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 Lipid Structure Main Role Other Features Triglyceride
Glycerol and three fatty acids
Compact energy store, insoluble in water so doesn’t affect water potential
Stored as fat, used for thermal insulation and protective properties
Phospholipd
Glycerol plus two fatty acids and a phosphate group
Molecule is part hydrophobic, part hydrophilic, ideal for membranes
Phosphate parts have carbohydrate parts attached called glycolipids for cell signalling
Cholesterol
Four carbon based ring structures joined together
Forms a small, thin molecule that fits to a lipid bilayer giving strength and stability
Used to form steroid hormones

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

27. Carbohydrate
Examples
Features
Role
Monosaccharides
(monomers)
Glucose
(6 carbon)
Deoxyribose
(5 carbon)
Small, soluble, sweet and crystalline
Provides energy via respiration
Part of DNA
Disaccharides
(dimers)
Maltose
(glucose + glucose)
A sugar obtained when starch is broken in hydrolysis reactions. It can be split further to glucose for respiration
Polysaccharides
(polymers)
Starch and Glycogen
Cellulose
Large molecules, α-glucose joined by condensation. Insoluble in water, forms grains/ granules
Large molecules, β-glucose joined by condensation. Insoluble in water. Very strong
Energy storage carbohydrates- starch in plants, glycogen in animals and fungi
Structural, only in plants forming cell walls