Biological Molecules: Lipids (AQA A Level Biology): Flashcards
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- FrontLipids
Define lipid.
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Cards in this collection (30)
Define lipid.
A lipid is a biological molecule made of carbon, hydrogen and oxygen, with a lower proportion of oxygen than carbohydrates. Unlike carbohydrates and proteins, lipids are not polymers.
What are the two main groups of lipids?
The two main groups of lipids are triglycerides and phospholipids.
Lipids are and .
Lipids are non-polar and hydrophobic.
Define triglyceride.
A triglyceride is a non-polar and hydrophobic molecule made from one glycerol and three fatty acids.
What are the components of a triglyceride?
The components of a triglyceride are glycerol and fatty acids.
The shorthand chemical formula for a fatty acid is .
The shorthand chemical formula for a fatty acid is RCOOH.
How do saturated and unsaturated fatty acids differ?
Saturated fatty acids have no double bonds between carbon atoms, while unsaturated fatty acids have one or more double bonds in their hydrocarbon chain.
A triglyceride is formed when fatty acids join to one molecule.
A triglyceride is formed when three fatty acids join to one glycerol molecule.
True or False?
The formation of a triglyceride involves a condensation reaction producing three water molecules.
True.
Each ester bond formation between glycerol and a fatty acid releases one water molecule, so three water molecules are produced in the formation of a triglyceride.
Define ester bond.
An ester bond is a chemical bond formed between the hydroxyl group of glycerol and the carboxyl group of a fatty acid during triglyceride synthesis.
Why are triglycerides good energy storage molecules?
Triglycerides release large amounts of energy per gram when oxidised because they have long hydrocarbon chains with many C–H bonds and little oxygen.
Triglycerides are , so they do not cause water uptake in cells.
Triglycerides are hydrophobic, so they do not cause osmotic water uptake in cells.
List two roles of triglycerides in organisms besides energy storage.
Triglycerides provide thermal insulation and protection of vital organs in organisms.
Define phospholipid.
A phospholipid is a type of lipid molecule that contains a hydrophilic head and two hydrophobic tails, and is a major component of cell membranes.
A phospholipid has a head and two tails.
A phospholipid has a hydrophilic head and two hydrophobic tails.
What does it mean that a phospholipid is amphipathic?
A phospholipid is amphipathic because it has both a hydrophilic (water-attracting) head and hydrophobic (water-repelling) tails.
The group of a phospholipid is hydrophilic, while the fatty acid tails are .
The phosphate group of a phospholipid is hydrophilic, while the fatty acid tails are hydrophobic.
What type of bonds join the fatty acids to glycerol and the phosphate group to glycerol in a phospholipid?
The fatty acids are joined to glycerol by ester bonds and the phosphate group is attached to glycerol by a phosphoester bond.
True or False?
Phospholipids form bilayers because they have both hydrophilic and hydrophobic parts.
True.
Phospholipids are amphipathic, so they spontaneously arrange into bilayers in water with hydrophilic heads facing out and hydrophobic tails facing in.
How does the fatty acid composition of phospholipids affect membrane fluidity?
If phospholipids have mainly saturated fatty acid tails, the membrane is less fluid. If there are mainly unsaturated fatty acid tails, the membrane is more fluid.
The hydrophobic core of the phospholipid bilayer acts as a barrier to molecules.
The hydrophobic core of the phospholipid bilayer acts as a barrier to water-soluble molecules.
Define hydrophobic core in the context of the cell membrane.
The hydrophobic core is the region in the center of the phospholipid bilayer formed by the hydrophobic fatty acid tails, which prevents water-soluble molecules from passing freely through the membrane.
Define emulsion test.
The emulsion test is a quick and easy laboratory method used to detect the presence of lipids in a sample.
What is the purpose of adding ethanol to a sample during the emulsion test?
Ethanol is added to dissolve any lipids present in the sample, allowing them to be detected when mixed with water.
The emulsion test for lipids is a test and does not provide a result.
The emulsion test for lipids is a qualitative test and does not provide a quantitative result.
What is observed if lipids are present when carrying out the emulsion test?
If lipids are present, a milky emulsion forms, making the solution appear cloudy.
True or False?
If no lipid is present in the emulsion test, the solution remains colourless.
True.
If no lipids are present, the solution remains colourless after performing the emulsion test.
In the emulsion test, after mixing with ethanol, the sample is added to a test tube of .
In the emulsion test, after mixing with ethanol, the sample is added to a test tube of water.
Why does a more obvious milky colour appear in the emulsion test when more lipid is present?
The milky colour is more obvious with more lipid because a greater amount of lipid forms more emulsion droplets in the water.
Define organic solvent.
An organic solvent is a liquid, such as ethanol, that can dissolve lipids.
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