Biological Molecules

• Define Momonmer


  Smaller units that join together to form larger molecules
• Define Polymer


  Molecules formed when many monomers join together
• What happens in a condensation reaction?


  A chemical bond forms between 2 molecules and a molecule of water is produced
• What happens in a hydrolysis reaction?


  A water molecule is used to break a chemical bond between 2 molecules
• Name the three hexose monosaccharides


  ~ Glucose

  ~ Fructose

  ~ Galactose
• Name the type of bond formed when monosaccharides react


  ~ two monomers = Disaccaride

  ~ Multiple monomers = Polysaccaride
• Name three disaccharides

  ~ Glucose + Glucose = Maltose

  ~ Glucose + Fructose = Sucrose

  ~ Glucose + Galactose = Lactose
• Describe the structure and functions of starch


  ~ Storage polymer for a-glucose in plant cells

  ~ insoluble so has no osmotic effect on cells

  ~ Large so does not diffuse out of cells

  ~ Made from amylose

  ~ Made from amylopectin which is highly branched
• Describe the structure and functions of glycogen

  ~ Main storage polymer of a-glucose in animal cells

  ~ Also found in plant cells

  ~ Insoluble so no osmotic effect and does not diffuse out of cells

  ~ Branched so can be hydrolised quickly

  ~ Compact
• Describe the structure and functions of cellulose


  ~ Polymer of b-glucose

  ~ Gives rigidity to plant cell walls

  ~ Straight and unbranched
• Describe the Benedict's test for reducing sugars


  ~ Add an equal volume of Benedict's reagent to a sample

  ~ Heat the mixture in an electric water bath at 100°c for 5 minutes

  ~ Positive result: Colour change from blue to orange and brick red precipitate forms
• Describe the Benedict's test for non-reducing sugars

  ~ Negative result: Benedict's reagent remains blue

  ~ Hydrolyse non-reducing sugars into their monomers by adding 1cm³ of HCl

  ~ Heat in a boiling water bath for 5 minutes

  ~ Neutralise the mixture using sodium carbonate solution

  ~Proceed with the benedict's test as usual
• Describe the test for starch

  ~ Add iodine solution

  ~ Postitive result: Colour change from orange to blue-black
• Outline how colorimetry could be used to give qualitative results for the presence of sugars and starch

  ~ Make standard solutions with known concentrations

  ~ Record absorbance or % transmission values

  ~ Plot calibration curve: absorbance or % transmission on the y-axis and concentration on the x-axis

  ~ Record absorbance or % transmission values of unknown samples.

  ~ Use calibration curve to read off concentration
• Describe how to test for lipids in a sample


  ~ Dissolve solid samples in ethanol

  ~ Add an equal volume of water and shake

  ~ Positive result: Milky white emulsion forms
• How do triglycerides form?

  Condensation reaction between one molecule of glycerol and three fatty acids forms ester bonds
• Contrast saturated and unsaturated fatty acids

  Saturated:

  ~ Contain only single bonds

  ~ Straight chain molecules

  ~ Higher melting point = solid at room temperature

  ~ Found in animals fats

  Unsaturated

  ~ Contain C=C double bonds

  ~ Kinked molecules have fewer contact points

  ~ Lower melting point = liquid at room temperature

  ~ Found in plant oils
• Relate the structure of triglycerides to their functions

  ~ High energy

  ~ Insoluble hydrocarbon chain so no effect on water potential of cells and used for waterproofing

  ~ Slow conductor of heat = thermal insulation

  ~ Less dense than water = buoyancy of aquatic animals
• Describe the structure and function of phospholipids

  ~ Glycerol backbone attached to two hydrophobic fatty acid tails and one hydrophilic polar phosphate head

  ~ Forms phospholipid bilayer in water

  ~ Tails can splay outwards = waterproofing
• Compare phospholipids and triglycerides


  ~ Both have glycerol backbone

  ~ Both may be attached to a mixture of saturated, monounsaturated and polyunsaturated fatty acids

  ~ Both contain the elements C, H, O

  ~ Both formed by condensation reactions
• Contrast phospolipids and triglycerides

  Phospholipids

  ~ 2 fatty acids and 1 phosphate attached

  ~ Hydriphilic head and hydrophobic tail

  ~ Used primarily in membrane formation

  Triglycerides

  ~ 3 fatty acids attached

  ~Entire molecule is hydrophobic

  ~ Used primarily as a storage molecule
• Why is water a polar molecule

  O is more electronegative than H, so attracts the electron density in the cobalent bond more strongly
• State four biologically important properties of water

  ~ Metabolite/ solvent for chemical reactions in the body

  ~ High specific heat capacity

  ~ High latent heat of vapouristation

  ~ Cohesion between molecules
• Explain why water is significant to living organisms

  ~ Solvent for polar molecules during metabolic reaction

  ~ Enables organisms to avoid fluctuations in core temperature

  ~ Cohesion tension of water molecules in transpiration stream
• What are inorganic ions and where are they found in the body

  ~ Ions that do not contain carbon atoms

  ~ Found in cytoplasm and extracellular fluid

  ~ May be in high or very low concentrations
• Explain the role of hydrogen ions in the body

  ~ High concentration of h+ = low pH

  ~ H+ ions interact with H-bonds and ionic bonds in tertiary structure of proteins which can cause them to denature
• Explain the role of iron ions in the body

  ~ Fe2+ bonds to porphyrin ring to form haem group in haemoglobin

  ~ Haem group has binding site to transport 1 molecule of 02 around the body in bloodstream
• Explain the role of sodium ions in the body

  ~ Involved in co-transport for absorption of glucose and amino acids in lumen

  ~ Involved in propagation of action potentials in neurons
• Explain the role of phosphateions in the body

  ~ DNA

  ~ ATP

  ~ NADP

  ~ cAMP
• What is the general structure of an amino acid

  ~ COOH: carboxyl/ carboxylic acid group

  ~ R: variable of side group consists of carbon chain and may include other functional groups

  ~ NH2: Amine/ amino group
• Describe how to test for proteins in a sample

  ~ Biuret test confirms presence of peptide bond

  ~ Add equal volume of sodium hydroxide to sample at room temperature

  ~ Add drops of dilute coppr (II) sulfate solution. Swirl to mix

  ~ Positive result: Colour changes from blue to purple

  ~ Negative result: Solution remains blue
• How many amino acids are there and how do they differ from one another

  ~ 20

  ~ Differ only by side R group
• How do dipeptides and polypeptides form


  ~ Condensation reaction forms a peptide bond and eliminates molecule of water

  ~ Dipeptide: two amino acids

  ~ Polypeptide three or more amino acids
• How many levels of protein structure are there

  4
• Define Primary structure of a protein

  ~ Sequence, number and type of amino acids in the polypeptide

  ~ Determined by sequence of codons on mRNA
• Define secondary structure of a protein

  Hydrogen bonds form between O (Slightly negative) attached to -C=O and H (Slightly positive) attached to -NH
• Describe the 2 types of secondary protein structure

  a-helix

  ~ All N-H bonds on same side of protein chain

  ~ Spiral shape

  ~ H-bonds parallel to helical axis

  b-pleated sheet

  ~ N-H and C=O groups alternate from one side to the other
• Define tertiary structure of a protein. Name the bonds present

  ~ 3D structure formed by further folding of polypeptide

  ~ Disulfide bridges

  ~ Ionic bonds

  ~ Hydrogen bonds
• Describe each type of bond in the tertiary structure of proteins

  ~ Disulfide bridges: Strong covalent S-S bonds between molecules of the amino acid cysteine

  ~ Ionic bridges: Relatively strong bonds between charged R groups

  ~ Hydrogen bonds: Numerous and easily broken
• Define quaternary structure of a protein

  ~ Functional proteins may consist of more than one polypeptide

  ~ Precise 3D structure held together by the same types of bond as tertiary structure

  ~ May involve addition of prosthetic groups