Biology Induction

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AS Biology

A-Level Biology

AS Practical Work

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Research Based IS Task Due date: 1st lesson back after the summer holidays Compare and contrast the structure and function of prokaryotic and eukaryotic cells. This should be no longer than 750 words Reducing sugars are a type of carbohydrate molecule. Produce an ISA style 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 Amino group (-NH2) Carboxyl group (carboxylic acid group) (-COOH) R group (side chain) (Varies with the amino acid) H H2N-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 More peptides can join to form a polypeptide Proteins are made up of one, 2 or more polypeptides R’ R R R’ Di-peptide

Hydrolysis - Breakdown of Proteins

Hydrolysis – addition of water OH- H+ H2O R’ R This reaction occurs by boiling in dilute HCl or by protease enzymes

Protein Structure Proteins are made up of 4 different structures Primary -1o Secondary -2o Tertiary -3o Quarternary –4o

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 1o structure is an unbranched polypeptide chain 2o structure is very tightly wound 3o structure is a chain twisted into a second helix 4o structure 3 of the 3o 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 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 Blue No proteins or peptides Violet/Lilac Proteins Pink Peptides

Method Add equal volume of Sodium Hydroxide solution to the solution being tested Add a few drops of copper (II) Sulphate solution Sodium Hydroxide solution creates alkaline conditions Evaluate this method! Could you carry out this investigation with the information that you have been supplied with in this method?

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