Chapter 3

BiologySixth Edition

Raven/Johnson

(c) The McGraw-Hill Companies, Inc.

www.nicholls.edu/biol-qcf

The Chemistry of Carbon

Because carbon only has 4 electrons in its outer shell, it can attach to four separate molecules

Organic molecules consisting of only C and H are called hydrocarbons.

Organic molecules contain C and H

Hydrocarbon chains can have functional groups that cause the macromolecule to behave in a certain way.

Carboxyl Group: -COOH -COO¯ + H+

Making and Breaking Macromolecules

• Macromolecules (polymers) are formed from smaller building blocks called monomers.

• Macromolecules are formed by dehydration synthesis (requires energy)

• Macromolecule bonds are broken by hydrolysis (releases energy in bonds)

Energy must be used to build macromolecules.

Energy is released when macromolecules are split.

Four Types of Organic Macromolecules

• Proteins• Nucleic Acids• Lipids• Carbohydrates

Protein Types and Function

• Enzyme Catalyst– Facilitate chemical

reactions• Defense

– Body’s hormone and immune system

• Transport– Specific small

molecules and ions

• Support– Structural roles

• Motion– Aid in muscle

movement• Regulation

– Intercellular messengers

Protein Building Blocks

• Proteins are made of linked amino acids

• Only 20 amino acids available

• Sequence of amino acids are unique for each protein

C

NH2

COOH

H R

Structure of Amino Acids

(AcidicGroup)

(R or FunctionalGroup)

(AminoGroup)

(HydrogenGroup)

Five Groups of Amino Acids

• Nonpolar • Polar• Aromatic• Ionizable• Special Structural Property

Contains –CH2 or –CH3

Contains –O or only H

Contains carbon ring that has alternating single and double bonds

Contains acids or bases

Special function

Amino acids are linked by peptide bonds:

Dehydration synthesis

Primary Structure - Amino Acid Sequence

Secondary Structure - Folding due to hydrogen bond

Motifs – Characteristic secondary structure ( creates a fold or crease)

Driven into its tertiary structure by hydrophobic reactions with water, disulfide bonds, and other ionic and covalent bonds

-remember: some amino acids are nonpolar.

Two or more polypeptide chains associate to form a functional protein

Domain – structurally independent functional unit

subunits

Protein Structure Viewed at Six Levels

• Amino acid sequence (primary structure)

• Coils and sheets (secondary structure)

• Folds or creases (motifs)

• Three-dimensional shape (tertiary structure)

• Functional units (domains)

• Individual polypeptide subunits associated in quaternary structure

Chaperonins – proteins that help other proteins fold correctly

Primary structure determines tertiary structure!

Nucleic Acids

Nucleic acids are polymers of nucleotides.

Examples include Deoxyribonucleic Acid (DNA) and Ribonucleic Acid (RNA).

All nucleotides have:1.) nitrogenous base2.) pentose sugar

-deoxyribose-ribose

3.) phosphate group

Fig. 3.14

Fig. 3.15

A chemical difference between DNA and RNA

Nucleotides (monomer) connected by phosphodiester bonds to form nucleic acid (polymer).

Hydrogen bonds between base pairs gives DNA its characteristic double-helix shape.

Purines always bond with a pyrimidine, and with DNA it is always:

A-T; G-C

Adenine

Guanine

Cytosine

Thymine

UracilDNA vs RNA: RNA has Uracil instead of Thymine

H instead of CH3

DNA – double stranded, contains thymine, #2 C attached to H

RNA – single stranded, contains uracil, #2 C attached to OH

Nucleotide bases also play an important part in other molecules crucial to life: ATP, NAD, and FAD.

Adenosine triphosphate

Lipids- triglycerides, phospholipids, steroids

Lipids serve as long-term energy stores in cells, form membranes, and serve as hormones and insulation.

Lipids contain more energy per gram than any other biological molecule.

Lipids are nonpolar, thus they do not dissolve in water (hydrophobic).

All lipids are insoluble in water!!

Structure of Triglycerides

unsaturated

saturated

functional group –COOH

Fatty Acids: long chains of hydrocarbons with an acidic functional group –COOH

Saturated: no double bonds between carbons, “saturated

with hydrogen”, higher melting point than unsaturated

Unsaturated: has one or more double bonds between carbons

Dehydration or

Solids (butter) at room temperature; fatty acids can align close to each other

Liquids (corn oil) at room temperature; double bonds prevent fatty acids from aligning close to each other

Phosphate

Phospholipids consist of:

Glycerol

2 Fatty acids

Phosphate group

Polar end

Non- Polar end

Contains a phosphate group

Cellular membranes

Terpenes – long chain lipids; components of many biologically important pigments

All steroids characteristically have four carbon rings.

Carbohydrates

Carbohydrates contain C, H, and O and serve as quick energy and short-term energy storage.

Monomers of carbohydrates are the monosaccharides (simple sugars)

6-Carbon sugars – primary energy storage

Empirical formula for a 6-C sugar:

C6H12O6

Glucose is metabolized by cellular respiration

Dehydration synthesis – consumes energy

Hydrolysis splits the disaccharides and releases energy

‘double sugars’ – important in sugar transport

Your taste buds can taste the difference!

Same empirical formula (C6H1206)– different arrangement.

Energy storage for plants

Energy storage for animals

Structural polysaccharide – chief component of plant cell walls

Modified form of cellulose with a nitrogen group added to the glucose units. Structural building material in insects, many fungi, and certain other organisms.

The End.