Biomolecules

Biology and Society: Does Thanksgiving Dinner Make You

Sleepy?

– After finishing a huge Thanksgiving dinner, many people feel especially lethargic and a few even doze off.

– Many people think that turkey makes you sleepy.• Is there a biological basis to this claim?

Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings

Figure 3.1

Turkey meat is high in tryptophan.

Tryptophan is a molecule that is converted in your body to serotonin, which promotes sleep.

However, there is little evidence that a turkey dinner encourages sleep more than any other meal.

Organic Molecules

A cell is mostly water.• The rest of the cell consists mostly of carbon-

based molecules.• Organic chemistry is the study of carbon

compounds.

Carbon Chemistry

Carbon is a versatile atom.• It has four electrons in an outer shell that holds

eight.• Carbon can share its electrons with other atoms to

form up to four covalent bonds.

Figure 3.2

Carbon can use its bonds to• Attach to other carbons• Form an endless diversity of carbon skeletons

Figure 3.3

The simplest organic compounds are hydrocarbons.

• These are organic molecules containing only carbon and hydrogen atoms.

• The simplest hydrocarbon is methane.

Figure 3.4

Larger hydrocarbons are the main molecules in the gasoline we burn in our cars.

The hydrocarbons of fat molecules provide energy for our bodies.

Figure 3.5

Giant Molecules from Smaller Building Blocks

On a molecular scale, many of life’s molecules are gigantic.

• Biologists call them macromolecules.• Examples: DNA, carbohydrates

Figure 3.6a

Most macromolecules are polymers.• Polymers are made by stringing together many

smaller molecules called monomers.• Cells link monomers by dehydration reactions.

Figure 3.6b

Organisms also have to break down macromolecules.

• Cells do this by a process called hydrolysis.

Biological MoleculesThere are four categories of large molecules in cells:

• Carbohydrates• Lipids• Proteins• Nucleic acids

Carbohydrates

Carbohydrates include:• Small sugar molecules in soft drinks• Long starch molecules in pasta and potatoes

MonosaccharidesMonosaccharides are simple sugars.

• Glucose is found in sports drinks.• Fructose is found in fruit.

Honey contains both glucose and fructose.

Figure 3.8

The monosaccharides glucose and fructose are isomers.

• They have the same formula, but their atoms are arranged differently.

Figure 3.9

In aqueous solutions, monosaccharides form rings.

Monosaccharides are the main fuel that cells use for cellular work.

Figure 3.10

Disaccharides

A disaccharide is a double sugar.

• It is constructed from two monosaccharides.

Disaccharides are joined through a dehydration reaction.

Figure 3.11

Lactose is another type of disaccharide.• Some people have trouble digesting lactose, a

condition called lactose intolerance.

The most common disaccharide is sucrose, common table sugar.

• It consists of a glucose linked to a fructose.• Sucrose is extracted from sugar cane and the

roots of sugar beets.

The United States is one of the world’s leading markets for sweeteners.

• The average American consumes about 64 kg of sugar per year.

Figure 3.13

Complex carbohydrates are called polysaccharides.• They are long chains of sugar units.• They are polymers of monosaccharides.

Figure 3.14

Grazing animals survive on a diet of cellulose because they have prokaryotes in their digestive tracts that can break down cellulose.

Simple sugars and double sugars dissolve readily in water.

• They are hydrophilic, or “water-loving.”

In aqueous solutions, _____________ form ring structures.

Name three different polysaccharides.

In aqueous solutions, _monosaccharides_ form ring structures.

Name three different polysaccharides.

In aqueous solutions, _monosaccharides_ form ring structures.

Name three different polysaccharides.Starch – form of energy storage in plantsGlycogen – form of energy storage in animalsCelluose – structural component of plant cells

Lipids

Lipids are hydrophobic.• They do not mix with water.• Examples: fats and steroids

Fats

Dietary fat consists largely of the molecule triglyceride.

• Triglyceride is a combination of glycerol and three fatty acids.

Figure 3.15b

Unsaturated fatty acids• Have less than the maximum number of hydrogens

bonded to the carbons.

Saturated fatty acids • Have the maximum number of hydrogens bonded to

the carbons.

Most animal fats have a high proportion of saturated fatty acids, which can be unhealthy.

• Example: butter

Most plant oils tend to be low in saturated fatty acids.

• Example: corn oil

Figure 3.16

Not all fats are unhealthy. Some fats perform important functions in the body and are essential to a healthy diet.

SteroidsSteroids are very different from fats in structure and

function.• The carbon skeleton is bent to form four fused rings.

Cholesterol is the “base steroid” from which your body produces other steroids.

• Example: sex hormones

Figure 3.17

Steroids

Figure 3.19

Proteins

The Monomers: Amino Acids

All proteins are constructed from a common set of 20 kinds of amino acids.

Figure 3.20

Each amino acid consists of• A central carbon atom

bonded to four covalent partners.

• A side group that is variable among all 20.

Figure 3.21

Cells link amino acids together by dehydration reactions.• The resulting bond

between them is called a peptide bond.

Figure 3.22

Primary structure = The specific sequence of amino acids in a protein

A slight change in the primary structure of a protein affects its ability to function.

Figure 3.23

The substitution of one amino acid for another in hemoglobin causes sickle-cell disease.

Figure 3.24

Proteins have four levels of structure.

What Determines Protein Structure?

A protein’s shape is sensitive to the surrounding environment.

• Unfavorable temperature and pH changes can cause a protein to unravel and lose its shape.

• This is called denaturation.

What type of biological molecules are hydrophillic? Hydrophobic?

What are the “building blocks” of proteins?

What type of biological molecules are hydrophillic? Hydrophobic?

Hydrophillic: simple sugars and double sugars

Hydrophobic: lipids such as fat and cholesterol

What are the “building blocks” of proteins?

What type of biological molecules are hydrophillic? Hydrophobic?

Hydrophillic: simple sugars and double sugars

Hydrophobic: lipids such as fat and cholesterol

What are the “building blocks” of proteins?

Amino Acids

Nucleic Acids

Nucleic acids are information storage molecules.• They provide the directions for building proteins.

There are two types of nucleic acids:• DNA, deoxyribonucleic acid• RNA, ribonucleic acid

Figure 3.25

Figure 3.26

A Nucleotide:

Figure 3.27

Each DNA nucleotide has one of the following bases:

Figure 3.28a

Figure 3.28b

Two strands of DNA join together to form a double helix.

RNA, ribonucleic acid, is different from DNA.

• Its sugar has an extra OH group.

• It has the base uracil (U) instead of thymine (T).

DNA and Proteins as Evolutionary Tape Measures

Evolutionary relationships between organisms can be assessed.

• Molecular genealogy extends to relationships between species.

• Biologists use molecular analysis of DNA and protein sequences for testing evolutionary hypotheses.

Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings

Figure 3.30

The Microscopic World of Cells

Organisms are either:• Single-celled, such as most bacteria and protists• Multicelled, such as plants, animals, and most

fungi

Figure 4.2a

The light microscope is used by many scientists.• Light passes through the specimen.• Lenses enlarge, or magnify, the image.

Cells were first discovered in 1665 by Robert Hooke.

The accumulation of scientific evidence led to the cell theory:

• All living things are composed of cells.• All cells are formed from previously existing cells.

Figure 4.3

The electron microscope (EM) uses a beam of electrons.

• It has a higher resolving power than the light microscope.

The electron microscope can magnify up to 100,000X.

• Such power reveals the diverse parts within a cell.

Figure 4.2b

The scanning electron microscope (SEM) is used to study the detailed architecture of the surface of a cell.

Figure 4.2c

The transmission electron microscope (TEM) is useful for exploring the internal structure of a cell.

The Two Major Categories of Cells

– The countless cells on earth fall into two categories:

• Prokaryotic cells• Eukaryotic cells

– Prokaryotic and eukaryotic cells differ in several respects.

Figure 4.4

Figure 4.5

Figure 4.6a

Figure 4.6b