BSC 1005-Topic 3

Water and Other Biological Molecules

Water : 71% of earth’s surface, 66% of weight of human body

Important Properties of water

1. Required and generated by cellular reactions.

2. Important Solvent: universal solvent (due to the chemical structure)

3. Ice (solid) is less dense than water (liquid): Important for marine organisms.

4. High specific heat-Important for insulating earth, for cooling living organisms by sweating

5. Cohesion and surface tension: enables small insects to walk on it, causes water to bead up on waxy or oily surfaces.

Hydrophilic: compounds that interact with water: ex: salt

Hydrophobic: compounds that won’t interact with water. Ex: oil

Acids and Bases

Acid: substance that yields hydrogen ions in solution. Ex: HCl (Fig 3.5)

Base: substance that accepts hydrogen ions (ex: sodium hydroxide (NaOH))

pH scale :measurement of H⁺ ion conc., logarithmic(Fig 3.6), Ranges from 0-14

Why does pH matter?

· Living things prefer pH around neutral (6-8)

· Health problems: diabetes, cardiac arrest, vomiting (acidosis)

· Buffering systems are used to counteract.

· Buffers: weak acids or bases that neutralize acids or bases

· The environment and pH: Acid rain

The Molecules of Life

· Carbon is the starting point for biological molecules

· Carbon’s importance comes from its bonding capacity, can make 4 bonds (covalent, stable)

Carbohydrates

Contains carbon, hydrogen and oxygen in a 1:2:1 ratio

Monomers: simple sugars

Ex: glucose, fructose, ribose, deoxyribose

Polymers are chains of monomers created by chemical reaction called condensation (Fig 3.10)

Simplest polymer is disaccharide (2 monomers). Ex. Sucrose, lactose, maltose

Condensation reactions can be reversed – digestion

Complex carbohydrates: Long chains of monomers (polysaccharides)

a. Starch: Form stored in plants

Abundant in potato, rice, carrots and corn

b. Glycogen: stored in the liver and muscle cells of animals (animal starch)

c. Cellulose: major component of the cell walls of plants and other organisms.

· Animals can not digest it.

· Source of fiber in the diet

d. Chitin: exoskeleton of insects

· similar to cellulose.

Lipids

Composed of C, H, and O , More H than carbohydrates

insoluble in water

Major function: Energy storage and insulation

Also function as hormones and outer lining of all cells

Types of Lipids

A. Glycerides: composed of glycerol and fatty acids (fig 3.13)

Triglycerides are the most important (90% lipid weight in food)

Fats are triglycerides (Three fatty acids linking to glycerol)

Saturated fattyacids: no double bonds between carbons

Monounsaturated = one double bond

Polyunsaturated = two or more double bonds (Fig 3.14)

Oils: Fat in their liquid form

Saturated fatty acids are linked with heart disease.

Glucose or Fat can be immediate source of energy or may be stored for future use (Fig 3.17)

B. Lipids- Steroids

Composed of linked sets of four carbon rings

Ex: Chloestrol, testosterone and estrogen

Chloestrol is a part of outer cell membrane, help breakdown fats

Estrogen and Testosterone important in reproduction

C. Lipids –Phospholipids

Composed of glycerol, 2 fattyacids and a phosphate group.

Part of cell membrane

Dual natured molecule: one end is hydrophilic and the other end is hydrophobic

Proteins

Made up of amino acids

There are 20 amino acids that make up thousands of proteins (polypeptides)

Variety of functions: Table 3.2

Protein shape (structure) is crucial to its proper functioning

Four levels of protein structure (Fig 3.24)

If protein lose their structure, they lose their function (denaturing)

Lipoprotein: combination of protein and lipids

HDLS and LDLS

Glycoprotein: protein and carbohydrate

Nucleic Acids

Made of nucleotides

Provides information for the structure of proteins Ex: DNA & RNA

Nucleotides: Building blocks of nucleic acids

Currency of the cell (ATP)