INTRODUCTORY BIOLOGY

By

HOANG ANH HOANG, Ph.D.

Department of Biotechnology,

Faculty of Chemical Engineering, HCMUT

Chapter 2 Chemical bonds and Macromolecules

Monomers - Macromolecules

• A cell Is mainly formed from Carbon compounds

I. Chemical bonds

• Covalent bonds

• Non-covalent bonds

- Hydrogen bonds

- Ionic bonds

- Van de waal interaction

- Hydrophobic effect

1. Covalent bonds

- Principle force to hold atoms together

- Sharing electrons

- Typical length: 0.15-0.2 nm

- strong bond

• Single-double-triple bonds

C – C

C = C

C C---

• Chirality (optical isomers)

• Polar-nonpolar bonds

C – C, C – H : nonpolar

H-O-H: polar

2. Noncovalent bonds

- Hydrogen bonds

- Ionic bonds

- Van der Waals bonds

- Hydrophobic effect

• Hydrogen bonds

- A hydrogen bond is the interaction of a partially positively charged hydrogen atom with O or N (negative charged)

- Strength: ~1/20 covalent bonds

• Example:

• Ionic bond (Electrostatic)

Ionic interactions result from the attraction of a positively charged ion—a cation—for a negatively charged ion—an anion.

• Van der Waals Interactions

When any two atoms approach each other closely, they create a weak, nonspecific attractive force called a van der Waals interaction.

• Weak: 1/3-1/4 hydrogen bonds

• Hydrophobic Effect

- Molecules that contain nonpolar bonds are usually insoluble in water and are termed hydrophobic

• Strength of the bonds

II. Macromolecules

• Carbohydrates

• Proteins

• Nucleic acids

• (Lipid)

Monomers Polymers

1. Carbohydrates

Monosaccharides

• The general formula (CH2O)n, n can be 3, 5, 6,… and have two or more hydroxyl groups.

• Ring formation

In aqueous solution, the aldehyde or ketone group of a sugar molecule tends to react with a hydroxyl group of the same molecule

• Isomers

- Many monosaccharides differ only in the spatial arrangement of atoms

Disaccharides

• The carbon that carries the aldehyde or the ketone can react with any hydroxyl group on a second sugar molecule to form a disaccharide.

• The linkage is called a glycosidic bond.

Oligosaccharides and Polysaccharides

• Short chains are called oligosaccharides

• Long chains are called polysaccharides

2. Nucleic acid

• Monomer: nucleotides

Two types of chemically similar nucleic acids, DNA (deoxyribonucleic acid) and RNA (ribonucleic acid), are the principal information-carrying molecules of the cell.

Five Different Bases to Build Nucleic Acids

• A DNA molecule is composed of two antiparallel DNA strands held together by hydrogen bonds between the paired bases.

The Structure of DNA Provides a Mechanism for Heredity

• How could the information to specify an organism be carried in a chemical form?

• How could this information be duplicated and copied from generation to generation?

3. Protein

• The amino acid

• Amino acid families:

- acidic

- basic

- uncharged polar

- nonpolar

• Basic side chains

- example:

• Acidic side chains

- example:

• Uncharged polar side chains

• Nonpolar side chains

- example:

• There are 20 different of amino acids in proteins

• Peptide bonds

• N-terminus; C-terminus

• Protein folding

- noncovalent bonds

The α Helix and the β Sheet Are Common Folding Patterns

• α Helix

• β Sheet

(A) An antiparallel β sheet; (B) A parallel β sheet.

Example: antiparallel β sheet

Covalent Cross-Linkages Stabilize Extracellular Proteins

• the most common cross-linkages in proteins are covalent sulfur–sulfur bonds.

• Protein structure

- Primary (sequence of aa)

- Secondary (local)

- Tertiary

The α Helix and the β Sheet

- Quaternary

> 1 polypeptide chain

4. Lipids• R-COOH (R: tail)

• Triacylglycerols (triglycerides)

• Phospholipids

- the major constituents of cell membranes.