Biological Molecules

Key Terms

Polymer: Chain of repeated sub-units

Macromolecule: Large, complex molecule

Monomer: Small sub-unit; basic

Anabolism: Process of building up molecules

Catabolism: Process of breaking down molecules

Metabolism: Sum of all reactions in the body

Hydrolysis: any chemical reaction in which a molecule of water breaks one or more chemical bonds.

Condensation Polymerisation: A reaction that produces a molecule plus at least 1 water molecule

Mono, Di, and Polysaccharides

General Formula: (CH₂O)_n

Monosaccharides

They are sweet, soluble

Benedict’s Reagent

1. Add 2 cm³ of food sample to be tested in a test tube; if sample is not a liquid, grind it up and put it in water

2. Add an equal volume of Benedict’s reagent to the solution

3. Heat mixture in a gently boiling water bath for 5 mins.

Solution turns orange-brown if sugar is present

Disaccharides

Maltose = 2 ALPHA glucose

Sucrose = 1 ALPHA glucose + 1 fructose

Lactose = 1 glucose + 1 galactose

Polysaccharide

Glycogen

It is found in animal muscle and liver cells

Monomer: Alpha glucose in a 1-4 glycosidic bond; highly branched with alpha glucose in a 1-6 glycosidic bond

Structure: Less dense and more soluble than starch; More branches, less glucose in these bonds than amylopectin

Function: Broken down rapidly due to higher metabolic requirement of animals compared to plants. Storage molecule for respiration

Starch

Found in plants

Monomer: Alpha glucose

Structure: Amylose

• Unbranched chain of alpha glucose in a 1-4 glycosidic bond compound helical structure

Structure: Amylopectin

• Chain of alpha glucose in a 1-4 glycosidic boond with more branched chains of alpha glucose in a 1-6 glycosidic bond.

Function: Storage, respiration and a source of carbon for other molecules

Cellulose

Found in plants

• Composed of beta glucose units linked by 1-4 glycosidic bonds, providing structural support in plant cell walls.

• Structure: A linear chain formation that allows for strong hydrogen bonding between adjacent chains, contributing to its rigidity and strength. Microfibrils between chains. Chains are anti-parallel to each other and have cross linkages

• Function: The primary function of cellulose is to provide structural integrity to plants, allowing them to maintain shape and resist external pressures when taking in excess water.

Tests for Carbs

• Benedict's Test: Used to detect reducing sugars by changing color when heated with a reducing sugar solution. Can only react with a sugar if the sugar has a carbonyl group (C=O) and at least one hydroxyl group (–OH) in its structure, which is characteristic of reducing sugars.

  • If Benedict’s Test has been carried out and no reducing sugars are present, a modified test can be done.

  • Tests for non-reducing sugars is performed by first hydrolyzing the sugar with dilute hydrochloric acid to break it down into its monosaccharide components. After hydrolysis, the solution is neutralized with sodium hydrogen carbonate before reapplying Benedict's Test to check for the presence of reducing sugars.

  • This two-step process is essential because non-reducing sugars, such as sucrose, do not react with Benedict’s reagent until they are broken down into their reducing monosaccharides.

• Iodine Test: A test for starch, where iodine solution turns blue-black in the presence of starch.

• Fehling's Test: Another test for reducing sugars that involves a color change when mixed with Fehling's solution.

Lipids

Monomers are fatty acids and glycreol, which combine to form triglycerides and phospholipids, essential components of cell membranes.

GLYCEROL + FATTY ACID = TRIGLYCERIDE + 3 WATER MOLECULES

Creates an ester bond.

Saturated fats are denser (no C=C DOUBLE BONDS) - SO they tend to be solid at room temperature, contributing to the structural integrity of cell membranes.

Unsaturated fats are less dense (at least 1 C=C double bond), so they are liquid at room temperature.

Phospholipids

They are a major component of cell membranes, consisting of two fatty acids and a phosphate group attached to a glycerol backbone, which allows them to form bilayers that provide a barrier between the interior of cells and their external environment.

Hydrophobic Tails have no charge so they do not want to interact with water

Hydrophilic Heads have a slight negative charge, so are attracted to the water molecule as water is polar.

Proteins

When 2 amino acids join together they produce water + dipeptide and the bond between them is called a peptide bond.

Key Functions

Carrier proteins: Used to transport smaller molecules

Defence proteins: Attack foreign invaders, e.g. antibodies

Structural proteins: for structure and support

Hormones: Chemical messengers e.g. a receptor molecule is one in which other molecules fit.

Enzymes: Biological catalysts that speed up biological reactions

Level of Protein Structure

1. Primary Structure:

   • This is the linear sequence of amino acids in a polypeptide chain. The primary structure determines the protein's unique characteristics and is held together by peptide bonds between amino acids.

2. Secondary Structure:

   • This level involves the local folding or coiling of the polypeptide chain into structures such as alpha-helixes and beta-pleated sheets. These structures are stabilized by hydrogen bonds between the backbone atoms (amine and carbonyl) of the amino acids.

3. Tertiary Structure:

   • The tertiary structure is the overall three-dimensional structure of a single polypeptide chain. This level of structure is formed by the interactions between the side chains of the amino acids, including hydrophobic interactions, ionic bonds, hydrogen bonds, and disulfide bridges, leading to a folded shape.

4. Quaternary Structure:

   • This level consists of the arrangement and interaction of two or more polypeptide chains (subunits) to form a single functional protein complex. The interactions between the subunits can include hydrophobic interactions, hydrogen bonds, and ionic bonds.

A different amino acid sequence means different bond positions. E.g. bonds forming between different R groups (disulfide, hydrophobic, ionic)

Biuret Test

Add biuret solution to the aqueous food solution, then if a purple colour is formed, it contains protein. If not, it stays blue

Protein Production, Transport and Release

• RNA transcripts DNA

• RNA heads to the RER where ribosomes translates the RNA into protein

• Protein is then transported by vesicles to the Golgi body where it can gain a lipid/carbohydrate/ion/another proteins

• Protein is then removed from the cell via exocytosis