lipids

• what is the bond called between a glycerol and fatty acid in a triglyceride?

  ester bond
• cholesterol contains the elements carbon, hydrogen and oxygen only as it's a lipid
• fats are insoluble thus don't affect water potential of cells
• fats have more carbon - carbon bonds

  they are energy rich

  more energy stored in less space

  fatty acids are long carbon chains
• Ethanol is a non-polar solvent. Non-polar solvents will dissolve non-polar molecules. The phospholipid bilayer is a non-polar structure which means that it dissolves in ethanol and this disrupts the structure to become more fluid and more permeable.
• Triglycerides

  • Triglycerides are fats and oils
  • Fatty acid and glycerol molecules are the components that make up triglycerides
  • Fats and oils have a number of important functions in organisms: energy storage, insulation, buoyancy, and protection
• Energy storage

  • The long hydrocarbon chains in triglycerides contain many carbon-hydrogen bonds with little oxygen (triglycerides are highly reduced)
  • So when triglycerides are oxidised during cellular respiration this causes these bonds to break releasing energy used to produce ATP
• • As triglycerides are hydrophobic they do not cause osmotic water uptake in cells so more can be stored
  • Plants store triglycerides, in the form of oils, in their seeds and fruits. If extracted from seeds and fruits these are generally liquid at room temperature due to the presence of double bonds which add kinks to the fatty acid chains altering their properties
  • Mammals store triglycerides as oil droplets in adipose tissue to help them survive when food is scarce (e.g. hibernating bears)
• Insulation

  • Triglycerides are part of the composition of the myelin sheath that surrounds nerve fibres
  • The myelin sheath provides insulation which increases the speed of transmission of nerve impulses
• • Triglycerides compose part of the adipose tissue layer below the skin which acts as insulation against heat loss (eg. blubber of whales)
• Buoyancy

  • The low density of fat tissue increases the ability of animals to float more easily
• Protection

  • The adipose tissue in mammals contains stored triglycerides and this tissue helps protect organs from the risk of damage
• Phospholipids

  • Phospholipids are a type of lipid, therefore they are formed from the monomer glycerol and fatty acids
  • Unlike triglycerides, there are only two fatty acids bonded to a glycerol molecule in a phospholipid as one has been replaced by a phosphate ion (PO43-)
  • As the phosphate is polar it is soluble in water (hydrophilic)
  • The fatty acid ‘tails’ are non-polar and therefore insoluble in water (hydrophobic)
• • Phospholipids are amphipathic (they have both hydrophobic and hydrophilic parts)
  • As a result of having hydrophobic and hydrophilic parts phospholipid molecules form monolayers or bilayers in water
• • Phospholipids are the main component (building block) of cell membranes
  • Due to the presence of hydrophobic fatty acid tails, a hydrophobic core is created when a phospholipid bilayer forms
  • The core acts as a barrier to water-soluble molecules
• • The composition of phospholipids contributes to the fluidity of the cell membrane
  • If there are mainly saturated fatty acid tails then the membrane will be less fluid
  • If there are mainly unsaturated fatty acid tails then the membrane will be more fluid
• • Just like phospholipid molecules, cholesterol molecules have hydrophobic and hydrophilic regions
  • Their chemical structure allows them to exist in the bilayer of the membrane
• • Cholesterol affects the fluidity and permeability of the cell membrane
  • It disrupts the close-packing of phospholipids, increasing the flexibility of the membrane
  • It acts as a barrier, fitting in the spaces between phospholipids. This prevents water-soluble substances from diffusing across the membrane
  • Molecules of cholesterol are used to produce steroid-based hormones such as oestrogen, testosterone and progesterone
• • The long hydrocarbon chains in triglycerides contain many carbon-hydrogen bonds with little oxygen (triglycerides are highly reduced)
  • So when triglycerides are oxidised during cellular respiration this causes these bonds to break releasing energy used to produce ATP
  • Triglycerides, therefore, store more energy per gram than carbohydrates and proteins
• • Plants store triglycerides, in the form of oils, in their seeds and fruits. If extracted from seeds and fruits these are generally liquid at room temperature due to the presence of double bonds which add kinks to the fatty acid chains altering their properties
  • Mammals store triglycerides as oil droplets in adipose tissue to help them survive when food is scarce
• fats are solid at room temperatures, oils are liquid
• all fats are made up of 3 fatty acids and glycerol alcohol

  glycerol has 3 OH/hydroxyl groups and each may combine with a separate fatty acid, to make a triglyceride
• glycerols 3 hydroxyl groups are esterified to fatty acids - condensation reaction as water is given out and the ester bonds hold the glycerol and fatty acids
• Which processes involve the formation of ester bonds?

  synthesis of polynucleotides (phosphodiester bonds between adjacent nucleotides)

  synthesis of triglycerides (ester bonds between glycerol molecule and fatty acids)
• What are lipids?

  A diverse group of chemicals that are neither polar nor charged and hence are insoluble in water.

  • The hydrophilic nature of the heads of phospholipids allows them to form membranes.
  • Glycolipids also contain fatty acids and form part of the membrane.
  • Lipids can be used for energy storage in the form of triglycerides
  • Some hormones are also lipids and they are similar in structure to cholesterol molecules
• What are glycolipids?

  Lipids with a carbohydrate attached.
• What are monounsaturated fatty acids?

  fatty acids containing 1 double carbon carbon bond
• What type of reaction is the breaking of ester bonds between fatty acids and glycerol?

  Hydrolysis
• What is the role of cholesterol in cell surface membranes in the human body?


  Cholesterol binds to phospholipid fatty-acid tails, increasing the packing of the membrane, therefore reducing the fluidity of the membrane.
• How does the structure of phospholipids allow them to form the bilayer of a plasma membrane?

  Phospholipids have hydrophilic heads and hydrophobic tails, the hydrophobic tails are repelled by water and the hydrophilic head forms hydrogen bonds with the water

  the hydrophobic nature of the fatty acid tails results in them facing towards each other
• What bond is formed between glycerol and 3 fatty acids and what molecules are formed when this bond is made?

  ester bond

  triglyceride and water
• What are the functions of triglycerides?

  energy storage

  • thermal insulation
  • physical protection of organs in adipose tissue layer
  • electrical insulation in myelin sheath
  • buoyancy
  • respiratory substrate
• How do the fatty acids in phospholipids allow the formation of membranes?

  the fatty acids are hydrophobic causing the tails to orientate towards the middle of the bilayer (pointing inwards)
• Why do lipids increase the buoyancy of aquatic animals?

  lipid is less dense than protein
• Lipids have many roles in living organisms.

  Some are used for energy storage in adipose cells.

  Unsaturated fatty acids contain at least one double bond between two carbon atoms and so contain fewer hydrogen atoms.

  All lipids are insoluble in water so need to be transported in the blood by lipoproteins.

  Cholesterol molecules increase the stability of membranes, and cholesterol is also used to synthesise steroid hormones and bile.
• Using the structure of triglyceride molecules as an example, explain what is meant by hydrolysis?

  the use of water to break 3 ester bonds

  lysis means the splitting of fatty acids from glycerol
• Phospholipids are modified triglycerides and contain the element phosphorous along with carbon, hydrogen and oxygen.

  Inorganic phosphate ions (PO43-) are found in the cytoplasm of every cell, they are negatively charged making them insoluble in water.

  One of the fatty acid chains in a triglyceride molecule is replaced with a phosphate group to make a phospholipid.