A-Level Biology - biological molecules

What are monomers?

Monomers are small units that are the components of larger molecules, such as monosaccharides, amino acids, and nucleotides.

What are polymers?

Polymers are molecules made from many monomers joined together.

Alpha glucose structure?

Beta glucose structure?

Glycerol structure?

triglyceride structure

Dipeptide structure

Maltose formation diagram

What is a condensation reaction?

A condensation reaction is a chemical process where monomers are joined by a chemical bond, eliminating a water molecule.

What is hydrolysis?

Hydrolysis is the opposite of a condensation reaction, where water is added to break a chemical bond between two molecules.

What are carbohydrates?

Carbohydrates are molecules consisting only of carbon, hydrogen, and oxygen, formed as long chains of sugar units called saccharides.

What is a monosaccharide?

A monosaccharide is a single sugar unit, with examples including glucose, galactose, and fructose.

What is a disaccharide?

A disaccharide is formed when two monosaccharides join together in a condensation reaction, producing a molecule of water.

What are the three dissacharide reactions?

glucose +glucose → maltose + water

glucose + galactose → lactose + water

glucose + fructose → sucrose + water

What is a polysaccharide?

A polysaccharide is formed from many monosaccharides joined together, such as glycogen, starch, and cellulose.

How is maltose formed?

Maltose is formed by the condensation of two glucose molecules, creating a 1,4 glycosidic bond.

What is glycogen and its function?

Glycogen is the main energy storage molecule in animals, formed from alpha glucose and has many side branches for quick energy release.

How is glycogen good as a storage molecule?

Insoluble so doesn't affect water potential, large so does not diffuse out of cells, compact so a lot can be stored in a small space. Has many side branches due to 1,6 glycosidic bonds, so more ends that can be simultaneously acted on by enzymes to hydrolyse it, so energy (glucose) can be released faster

What is starch and its structure?

Starch is an energy storage polysaccharide in plants, made of branched or unbranched chains of alpha glucose monomers joined by glycosidic bonds.

Why is starch a good storage molecule?

It is coiled, making it compact

It has branched ends for fast hydrolysis of terminal glucose monomers

It can provide glucose for respiration

It is a large molecule, so cannot cross the cell membrane

What is cellulose and its role in plants?

Cellulose is a polysaccharide composed of long, unbranched chains of beta glucose, providing structural support in plant cell walls.

Cellulose structure

Long unbranched chains of beta glucose joined by 1,4 glycosidic bonds. Alternate molecules are inverted to from straight chains running parallel. Chains are joined by hydrogen bonds which causes microfibrils to form.

What is the Benedict's test used for, and what is the process?

The Benedict's test is used to test for the presence of reducing sugars. It is an alkaline solution of copper (II) sulfate, which is reduced to form copper (I) oxide (insoluble red precipitate) in the presence of a reducing sugar. Add 2cm3 to the sample, heat gently in a water bath, and a positive result is brick red, yellow or green.

What is the procedure for testing non-reducing sugars?

To test for non-reducing sugars, do the reducing sugars test first. If negative, hydrolyse the sample with dilute hydrochloric acid, neutralize with sodium hydrogencarbonate, then retest with Benedict's reagent.

What indicates the presence of starch in a solution?

The presence of starch is indicated by a color change to blue/black from orange when iodine solution is added.

What are lipids?

Lipids are biological molecules made of carbon, hydrogen, and oxygen, soluble only in organic solvents like alcohols.

What are triglycerides?

Triglycerides are a type of lipid formed from glycerol and three fatty acids, joined by ester bonds in a condensation reaction.

What are phospholipids?

Molecules where one of the fatty acids of a triglyceride is replaced by a phosphate group.

What is the general formula for monosaccharides?

The general formula for monosaccharides is (CH2O)n, where n can be any number from three to seven.

What is the role of microfibrils in cellulose?

Microfibrils are strong threads made of cellulose chains that provide structural support to plant cell walls.

What are triglycerides made of?

Triglycerides are made of one molecule of glycerol and three fatty acids joined by ester bonds.

What distinguishes saturated lipids from unsaturated fatty acids?

Saturated lipids do not contain carbon-carbon double bonds - all the carbon atoms are saturated with hydrogen

What is a monounsaturated fatty acid?

fatty acid with one carbon double bond

Polyunsaturated fatty acid?

a fatty acid containing two or more carbon-carbon double bonds

Why are unsaturated fats liquid at room temperature?

Unsaturated fats contain double bonds that cause bending in the chain, preventing tight packing.

How does triglyceride structure relate to properties?

They release water when oxidized, providing an important source of water in dry environments. They provide an excellent energy store due to the high number of C

Functions of lipids?

Source of energy - when oxidised they release twice the energy as the same mass of carbohydrates. Waterproofing - insoluble in water do used as waxy cuticles.

Protection - fat is found around delicate organs

Insulation - heat retention as lipids are slow conductors, and also electrical (myelin sheath).

Biological membranes - phospholipids contribute to membrane flexibility.

What is the structure of phospholipids?

Phospholipids consist of a glycerol backbone, two fatty acids, and a phosphate group.

What property of phospholipids allows them to form a bilayer in aqueous environments?

They are polar, with hydrophilic heads and hydrophobic tails, so in an aqueous environment a bilayer forms with the hydrophilic heads facing outwards and the hydrophobic tails facing inwards. This forms a hydrophobic barrier between the cell and the environment.

Emulsion test process?

Shake with ethanol then add water. A cloudy emulsion will appear if positive

What are the basic components of amino acids?

Amino acids contain an amino group (NH2), a carboxylic acid group (COOH)

Amino acid basic structure:

How are amino acids linked to form proteins?

Amino acids are joined by peptide bonds formed through condensation reactions.

How are dipeptides formed and broken down?

Via a condensation reaction where a water molecule is eliminated by a peptide bond forming between adjacent carboxyl and amine groups. Broken down by the hydrolysis of the peptide bond

What defines the primary structure of a protein?

The primary structure is the specific sequence and number of amino acids in the protein, formed by a series of condensation reactions. A change in one amino acid in a sequence can change the whole protein shape.

Secondary protein structure definition?

Different sections of the polypeptide are attracted to each other and form weak hydrogen bonds that hold the polypeptide in a specific shape, either the alpha helix or beta pleated sheet.

How is the tertiary structure formed, and why is it important?

The twisted structure continues to fold to give the complex 3D shape. Interactions between R groups cause bonds to form that hold it in place - ionic bonds, H bonds and disulfide bridges. It gives the protein its 3D shape and functionality, allowing the protein to be recognised and interact in a specific way.

What is quaternary structure of a protein?

2 or more polypeptide chains weakly associating with each other, and there may be the addition of a non protein group.

What is the difference between globular and fibrous proteins?

Globular proteins are compact (e.g., enzymes), while fibrous proteins are long and form fibers (e.g., keratin).

What does the Biuret test detect?

The Biuret test detects the presence of peptide bonds in proteins. Lilac = present, blue = not present

How do enzymes function in biochemical reactions?

Enzymes lower the activation energy, increasing the rate of reaction.

Water structure?

What makes water a polar molecule?

Water is polar due to the uneven distribution of charge, with oxygen attracting electrons more strongly than hydrogen.

Why is water a dipole and how do the H bonds form?

There is a large difference in electronegativity, so the Hydrogen has a slight + charge and the O has a slight

What role does water play in metabolic reactions?

Water acts as a metabolite in condensation and hydrolysis reactions such as photosynthesis , forming and breaking chemical bonds.

Why is water being cohesive useful?

Water molecules stick together due to hydrogen bonds, meaning columns of water can move through xylem in plants or blood vessels in animals.

Why is water considered a good solvent?

Water allows gases, enzymes, and waste products to readily diffuse due to its polar nature. Substances can dissolve in water, so chemical reactions can occur in cells, and these substances can easily be transported.

What is the significance of water's high specific heat capacity?

Water's high specific heat capacity minimizes temperature fluctuations in living organisms, so water acts as a buffer against sudden temperature variations

How does water's latent heat of vaporization benefit organisms?

Water's high latent heat of vaporization (means that much energy is needed to vaporise it) provides a cooling effect with minimal water loss, such as during sweating.

How is water being transparent an advantage?

Allows for photosynthesis

Significance of high surface tension of water?

Benefits small aquatic organisms like pond skaters