Biological Molecules (Combined) 1

Monomer, dimer, trimer, polymer

Hydrolysis

Breaking down a large molecule into smaller molecules (e.g., polymer to monomer). Each bond is broken after reaction with one molecule of water.

Condensation

Forming a large molecule from smaller molecules (e.g., monomer to polymer). As each bond is formed, one molecule of water is released. This reaction is also known as dehydration, since water is lost.

Sugars, starch, cellulose

Examples of carbohydrates

Monosaccharide

Monomer form of carbohydrates

Glucose, galactose, fructose, ribose

Examples of monosaccharides

Chemical formula of monosaccharides

Usually (CH₂O)_n. For example, glucose, galactose, and fructose are C₆H₁₂O6.

Disaccharide

Dimer form of carbohydrates

Maltose, lactose, sucrose

Examples of disaccharides

Simple sugars

Monosaccharides and disaccharides

Isomers

Molecules with the same chemical formula but different arrangements of atoms. E.g., Glucose, galactose, and fructose are isomers. They all have the chemical formula C₆H₁₂O₆.

Main function of simple sugars

Most serve as the main energy source for living things. Cellular respiration converts glucose and oxygen to form carbon dioxide, water, and energy.

Polysaccharide

Polymer form of carbohydrates (also known as ‘complex carbohydrate’)

Starch, glycogen, cellulose

Examples of polysaccharides. All three are formed from glucose.

Main function of starch

Energy storage in plants

Main function of glycogen

Short-to-medium-term energy storage in animals and fungi

Main function of cellulose

Makes up the cell walls in plants

Glycosidic bond

Bond formed between monomers of carbohydrates to produce dimers or polymers.

Polysaccharide (carbohydrate)

Polysaccharide (carbohydrate)

Oils, fats, cholesterol, waxes

Examples of lipids

Triglycerides

Oils and fats. Made from 1 glycerol + 3 fatty acids.

Main functions of triglycerides

Long-term energy storage

Triglyceride (lipid)

Triglyceride (lipid)

Saturated fatty acid

Fatty acid molecule with no C=C double bonds. Triglycerides made from a greater number of saturated fatty acids pack closely together and tend to be solid at room temperature.

Unsaturated fatty acid

Fatty acid molecule with C=C double bond(s), which provide kink(s) in the molecule Triglycerides made from a greater number of unsaturated fatty acids do not pack closely together and tend to be liquid at room temperature.

Phospholipids

Found in cell membranes. Made from 1 glycerol + 1 phosphate and choline (‘head’) + 2 fatty acid ‘tails’.

Phospholipid (lipid)

Hydrophilic

“Water-loving”. Hydrophilic molecules are polar molecules which dissolve in water but not oil.

Hydrophobic

“Water-hating”. Hydrophobic molecules are non-polar molecules which dissolve in oil but not water.

Amphipathic

Amphipathic molecules contain both hydrophobic and hydrophilic parts. Examples: Phospholipids, fatty acids, soaps, some proteins.

Head and tails of phospholipids

Heads are hydrophilic and like to be surrounded by water. Tails are hydrophobic and like to avoid water.

The cell membrane is mostly made of a …

Phospholipid bilayer

Phospholipid bilayer

Ester bond

Bond formed between glycerol and fatty acids.

Enzymes, hemoglobin, collagen, keratin, insulin

Examples of proteins

Amino acid (There are 20 standard types of amino acids.)

Monomer form of proteins

Amino acid (protein monomer) – Notice how it must contain C, H, N and O!

Polypeptide

Polymer form of proteins

Polypeptide (protein)

Functions of proteins

Proteins take part in many important biological processes. A few examples: Enzymes are proteins that speed up chemical reactions. Some proteins like collagen and keratin are structural proteins. Some proteins like insulin are chemical signaling molecules.

Protein folding

Polypeptide twists and folds into a specific 3D shape. The shape of a protein is very important to the protein’s function.

Protein denaturation

A protein unfolds and loses its shape under high temperatures, extreme pH, or when certain chemicals are added. This denaturation is usually irreversible, meaning the protein loses its function.

DNA, RNA

Examples of nucleic acids

Nucleotide

Monomer form of nucleic acids

Components of a nucleotide

(1) Phosphate, (2) sugar (ribose for RNA, deoxyribose for DNA), and (3) nitrogen-containing base (determines ATCG in DNA and AUCG in RNA).

Nucleotide (nucleic acid monomer)

Polynucleotide

Polymer form of nucleic acid

Phosphodiester bond

Bond formed between nucleotides to produce polynucleotides.

Function of DNA

Contains genetic information, “blueprint for life”, passed down via inheritance.

DNA (nucleic acid)

DNA (nucleic acid)

The Benedict’s test tests for …

Reducing sugars (all monosaccharides, and disaccharides except sucrose).

Procedure for Benedict’s test

Add Benedict’s reagent (blue) and warm.

Positive result for Benedict’s test

Green/yellow/orange/red precipitate is formed. (Colors from left to right: increasing concentration of reducing sugar)

The iodine test tests for …

Starch

Procedure for iodine test

Add a few drops of iodine solution (yellowish-brown).

Positive result for iodine test

Turns dark blue

The Biuret test tests for …

Proteins

Procedure for Biuret test

Add Biuret’s reagent (blue) and wait.

Positive result for Biuret test

Purple solution.

The ethanol emulsion test tests for …

Fats and oils (lipids)

Procedure for ethanol emulsion test

Add ethanol and mix

Positive result for ethanol emulsion test

Cloudy emulsion forms