Biological Molecules

• What are monomers?


  Small units which are the components of larger molecules.
• What are polymers?


  Molecules made from many monomers joined together.
• What are examples of monomers?

  Monosaccharides, amino acids and nucleotides
• What are examples of polymers?

  Polysaccharides, polypeptides and polynucleotides
• What reaction allows two monomers to bond together?

  A condensation reaction, releases a water molecule.
• What reaction breaks the chemical bond between two molecules?


  A hydrolysis reaction, happens due to the addition of water.
• What are carbohydrates?

  Molecules which consist only of carbon, hydrogen and oxygen.
• What is the small unit that makes up a carbohydrate.

  Monosaccharides
• What is formed when two monosaccharides go through condensation reaction?


  A disaccharide
• What is the bond that's formed during the condensation reaction between two monosaccharides?

  A glycosidic bond
• What's formed when many monosaccharides go through condensation reaction?

  A polysaccharide
• What are examples of monosaccharides?

  • Glucose(α-glucose and β glucose)
  • Galactose
  • Fructose

  
• What is the structure of both α-glucose and β glucose?

  They both have 6 carbon atoms, α-glucose has its OH group attached at the bottom right and β glucose has its OH group attached at the top right.

  
• Which disaccharide is formed when two α-glucose molecules join together?

  Maltose

  
• Which disaccharide is formed when a glucose molecule and fructose join together?

  Sucrose

  
• Which disaccharide is formed when a glucose molecule and galactose join together?

  Lactose

  
• What are the three polysaccharides that are formed from glucose monomers?


  • Glycogen (formed by the condensation of α-glucose)
  • Starch (formed by the condensation of α-glucose)
  • Cellulose (formed by the condensation of β glucose)
• What is starch?

  Starch is what plants store as excess glucose. When plants require glucose for respiration and energy, starch is broken down into glucose.
• What mixture does starch consist of?

  Amylose and Amylopectin
• Describe the structure of starch?


  Amylose is a long, unbranched chain of α-glucose molecules. Due to its specific glycosidic bonding, its shape becomes coiled, which makes it very compact.

  
  

  Amylopectin is a long, branched chain of α-glucose molecules. It has got many side branches on it.

  
• Explain the relationship between the structure and function in starch.

  The coiled and compact shape of amylose allows a lot of energy to be stored, making it a good energy store.

  
  

  The side branches on amylopectin allow enzymes to break down the molecule and make it easier to break the glycosidic bond meaning energy can be released quicker for processes e.g respiration.

  
  

  Starch is also insoluble and therefore doesn't affect the water potential, so water cannot enter cells by osmosis.
• What is the test for starch?


  Add the test sample to iodine solution(potassium iodide solution).

  If the solution turns frombrown/orange to blue/black, thenstarch is present.
• What is glycogen?

  The main energy storage in animals, it stores excess glucose to be used later on (respiration).
• Describe the structure of glycogen.

  Glycogen has a large number of side branches, similar to amylopectin.
• Explain the relationship between the structure and function in glycogen.

  The side branches in glycogen allow it to be broken down much quicker by enzymes, meaning that energy can be released quickly as well.

  
  

  Also, since it is highly branched, a high amount of energy is released. The energy released can be used for important processes.

  
  

  Glycogen is also insoluble and therefore doesn't affect the water potential, so water cannot enter cells by osmosis.
• What is cellulose?

  The main component found in cell walls to help provide structural support.

  
• Describe the structure of cellulose.


  Cellulose is a long, straight, unbranched chains of B glucose molecules. Each chain is linked together by hydrogen bonds to form strong cross links and strong fibres known as microfibrils.
• Explain the relationship between the structure and function of cellulose.

  The microfibrils help provide structural support for the cell wall, so it can help the cell wall to not burst when water tries to enter in.

  
  

  The strength of the cell wall is contributed by the many hydrogen bonds that are between the cellulose chains, making cellulose a strengthening material for plants .
• What is the test for reducing sugars?


  • Add test sample to Benedict's Reagent.
  • Heat it gently
  • If solution turns brick red, then a reducing sugar is present.
  • If the solution stays blue, then no reducing sugar is present.
• What is the test for non-reducing sugars?

  After the test for reducing sugars, you should:

  • Add dilute HCl to the test sample (hydrolyse the polysaccharides/disaccharides into its constituent monosaccharides)
  • Then add sodium hydrogen carbonate to neutralise the acid. (Benedict's reagent doesn't work in acidic conditions)
  • Add the sample to Benedict's reagent and then heat the sample.
  • If the solution turns brick red then a non-reducing sure is present. If the solution stays blue then there isn't a non-reducing or reducing sugar present.
• What are lipids?

  Biological molecules that are composed of carbon, hydrogen and oxygen and they are only soluble in organic solvents (such as alcohols) and insoluble in water.
• What are the two types of lipids called?

  Triglycerides and Phospholipids
• How are triglycerides formed?


  The condensation reaction of one glycerol molecule and three fatty acid chains.
• What is the bond formed between the glycerol molecule and each fatty acid chain?

  Ester bond
• What are the two types of fatty acids called?

  Saturated fatty acids and unsaturated fatty acids
• What is the difference between saturated and unsaturated fatty acid chains?


  Saturated fats don't have double bonds between their carbon atoms.

  
  

  Unsaturated fats do have double bonds between carbon atoms.
• What does the double bonds cause the fatty acid chain to do?

  Causes it to kink/bend, so the chain can't pack together tightly and therefore are liquids in room temperature (oils).
• How does triglyceride's structure relate to their properties?

  • Have a high ratio of energy storing carbon-hydrogen bonds to carbon atoms and so an excellent source of energy.
  • Have a low mass to energy ratio, meaning that they are good storage molecules.
  • Their insolubility (due to being large and non-polar) in water means that their storage doesn't affect the water potential of cells.
• How does the structure of a phospholipid molecule look like?

  In phospholipids, one of the fatty acid chains is replaced by a phosphate group/phosphate head.
• Fill in the gap: The phosphate group is _________to water and therefore is ___________.

  The phosphate group is attracted to water and therefore is hydrophilic.