Lipids and Carbohydrates

1. Lipids and Carbohydrates Revision PowerPoint

2. Lipids • At room temperature, a solid lipid is called a fat and a liquid lipid called an oil • Lipid functions include: energy source for respiration, energy storage as adipose cells, cell membranes, insulation e.g. blubber in whales, protection e.g. cuticle of leaf and hormones • Lipids contain carbon, hydrogen and oxygen • Lipids are insoluble in water (they don’t dissolve)

3. Glycerol and Fatty Acids • Found in all storage fats and oils, including membranes • The glycerol molecule is always the same, but the fatty acid differs • Most fatty acids can be made, except for ones called essential fatty acids which must be eaten

4. Fatty Acids • All fatty acids have an acid group (part) at one end, like an amino acid, the rest of the molecule is a hydrocarbon chain (a chain made of carbons and hydrogens) • The hydrocarbon chain can be 2 to 20 carbons long, but most have around 18 Acid Group Hydrocarbon chain

5. Saturated vs. unsaturated • These terms refer to the hydrocarbon chain and whether it is ‘saturated’ (full) of hydrogen or not. • Unsaturated fatty acids have C=C double bonds, so fewer hydrogen atoms can be bonded to the molecule. • If there is on C=C bond it is called monounsaturated, two or more makes it polyunsaturated (poly means many) • The presence of C=C bonds changes the shape of the hydrocarbon chain and makes the molecules in the lipid push apart making them more fluid e.g. olive oil

6. Triglycerides • A triglyceride is made of one glycerol molecule bonded to three fatty acid molecules • They are joined by a condensation reaction between the acid part of a fatty acid and an OH group (called the hydroxyl part) by a covalent bond • The bond is called an ester bond. • It is called a monoglyceride at this stage, however two more fatty acid chains form ester bonds causing it to become a triglyceride. (tri means three, so it is one glycerol molecule with 3 fatty acids joined) • It is insoluble in water (hydrophobic)

7. Phospholipids • Almost the same as a triglyceride, but the third fatty acid is not added, instead a phosphate joins to the 3rd OH by a condensation reaction • The phosphate head is hydrophilic, and the fatty acids are hydrophobic. • As the majority of the molecule is insoluble, but the phosphate head is hydrophilic it is able to form membranes

8. Phospholipids in membranes • Phospholipids may still be saturated or unsaturated. • Organisms can control the fluidity of their membranes using this feature • Organisms living in colder climates have more unsaturated fatty acids in their phospholipid molecules ensuring their membranes remain fluid in low temperatures

9. Lipids and respiration • Hydrolysis of the ester bonds then molecular breakdown releases water, carbon dioxide and energy which is used to generate ATP • The respiration of one gram of lipid gives out twice as much energy as the respiration of a carbohydrate • As they are insoluble they can be stored in a compact way and don’t affect water potential of surrounding cells • As the respiration of lipids releases more water than carbohydrates, some organisms use stored fat as a water supply

11. Cholesterol and Steroid Hormones • Cholesterol is a type of lipid • It is made of four carbon based rings • It is found in all membranes • Its small, narrow hydrophobic nature allows it to sit between phospholipid hydrocarbon tails and help regulate the strength and fluidity of membranes • Testosterone, oestrogen and vitamin D are made from cholesterol • The lipid nature means they can pass through the phospholipid bilayer to reach their target receptor (site) usually inside the nucleus, they can also pass through the nuclear envelope

12. Cholesterol Dangers • Many cells can make cholesterol as it is essential e.g. the liver, but excess cholesterol can: • Stick together in bile to form gallstones • Cause atherosclerosis by depositing in inner linings of blood vessels • FHC (familial hypercholesterolaemia)is a genetic disorder meaning cholesterol is made even if there is enough in the blood. The cells don’t have a receptor that tells them when the ideal amount has been made. People with this genetic disease can suffer heart attacks and strokes by the time they are 2 years old.

13. Summary Table

14. Carbohydrates • Functions: energy source from respiration, energy store e.g. starch, structure e.g. cellulose cell walls • Can form nucleic acids and glycoproteins (cell signalling) • Contain carbon, hydrogen and oxygen • Have the general formula Cn(H2O)n • This means for every 1 carbon and oxygen atoms, there are 2 Hydrogen atoms

15. Simple Sugars • Called monosaccharides which are monomers (basic units) • Larger carbohydrates made by joining monosaccharides together • They are all: soluble in water, sweet and form crystals • Triose sugars have 3 carbons, pentose have 5 carbons and hexose have 6 carbons • Hexose sugars are the most common e.g. glucose and fructose • They occur in ring structures

16. Two Forms of Glucose • Glucose can be in chain or ring form • Ring glucose can also be in 2 forms called alpha and beta glucose Alpha (α) glucose Beta (β) glucose

17. Joining monosaccharides • Condensation reaction forming a disaccharide (2 saccharides) • Covalent bond forms called a glycosidic bond • One water molecule is released • Starch, glycogen and cellulose are all polysaccharides made this way • Disaccharides are still called sugars

18. Carbohydrates and Energy • In respiration, glucose is broken down to release energy used to make ATP • The equation for respiration is: • Glucose + oxygen  carbon dioxide + water • Each step in respiration is controlled by enzymes • Animals and plants only have enzymes that can break down alpha (α) glucose. • Due to its shape, beta (β) glucose cannot be broken down Remember: the numbers stand for Carbon atoms that are not drawn in on these diagrams

19. Carbohydrates for Storage • Two alpha glucose molecules joined are called maltose (a disaccharide). If more are joined, it is known as amylose • Amylose can be made of many thousands of glucose molecules bonded together • As the glycosidic bonds are between carbon number 1 and carbon number 4, it is called a 1,4- glycosidic bond Amylose coils into a spring making it compact- iodine molecules become trapped in the coils and turn blue/black which is the basis of the starch test

20. Starch • A mixture of a long, straight chain of spring like amylose, and a branched molecule called amylopectin • It is stored in chloroplasts in plant cells and as starch grains • Starch can be broken down to glucose and used for respiration

21. Glycogen • Sometimes called animal starch • Made up of alpha glucose • Different from starch as the 1-4 glucose chains are shorter and have more 1-6 branches • It is more compact and forms glycogen granules in the liver and muscle cells

22. Starch and glycogen • Described as energy storage molecules as they are so long • Do not dissolve so does not affect water potential of cell • Hold glucose in chains so they can easily be broken off at the ends fro respiration when required

23. Cellulose • Made of beta glucose (the H is below Carbon 1 and the OH is above, the opposite of alpha glucose) • When beta glucose forms glycosidic bonds, they are long and straight and are not spring like • They are stronger than amylose chains • So many beta glucose joined together forms cellulose and is only found in plants

24. Cellulose in Plants • Arranged in a specific way to form plant cell walls • Many hydrogen bonds form as there are so many OH groups • 60-70 cellulose molecules become cross linked with hydrogen bonds to form microfibril bundles • These are held together by more hydrogen bonds forming macrofibrils • Almost as strong as steel • They are embedded in a polysaccharide ‘glue’ of substances called pectins, to form cell walls

25. Structure and Function of Plant Cell Walls • Gives strength to each cell • Supports plant • Macrofibril arrangement allows water to pass in and out of cell easily • Prevents bursting when cell is turgid (full of water) • Allows cells to be different shapes e.g. guard cells opening and closing stoma • Can be reinforced with other substances to make the walls waterproof

26. Other Structural Carbohydrates • Chitin: polysaccharide forming insect exoskeleton • Peptidoglycan: polysaccharide forming bacterial cell walls