Question

refer to the table below. three different proteins were isolated from the same bacterial cells and their biological activity measured. each protein was then subjected to 10 - minute periods of increasing temperature, followed by measurement of biological activity. the results are shown in the table. based on these data, which statement is correct?

temperature	protein a activity	protein b activity	protein c activity
45°c	100%	95%	100%
50°c	100%	80%	100%
55°c	97%	10%	95%
60°c	90%	0%	78%
65°c	75%	0%	4%
70°c	2%	0%	0%

options:

1. protein b contains no disulfide bonds, whereas proteins a and c likely contain disulfide bonds
2. interactions between r groups in protein a add up to greater stabilization of tertiary structure than interactions between r groups in protein b or protein c
3. secondary structure in protein b is weaker than secondary structure in protein a or protein c
4. protein b is smaller than proteins a or c, giving it fewer amino acid r groups that can interact to stabilize its tertiary structure

Explanation:

To determine the correct statement, we analyze the data on protein activity at different temperatures:

1. Analyze Protein B's stability: Protein B loses all activity at 60°C (0% activity), while Protein A still has 90% at 60°C and Protein C has 78% at 60°C. This suggests Protein B is less stable. Disulfide bonds (covalent bonds) increase protein stability. If Protein B has no disulfide bonds (unlike A and C, which likely have them), it would be less stable, matching its earlier loss of activity.

1. Evaluate other options:

• The "secondary structure" option: The data reflects tertiary structure stability (overall protein folding, affected by disulfide bonds, R - group interactions), not secondary structure (alpha - helices, beta - sheets) directly.
• The "R - group interactions sum" option: There's no data to support R - group interactions in A being greater than in B/C.
• The "Protein B size" option: The data doesn't relate to protein size or number of R - groups for stabilization.

So the statement "Protein B contains no disulfide bonds, whereas Proteins A and C likely contain disulfide bonds" is correct.

Answer:

Protein B contains no disulfide bonds, whereas Proteins A and C likely contain disulfide bonds