Biological molecules

What are monomers?

Smaller simpler single units that make up larger molecules (polymers)

What are examples of monomers?

• Amino acids

• Monosaccharides

• Nucleotides

What are polymers?

Larger more complex molecules formed from many repeating units of monomers joined together

What are examples of polymers ?

• Starch

• Proteins

• DNA

What are condensation reactions?

Reaction between the functional groups on 2 separate monomers to form a chemical bond between the monomers with the expulsion of a molecule of water

What are hydrolysis reactions?

Reactions that use the input of a water molecule to break the chemical bond between 2 separate monomers and release the separate monomers

What are carbohydrates made up of?

Made up of the elements carbon (C) hydrogen (H) and oxygen (O) therefore they are biological molecules as they contain carbon

What are roles of carbohydrates in living organisms?

• Energy supply for cells and storage in the form of starch and glycogen

• Structural components such as cellulose or chitin in the cell walls

• Cellular recognition in glycoproteins to aid cells in communication and identification

• Building blocks for biological moleucles where deoxyribose and ribose sugars to make nucleic acids

What are examples of monosaccharides?

• Glucose

• Fructose

• Galactose

How are disaccharides formed?

Condensation reaction between the hydroxyl groups on 2 separate monosaccharides, forming a glycosidic bond and releasing a molecule of water

What are examples of disaccharides?

• Maltose - 2 alpha glucose molecules

• Sucrose - alpha glucose and fructose

• Lactose - alpha glucose and galactose

What are the isomers of glucose?

Alpha glucose (hydroxyl located on the bottom)

Beta glucose (hydroxyl located on the top)

What are the types of starch?

• Amylopectin

• Amylose

Describe the structure of amylose

• Long unbranched chains of alpha glucose

• Angle of glycosidic bonds give it a coiled and compact structure, making it a good storage molecule

Describe the structure of amylopectin

• Long branched chains of alpha glucose

• Contains many side branches

• This provides many terminal ends which increase the surface area for enzymes to rapidly hydrolyse glycosidic bonds to quickly release glucose

What are the properties of starch?

• Insoluble

• Large

• Compact

• Good energy supply

Why is starch large and insoluble?

• Insoluble - doesn't affect the water potential of the cell, so no osmotic effects so cell doesn't swell or shrink, hence are good storage molecules

• Large - so cannot diffuse out of the cell so stays inside the cell, so is a good storage molecule

Describe the structure of glycogen

• Highly branched - contains more terminal ends and side branches than amylopectin for rapid hydrolysis of glycosidic bonds

• Coiled and compact molecule makes it a good storage molecule

• Large

• Insoluble

Describe the structure of cellulose

• Made from long unbranched chains of beta glucose which form straight cellulose chains with glycosidic bonds between them

• These cellulose chains are linked together by hydrogen bond cross linkages to form strong microfibrils between chains

• There are a lot of microfibrils that provide cellulose with mechanical strength

What makes cellulose different to glycogen and starch?

• In starch, due to the positioning of the hydroxyl group on the beta glucose molecules, the position of the glycosidic bonds are inverted

• This is because the hydroxyl groups must be flipped 180 degrees to form a glycosidic bond

What are the properties of cellulose?

• Mechanical strength provides rigidity in the cell wall and allows it to resist high water pressure

• Freely permeable - due to spaces between the cellulose fibers allowing water and dissolved substances to pass through

Which molecules are reducing sugars?

• All monosaccharides are reducing sugars

• Some disaccharides are reducing sugars like maltose and lactose

How do you test for reducing sugars?

• Add some benedict's reagent to a sample

• Heat it in a water bath thats been brough to boil

• If test is positive then it will form a red or orange precipitate

How to test for non reducing sugars?

• Break down sample by adding dilute HCl

• Heat in a water bath brought to boil

• Neutralise with sodium hydrogencarbonate

• Carry out reducing sugar test

• Positive test will produce a red or orange precipitate

How to test for starch?

• Add a few drops of potassium iodide solution

• If positive, solution turns blue/black

What are lipids made up of?

Made up of the elements carbon (C) hydrogen (H) and oxygen (O) therefore they are biological molecules as they contain carbon

Why are lipids not considered to be polymers