Biology Induction
Course Content
AS Biology
A-Level Biology
AS Practical Work
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Research Based IS Task Due date: 1 st lesson back after the summer holidays 1. Compare and contrast the structure and function of prokaryotic and eukaryotic cells. This should be no longer than 750 words 2. Reducing sugars are a type of carbohydrate molecule. Produce a detailed apparatus list, method and risk assessment to describe how you would safely test for the presence of reducing sugars in an unknown solution Solution A Both tasks require you to carry out independent research and your sources of information must be listed at the end of each task.
Lesson Objectives Know the biochemical structure of protein molecules Work independently to carry out Biuret tests to investigate if foods contain protein Be confident at safely carrying out investigations in the science laboratory in preparation for the Unit 3 ISA/PSA skills tests
Biological Molecules - Proteins Biological molecules are made up of subunits called MONOMERS Monomers join together in chains to form POLYMERS
Proteins Made up of: CHONS Carbon Hydrogen Oxygen Nitrogen Sulphur (sometimes) The monomers in proteins are called AMINO ACIDS There are 20 different commonly occurring amino acids
Proteins - Amino Acids Amino acids are made up of 3 groups 1. Amino group (-NH 2 ) 2. Carboxyl group (carboxylic acid group) (-COOH) 3. R group (side chain) (Varies with the amino acid) H H 2 N-C-COOH R
There are 20 different amino acids and so there are 20 different R groups
Condensation reactions Condensation reactions create peptide bonds which hold the individual amino acid monomers together This creates a peptide Water Amino acid monomer R Amino acid monomer R
Condensation reaction creating a peptide R R R R Di-peptide More peptides can join to form a polypeptide Proteins are made up of one, 2 or more polypeptides
Hydrolysis - Breakdown of Proteins
Hydrolysis addition of water R R OH - H + H 2 O This reaction occurs by boiling in dilute HCl or by protease enzymes R R
Protein Structure Proteins are made up of 4 different structures 1. Primary -1 o 2. Secondary -2 o 3. Tertiary -3 o 4. Quarternary 4 o
YouTube - Protein Structure
Primary structure Order of amino acid monomers in the peptide chain The sequence of amino acids determines the 3-D shape A simple protein may be made up of one polypeptide chain
Secondary Structure When the amino acids join together as a peptide they form shapes or patterns Weak Hydrogen bonds form between polar molecules Peptide bonds contain polar H atoms and Polar O atoms Polar H atoms on the amino group have a small +ve charge Polar O atoms of the carboxyl group have a small -ve charge
Secondary Structure The charges allow H bonds to form between peptide bonds in different parts of the chain
Secondary Structure 2 shapes formed Alpha helix Beta-pleated sheet The secondary shape depends on the primary structure, i.e. the order of the amino acids
Tertiary Structure 3-D shape Determines the function of the protein Very important in creating the active site in enzymes Shape is held together by Hydrogen bonds numerous but easily broken Ionic Bonds formed by any carboxyl and amino group not involved in forming peptide bonds Easily broken by ph changes Disulphide bonds fairly strong
Hydrogen bonds are weak and easily disrupted Ionic bonds formed between carboxyl group and amino group NOT peptide formation Easily broken with ph changes Disulphide bonds are covalent bonds between sulphur atoms in R groups Fairly stong, not easily broken
Tertiary Structure 3 types of bonds lead to 2 main kinds of protein Fibrous Globular
Globular Proteins Approximately spherical in shape Usually water soluble Tend to have a biochemical function rather than structural E.g. Enzymes or haemoglobin
Fibrous Proteins Polypeptides join together to form long fibres or sheets Very strong Insoluble in water Tend to have structural functions E.g. fingernails and hair Keratin E.g. Skin, Bone, Blood vessels and teeth - collagen
Fibrous Proteins 1 o structure is an unbranched polypeptide chain 2 o structure is very tightly wound 3 o structure is a chain twisted into a second helix 4 o structure 3 of the 3 o structure chains wound together like fibres in a rope
Quarternary Structure A number of polypeptide chains Associated non-protein components called prosthetic groups Together producing the quarternary structure
Testing for protein molecules in unknown solutions You will be investigating 5 unknown solutions and carrying out a simple practical investigation to determine whether they contain protein, dipeptides or none
Testing for Protein Molecules Biuret test Biuret 1 = Sodium Hydroxide solution Biuret 2 = Copper (II) Sulphate solution Blue No proteins or peptides Violet/Lilac Proteins Pink Peptides Copper atoms in the copper (II) sulphate solution form a complex with the N atoms in the amino group of the peptide bond this causes a colour change
Method 1. Add equal volume of Sodium Hydroxide solution to the solution being tested 2. Add a few drops of copper (II) Sulphate solution Evaluate this method! Could you carry out this investigation with the information that you have been supplied with in this method? Sodium Hydroxide solution creates alkaline conditions
Testing for protein molecules in unknown solutions Health and Safety http://www.sciencelab.com/msds.php?msdsid=9925783 http://www.genesisenergy.com/assets/_refineryservices/ MSDS/MSDS_Caustic_50_TDC_2010.pdf