Biological molecules 生物分子复习笔记

Chapter 2: Biological molecules

The building blocks of life

4 most common elements in living organisms: hydrogen, carbon, oxygen and nitrogen (in order of abundance) Organic molecules always contain carbon and hydrogen

Monomers, polymers and macromolecules

Macromolecules: giant biological molecules-polysaccharides,

proteins and nucleic acids (are all polymers)

Polymers: giant molecules made from many similar repeating

subunits (monomers) joined together in a chain

Monomers: relatively simple molecules which are used as basic

building blocks for the synthesis of polymers-monosaccharides,

amino acids and nucleotides

Carbohydrates

All carbohydrates contain the elements carbon, hydrogen and oxygen

Hydrate refers to water

General formula: C x(H2O)y

Carbohydrates are divided into 3 main groups: monosaccharides, disaccharides and polysaccharides Saccharide refers to a sugar or sweet substance

Monosaccharides

Monosaccharide: a molecule consisting of a single sugar unit with the general formula (CH2O)n

General formula: (CH2O)n

Monosaccharides are sugars

Classified according to the number of carbon atoms in each molecule: trioses (3C) pentoses (5C) and hexoses (6C) Common hexoses: glucose, fructose and galactose

Common pentoses: ribose and deoxyribose

➢Molecular and structural formulae

Molecular formula for a hexose: C6H12O6

Structural formula: a diagram that shows the arrangements of the atoms

➢Ring structures

For pentoses and hexoses, the

chain of carbon atoms is long

enough to close up on itself and

form a more stable ring structure

ɑ-glucose: hydroxyl group, -OH,

on carbon atom 1 is below the

ring

β-glocose: -OH is above the ring

Isomers: two forms of the same

chemical

➢Roles of monosaccharides in living organisms

Two major functions:

1.A source of energy in respiration: the carbon-hydrogen bonds can be broken to release a lot of energy, which is transferred to help make ATP

Glucose-the most important monosaccharide in energy metabolism

2.Building blocks for larger molecules

Disaccharides and the glycosidic bond

Disaccharide: sugar molecule consisting of two monosaccharides joined together by a glycosidic bond Disaccharides are sugars

Common disaccharides: maltose, sucrose and lactose

Maltose=glucose+glucose

Sucrose (in plants) =glucose+fructose

Lactose (in milk) =glucose+galactose

Lactose is an important constituent of the diet of young mammals

Condensation: the process of two monosaccharides joining together with a glycosidic bond by losing water

Two hydroxyl (-OH) groups line up alongside each other

One combines with a hydrogen atom form the other to form a H2O molecule

Glycosidic bond: oxygen bridge between the two molecules

Hydrolysis: the reverse of condensation-disaccharides or polysaccharides are broken down to monosaccharides by adding water

Polysaccharides

Polysaccharides: polymers whose subunits are monosaccharides joined together by glycosidic bonds

Common polysaccharides: starch, glycogen and cellulose