Lipids (Biologie Woche 1 und 2; Pages 81 and 82)

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1 Lipids (Biologie Woche 1 und 2; Pages 81 and 82) Lipids Features Have oily, greasy or waxy consistency Relatively insoluble in water Protein and carbohydrates may be converted into lipids by enzymes an then may be stored as lipids in cells of tissues, which are called adipose tissues for having the feature to store lipids. Functions Lipids are very important and appear in form of: Biological fuel During times of plenty, this storage is increased, to be used in times of shortage of food. Hormones Structural components in cell membranes Can provide the cell with water When glycerol bonds with 3 fatty acids (see occurrence 1.2), a triglyceride is formed and water is released Occurrence The most abundant (=rich) fats are neutral Rich fats: Fat that stores a lot of energy (more than other fats). Neutral fats: Neutral fats are made out of an glycerol molecule attached to one, two or three fatty acids o Glycerol attached to 1 glycerol molecule: Monoglyceride o Glycerol attached to 2 glycerol molecules: Diglyceride o Glycerol attached to 3 glycerol molecules: Triglyceride Lipids are similar to waxes ; Waxes are formed with a complex alcohol instead of glycerol

2 Fatty acids Fatty acids are a major component of neutral fats. The fatty acid chains may be saturated or unsaturated Fatty acid chains are the fatty acids attached to the glycerol molecule Saturated fatty acids: Contain the maximum of hydrogen atoms Unsaturated fatty acids: Contain some carbon atoms that are double bonded with each other and are not fully saturated with oxygen. Lipids containing a high proportion of saturated fatty acids tend to be solid at room temperature (e.g. butter). Saturated fats are solid at room temperature because they comprise mostly saturated fatty acids. These contain the maximum number of hydrogen atoms and form straight molecules that pack tightly together. Lipids containing a high proportion of unsaturated fatty acids are oils and tend to be liquid at room temperature. Unsaturated fats are liquid at room temperature because they comprise mostly unsaturated fatty acids. These don t contain the maximum number of hydrogen atoms and don t form molecules that pack tightly together. Fatty acids release a large amount of energy when they come in touch with oxygen (regardless of degree of saturation). Exercises 1. Fatty acids: a) Distinguish between unsaturated and saturated fatty acids: Unsaturated fatty acids Saturated fatty acids Contain the maximum of hydrogen atoms Contain some carbon atoms that are double bonded with each other and are not fully saturated with oxygen. b) Explain how the type of fatty acid present in a neutral fat or phospholipid is related to that molecule s properties. Lipids containing a high proportion of saturated fatty acids tend to be solid at room temperature (ex.: butter). Lipids containing a high proportion of unsaturated fatty acids are oils and tend to be liquid at room temperature. 2. Explain how neutral fats can provide an animal cell with: a) Energy: b) Water: Lipids store huge amounts of energy which they release when they get in touch with oxygen. Metabolism of lipids release water; oxidation of triglycerides releases lots of water. c) Insulation: Heat does not dissipate easily through fat therefore thick rat insulates against heat loss.

3 Phospholipids: Main component of cell membrane Consist of a glycerol and a phosphate group attached to two fatty acid chains The phosphate end of the molecule is attracted to water while the fatty acid chains are repelled by water. The phosphate end is hydrophilic The fatty acid chains are hydrophobic In a membrane, the hydrophobic fatty acids turn inward and form a phospholipid bilayer. Steroids Classified as lipids but have a quite different structure than the structure of other lipids. Are made out of 4 rings: o The first three are made out of 6 carbon atoms each o The fourth is made out of 5 carbon atoms Examples of steroids are the male and the female sex hormones Cholesterol Cholesterol is not a steroid itself but acts as a precursor (Vorbote) to many steroid hormones. It is like the phospholipids in the cell membrane amphipathic too. It has a polar hydrophilic side as well as a nonpolar hydrophobic side. It is present in the plasma membrane where it regulates the membrane fluidity and the permeability. It prevents the phospholipids from sticking together It is in-between the phospholipid bilayer The hydroxyl (-OH) group on cholesterol interacts with the polar head groups of the membrane phospholipids, while the steroid ring and hydrocarbon chain tuck into the hydrophobic portion of the membrane. This prevents the hydrophobic tails from sticking together and makes them less compact, which makes the membrane more liquid. o This helps to stabilize the outer surface of the membranes and reduce its permeability to small water-solute molecules. Exercises: 3. Outline the key chemical difference between a phospholipid and triglyceride: The third fatty acid of the triglyceride is replaced by a phosphate; the molecule is ionized and the head is water-soluble, a triglyceride isn t water-soluble at all. 4. Explain why saturated fats are solid at room temperature: Saturated fats are solid at room temperature because they comprise mostly saturated fatty acids. These contain the maximum number of hydrogen atoms and form straight molecules that pack tightly together. 5. Structure of phospholipids: a) Relate the structure of phospholipids to their chemical properties and their functional role in cellular membranes: The amphipathic nature of phospholipids causes them to orientate in aqueous Solutions so that the hydrophobic tails point in together. This creates the structure of a cell membrane.

4 b) Suggest how the cell membrane structure of an Arctic fish might differ from that of tropical fish species: My answer: More phospholipids in shorter amount of space to insulate the heat better. Sample solution: The cellar membranes of an Arctic fish could be expected to contain a higher proportion of unsaturated fatty acids and more cholesterol than those of a tropical fish species. This would help them to remain fluid at low temperatures. 6. Explain how the structure of cholesterol enables it to perform structural and functional roles within membranes: Cholesterol is an amphipathic molecule. It contains a hydroxyl (-OH) group as well a steroid ring structure and a hydrocarbon chain. The -OH group can interact with the polar head groups of the membrane phospholipids, stabilizing the outer surface of the membrane and making It less permeable to some ions (less leaky).the steroid ring and hydrocarbon chain tuck into the hydrophobic part of the membrane, where the kinked structure increases membrane fluidity On the same way that unsaturated fatty acids do) by preventing the phospholipids from packing too closely together. Enzymes (Biologie Woche 2, 3; Pages ) Most enzymes are proteins They speed up biochemical reactions Therefore are called biological catalysts Enzymes act on one or more compounds (Verbindungen) at once These compounds are called substrate Enzymes may break down complex substrate molecules into simpler substances or they may join two or more molecules together Enzymes never change during the reactions they accelerate, they just make reactions happen faster The part of the enzyme to which the substrate binds is called the active site Enzymes at work: Enzymes help out at first steps of photosynthesis Catalyze production of ATP and NADPH. These provide the energy and hydrogen molecules needed for the second stage of photosynthesis Enzymes also accelerate the process of producing carbohydrates

5 Enzyme Structure Exercise:

6 How enzymes work Each reaction in cells is accompanied with energy changed, even exothermic reactions. Before each reaction the energy level of the substrate has to be raised until an unstable transition state is reached; then the reaction will occur The energy needed that the reaction occurs is called the activation energy ( ) Enzymes lower the activation energy for any given chemical reaction. They do this by destabilizing bond; they destabilize the bonds by either of these ways: Orienting the substrate in a particular way Adding charges Otherwise inducing strain Exothermic reactions Exothermic reactions are reactions that release energy in form of light and heat. The breaking down of large molecules into smaller ones by enzymes can cause exothermic reaction. Examples where acting enzymes cause exothermic reactions: o Hydrolysis o Cell respiration Enzyme Reaction Rates Enzymes are very sensitive molecules. They often have a pretty small range of conditions under which they function properly. Temperature: For most of the enzymes in plant and animal cells this law applies: They function slower under too low and too high temperatures, until the point is reached, on which the temperature is so high or low that the enzymes structure gets damaged. If this point is reached, the enzyme stops working completely. This is called enzyme or protein denaturation. ph value: Extremes in ph can also cause an enzyme to denature. Poisons often work by denaturing enzymes or occupying all of the enzyme s active sites. Cofactors: In some cases, enzymes wont function without cofactors like vitamins or trace elements (=Spurenelemente, just a little bit of an substance).

7 Exercises:

8 Enzyme Cofactors Most enzymes are made of proteins RNA has enzymatic properties, but isn t a protein Some enzymes contain only one protein (ex: pepsin) while other need to have additional non-protein parts attached to the protein in order to complete their catalytic properties The protein portion is called the apoenzyme The non-protein portion is called the cofactor. o Cofactors may be organic molecules or inorganic ions; some cofactors are both, they include organic parts as well as inorganic parts Ex: The heme prosthetic groups o They also may be tightly or loosely bound to the enzyme Cofactors may be temporary or permanently attached They may fall off after the reaction and may be take place in other reactions Permanently bound cofactors are called prosthetic groups Temporary bound cofactors are called coenzymes Cofactors don t have catalytic activity on their own. They provide an essential part of the active site (see graph below).

9 Exercises: Inhibitors:

10 Exercises: