B1.1 Carbohydrates and Lipids

Monosaccharide

Monomers of carbohydrates

Glycosidic bond

A covalent bond formed between two hydroxyl (OH) groups on different monosaccharides

Hydrolysis reaction

When covalent bonds are broken with the addition of water

Disaccharide

When two monosaccharides join together

Polysaccharide

When many monosaccharides join together

General formula of monosaccharides

C_nH_2nO_n

• ‘n’ is the number of carbon atoms in the molecule

Explain the properties of glucose

Glucose has 5 different OH groups in its molecules. The OH groups form a polar covalent bond, making glucose a polar molecule

1) Molecule stability - stable covalent bonds are strong and hard to break

2) Highly soluble in water - Glucose is polar so dissolves in other polar solvents

3) Easy transportable - High solubility allows it to circulate in blood + fluids between cells

4) High yield of chemical energy - When covalent bonds break, a large amount of chemical energy is released.

• Occurs in oxidation reactions and makes glucose a good energy store

Draw the structure of alpha glucose

Draw the structure of beta glucose

Categorize the different polysaccharides into one of the two isomers of glucose

• Starch and glycogen are made from alpha glucose molecules

• Cellulose is made from beta glucose molecules

Explain why starch and glycogen are effective storage polysaccharides

1) Compact - large quantities of glucose can be stored in a small space

2) Insoluble - Prevents glucose from dissolving in the cell cytoplasm + other fluids, which would disrupt osmotic balance in loving tissues

Starch

A polymer of glucose used as present in plants, primarily used for energy storage

Compare and contrast amylose and amylopectin

• Both are starches and made of alpha glucose monomers

• Amylose has 1,4 glycosidic bonds between glucose molecules while amylopectin has1,4 AND 1,6 glycosidic bonds between glucose molecules

• Amylose has a linear but helical structure, while amylopectin has a branched structure

Glycogen

A polysaccharide found primarily in animals and fungi, used for energy storageD

Describe the structure of glycogen

• Glycogen is composed of 1,4 and 1,6 glycosidic bonds between alpha glucose monomers

• It is more branched than amylopectin, which offers more free ends for hydrolysis to remove glucose molecules

• Large quantities in muscle and liver cells

Describe the structure and properties of saturated fatty acids

• Fatty acids with single bonds between the carbons

• All other carbons are bonded with hydrogen making the molecule “saturated”

• Straight molecules so can be packed more tightly

• Relatively high melting points, typically solid at room temp

  • Triglycerides with only saturated fatty acids are used by animals to store excess energy —> “fats”, butter, animal meat

Describe the structure and properties of monosaturated fatty acids

• Fatty acids with one double bond between two of the carbons in hydrocarbon chain of molecule

• Kink/bend due to double bond

• Triglycerides with one or more monosaturated fatty acids have lower melting points than saturated fatty acids —> liquid/ oil at room temp

  • Plants and animal use for storage

Describe the structure and properties of polyunsaturated fatty acids

• Fatty acids with more than one double bond in the hydrocarbon chain

• Kink/ bends due to double bonds

• Triglycerides composed of polyunsaturated fatty acids have relatively low melting points and are liquid (oil) at room temperature

• Plants use for energy store

Describe the structure of lipids and how it impacts its solubility

• Contain hydrocarbon molecules which have many non-polar bonds

• Results in lipids being non-soluble in water but soluble in non-polar solvents

• Lipids can be combined with other molecules to be more soluble

Describe how triglycerides are formed

Through a process called esterification, one glycerol combines with 3 fatty acids to form one triglyceride and 3 water molecules

• A condensation reaction forms an ester bond between the OH group of one glycerol molecule and the carboxyl group of a fatty acid

Describe how phospholipids are formed

• When a glycerol molecule combines with 2 fatty acids and one inorganic phosphate group, resulting in one phospholipid and 3 water molecules

• Phosphate is polar, while the fatty acid tails are non-polar, causing the phospholipid to be amphipathic

Describe the properties of lipids

• Energy dense - lipids contain 2x more energy per gram than most carbohydrates due to high number of C-H bonds

• Insoluble - Lipids are insoluble so not transported around the body, remaining as storage cells

• Release of water - When lipids are respired, more water is released compared to the respiration of carbohydrates

  • This is called metabolic water and is used as a dietary water source if drinking water in unavailable