Biology Induction

Course Content

AS Biology

A-Level

Biology

AS Practical Work

Career options

Degree options

Research Based IS Task Due date: 1st 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

(-NH2)

2. Carboxyl group (carboxylic

acid group)

(-COOH)

3. 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

R R’

H2O

OH- H+

R R’

This reaction occurs by boiling in dilute HCl or by protease enzymes

Protein Structure

Proteins are made up of 4

different structures

1. Primary -1o

2. Secondary -2o

3. Tertiary -3o

4. 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

1. Add equal volume of Sodium Hydroxide solution to the solution

being tested

2. 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

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http://www.genesisenergy.com/assets/_RefineryServices/

MSDS/MSDS_Caustic_50_TDC_2010.pdf