Biological Molecules (2c)

Unit 2, Structure & Functions in Living Organisms: Part 1, c

Types of Biological Molecules

Categories:

• Carbohydrates

• Proteins

• Lipids (fats and oils)

All contain carbon, so are called organic molecules

Molecules and Chemical Elements

• Carbohydrates: Carbon, Hydrogen, Oxygen

• Proteins: Carbon, Hydrogen, Nitrogen, Oxygen, additional elements including Sulfur

• Lipids: Carbon, Hydrogen, Oxygen

Structure of Carbohydrates

• Contain C, H, O

• made of starch and glycogen

• can be small, simple sugars or larger, more complex molecules

• monosaccharide: simple sugar, eg, glucose (C₆H₁₂O₆)

• disaccharide: two monosaccharides joined together, eg, maltose = 2 glucose joined together

• large polysaccharides: many monosaccharides joined together, eg, starch, glycogen or cellulose = many simple glucose molecules joined together

• polysaccharides: insoluble = storage molecules

Structure of Lipids

• large molecules made of smaller basic units like glycerol and 3 fatty acids

• solid at room temperature (fats) or liquid at room temperature (oils)

Storage of Glucose: Plants vs Animals

plants: starch

animals: glycogen

Structure of Proteins

• made of smaller molecules called amino acids

• when these are joined, proteins are formed

• can be arranged in any order

• specific amino acid gives protein its shape

• shape determines function

• ex: keratin, haemoglobin

Molecule vs Monomer

• Carbohydrate : glucose

• Lipids: glycerol and fatty acids

• Protein: amino acids

Food Samples can be investigated for:

• glucose

• starch

• fat

• protein

Preparing a Sample

• break up food with a mortar and pestle

• dilute with distilled water

• stir with a glass rod to mix

• filter through filter paper and collect solution

• proceed with food tests

OR

use powdered food

Preparing a Sample: Precautions

• eye protection

• wash splashes quickly

• don’t taste food substances

• avoid spilling hot water

Test for Glucose

Benedict’s Test

• add a few drops of bright blue reagent to the sample

• heat in very hot water for 5 mins

• observe if there’s a colour change

• positive result: blue → green → yellow → orange → brick red (depending on conc.)

Benedict’s Solution: Safety Precautions

• wear safety goggles

• switch off bunsen burner after water is almost boiling / use water bath

Test for Starch

Iodine Test

• Iodine solution is yellow-brown

• add several drops to the sample

• positive result: yellow-brown → blue-black

Protein Test

Biuret Test

• Biuret solution is blue

• positive test: blue → lilac

Lipids (Fats) Test

Ethanol Emulsion Test

• mix food sample with 4cm³ of ethanol

• ethanol is a clear and colourless liquid

• place the bung firmly and shake vigorously

• allow the sample time to settle

• strain the solution into another test tube

• add the ethanol solution to an equal volume of cold distilled water (4cm³)

• positive result: cloudy emulsion

Food Tests Hazards

• Biuret solution contains copper (II) sulfate, which is dangerous if it gets into eyes → always wear goggles

• Iodine solution irritates eyes

• NaOH in Biuret solution is corrosive → wash hands immediately if any chemicals get onto skin

• Ethanol is highly flammable → keep away from Bunsen burner

• Bunsen burner is an open flame → keep off when not in use

Enzymes as Biological Catalysts

• enzymes are proteins that speed up the rate of reaction without being used up in it

• called biological because made in living cells

• necessary because they maintain reaction speeds of all metabolic reactions at a rate that can sustain life

• if we didn’t produce enzymes, digestion would take 2-3 weeks, with enzymes it takes 4 hours

• often the products of one reaction are the reactants of another and so on

Enzyme Action Mechanism

• an enzyme’s active site is a complementary shape to the substrate, so enzymes are specific to one particular substrate

• when the substrate moves into the active site, they become known as an enzyme-substrate complex

• after reaction, products leave the active site as they no longer fit it

• the enzyme takes up another substrate

Enzyme Process

• enzymes and substrates move randomly in solution

• when an enzyme and complementary substrate collide, an enzyme-substrate complex forms and a reaction occurs

• products are formed and released from the active site. enzyme is unchanged and can catalyse further reactions

Amylase digests __________ into _________

starch, maltose

Starch

large biological molecule formed from many glucose molecules joined together

Maltose

molecule formed from two glucose molecules joined together

Enzymes and Temperature Practical: Safety

• Iodine and Amylase can irritate eyes → wear safety goggles

• Amylase irritates skin → wear gloves

• Avoid burns from very hot water → handle equipment with tongs

Enzymes and Temperature Practical: Method

• add 5cm³ of starch solution to test tube and heat in a 20^oC water bath

• add a drop of Iodine solution to each well of the spotting tile

• use a syringe to transfer 2cm³ amylase to starch solution and mix.

• start timer

• after one minute, transfer one drop of solution to the spotting tile’s first well

• repeat every minute until iodine stops changing colour → amylase has broken down all the starch by now

• record time taken by counting to the first well where there is no colour change in Iodine

• repeat at same temperature at least twice

• repeat for a range of temperatures (eg. 30-60^oC)

Enzymes and Temperature Practical: Limitations

• temperature may not be constant/stable/precise since Bunsen burner is used → store starch and amylase solutions in a water bath for about 10 mins before being mixed

• determining when starch has been digested relies on visual observation, which is subjective → use colorimeter (measures intensity of colour by shining light through it and measuring how much light passe through)

Enzymes and Temperature Practical: CORMMS

• C: changing the temperature

• O: irrelevant

• R: repeat several times for each temperature to increase reliability

• M1: measure the time taken for iodine to stop turning blue-black

• M2: by counting the number of spotting tiles

• S: control the concentration and volume of starch solution, iodine, and amylase used

Enzymes and Temperature Practical: Optimum Temperature

• iodine stops turning blue-black the fastest

• enzyme is working at its fastest rate and has digested all the starch in the solution

Enzymes and Temperature Practical: Colder Temperature

• iodine takes longer time to stop turning blue-black

• Amylase is working slowly due to low kinetic energy and fewer collisions between Amylase and starch

Enzymes and Temperature Practical: Hotter Temperatures

• iodine turned blue-black throughout investigation

• Amylase denatures and can no longer bind with starch or break it down

Optimum pH for most enzymes is _____________

7

ph for enzymes in acidic conditions like stomach

low, pH 2

pH for enzymes in alkaline conditions like duodenum

high, pH 9

Effect of pH being too high/too low

• bonds holding amino acid chain together to make up protein will be destroyed

• active site shape will change, substrate will no longer fit

• moving too far from optimum pH → enzyme denatures, activity stops

Effect of pH on Enzymes Practical: Apparatus

• Spotting tile

• Measuring cylinder

• Test Tube

• Syringe

• Pipette

• Stopwatch

• Buffer solutions at different pH levels

• Iodine

• Starch solution

• Amylase solution

Effect of pH on Enzymes Practical: Safety

• both Iodine and Amylase cause irritation- wear goggles

• Amylase causes irritation- wear gloves

Effect of pH on Enzymes Practical: Method

• add drops of I to each well of the spotting tile

• use syringe to place 2cc of amylase into test tube

• add 1cc of buffer (pH 3) to test tube with syringe

• use another test tube to add 2cc of starch solution to amylase and buffer solution, start stopwatch while mixing with a pipette

• every 10s, transfer a drop to a well of I solution (should turn blue-black)

• repeat until I solution stops turning blue-black (amylase has broken down all the starch)

• record time taken by counting wells until the solution stopped changing colour

• repeat at different pH values

Effect of pH on Enzymes Practical: Results and Analysis

• Amylase is an enzyme that breaks down starch

• when I solution remains orange-brown, all the starch has been digested

• at optimum pH, colour stopped changing in the shortest time

• because enzyme is working at its fastest rate and has digested all the starch

• at higher or lower pH’s (above/below the optimum): I took longer to stop changing colour or continued to change colour throughout

• because on either side of the optimum pH, enzymes are denaturing and are unable to bind with the starch or break it down

Effect of pH on Enzymes Practical: CORMMS

• C - change the pH of the environment

• O - same concentration of enzyme

• R - repeat the investigation several times to ensure reliability

• M1 - measure the time taken by counting the number of wells for

• M2 - the iodine to stop turning blue-black (1 well = 10 seconds)

• S -control the temperature and volume of the amylase, iodine and starch solution used in the investigation