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Biomolecules Lab: Testing for Carbohydrates, Lipids, and Proteins

This lab focuses on testing for the presence of biomolecules such as carbohydrates, lipids, and proteins in various food samples. It includes procedures for conducting tests using reagents, observing color changes, and recording results. Safety precautions and clean-up instructions are also provided.

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Biomolecules Lab: Testing for Carbohydrates, Lipids, and Proteins

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  1. Agenda • Turn in Pre-lab #4: biomolecules • Lab Quiz #3 (pH) • 2nd two Microworlds due at the end of the lab today. • Samples for Microwords today include thin & squished slices of banana and potato (peanut does not work as it is baked).

  2. Microworlds • Each Microword is worth 5 pts totaling 60 points. • Turn in the graded and ungraded Microworlds totaling 12 at the end of the term, due date is the last lab. • Field Sizes • 40X = 5mm • 100X = 2mm • 400x = 0.5mm = 500μm • 1000x = 0.2mm = 200μm • State/label what you’re estimating the size of • Label at least 2 structures • More than 2 gives you a safety cushion • Animal cells don’t have a cell wall! • Bacteria don’t have a nucleus! • You normally can’t see the cell membrane of a plant cell.

  3. Lab 3: Testing for biomolecules • Testing for the presence of • Carbohydrates • Lipids • Proteins • Or all the biological molecules except for nucleic acids

  4. Testing for Carbohydrates • Monomers = monosaccharides • Glucose • Fructose • Disaccharides • Sucrose = glucose + fructose • Polysaccharides • Starch (plants) • Glycogen (animals)

  5. Testing for Reducing Sugars • BENEDICT’S REAGENT • Tests for the presence of any monosaccharide & some disaccharides • Positive results are: a change from clear blue to a cloudy or opaque green, yellow, orange or red.

  6. BENEDICT’S REAGENT • Tests for all monosaccharides but only some disaccharides • Does not detect sucrose • Tube 1 = Glucose (is a positive control) • What could be our negative control (a tube that will not react)?

  7. Testing for Carbohydrates • Add 2 mls of your stock solution to 2 mls of Benedicts reagent. • Benedicts Test uses a boiling water bath, Heat tubes for 5 minutes and observe. • Must wear goggles f/ this test! (Boiling Benedicts is an eye hazard!) • Dispose of Benedict’s waste in appropriate container (heavy metals harm the environment).

  8. Testing for Carbohydrates • IODINE REAGENT tests for the presence of starch (what do we know about starch?

  9. Testing for Carbohydrates • TUBE 1 = Starch (from potato) as a positive control • What can we use as a negative control? • In Ex4. change from adding 5 drops to 3 drops of iodine and observe immediately. (5 drops is rather dark even in water.) • NOTE: Iodine stains badly

  10. Testing for Lipids • PAPER TEST – paper will look translucent and greasy in the presence of lipids (KFC napkins) • Do early if you want it to dry (takes ~15 min) • You can usually tell immediately just by holding it up to the light

  11. Testing for Proteins • BIURET REAGENT reacts with proteins to give a purple or pinkish color • Longer polypeptides give a darker purple, shorter are pinker

  12. Testing for Proteins • TUBE 1 = Egg Albumen (positive control) • TUBE 2 = negative control (?) • Other tubes from your stock solutions • Add 1mL (about two droppers FULL) of Biuret to the tube. Let stand for ~ 2 min and then record your results. • Dispose of Biuret’s waste in appropriate container (contains the heavy metal Cu).

  13. Testing for biomolecules in food • This lab was re-written and is not very clear. • In Ex. 1 you set up your stock cultures of food. • If the food is a liquid, just add the proper amount (about 6 ml) to each tube. • If the food is a solid, mince 1-2 cm3 very finely, add it to a tube & mix with ~9 mL distilled water. • Use these stock cultures to set up Ex. 2, 4-5. Note, for the lipid test, Ex. 3, crush solid food & add undiluted liquid foods directly to the paper.

  14. Testing for biomolecules in food For Ex. 2,& 5, add 2 ml of your stock solutions to the tubes for that Exercise. For Ex. 4, use 1 ml of your stock solutions. (For example, if you want to test banana for the presence of reducing sugars in Ex. 2, add 2 mls of your stock solution to the banana tube of Ex. 2.) You can greatly speed up this lab by dividing and conquering! When you are waiting for a test, start setting up for the next test or start cleaning.

  15. Debriefing: • This lab has a debriefing study guide. • After completing the lab, check it out to see how well you understood the lab! Safety: Wear GOGGLES at all times when people are working with hazardous chemicals (Benedict’s Solutions)

  16. CLEAN UP REALLY WELL • Wash your test tubes BEFORE you start – this lab gets cross-contaminated OFTEN • Wash out all test tubes using test tube brush when you’re done, get the goo out! Put tubes away upside-down in drawer to drain • Make sure your tray is returned to its original position & looks neat and clean up the food table! No food scraps lying around. • Attendance points today, but a penalty if you leave a mess!

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