Molecules of Life

Chapter 3

3.1 Molecules of Life

Molecules of life are synthesized by living cells

• Carbohydrates

• Lipids

• Proteins

• Nucleic acids

Structure to Function

Molecules of life differ in three-dimensional

structure and function

• Carbon backbone

• Attached functional groups

Structures give clues to how they function

Organic Compounds

Consist primarily of carbon and hydrogen atoms

• Carbon atoms bond covalently with up to four

other atoms, often in long chains or rings

Functional groups attach to a carbon backbone

• Influence organic compound’s properties

An Organic Compound: Glucose

Four models

Functional Groups

Functional Groups:

The Importance of Position

Processes of Metabolism

Cells use energy to grow and maintain

themselves

Enzyme-driven reactions build, rearrange, and

split organic molecules

Building Organic Compounds

Cells form complex organic molecules

• Simple sugars → carbohydrates

• Fatty acids → lipids

• Amino acids → proteins

• Nucleotides → nucleic acids

Condensation combines monomers to form

polymers

Condensation and Hydrolysis

Key Concepts:

STRUCTURE DICTATES FUNCTION

We define cells partly by their capacity to build

complex carbohydrates and lipids, proteins, and

nucleic acids

The main building blocks are simple sugars, fatty

acids, amino acids, and nucleotides

These organic compounds have a backbone of

carbon atoms with functional groups attached

3.2 Carbohydrates –

The Most Abundant Ones

Three main types of carbohydrates

• Monosaccharides (simple sugars)

• Oligosaccharides (short chains)

• Polysaccharides (complex carbohydrates)

Carbohydrate functions

• Instant energy sources

• Transportable or storable forms of energy

• Structural materials

Simple Sugars: Glucose and Fructose

Oligosaccharides: Sucrose

Complex Carbohydrates:

Bonding Patterns

Complex Carbohydrates:

Starch, Cellulose, and Glycogen

Complex Carbohydrates:

Starch, Cellulose, and Glycogen

Fig. 3.8, p. 39

c Glycogen. In animals, this

polysaccharide is a storage form

for excess glucose. It is

especially abundant in the liver

and muscles of highly active

animals, including fishes and

people.

Structure of

cellulose

Complex Carbohydrates:

Chitin

Key Concepts:

CARBOHYDRATES

Carbohydrates are the most abundant biological

molecules

Simple sugars function as transportable forms of

energy or as quick energy sources

Complex carbohydrates are structural materials

or energy reservoirs

3.3 Greasy, Oily – Must Be Lipids

Lipids

• Fats, phospholipids, waxes, and sterols

• Don’t dissolve in water

• Dissolve in nonpolar substances (other lipids)

Lipid functions

• Major sources of energy

• Structural materials

• Used in cell membranes

Fats

Consists of –

• Glycerol and fatty acids

• Lipids with one, two, or three fatty acid tails

• Saturated – solid at room temp

• Unsaturated - liquid at room temp

• cis -same side

• trans - opposite side

Triglycerides (neutral fats )

• Three fatty acid tails

• Most abundant animal fat (body fat)

• Major energy reserves

Triglyceride Formation

Phospholipids

Main component of

cell membranes

• Hydrophilic head,

hydrophobic tails

hydrophilic head

two hydrophilic tails

Fig. 3.13, p. 41

b

Fig. 3.13, p. 41

c Cell membrane section

Waxes

Firm, pliable, water repelling, lubricating

Sterols: Cholesterol

Membrane components; precursors of other

molecules (steroid hormones)

Key Concepts:

LIPIDS

Complex lipids function as energy reservoirs,

structural materials of cell membranes, signaling

molecules, and waterproofing or lubricating

substances

3.4 Proteins –

Diversity in Structure and Function

Proteins have many functions

• Structures

• Nutrition

• Enzymes

• Transportation

• Communication

• Defense

Protein Structure

Built from 20 kinds of amino acids

Fig. 3.15, p. 42

Four Levels of Protein Structure

1. Primary structure

• Amino acids joined by peptide bonds form a

linear polypeptide chain

2. Secondary structure

• Polypeptide chains form

sheets and coils

3. Tertiary structure

• Sheets and coils pack into functional domains

Four Levels of Protein Structure

3. Tertiary structure

• Sheets and coils pack into functional domains

Four Levels of Protein Structure

4. Quaternary structure

• Many proteins (e.g. enzymes) consist of two or

more chains

Other protein structures

• Glycoproteins

• Lipoproteins

• Fibrous proteins

Levels of Protein Structure

Levels of Protein Structure

Levels of Protein Structure

Levels of Protein Structure

3.5 Why is Protein Structure

So Important?

Protein structure dictates function

Sometimes a mutation in DNA results in an

amino acid substitution that alters a protein’s

structure and compromises its function

• Example: Hemoglobin and sickle-cell anemia

Normal Hemoglobin Structure

Normal Hemoglobin Structure

Sickle-Cell Mutation

Fig. 3.19, p. 45

VALINE HISTIDINE LEUCINE GLUTAMATE VALINE THREONINE PROLINE

sickle cell

normal cell

b One amino acid substitution results in the

abnormal beta chain in HbS molecules. Instead

of glutamate, valine was added at the sixth

position of the polypeptide chain.

c Glutamate has an overall negative charge; valine

has no net charge. At low oxygen levels, this

difference gives rise to a water-repellent, sticky

patch on HbS molecules. They stick together

because of that patch, forming rodshaped clumps

that distort normally rounded red blood cells into

sickle shapes. (A sickle is a farm tool that has a

crescent-shaped blade.)

Sickle-Cell Mutation

Denatured Proteins

If a protein unfolds and loses its three-

dimensional shape (denatures), it also loses its

function

Caused by shifts in pH or temperature, or

exposure to detergent or salts

• Disrupts hydrogen bonds and other molecular

interactions responsible for protein’s shape

Key Concepts:

PROTEINS

Structurally and functionally, proteins are the

most diverse molecules of life

They include enzymes, structural materials,

signaling molecules, and transporters

3.6 Nucleotides, DNA, and RNAs

Nucleotide structure, 3 parts:

• Sugar

• Phosphate group

• Nitrogen-containing base

Nucleotide Functions:

Reproduction, Metabolism, and Survival

DNA and RNAs are nucleic acids, each

composed of four kinds of nucleotide subunits

ATP energizes many kinds of molecules by

phosphate-group transfers

Other nucleotides function as coenzymes or as

chemical messengers

Nucleotides of DNA

Fig. 3.21, p. 46

THYMINE

(T)

base with a

single-ring

structure

Fig. 3.21, p. 46

CYTOSINE

(C)

base with a

single-ring

structure

DNA, RNAs, and Protein Synthesis

DNA (double-stranded)

• Encodes information about the primary structure

of all cell proteins in its nucleotide sequence

RNA molecules (usually single stranded)

• Different kinds interact with DNA and one another

during protein synthesis

The DNA Double-Helix

Key Concepts:

NUCLEOTIDES AND NUCLEIC ACIDS

Nucleotides have major metabolic roles and are

building blocks of nucleic acids

Two kinds of nucleic acids, DNA and RNA,

interact as the cell’s system of storing, retrieving,

and translating information about building

proteins