltose is formed from two glucose monomers.

Animation: Disaccharides

Figure 3.5-1

Glucose Glucose

Figure 3.5-2

Glucose Glucose

Maltose

3.6 CONNECTION: What is high-fructose corn syrup, and is it to blame for obesity?

• Most sodas and fruit drinks contain high-fructose corn syrup (HFCS).

• Fructose is sweeter than glucose. • To make HFCS, glucose atoms are rearranged to

make the glucose isomer fructose.

• High-fructose corn syrup (HFCS) • is used to sweeten many beverages, • consists of about 55% fructose and 45% glucose,

and • is a mixture with about the same proportions as in

sucrose. • Most scientific studies have not shown health

consequences associated with replacing sucrose with HFCS.

• Although HFCS consumption has declined somewhat in recent years, obesity rates continue to rise, with almost 36% of U.S. adults now considered obese.

• Good health is promoted by • a diverse diet of proteins, fats, vitamins, minerals,

complex carbohydrates, and • exercise.

Figure 3.6

3.7 Polysaccharides are long chains of sugar units

• Polysaccharides are macromolecules, polymers composed of thousands of monosaccharides.

• Polysaccharides may function as • storage molecules or • structural compounds.

• Starch is • a polysaccharide, • composed of glucose monomers, and • used by plants for energy storage.

• Glycogen is • a polysaccharide, • composed of glucose monomers, and • used by animals for energy storage.

• Cellulose • is a polymer of glucose and • forms plant cell walls.

• Chitin is • a polysaccharide, • used by insects and crustaceans to build an

exoskeleton, and • found in the cell walls of fungi.

Figure 3.7-0

Starch granules ina potato tuber cell Starch

Glycogen granules in muscle tissue

Cellulose microfibrils in a plant cell wall

Cellulosemolecules Hydrogen bonds

Cellulose

Glycogen

Glucose monomer

Figure 3.7-1

Starch granules ina potato tuber cell Starch

Glucose monomer

Figure 3.7-2

Glycogen granules in muscle tissue

Glycogen

Figure 3.7-3

Cellulose microfibrils in a plant cell wallCellulosemolecules Hydrogen bonds

Cellulose

Figure 3.7-4

• Polysaccharides are usually hydrophilic (water-loving).

• Bath towels, for example, are often made of cotton, which is mostly cellulose, and therefore water absorbent.

Animation: Polysaccharides

LIPIDS

3.8 Fats are lipids that are mostly energy-storage molecules

• Lipids • are water insoluble (hydrophobic, or water-fearing)

compounds, • are important in long-term energy storage, • contain twice as much energy as a polysaccharide,

and • consist mainly of carbon and hydrogen atoms linked

by nonpolar covalent bonds.

• Lipids differ from carbohydrates, proteins, and nucleic acids in that they are

• not huge molecules and • not built from monomers.

• Lipids vary a great deal in structure and function.

• We will consider three types of lipids: 1. fats, 2. phospholipids, and 3. steroids.

• A fat is a large lipid made from two kinds of smaller molecules:

• glycerol and • fatty acids.

• A fatty acid can link to glycerol by a dehydration reaction.

• A fat contains one glycerol linked to three fatty acids.

• Fats are often called triglycerides because of their structure.

Animation: Fats

Figure 3.8a

Glycerol

Fatty acid

Figure 3.8b

Figure 3.8c-0

Saturated fats Unsaturated fats

Figure 3.8c-1

Saturated fats

Figure 3.8c-2

Unsaturated fats

• Some fatty acids contain one or more double bonds, forming unsaturated fatty acids.

• These have one fewer hydrogen atom on each carbon of the double bond.

• These double bonds cause kinks or bends in the carbon chain, preventing them from packing together tightly and solidifying at room temperature.

• Fats with the maximum number of hydrogens are called saturated fatty acids.

• Unsaturated fats are referred to as oils. • Most animal fats are saturated fats. • Hydrogenated vegetable oils are unsaturated fats

that have been converted to saturated fats by adding hydrogen.

• This hydrogenation creates trans fats, which are associated with health risks.

3.9 SCIENTIFIC THINKING: Scientific studies document the health risks of trans fats

• In the 1890s, the process of adding hydrogen atoms to unsaturated oils was developed to

• reduce spoilage of oils, • help oils withstand repeated heating for frying, and • reduce consumption of animal fats, thought to be

less healthy than partially hydrogenated vegetable oils.

• By the 1990s, partially hydrogenated oils were common in cookies, crackers, snacks, baked goods, and fried foods.

• Recent research has shown that trans fats pose an even greater health risk than saturated fats.

• One study estimated that eliminating trans fats from the food supply could prevent up to one in five heart attacks!

• In 2006, the U.S. Food and Drug Administration required the listing of trans fat on food labels.

• Many cities and states have passed laws to eliminate trans fats in unlabeled foods served in restaurants and schools.

• An increasing number of countries have banned trans fats.

• Experimental studies have tested the health risks of consuming trans fats.

• In experimental controlled feeding trials, the diets of participants contained different proportions of saturated, unsaturated, and partially hydrogenated fats.

• For ethical and practical reasons, controlled feeding trials are usually fairly short in duration, involve only limited dietary changes, generally use healthy individuals, and measure intermediary risk factors, such as changes in cholesterol levels, rather than actual disease outcomes.

• Observational scientific studies on dietary health effects can

• extend over a longer time period, • use a more representative population, and • measure disease outcomes and risk factors.

• The Nurses’ Health Study • began in 1976 with more than 120,000 female

nurses and • is an example of an observational study on dietary

health.

• The results indicate that • for each 5% increase in saturated fat, there was a

17% increase in the risk of heart disease and • for each 2% increase in trans fat, there is a 93%

increase in risk. • Trans fats are indeed a greater health risk than

saturated fats.

Table 3.9-0

Table 3.9-1

Table 3.9-2

3.10 Phospholipids and steroids are important lipids with a variety of functions

• Phospholipids are the major component of all cell membranes.

• Phospholipids are structurally similar to fats. • Fats contain three fatty acids attached to glycerol. • Phospholipids contain two fatty acids attached to

glycerol.

Figure 3.10

Phosphate group

Glycerol

Hydrophilic heads

Hydrophobic tails

Symbol for phospholipid

Figure 3.10a

Phosphate group

Glycerol

Hydrophilic heads

Hydrophobic tails

• Phospholipids cluster into a bilayer of phospholipids.

• The hydrophilic heads are in contact with • the water of the environment and • the internal part of the cell.

• The hydrophobic tails cluster together in the center of the bilayer.

Figure 3.10b

Hydrophilic heads

Hydrophobic tails

Symbol for phospholipid

• Steroids are lipids in which the carbon skeleton contains four fused rings.

• Cholesterol is • a common component in animal cell membranes

and • a starting material for making steroids, including sex

hormones.

Figure 3.10c

3.11 CONNECTION: Anabolic steroids pose health risks

• Anabolic steroids are synthetic variants of the male hormone testosterone that are abused by some athletes with serious consequences, including

• violent mood swings, • depression, • liver damage, • cancer, • high cholesterol, and • high blood pressure.

PROTEINS

3.12 Proteins have a wide range of functions and structures

• Proteins are • involved in nearly every dynamic function in your

body and • very diverse, with tens of thousands of different

proteins, each with a specific structure and function, in the human body.

• Proteins are composed of differing arrangements of a common set of just 20 amino acid monomers.

• Probably the most important role for proteins is as enzymes, proteins that

• serve as catalysts and • regulate virtually all chemical reactions within cells.

• Other types of proteins include • transport proteins embedded in cell membranes,

which move sugar molecules and other nutrients into your cells,

• defensive proteins, such as antibodies of the immune system,

• signal proteins such as many hormones and other chemical messengers that help coordinate body activities,

• Other types of proteins include (continued) • receptor proteins, built into cell membranes, which

receive and transmit signals into your cells, • contractile proteins found within muscle cells, • structural proteins such as collagen, which form the

long, strong fibers of connective tissues, and • storage proteins, which serve as a source of amino

acids for developing embryos in eggs and seeds.

• The functions of different types of proteins depend on their individual shapes.

• A polypeptide chain contains hundreds or thousands of amino acids linked by peptide bonds.

• The amino acid sequence causes the polypeptide to assume a particular shape.

Figure 3.12a

Groove

Figure 3.12b

Groove

Figure 3.12c

• If a protein’s shape is altered, it can no longer function.

• In the process of denaturation, a protein • unravels, • loses its specific shape, and • loses its function.

• Proteins can be denatured by changes in salt concentration, changes in pH, or high heat.

3.13 Proteins are made from amino acids linked by peptide bonds

• Amino acids all have • an amino group and • a carboxyl group (which makes it an acid).

• Also bonded to the central carbon is • a hydrogen atom and • a chemical group symbolized by R, which

determines the specific properties of each of the 20 amino acids used to make proteins.

Figure 3.13a

Amino group

Carboxyl group

• Amino acids are classified as either • hydrophobic or • hydrophilic.

Figure 3.13b

Hydrophobic Hydrophilic

Leucine (Leu) Serine (Ser) Aspartic acid (Asp)

• Amino acid monomers are linked together in a dehydration reaction,

• joining the carboxyl group of one amino acid to the amino group of the next amino acid, and

• creating a peptide bond. • Additional amino acids can be added by the same

process to create a chain of amino acids called a polypeptide.

Figure 3.13c-1

Carboxylgroup

Aminogroup

Amino acid Amino acid

Figure 3.13c-2

Carboxylgroup

Aminogroup

Amino acid

Dehydrationreaction

Peptide bond

DipeptideH2O

Amino acid

3.14 VISUALIZING THE CONCEPT: A protein’s functional shape results from four levels of structure

• A protein can have four levels of structure: 1. primary structure, 2. secondary structure, 3. tertiary structure, and 4. quaternary structure.

Animation: Protein Structure Introduction

Animation: Primary Protein Structure

Animation: Secondary Protein Structure

Animation: Tertiary Protein Structure

Animation: Quaternary Protein Structure

Figure 3.14-0-1

Aminoacids

+H3N Amino end

Peptide bonds connect aminoacids.

PRIMARY STRUCTURE

Figure 3.14-0-2

Aminoacids

+H3N Amino end

Alphahelix

Secondary structuresare maintained by hydrogen bonds between atoms

of the backbone.

Beta pleated sheet

PRIMARY STRUCTURE

Two types of SECONDARY STRUCTURES

Figure 3.14-0-3

Aminoacids

+H3N Amino end

Alphahelix

of the backbone.

Beta pleated sheet

Tertiary structure isstabilized by interactions between R groups.

TERTIARY STRUCTURE

PRIMARY STRUCTURE

Figure 3.14-0-4

Aminoacids

+H3N Amino end

Alphahelix

of the backbone.

Beta pleated sheet

Polypeptides are associatedinto a functional protein.

TERTIARY STRUCTURE

PRIMARY STRUCTURE

QUATERNARYSTRUCTURE

Figure 3.14-0

Aminoacids

+H3N Amino end

Alphahelix

of the backbone.

Beta pleated sheet

TERTIARY STRUCTURE

PRIMARY STRUCTURE

QUATERNARYSTRUCTURE

Figure 3.14-1

Aminoacids

+H3N Amino end

PRIMARYSTRUCTURE

Figure 3.14-2

Alphahelix

of the backbone.

Beta pleated sheet

Figure 3.14-3

Tertiary structure is stabilized by interactions between R groups.

TERTIARY STRUCTURE

Figure 3.14-4

QUATERNARYSTRUCTURE

NUCLEIC ACIDS

3.15 DNA and RNA are the two types of nucleic acids

• The amino acid sequence of a polypeptide is programmed by a discrete unit of inheritance known as a gene.

• Genes consist of DNA (deoxyribonucleic acid), a type of nucleic acid.

• DNA is inherited from an organism’s parents. • DNA provides directions for its own replication. • DNA programs a cell’s activities by directing the

synthesis of proteins.

3.15 DNA and RNA are the two types of nucleic acids

• DNA does not build proteins directly. • DNA works through an intermediary, RNA

(ribonucleic acid). • DNA is transcribed into RNA in a cell’s nucleus. • RNA is translated into proteins in the cytoplasm.

Figure 3.15-1

Figure 3.15-2

Transcription

Nucleic acids

Figure 3.15-3

Transcription

Translation

Aminoacid

Protein

Nucleic acids

3.16 Nucleic acids are polymers of nucleotides

• DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are composed of monomers called nucleotides.

• Nucleotides have three parts: 1. a five-carbon sugar called ribose in RNA and

deoxyribose in DNA, 2. a phosphate group, and 3. a nitrogenous base.

Figure 3.16a

Phosphate group

Nitrogenous base

(adenine)

• DNA nitrogenous bases are • adenine (A), • thymine (T), • cytosine (C), and • guanine (G).

• RNA also has A, C, and G, but instead of T, it has uracil (U).

• A nucleic acid polymer, a polynucleotide, forms from the nucleotide monomers when the phosphate of one nucleotide bonds to the sugar of the next nucleotide by dehydration reactions.

• This produces a repeating sugar-phosphate backbone with protruding nitrogenous bases.

Figure 3.16b

Nucleotide

Sugar-phosphate backbone

• RNA is usually a single polynucleotide strand. • DNA is a double helix, in which two polynucleotide

strands wrap around each other. • The two strands are associated because particular

bases always hydrogen-bond to one another. • A pairs with T, and C pairs with G, producing base

pairs.

Figure 3.16c

Base pair

3.17 EVOLUTION CONNECTION: Lactose tolerance is a recent event in human evolution

• The majority of people • stop producing the enzyme lactase in early

childhood and • do not easily digest the milk sugar lactose after

childhood. • Lactose tolerance represents

• a relatively recent mutation in the human genome and

• a survival advantage for human cultures with milk and dairy products available year-round.

3.17 EVOLUTION CONNECTION: Lactose tolerance is a recent event in human evolution

• Researchers identified three new mutations in 43 ethnic groups in East Africa that keep the lactase gene permanently turned on.

• The mutations • are all different from each other and from the

European mutation, • appear to have occurred about 7,000 years ago, and • occurred about the same time as the domestication

of cattle in these regions.

Figure 3.17

You should now be able to

1. Describe the importance of carbon to life’s molecular diversity.

2. Describe the chemical groups that are important to life.

3. Explain how a cell can make a variety of large molecules from a small set of molecules.

4. Define monosaccharides, disaccharides, and polysaccharides and explain their functions.

5. Define lipids, phospholipids, and steroids and explain their functions.

You should now be able to

6. Explain how trans fats are formed in food. Describe the evidence that suggests that eating trans fats is more unhealthy than consuming saturated fats.

7. Describe the chemical structure of proteins and the importance of proteins to cells.

8. Describe the chemical structure of nucleic acids and explain how they relate to inheritance.

9. Explain how lactose tolerance has evolved in humans.

Figure 3.UN01

Dehydration

Hydrolysis

H2OShort polymer Monomer Longer polymer

Figure 3.UN02-0

Figure 3.UN02-1

Figure 3.UN02-2

Figure 3.UN03

Figure 3.UN04

Sucrose

Figure 3.UN05

Figure 3.UN06

Enzyme A Enzyme B

Temperature (°C)

0 20 40 60 80 100

Chapter 3 · 2020-03-17 · 3.1 Life’s molecular diversity is based on the properties of carbon...

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