Biological Molecules- Biology

• Monomers -> Polymers is condensation + produces water
• Polymers -> Monomers = hydrolysis + uses water
• Monomer is a small molecule that can join together to form a polymer
• Examples of monomers- monosaccharides, amino acids, nucleotides
• Polymer is many monomers joined together
• Examples of polymers- polysaccharides, polypeptides, DNA/RNA
• glucose + glucose -> maltose

  glucose + fructose -> sucrose

  glucose + galactose -> lactose
• Bond formed from condensation of monosaccharides= 1,4 and 1,6 glycosidic bond

  Bond formed from condensation of amino acids= peptide bond

  Bond formed from condensation of glycerol and fatty acids= ester bond

  Bond formed from condensation of nucleotides= phosphodiester bond
• Structure and function of starch

  insoluble- doesn't affect water potential of the cell

  large- does not diffuse out of cell

  Made from amylose and amylopectin

  alpha helix- compact

  branched- can easily be hydrolysed to form glucose
• Structure and function of glycogen

  • 1,4 & 1,6 glycosidic bonds
  • branched- easy to hydrolyse to form glucose
  • insoluble- doesn't affect water potential nor diffuse out of cells
  • helical- compact
• Structure and function of cellulose

  • 1,4 glycosidic bonds
  • straight chain, unbranched molecule
  • Alternate inverted glucose molecules
  • H crosslinks between straight parallel chains
  • Form microfibrils and fibrils- high tensile strength
• Test for starch. Add iodine + potassium iodide.

  Positive result= blue/black colour

  Negative result= orange colour
• Benedict's Test- reducing sugar

  Add benedict's solution to the sample and boil the test tubes. Any with reducing sugar should form a red precipitate. However the colours are rainbow- more red- more reducing sugar
• Benedict's test- non reducing sugar

  Do reducing sugar test- solution remains blue.

  Add HCl and heat. Add NaOH to neutralise.

  Add Benedict's and boil- red precipitate should form
• Biuret test- proteins.

  Add biurets reagent. Positive result = purple

  Negative result= blue
• Test for lipids in a sample

  1. Dissolve solid samples in ethanol

  2. Add an equal volume of water and shake

  3. Positive result: milky white emulsion forms
• Triglycerides

  Formed by a condensation reaction between 1 molecule of glycerol & 3 fatty acids, forming ester bonds

  
• Saturated fatty acids

  • Contain only single bonds, straight-chain molecules have many contact points, higher melting point = solid at room temperature, found in animal fats

  
• Unsaturated fatty acids

  • Contain C=C double bonds, 'kinked' molecules have fewer contact points, lower melting point = liquid at room temperature, found in plant oils

  
• Structure of triglycerides

  High energy:mass ratio = high calorific value from oxidation (energy storage), insoluble hydrocarbon chain = no effect on water potential of cells & used for waterproofing, slow conductor of heat = thermal insulation e.g. adipose tissue, less dense than water = buoyancy of aquatic animals

  
• Phospholipids

  Amphipathic molecule: glycerol backbone attached to 2 hydrophobic fatty acid tails & 1 hydrophilic polar phosphate head, forms phospholipid bilayer in water = component of membranes, tails can splay outwards = waterproofing

  
• Phospholipids and triglycerides are not polymers
• Water polarity

  O is more electronegative than H, so attracts the electron density in the covalent bond more strongly, forms O δ- (slight negative charge) & H δ+ (slight positive charge)
• Biologically important properties of water

  • Metabolite / solvent for chemical reactions in the body, high specific heat capacity, high latent heat of vapourisation, cohesion between molecules
• Significance of water to living organisms

  Solvent for polar molecules during metabolic reactions, enables organisms to avoid fluctuations in core temperature, cohesion-tension of water molecules in transpiration stream
• Inorganic ions

  Ions that do not contain carbon atoms, found in cytoplasm & extracellular fluid, may be in high or very low concentrations
• Role of hydrogen ions in the body

  High concentration of H+ = low (acidic) pH, H+ ions interact with H-bonds & ionic bonds in tertiary structure of proteins, which can cause them to denature
• 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 O2 around body in bloodstream, 4 haem groups per haemoglobin molecule
• Role of sodium ions in the body

  Involved in co-transport for absorption of glucose & amino acids in lumen of gut, involved in propagation of action potentials in neurons
• Role of phosphate ions in the body

  Component of DNA, ATP, NADP, cAMP
• Draw the structure of a nucleotide

  1. nitrogen-containing base

  2. pentose sugar

  3. phosphate group
• Nucleotide


  The basic structural unit of nucleic acids, consisting of a pentose sugar, a nitrogen-containing base, and a phosphate group
• Pentose sugars

  DNA: deoxyribose

  RNA: ribose
• DNA

  • Base sequence of genes codes for functional RNA & amino acid sequence of polypeptides

  Genetic information determines inherited characteristics = influences structure & function of organisms
• RNA

  • mRNA: Complementary sequence to 1 gene from DNA with introns (non-coding regions) spliced out. Codons can be translated into a polypeptide by ribosomes.

  rRNA: component of ribosomes (along with proteins)

  tRNA: supplies complementary amino acid to mRNA codons during translation
• How polynucleotides form

  Condensation reactions between nucleotides form strong phosphodiester bonds (sugar-phosphate backbone)
• DNA structure

  • double helix of 2 polynucleotide strands (deoxyribose)

  1. bonds between complementary purine & pyrimidine base pairs on opposite strands: adenine (A) + thymine (T), guanine (G) + cytosine (C)
• Purine

  1. ring bases: adenine (A) & guanine (G)
• Pyrimidine

  1. ring bases: thymine (T), cytosine (C) & uracil (U)
• Complementary base pairs in DNA

  2 H-bonds between adenine (A) + thymine (T)

  3 H-bonds between guanine (G) + cytosine (C)