Biological Molecules

• What is a monomer?

  A smaller unit from which polymers are made
• Biochemical test for non-reducing sugars?

  1. Heat with acid and neutralise
  2. Heat with Benedict's solution
  3. Red precipitate
• Describe 2 differences between the structure of a cellulose and glycogen molecule?

  1. Cellulose is made up of beta-glucose and glycogen is made up of alpha-glucose
  2. Cellulose molecule has a straight chain and glycogen molecule is branched
• Describe and explain 2 features of starch that make it a good storage molecule?

  1. Insoluble in water, so doesn't affect water potential
  2. Branched, so makes molecules compact
• Describe the structure of glycogen?

  1. Polymer of alpha-glucose
  2. Joined by glycosidic bonds
• Suggest how glycogen acts as a store of energy?

  1. Hydrolysed to glucose
  2. Glucose used in respiration
• Explain how cellulose molecules are adapted for their roles in plant cells?

  1. Long and straight chains
  2. Become linked together by many hydrogen bonds to form fibrils
  3. Provide strength to cell wall
• Describe the induced-fit model of enzyme action and how an enzyme acts as a catalyst?

  1. Substrate binds to active site
  2. Active site changes shape so it is complementary to substrate
  3. Reduces activation energy
• A competitive inhibitor decreases the rate of an enzyme controlled reaction. Explain how?

  1. Inhibitor is similar shape to substrate
  2. Binds to active site
  3. Prevents enzyme-substrate complex forming
• Describe how the structure of a protein depends on the amino acids it contains?

  1. Structure determined by position of amino acid
  2. Primary structure is sequence of amino acid
  3. Secondary structure formed by hydrogen bonding
  4. Tertiary structure formed by interactions between R groups
  5. Creates active site in enzymes
  6. Quaternary structure contains more than 1 polypeptide chain
• Explain how the active site of an enzyme causes a high rate of reaction?

  1. Lowers activation energy
  2. Induced fit causes active site to change shape
  3. So enzyme-substrate complex causes bonds to form/break
• Describe a biochemical test to confirm the presence of protein in a solution?

  1. Add Biuret's reagent
  2. (Positive result) lilac
• Describe how a non-competitive inhibitor can reduce the rate of an enzyme-controlled reaction?

  1. Attaches to allosteric site
  2. Changes shape of the active site
  3. So active site and substrate no longer complementary so less substrate can bind
• Describe the structure of DNA?

  1. Polymer of nucleotides
  2. Each nucleotide formed from deoxyribose, a phosphate group and an organic base
  3. Phosphodiester bonds between nucleotides
  4. Double helix held by hydrogen bonds
  5. Hydrogen bonds between adenine, thymine and cytosine, guanine
• Describe how a phosphodiester bond is formed between 2 nucleotides?

  1. Condensation reaction
  2. Between phosphate and deoxyribose
  3. Catalysed by DNA polymerase
• Contrast the structure of ATP and a nucleotide found in DNA?

  1. ATP has ribose and DNA has deoxyribose
  2. ATP has 3 phosphate groups and DNA nucleotide has 1 phosphate group
• Describe how an ATP molecule is formed from its component molecules?

  1. Adenine, ribose and 3 phosphates
  2. Joined together in a condensation reaction
  3. Catalysed by ATP synthase
• Give 2 ways in which ATP is a suitable energy source for cells to use?

  1. Phosphorylates other compounds, making them more reactive
  2. Releases energy instantaneously (energy is readily available)
• Describe how ATP is resynthesized in cells?

  1. From ADP and phosphate
  2. By ATP synthase
  3. During respiration
• Give 2 ways in which the hydrolysis of ATP is used in cells?

  1. To phosphorylate other compounds and make them more reactive
  2. To provide energy for other reactions
• Explain 5 properties that make water important for organisms?

  1. A metabolite in condensation/hydrolysis reactions
  2. A solvent so metabolic reactions can occur
  3. High specific heat capacity so buffers changes in temperature
  4. Large latent heat of vaporisation so provides a cooling effect through evaporation
  5. Cohesion between water molecules so supports columns of water in plants
• Describe the roles of iron ions in cells?

  Haemoglobin associates with oxygen
• Describe the roles of sodium ions in cells?

  1. Co-transport of glucose/amino acids into cells
  2. Sodium moved out by active transport/Na-K pump
  3. Creates a diffusion gradient
  4. Affects osmosis/water potential
• Describe the roles of phosphate ions in cells?

  1. Joins nucleotides in backbone of DNA
  2. Used to produce ATP
  3. Phosphorylates other compounds making them more reactive
  4. Hydrophilic part of phospholipid bilayer