INTRODUCTORY BIOLOGY By HOANG ANH HOANG, Ph.D. Department of Biotechnology, Faculty of Chemical Engineering, HCMUT
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.