A Level Biology - Biological Molecules (Part 1)

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  • Created on: 31-10-17 15:39
What are monomers?
Monomers are the smaller units from which larger molecules are made.
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What are polymers?
Polymers are molecules made from a large number of monomers joined together.
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Give three examples of monomers.
Monosaccharides, amino acids and nucleotides.
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What does a condensation reaction do?
A condensation reaction joins two molecules together with the formation of a chemical bond and involves the elimination of a water molecule.
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What does a hydrolysis reaction do?
A hydrolysis reaction breaks a chemical bond between two molecules using a water molecule.
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What are the monomers that make up large carbohydrates called?
Monosaccharides.
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Name three common monosaccharides.
Glucose, alactose and fructose are common monosaccharides
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What elements do all carbohydrates have?
Carbon, hydrogen and oxygen.
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Are all monosaccharides soluble in water?
Yes
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Give an example of a monosaccharide, state what type of sugar it is and hence state how many carbon atoms it has.
Glucose is a hexose sugar - it has six carbon atoms in each molecule.
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Recall the two types of glucose.
Alpha-glucose and beta-glucose.
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Alpha-glucose and beta-glucose are isomers. What is meant by the term 'isomers'?
Isomers are molecules with the same molecular formula but with the atoms arranged in a different way.
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Draw the structure of alpha-glucose and beta-glucose.
.....
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What type of reaction joins monosaccharides together? What bond forms? Is water released or used?
Condensation reaction. A glycosidic bond forms between the two monosaccharides as a molecule of water is released.
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How are disaccharides formed?
Disaccharides are formed by the condensation of two monosaccharides.
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How is maltose formed?
Maltose is a disccharide formed by the condensation of two glucose molecules.
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How is Sucrose formed?
Sucrose is a disaccharide formed by the condensation of a condensation of a glucose molecule and a fructose molecule.
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How is Lactose formed?
Lactose is a disaccharide formed by the condensation of a glucose and a galactose molecule.
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What happens when a carbohydrate undergoes a hydrolysis reaction?
The carbohydrate is broken down into it's constituent monosaccharidey.
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Describe the process of the Benedict's Test for sugars and state the outcomes.
1. Heat the sample in Benedict's reagent. 2. If the sample stays blue, there's no reducing sugar present. However, if there's a colour change (green- brick red) there's a reducing sugar present.
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If the result to the reducing sugars test is negative, there may still be some non-reducing sugars present. Explain how to test for non-reducing sugars.
1. Heat new sample with dilute hydrochloric acid, then neutralise by adding sodium hydrogencarbonate. 2. If sample stays blue, there's no non-reducing sugar present. If there's a colour change (green- brick red) there's a reducing sugar present.
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How is a polysaccharide formed?
A polysaccharide is formed when more than two monosaccharides are joined together by a condensation reaction.
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Recall the three main polysaccharides.
Starch, Glycogen and Cellulose.
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Cells get energy from glucose. How do plants store excess glucose?
Excess glucose is stored as starch.
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Recall the two polysaccharides that starch is made of.
Amylose and amylopectin.
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Describe amylose.
Long unbranched chains of alpha glucose. The angles of the glycosidic bonds give it a coiled structure.
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Describe amylopectin.
Long, branched chains of alpha glucose. Its side branches allow the enzymes that break down the molecule to get at the glycosidic bonds quickly. This means that the glucose can be released quickly.
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Is starch soluble soluble in water? Does it affect water potential? Explain how this makes starch suitable for osmosis.
Starch is insoluble in water and doesn't affect water potential, so it doesn't cause water molecules to enter the cell via osmosis (which would cause it to swell).
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Describe the iodine test for starch.
Add iodine dissolved in potassium iodide solution to test for starch. If there's starch present, the sample changes from orange/brown to a blue/black colour.
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Animal cells get energy from glucose. What do animals store excess glucose as?
Animal cells store excess glucose as glycogen- another polysaccharide of alpha glucose.
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The structure of glycogen is very similar to amylopectin, apart from one key difference. Recall this difference. Explain the effect of this difference.
Glycogen has many more side branches. Many branches means that stored glucose can be released quickly, which is important for energy release in animals.
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Is glycogen spaced out or compact? Explain the effect of this quality.
Glycogen is a compact molecule and so it's good for storage.
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Describe cellulose.
Cellulose is made up of long, unbranched chains of beta glucose.
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What type of bonding links cellulose chains together? What does this form and what properties does this give the cellulose chains?
The cellulose chains are linked together by hydrogen bonding to form strong fibres called microfibrils. These strong fibres mean that cellulose provides structural support for cells.
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What are triglycerides?
Triglycerides are a type of lipid.
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Draw the structure of a triglyceride. Describe the structure.
Trig;ycerides have one molecule of glycerol with three fatty acid molecules attached to it.
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Fatty acids have a long hydrocarbon tail. Are these tails hydrophobic or hydrophilic? Comment on what this does to the solubility of the triglycerides.
These hydrocarbon tails are hydrophobic, making them insoluble in water.
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Draw and describe the structure of a hydrocarbon tail.
The carbon atom links the fatty acid to the glycerol. There is a variable R group hydrocarbon tail.
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Are triglycerides formed by condensation reactions or hydrolysis? What bond forms between a glycerol and a fatty acid. What happens when this bond is formed?
Triglycerides are formed by condensation reactions. An ester bind is formed when glycerol joins with a fatty acid. When the ester bond is formed a molecule of water is released.
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draw the process that takes place when glycerol and three fatty acids join to form a triglyceride.
....
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Descirbe the difference between saturated and unsaturated fatty acids.
Saturated fatty acids don't have any double bonds between carbon atoms whereas unsaturated fatty acids have at least one double bond between carbon atoms.
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Where are phospholipids found?
They're found in cell membranes.
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There is one main difference between phospholipids and triglycerides. Recall this difference. Is this part hydrophobic or hydrophilic?
Phospholipids have a phosphate group instead of one of the fatty acids. The phosphate group is hydrophilic.
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State the three ways the structure of triglycerides relate to their functions.
1) The long hydorgcarbon tails of the fatty acids contain lots of chemical - a lot of energy is released when they're broken down. 2) They're insoluble so they don't affect water potential, so they don't cause water to enter the cell by osmosis.
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State the three ways the structure of triglycerides relate to their functions. (CONTINUED)
Triglycerides clump together as insoluble droplets in cells because the fatty acids tails are hydrophobic - the tails face inward, shielding themselves from water with their glycerol heads.
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State three ways by which the structure of phospholipids relate to their function.
1) Phospholipids make up the bilayer of cell membranes. 2) Their heads are hydrophilic and their tails are hydrophobic, so they form a double layer with their heads facing out towards the water on either side.
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State three ways by which the structure of phospholipids relate to their function. (CONTINUED)
3) The centre of the bilayer is hydrophobic, so water-soluble substances can't easily pass through it - the membrane acts as a barrier to those substances.
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Describe how to test for lipids.
Shake the test substance with ethanol for about one minute so that it dissolves, then pour the solution into water. Any lipid will show up as a milky emulsion.
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What happens to the colour as the amount of lipid increases?
The more lipid present, the more milky the colour will be.
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What are the monomers of proteins?
Amino acids.
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What is formed when two amino acids are joined together?
Dipeptide
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What is formed when more than two amino acids are joined together?
Polypeptide
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What are proteins made of?
One or more polypeptide/s.
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Draw and describe the structure of an amino acid.
... Amino acids have a carboxyl group, an amine group, and a carbon-containing R group.
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What type of reaction forms polypeptides?
Condensation Reactions.
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What do condensation reactions link together to form polypeptides?
Amino acids.
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A bond forms between amino acids when they're joined together. What is this bond called?
Peptide Bond.
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Draw the reaction between two amino acids to form a dipeptide.
...
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Proteins have four structural levels - what does its primary structure refer to?
The primary structure refers to the sequence of amino acids in the polypeptide bonds.
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What does the secondary structure refer to?
Hydrogen bonds form between the amino acids in the chanin. This makes it coil into an alpha-helix or a beta-pleated sheet.
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What does the tertiary structure refer to?
The chain of amino acids coils or folds further; more hydrogen + ionic bonds form. Disulfide bridges form whenever two molecules of the amino acids cysteine come together. For proteins made from one polypeptide chain, this is the final 3-D structure.
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What does the quaternary structure refer to?
The quarternary structure refers to the way the polypeptide chains are assemebled together. For proteins made from more than one polypeptide chain, this is the final 3-D structure.
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Name three functions of proteins and briefly describe the arrangement of polypeptide chains in these for things.
1) ENZYMES- Tight folding of polypeptide chains so they're spherical in shape 2) ANTIBODIES- 2 light + 2 heavy polypetide chains joined together. 4) STRUCTURAL PROTIENS- Long polypeptide chains lying parallel, with cross-links between them.
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Describe the biuret test for proteins and the outcomes.
First, add a few drops of sodium hydroxide solution. Then, add some copper (II) sulfate. If there is protein present the solution turns purple. If there's no protein present, the solution will stay blue.
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What do enzymes catalyse?
Enzymes catalyse metabolic reactions.
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Enzymes catalyse metabolic reactions on a cellular level and for the organism as a whole. Give an example of each.
Cellular level: Respiration. Organism: Digestion in mammals.
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Enzymes can affect structures and functions. Give an example of how it affects each.
Structural: Production of collagen Functions: Respiration
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Enzyme action can be divided into two categories. What are these?
Intracellular (Inside the cell) and extracellular (outside the cell)
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What is meant by the term 'activation energy'?
Activation energy refers to the minimum amount of energy needed to initiate a chemical reaction.
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Do enzymes lower or raise the activation energy?
Enzymes lower the activation energy.
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When enzymes lower the activation energy, do reactions happen at lower or higher temperatures?
Enzymes make reactions happen at lower temperatures. This speeds up the rate of reaction.
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What is formed when the substrate binds to the enzyme?
An enzyme substrate complex.
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Enzymes substrate complex, its this that lowers the activation energy. How is this?
If two enzymes need to be joined together, being attached to the enzyme holds them close together, reducing any repulsion between the molecules so they can bond more easily.
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Which is a better theory; 'Lock and Key' or 'Induced fit'?
Induced Fit
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What does new evidence show (in terms of Induced Fit)?
New evidence showed that the enzyme-substrate complex changes shape slightly to complete the fit. This locks the substrate even more tightly to the enzyme.
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What are polymers?

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Give three examples of monomers.

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Card 4

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What does a condensation reaction do?

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Card 5

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What does a hydrolysis reaction do?

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