Biological molecules( Topic 1A)

• evidence for evolution


  It hs been found that a large variety of different organisms on the earth share some biochemistry however they all contained the same group of carbon compounds such as DNA and RNA which are used to build proteins. the similarities between animals and plants provides indirect evidence for evolution
• Polymers


  Lage complex structure composed of long chains of single units called monomers joined together e.g

  • carbohydrates
  • proteins
  • nucleic acids
• Monomers

  Small basic molecular units that can join together to form a polymer

  • monosaccharides
  • amino acids
  • nucleotides
• condensation reaction


  biological polymers are formed from their monomers by condensation reactions by which they also release a molecule of water

  
• Hydrolysis reaction


  Biological polymers are broken down back into it's monomers through a hydrolysis reaction where a molecule of water is used to break the chemical bond between the monomers.

  
• Monosaccharides 


  monomers that carbohydrates are made from are monosaccharides e.g

  • glucose
  • fructose
  • galactose
• a-glucose & B-glucose(glucose isomers)

  • glucose is a hexose sugar( monosacharide with 6 carbon atoms in each element)
  • 2 types of glucose- alpha and beta glucose
  • Alpha and beta glucose are 'Isomers'- they have the same molecular formula but with the atoms connected in a different way

  
• Disaccharide


  Disaccharides are formed when two monosaccharides are joined together by a condensation reaction to form a glycosidic bond where a molecule of water is released.

  Disaccharides

  • Lactose(galactose+glucose)(reducing sugar)
  • Maltose(glucose +glucose)(reducing sugar)
  • Sucrose(fructose+glucose)(non reducing sugar)
• Benedicts Test for sugars


  All sugars are classified as reducing or non reducing

  • all monsaccharides are reducing sugars
  • some disaccharides are also reducing sugars e.g maltose and lactose
• Benedicts test for reducing sugar


  A more accurate way of doing this is to filter the solution and weight the percipitate or to remove the percipitate and use a colorimeter to measure the absorbance of the benedict reagent

  
• Benedicts test for Non reducing sugars


  If the result of reducing sugar is negative it may till contain a non reducing sugar e.g sucrosebut first you have to break them down into monosaccharides.

  *hydrolyse the sugar with dilute HCL and heat the sample in a boiling water bath.The acid breaks the glycosidic bonds splitting the non reducing sugar into monosaccharides. Then neutralise the solution by adding sodium hydrogencarbonate to avoid interference in the benedict test

  
• Polysaccharides

  • Polysacharides is formed when more that two monosaccharides are joined together by condensation reaction
  • They can also be broken down intto there constituent monosaccharids through hydrolysis

  Examples of polysaccharides

  • Starch
  • glycogen
  • cellulose
• polymer example

  
• Starch (Energy storage in plants)

  Starch consists of amylose and amylopectin both made from alpha -glucose

  Starch is insoluable in water meaning it doesn't effect water potential so it doesn't cause water to enter the cell by osmosis which could make them swell- This makes it good for storage
• Amylose(STRUCTURE)

  Unbranched coiled and compact. It's structure allows starch to store a large amount of glucose in a small space making it efficient for storage(efficient for storing energy in small spaces)
• Amylopectin(STRUCTURE)

  Branched structure with side chains allowing enzymes quick access to the glycosidic bonds which help in the rapid release of glucosewhen energy is needed(rapid energy release)
• Starch(FUNCTION)


  The compct amylose stores glucose efficiently while the branched amylopectin allows plants to quickly break down starch to meet energy demands.
• Glycogen(Energy store in animals) STRUCTURE


  Similar to amylopectin but with more branches.These extensive branches provide many ends where enzymes can act speeding up the breakdown of glycogen.
• Glycogen (energy storage in animals)FUNCTION


  The highly branched structure makes glycogen ideal for animals allowing for a quick glucose release during periods of high energy demands (e.g excercise ) ensuring energy is readily available
• Cellulose (structural support in plants)STRUCTURE


  Made of beta glucose forming long unbranched chains that run parallel. These chains are linked by hydrogen bonds to form strong fibres called microfibrils (provides strong structural support)
• Cellulose(Structural support in plants)FUNCTION


  The hydrogen-bonded microfibrils provide rigidity and strength giving structural support to plant cell walls. This allows plants to maintain shape and resist external forces (e.g wind or water pressure)
• Iodine test fo starch


  Add iodine dissolved in potassium iodide solution to the test sample. If there is starch pesent the sample changes from a browny- orange to a dark blue black colour.
• Lipids


  Lipids are not like carbohydrates or protein which are polymers made from long chains of monomers. Lipids are made from a variety of different components but they all contain HYDROCARBONS.

  2 types of lipids

  • Triglycerides
  • Phospholipids
• Triglycerides 


  3 fatty acids (hydrocarbon)joined to one molecule of glycerol

  
• Fatty acids


  Contains long tails made of hydrocarbons. The tails are hydrophobic (they repel water moecules)This makes lipids insoluable in water

  • This does not effect water potential which doesn't effect osmosis e.g doesn't make us dehydrated

  Two kind of fatty acids -Saturated and unsaturated

  (The difference is in their hydrocarbon tails -R groups)

  
• Saturated fatty acids


  Has a single bond (one carbon carbon bond ) therefoe no room for reaction

  
• Unsaturated fatty acids

  has a double bond (2 carbon carbon bond) meaning there is room for reaction which make the chain to kink.

  
• Triglyceride formation


  formed by condensation reaction. fatty acid joins to a glycerol molecule. An ester bond is formed between the two molecules releasing a molecule of water .This process occurs two more times to form a tryglyceride.

  
• Phospholipids


  Found in cell membranes

  It has a phosphate group(hydrophilic-attracts water)attached to a molecule of glycerol and 2 fatty acids(hydrophobic-repel water)with an ester bond in between.

  
• Properties of triglycerides


  good energy storage moleculegood energy storage molecule

  • long hydrocarbon tails of fatty acids contain alot of chemical energy. load of energy released when lipids are broken down.
  • insoluable in water doesn't effect water potential of the cell causing water to enterthe cells by osmosis(which would make them swell)- they bundle together as insoluable droplets with fatty acids facing inwards since they are hydrophobic shielding them selves with their glycerol heads

  
• properties of a phospholipid


  make up the bilayer of cell membranes(control what enter and leave the cell)

  phospholipid 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. The centre of the bi layer is hydrophobic so water soluable substances can't easily pass through it - the membrane acts as a barrier to those substances

  
• The emulsion test for lipids


  Shake test tube with ethanol for about a minute then pour the solutionn into a test tube with water

  • Any lipid will show up as a milky emulsion

  the more lipids the more noticable the milky colour

  
• Proteins made from


  Monomer-one amino acid

  Dipeptide- two amino acids

  Polypeptide- more than two amino acids

  Protein-one or more polypeptides
• Amino acid structure


  general structure - a carboxyl group(COOH)an amine or anim group(NH2) and an R group(know as the variable side group) attached to a carbon

  • R group generally contains carbon except for glycine it's R group contains one hydrogen group
  • All liviing things share a bank of 20 amino acids te only difference is what makes up their R group

  
• Dipeptide and polypeptide formation


  Amino acids are joned together by condensation reactions to for dipeptides and polypeptides.

  • bond formed between the amino acids are called peptide bond.

  hydrolysis is when a dipepide and polypeptide is broken down

  
• Protein structure


  4 Levels

  • primary structure
  • secondary structure
  • tertiary structure
  • quaternary structure
• Primary structure


  This is the sequence of amino acids in a polypeptide chain

  
• Secondary Structure


  The polypeptide chain doesn't remain straight and flat . It's bonds form between amino acids in the chan. This makes it automatically coil into an alpha helix or fold into a beta pleated sheet

  
• Tertiary Structure (Enzymes)

  Coiled or folded chain of amino acids is often further coiled and folded. More bonds form between different parts of the polypeptide chain including hydrogen bonds and ionic bonds.( attraction of -and+ cahrges on different parts of the molecule.Disulfide bridges form when two molecule of the amino acid cysteine come close the sulfur atoms of each cyteine bond. For proteins made from a single polypeptide cahin the tertiary structure form their final 3D
• Quaternary Structure


  Some proteins are made of several different polypeptide chains held together by hydrogen bonds. The quaternary structure is the way these polypeptides chains are assembled together. For proteins made from more than one polypeptide chain(e.g haemogoblin, insulin ,collegen) the quaternary structure is the proteins final 3D structure.