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MBH - Bio Molecules
OCR A level Biology F212
| Question | Answer |
|---|---|
| What are proteins made up of? | One or more polypeptides. |
| How are dipeptides and polypeptides formed? | When two or more amino acids join together. |
| What is the general structure of an amino acid? | A carboxyl group (COOH) and an amino group (NH2) attached to a carbon atom, which is also attached to a hydrogen atom, and a functional group. |
| What is the reaction to form a peptide bond? | Condensation reaction – releases a molecule of water. |
| What is the reaction to break a peptide bond? | Hydrolysis – adds a molecule of water. |
| What is the primary structure of a protein? | Sequence of amino acids in polypeptide chain, held together by peptide bonds. |
| What is the secondary structure of a protein? | Amino acid chain held together by hydrogen bonds between amino acids, coiling the chain into an alpha helix or a beta pleated sheet. |
| What is the tertiary structure of a protein? | Formed when the coiled or folded chain is coiled and folded further – more bonds form between parts of the chain. Final 3D structure of molecules with only one polypeptide chain. |
| Which bonds are involved in the tertiary structure? | Ionic interactions, disulfide bonds, hydrophobic and hydrophilic interactions, and hydrogen bonds. |
| What are ionic interactions? | Weak attractions between negative and positive charges on different parts of the molecule. |
| What are disulfide bonds? | When the sulphur atom in one molecule of cysteine bonds to the sulphur atom in another molecule of cysteine. |
| What are hydrophobic and hydrophilic interactions? | Hydrophobic groups close together in the protein tend to clump, pushing hydrophilic groups to the outside. |
| What is a quaternary structure? | Proteins made from several different polypeptide chains have a quaternary structure: the way the different chains are held together (same bonds as in tertiary structure). |
| How does collagen being a fibrous protein help it? | Makes it strong, which it needs to be to form supportive tissues in animals. |
| How else is collagen adapted to its function? | Made of three polypeptide chains coiled tightly into strong triple helix; chains are interlinked by strong covalent bonds. |
| How does it help collagen that minerals can bind to the triple helix? | Increase its rigidity. |
| What is haemoglobin? | Globular protein with iron containing haem group that binds to oxygen, carrying it around the body. |
| How does structure of haemoglobin help its function? | Curled up, hydrophilic side chains on the outside and hydrophobic face inwards. Make it soluble in water, so good for transport in blood. |
| What is the Biuret test for proteins? | Make test solution alkaline with NaOH solution, then add copper (II) sulfate solution. |
| What does Biuret test show? | Purple layer forms if protein present, solution stays blue if no protein. |
| What are most carbohydrates? | Large, complex molecules composed of long chains of monosaccharides. |
| What is glucose? | A monosaccharide with six carbons in each molecule. |
| What is the function of glucose? | The main energy source in animals and plants. |
| How does the structure of glucose help its function? | Makes it soluble and can easily be transported, and its chemical bonds contain a lot of energy. |
| What is the Benedict’s test for reducing sugars? | Add Benedict’s reagent, and heat sample without boiling. |
| What is the colour change with Benedict’s solution if sugar is present? | Blue to green to yellow to orange to brick red. Further colour change means more sugar present. |
| What is the test for non-reducing sugars? | Boil solution with dilute hydrochloric acid to break sugars down. Then neutralise with sodium hydrogencarbonate before the test. |
| What is colorimetry to determine the concentration of a glucose solution? | Quantitative version of Benedict’s test – allows to estimate amount of reducing sugar in a solution. |
| Colorimetry information? | Tests light passing through solution, to judge absorbance of light by it. More concentrated solution absorbs more light. Higher concentration means more Benedict’s solution left, therefore the more light a solution absorbs, the less glucose it contained. |
| How are disaccharides and polysaccharides formed? | When monosaccharides join by glycosidic bonds. A hydrogen atom on one monosaccharide bonds to an OH group on the other, releasing a molecule of water. |
| What is the name for the reaction to make and break glycosidic bonds? | Synthesis and hydrolysis. |
| What do two molecules of alpha glucose form? More than two molecules of alpha glucose? | Maltose. Amylase. |
| What is starch’s function? | Plants store excess glucose as starch, and break it down when it needs more glucose for energy. |
| What is starch a mixture of? | Two polysaccharides of alpha-glucose – amylase and amylopectin. |
| What is the structure of amylose? | A long, unbranched chain of alpha glucose, with a coiled structure like a cylinder, making it compact and good for storage. |
| What is the structure of amylopectin? | Long, branched chain of alpha glucose. Side branches allow enzymes that break down molecule to get to glycosidic bonds easily, so glucose can be released quickly. |
| How else is starch good for storage? | Insoluble in water, so doesn’t cause water to enter cells by osmosis, which would make them swell. |
| Describe the test for starch? | Add iodine dissolved in potassium iodide solution to the test sample. If starch is present, the sample changes from browny-orange to a dark blue-black colour. If there is no starch, it stays browny-orange. |
| What do animals store excess glucose as? | Glycogen, another polysaccharide of alpha glucose. |
| What is the structure of glycogen? | Very similar to amylopectin, but with more side branches, so can be broken down to glucose faster which is important for energy release in animals. Also very compact, so good for storage. |
| What is the major component of cell walls in plants? | Cellulose. |
| Describe the structure of cellulose? | Made of long, unbranched chains of beta-glucose. Bonds between sugars are straight, so cellulose chains are straight. Chains linked by hydrogen bonds to form strong support for cells. |
| What is the structure of a triglyceride? | Made from one molecule of glycerol attached to three fatty acids, which have long hydrophobic tails made from hydrocarbons. Hydrophobic tails make lipids insoluble in water. |
| What stays the same between fatty acids, and what varies? | Basic structure stays the same, but hydrocarbon tail varies. |
| What is the function of a triglyceride? | Energy storage molecules. |
| How are triglycerides good as energy storage molecules? | Long hydrocarbon tails of fatty acids contain lots of chemical energy, which they release when broken down. Insoluble, so don’t cause cell to swell. Bundle as droplets, because fatty acids are hydrophobic and face inwards. |
| Where are phospholipids found? | In the cell membrane (make up the bilayer). |
| What is the structure of a phospholipid? | Like triglycerides, but one fatty acid molecule is replaced by a phosphate group. |
| Which parts of phospholipids are hydrophilic / hydrophobic? | Phosphate group is ionised, so it is hydrophilic. Fatty acid tails are hydrophobic. |
| How does the structure of a phospholipid help it to form the bilayer? | Hydrophilic head faces out towards water on either side of double layer, and hydrophobic tail faces inwards. Hydrophobic centre does not allow water-soluble substances through – acts as a barrier. |
| What is cholesterol? | Type of lipid often found in cell membranes and also used to make other things, like steroids. |
| What is the structure of cholesterol? | A hydrocarbon ring attached to a hydrocarbon tail. Hydrocarbon ring has a polar hydroxyl group attached to it, so cholesterol is soluble. |
| What is the function of cholesterol? | Helps strengthen cell membrane by interacting with phospholipid bilayer. |
| How is cholesterol adapted to its function? | Small size and flattened shape means it can fit between phospholipid molecules in the membrane. Binds to hydrophobic tails of phospholipids, so they pack more closely together, making the membrane less fluid and more rigid. |
| Describe the emulsion test for lipids? | Shake test substance with ethanol for about a minute, then pour the solution into water. If lipid present, solution turns milky. More lipid leads to a more noticeable milky colour. |
| What is the structure of water? | Two hydrogen atoms covalently bonded to one oxygen atom. |
| Why is water polar? | Shared electrons pulled closer to oxygen than hydrogen, so molecule is slightly negatively charged at oxygen end and slightly positively charged at hydrogen end. |
| How is it useful that water is a liquid? | Makes it a good transport medium. |
| Why is ice less dense than water? | Hydrogen bonds in solid water hold it in a semi-crystalline form – the molecules are further apart than in the liquid form. |
| Why is it helpful that ice floats on water? | Insulates water below ice, providing more stable environment for aquatic life. |
| Why is water a good solvent? | Because it is polar so dissolves other polar molecules. |
| Why is water being a good solvent helpful? | Metabolic processes require chemicals to react in solution. |
| Why is water cohesive? | Hydrogen bonds stick molecules together and create surface tension. |
| Why is water’s cohesion helpful? | Sticks together in long, thin water columns which are difficult to break, which is useful in xylem of plants. Some organisms use surface tension to walk on water. |
| Why does water have high thermal stability? | Hydrogen bonds can absorb a lot of heat, so it requires a lot of energy to raise the temperature of water – water has a high specific heat capacity. |
| Why is water’s thermal stability helpful? | Makes it a stable living environment. |
| Why does water have a high latent heat of evaporation? | A lot of energy is required to evaporate it. |
| How is water useful to metabolism? | Takes part as a reactant in many chemical processes – for example in hydrolysis and photosynthesis. |
Created by:
emm142
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