Biomolecule Tests SL9

In a clinical setting, a new urine sample from a patient is tested for glucose using the Benedict's test. The test shows a moderate level of reducing sugars. However, the patient's medical history indicates they are on a new medication known to contain high levels of ascorbic acid (Vitamin C), a reducing agent. What kind of error would the Vitamin C pose to the test result and the effect?

• False positive. The Vit.C will reduce the CuSO4 in the Benedict's reagent, showing a positive result regardless of reducing sugar presence in the sample.

• False positive. The Vit.C will reduce the CuSO4 in the Benedict's reagent, showing a negative result regardless of reducing sugar presence in the sample.

• False negative. The Vit.C will reduce the CuSO4 in the Benedict's reagent, showing a positive result regardless of reducing sugar presence in the sample.

• False negative. The Vit.C will reduce the CuSO4 in the Benedict's reagent, showing a negative result regardless of reducing sugar presence in the sample.

A student is testing a sample to determine the presence of amylase, an enzyme that breaks down starch. They first perform an iodine test on the sample, which results in a blue-black color. They then allow the enzyme to react for 30 minutes and repeat the iodine test. Which result would best indicate that the enzyme was active?

• The blue-black color fades or disappears.

• The blue-black color remains unchanged.

• A purple color appears.

• A cloudy white emulsion forms.

A student performs an ethanol emulsion test on a sample and observes a translucent, cloudy white emulsion. However, the student used a non-standard procedure, mixing the ethanol and water before adding the sample. How would you evaluate the validity of this result, and what specific step in the procedure is most critical to ensure a reliable outcome?

• The result is valid as long as the emulsion is white.

• The result is invalid because the order of mixing does not affect the outcome.

• The result may be invalid because the lipid must first dissolve in ethanol before adding water to create the emulsion; the critical step is dissolving the lipid in ethanol first.

• The result is valid if the sample was shaken vigorously.

A student performs a Biuret test on an unknown sample. The solution turns dark purple. Which of the following conclusions can be best supported by this result?

• The sample definitely contains amino acids but not necessarily proteins.

• The sample contains reducing sugars and proteins.

• The sample definitely contains proteins.

• The sample does not contain starch.

A scientist is testing different plant extracts to identify those with high starch content. They perform the iodine test on four extracts and observe the following colors:

Extract 1: Light brown

Extract 2: Dark blue-black

Extract 3: Yellow-brown

Extract 4: Medium blue-black

Which extract has the highest starch content?

• Extract 1

• Extract 2

• Extract 3

• Extract 4

Which of the following tests is used to detect the presence of peptide bonds in a sample, indicating the presence of proteins?

• Benedict's test

• Iodine test

• Biuret test

• Emulsion test

Which statement best describes the quaternary structure of a protein?

• The arrangement of multiple polypeptide subunits into a functional protein complex.

• The overall three-dimensional shape of a single polypeptide chain, determined by interactions between R-groups.

• The folding patterns (alpha-helices and beta-pleated sheets) formed by hydrogen bonding within the polypeptide chain.

• The sequence of amino acids in the polypeptide chain.

Which statement correctly describes the relationship between enzyme structure and function?

• Enzymes are primarily composed of lipids, which provide a hydrophobic environment for catalysis.

• Enzymes are globular proteins whose specific tertiary structure determines the active site's shape and function.

• Enzymes are carbohydrates that determine the rate of reaction through their specific ring structures.

• Enzymes are nucleic acids that directly participate in bond formation and breakage during a reaction.

According to the induced-fit hypothesis, what happens when a substrate binds to an enzyme?

• The enzyme changes shape slightly to better accommodate the substrate.

• The enzyme denatures, allowing the substrate to enter the active site.

• The active site remains rigid and unchanged.

• The substrate is held in place by covalent bonds.

A student performs a Benedict's test on an unknown solution. The solution turns green after heating. What can the student conclude about the original solution?

• It contains a high concentration of reducing sugars.

• It contains a moderate concentration of reducing sugars.

• It contains a low concentration of reducing sugars.

• It contains no reducing sugars.