Lab 3 background

For this lab, I highly recommend that you look at the lab review page.

The pictures there demonstrate types of questions that you may see on the lab practical
 

4 classes of basic macromolecules

Polymers                            Monomers/subunits

Proteins                                Amino acids

Lipids                                   Fats and oils

Carbohydrates                       Sugars

Nucleic acids                        Nucleotides

Different tests

1. Reducing sugars
    monosaccharides and some dissacharides

              glucose - monosaccharide

              lactose  -  dissacharide

              sucrose - dissacharide

    react when heated with a copper containing compound = Benedict's reagent

    Benedict's reagent changes from blue to green to yellow to orange to red
    The color change depends on how much sugar is present

You should go to the lab review page to see protocols and pictures of what a positive reaction looks like

2. Starch - polysaccharide

Use Lugol's Iodine test

add Potassium Iodide (KI₂)

changes from yellow to blue or black when starch is present

You should go to the lab review page to see protocols and pictures of what a positive reaction looks like

3. Lipid

are insoluble in water

lipids do not dry like water

place a sample on brown paper and it will leave a wet spot

dry with a heat lamp

if lipid is present, it will leave a wet spot (dark brown)

You should go to the lab review page to see protocols and pictures of what a positive reaction looks like

4.  Proteins

use Biuret Reagent = NaOH + CuSO₄ (sodium hydroxide + copper sulfate)

Biuret reagent reacts with peptide bonds

It changes from blue to dark blue or violet

The more peptide bonds, the more amino acids, and the more intense the color change

You should go to the lab review page to see protocols and pictures of what a positive reaction looks like

Things to do:

Exercise 3.1 A: reducing sugar

Number test tubes 1 -5

Add 5 ml of Benedicts reagent to each tube.

Add 2 ml of the solution to be tested to each tube. Use a clean pipet each time.

    Tube 1 - water

    Tube 2 - glucose

    Tube 3 - lactose

    Tube 4 - sucrose

    Tube 5 - starch

Record initial color on your report sheet

Heat for 3 minutes - place samples in the water bath
       You can place your entire rack in the water bath or find space in the racks already there

Record the color after heating on your report sheet

Interpretation:  + if it contains reducing sugar, - if it does not contain reducing sugar

Exercise 3.1 B: starch

Number test tubes 1 -5

Add 1 drop of Lugol's Iodine reagent to each tube.

 Use a clean pipet each time.

    Tube 1 - water

    Tube 2 - glucose

    Tube 3 - lactose

    Tube 4 - sucrose

    Tube 5 - starch

Record initial color on your report sheet

Do NOT heat these samples

Record the final color on your report sheet

Interpretation:  + if it contains starch, - if it does not contain starch

Exercise 3.2: protein

Label 3 tubes

Add 3 drops of NaOH and 3-5 drops of CuSO₄ (Biuret reagent)

Record initial color

Pipet 1 ml of each the following solutions:

    Tube 1 - water

    Tube 2 - albumin

    Tube 3 - starch

Record color after adding solutions

Interpretation:  + if it contains protein, - if it does not contain protein

Exercise 3.3: lipid

Get a piece of brown paper and divide it into squares.

DO NOT use one piece of piece for each sample

Dip a swap in distilled water and rub it on one square

Dip a swap in oil  and rub it on another square

Put your swabbed piece of brown paper under a light bulb for 5-10 minutes until the water dries

Interpretation:  + if it contains lipid, - if it does not contain lipid

Exercise 3.4:  Food

Select 4 different food items.

Do the 4 different tests on these items

    lipid

    reducing sugars

    starch

    protein

Interpretation:  record if it is + or - for each substance