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32 Cards in this Set
- Front
- Back
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What are the characteristics of lipids? |
-Contain hydrogen, carbon and oxygen -Proportion of oxygen to carbon and hydrogen is smaller than in carbohydrates -Insoluble in water -Soluble in organic solvents e,g alcohols and acetone |
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What is the main groups of lipids? |
Triglycerides Phospholipids Waxes |
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What are triglycerides? |
Fats and oils |
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Where is the main function of lipids located? |
In the plasma membrane |
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How do phospholipids contribute to the plasma membrane? |
Helps flexibility Transfer of lipid-soluble substances across membrane
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What are the roles of lipids? |
-Energy source- When oxidised, lipids provide more than twice the energy as the same mass of carbohydrate -Waterproofing-Lipids are insoluble in water so therefore used as a waterproof -Insulation- Fats are slow conductors of heat, when stored beneath the body surface they help to retain body heat -Protection- Fat is often stored around organs |
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What is the difference between fats and oils? |
Fats are solid at room temperature whereas oils are liquids |
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Why are triglycerides called triglycerides? |
They have three fatty acids combined with glycerol |
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What reaction bonds the fatty acids to glycerol? |
Condensation |
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What is produces when a triglyceride is hydrolysed? |
Glycerol and three fatty acids |
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What is the structure of a triglyceride? |
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Why is there variation in triglycerides? |
- Due to the fatty acids- Over 70 fatty acids - All have a carboxylic group (-COOH) and hydrocarbon chain attached. - If chain has no carbon-carbon double bond, fatty acid is saturated (all carbons linked to maximum number of hydrogens) - If there is a single double bond it's mono-unsaturated - If more than one double bond is present it's polyunsaturated
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What is the difference between lipids and phospholipids? |
In a phospholipid one of the fatty acid molecules is replaced by a phosphate molecule |
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Are fatty acid molecules hydrophobic or hydrophilic? |
Hydrophobic- Repel water |
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Are phosphate molecules hydrophobic or hydrophilic? |
Hydrophilic |
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What is a phospholipid made of? |
Hydrophilic head- Attracted to water but not with fat Hydrophobic tail- Orients itself away from water but mixes with fat |
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What is the test of lipids known as? |
The emulsion test |
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How is the emulsion test carried out? |
1. Take completely dry and grease-free test tube 2. Add 5cm of ethanol to 2cm of sample 3. Shake tube to dissolve and lipid in sample 4. Add 5cm of water and shake 5. Cloudy-white colour indicates presence of lipid 6. As a control, repeat procedure using water, final solution should remain clear |
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Why does the solution turn cloudy during the emulsion test if a lipid is present? |
Lipid is finely dispersed in water to form emulsion Light passing through this emulsion is refracted as it passes from oil droplets to water droplets |
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What is the cell-surface membrane? |
The plasma membrane that surrounds cells and forms the boundary between cytoplasm and environment |
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What does the cell-surface membrane allow? |
Allows different conditions to be established inside and outside of cell |
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What does the cell-surface membrane control? |
Movement of substances |
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What do phospholipids form to create the cell-surface membrane? |
Bilayer sheet |
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Why does one layer of phospholipids face inwards in a cell-surface membrane? |
They have hydrophilic heads so they are attracted by the water in the cytoplasm |
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Why does one layer of phospholipids face outwards in the cell-surface membrane? |
Hydrophilic heads are attracted to the water which surrounds all cells |
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Why do the hydrophobic tails point to the centre of the membrane? |
So they are protected from the water |
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What are the functions of phospholipids? |
Allow lipid-soluble substances to enter and leave the cell Prevent water-soluble substances entering and leaving the cell Make membrane flexible |
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How are protein molecules arranged in the cell-surface membrane? |
Randomly Embedded in the phospholipid bilayer in 2 ways -Extrinsic protein (Partly embedded) -Intrinsic protein (Go from one side to the other of bilayer) |
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What are the functions of extrinsic proteins? |
Give mechanical support to the membrane Work with glycolipids as cell receptors for molecules such as hormones |
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What are the functions of intrinsic proteins? |
Act as carriers to transport water-soluble material across the membrane Some are enzymes |
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What are the functions of the proteins in the membrane? |
Provide structural support Act as carriers transporting water-soluble substances across the membrane Allow active transport across membrane by forming ion channels Form recognition sites by identifying cells Help cells adhere together Act as receptors e.g for hormones |
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Why is the plasma membrane described as being a fluid-mosaic model? |
Fluid- Individual phospholipid molecules can move relative to one another, membrane can constantly change shape
Mosaic- Proteins embedded in phospholipid bilayer vary in shape, size and pattern so it looks like a mosaic |
