Lab 5 - it may help for biology 4a or human physiology PDF

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An Huynh Bio 4A Fall 2020 9/23/20 Lab 5

Practice Summary Review of All Test Results. 1. Which type of molecule is detected if you observe a positive result for: 1. Benedict’s test: sugar molecule. 2. Biuret test: Protein molecules. 3. Lugol’s Test: it is also Iodine. It is test for the present of starch( carbohydrate) 4. Ninhydrin Test (Purple): this test is for present of protein. The high level of protein is present in dark purple color. 5. Ninhydrin Test (Yellow): no protein present in the test sample. 6. Sudan IV Test: it is a reagent. It is test for present of lipid. If the lipid present, the yellow color will show on the sample test. 2. Using your results from the Labster exercise, indicate if simple sugars, polysaccharides, proteins, and lipids are found in the following food (You may enter your data as a table if you wish): Baked potato, milk, glucose, apple, water, egg, bread, vegetable oil, Alice’s salad.

Baked potato milk glucose apple water egg bread vegetable oil Alice’s salad

simple sugars yes yes yes yes no no yes no yes

polysaccharide s yes no no no no no yes no yes

proteins

lipids

yes yes no no no yes yes no no

no yes no no no yes no yes no

3. Can the Benedict’s test be used to detect all simple sugars (monosaccharides, disaccharides, and polysaccharides)? Explain.  No, because they cannot detect all sugar. With the monosaccharides, they all have either a ketone or aldehyde group that is free. They can easily open up to their noncyclic forms and react with benedict reagent to give the test positive result because their ability to react with the cation Cu2+ in Benedict’s reagent. However, in disaccharides the power to reduce Cu2+ varies depending upon the position of the reactive aldehyde or ketone groups. 4. In this lab, you used a Biuret reagent to determine the presence of albumin (egg white) in solution. Why didn’t you use Ninhydrin as the colorimetric reagent to detect albumin?

An Huynh Bio 4A Fall 2020 9/23/20 Lab 5

We are not using Ninhydrin as the colorimetric reagent to detect albumin because There is no -NH2 group to detect in albumin structure. Biuret Test The Biuret Test is a general test for proteins. When a protein reacts with copper(II) sulfate (blue), the positive test is the formation of a violet colored complex

Ninhydrin Test The Ninhydrin Test is a test for amino acids and proteins with a free -NH2 group to detect test

5. Using your Biuret set-up, can you identify/explain what is meant by a negative and a positive control? The positive control for the Biuret experiment is an egg. Egg have are high in protein content, therefore they will exhibit a purple color after this biochemistry test. Water, on the other hand, the negative control, will exhibit a blue color. 6. Does the Biuret test identify peptide bonds in starch or glucose molecules?  No, the Biuret test identify peptide bonds which is present in present in protein. 7. Which solutions reacted with the Biuret reagent? Why?  The chemical bonds that hold amino acids together. Because the protein is present of a long chain amino acid that link together by peptide bonds. 8. The leaves of many plants are coated with a waxy covering. If you subjected that substance to all the tests you used in this lab, which test(s) would be positive? Why?  We would use Sudan IV test in this lab to test for the present of the lipid. If the tests is positive, it will present 2 layers of fat and orange color. Because lipid is a non-polar molecule substance and it won’t mix with the water which is polar molecule solution 9. After testing seven unknown solutions you obtain the following results: Which molecules are in each solution?

Table 1: Results of Biochemical Tests Results

Benedict’s Lugol’s Test Test Solution (Starch) (sugar)

Ninhydrin Test

Biuret Test

Sudan IV Test

(protein, (protein) (lipid) amino acid)

Which molecules are in t solution?

An Huynh Bio 4A Fall 2020 9/23/20 Lab 5

Yellow

Blue

Yellow

Violet

Pink

no

no

no

no

no

Yellow

Blue

Violet

Blue

Pink

no

no

yes

no

no

Yellow

Blue

Clear

Blue

Pink

no

no

no

no

no

blue/black

Clear

Clear

Blue

Pink

yes

no

no

no

no

Brown

Orange

Violet

Violet

Red

no

yes

yes

yes

no

1

Water molecules

2

3

Protein molecules

Water molecules

Starch (carbohydrate)

4

Simple sugar Protein

5

Amino acid Starch 6

blue/black

Red

Violet

Violet

Pink

yes

yes

yes

yes

no

Simple sugar Protein ( amino acid)

Yellow

Blue

Clear

Blue

Red

no

no

no

no

no

Water molecules

7...