chapter 2 - chemical bonds and macromolecules
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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.