Question

With which of the following statements concerning the stiffening of aging tissues would the author most likely agree?

• A. It is caused to a large degree by an increased rate of cell multiplication.
• B. It paradoxically both helps and hinders the longevity of proteins in the human body.
• C. It can be counteracted in part by increased ingestion of glucose-free foods.
• D. It is exacerbated by increased enzymatic glycosylation.
• E. It probably involves the nonenzymatic glycosylation of proteins.
  % Correct answer \textbf{Correct Answer:} (E) It probably involves the nonenzymatic glycosylation of proteins.
• A. It takes place more slowly than glycosylation in the human body.
• B. It requires a higher ratio of glucose to protein than glycosylation requires in the human body.
• C. It does not require the aid of enzymes to attach glucose to protein.
• D. It proceeds more quickly when the food proteins have a molecular structure similar to that of crystallin proteins.
• J. Its effectiveness depends heavily on the amount of environmental moisture.
  % Correct answer \textbf{Correct Answer:} (C) It does not require the aid of enzymes to attach glucose to protein.
• A. AGE's are formed after a period of months or years.
• B. Proteins affected by the process are made unstable.
• C. Glucose attachment impairs and stiffens tissues.
• D. Glucose is attached to proteins for specific purposes.
• O. Amino groups combine with aldehyde groups to form Schiff bases.
  % Correct answer \textbf{Correct Answer:} (D) Glucose is attached to proteins for specific purposes.
• A. They are more plentiful in a dehydrated environment.
• B. They are created through enzymatic glycosylation.
• C. They are composed entirely of glucose molecules.
• D. They are derived from Schiff bases.
• T. They are derived from AGE's.
• A. It offers evidence that contradicts the findings described in the first two paragraphs.
• B. It presents a specific example of the process discussed in the first two paragraphs.
• C. It explains a problem that the researchers mentioned in the second paragraph have yet to solve.
• D. It evaluates the research discoveries described in the previous paragraph.
• Y. It begins a detailed description of the process introduced in the previous two paragraphs.
• A. The likelihood that the tissue has been exposed to free glucose
• B. The color and spectrographic properties of structures within the tissue.
• C. The amount of time that the proteins in the tissue have persisted in the body
• D. The number of amino groups within the proteins in the tissue
• ^. The degree of elasticity that the tissue exhibits
• A. have increased elasticity
• B. do not respond to enzymatic glycosylation
• C. are more susceptible to stiffening than are other proteins
• D. are at least several months old
• c. respond more acutely than other proteins to changes in moisture levels

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
This question asks us to identify the main cause of tissue stiffening in aging, according to the author of the passage. We need to find the statement that best reflects the author's explanation.
Step 2: Detailed Explanation:
Let's locate the relevant parts of the passage. The passage introduces nonenzymatic glycosylation as a process that may "contribute to age-related impairment of both cells and tissues" (lines 10-11). It later explains that this process leads to the formation of Advanced Glycosylation End products (AGE's), which can "cross-link adjacent proteins" (line 38). The author then states, "many investigators agree that extensive cross-linking of proteins probably contributes to the stiffening and loss of elasticity characteristic of aging tissues" (lines 41-44). This directly links nonenzymatic glycosylation to the stiffening of tissues.
Now let's evaluate the options:

(A) The passage mentions that cells become "less able to replace damaged components" (lines 1-2), which suggests a decreased, not increased, rate of cell multiplication. This is incorrect.
(B) The passage presents nonenzymatic glycosylation as a purely detrimental process ("impairment," "haphazardly"), not one that helps or hinders. This is incorrect.
(C) The passage mentions that the process involves glucose attaching to proteins. While avoiding glucose might seem logical, the passage doesn't explicitly state that eating glucose-free foods can counteract the stiffening. This is an unsupported inference.
(D) The passage explicitly contrasts the harmful, haphazard nonenzymatic glycosylation with the purposeful, specific enzymatic glycosylation (lines 13-18). It does not suggest that the enzymatic process exacerbates stiffening. This is incorrect.
(E) This statement directly summarizes the main hypothesis presented in the passage. The author builds a case that the stiffening of tissues is a likely result of the cross-linking caused by nonenzymatic glycosylation. The use of "probably" aligns with the passage's cautious tone ("may also contribute," "probably contributes"). This is the correct answer.
Step 3: Final Answer:
The passage strongly suggests that the stiffening of aging tissues is a result of protein cross-linking caused by nonenzymatic glycosylation.

Answer 2

Step 1: Understanding the Concept:
This is a detail-oriented question. We need to find a specific fact in the passage about the process of nonenzymatic glycosylation, which is identified as the process that "discolors and toughens foods."
Step 2: Detailed Explanation:
The passage first mentions the process in lines 8-11, stating that "a process long known to discolor and toughen foods may also contribute to age-related impairment." The next sentence defines this process: "That process is nonenzymatic glycosylation, whereby glucose becomes attached to proteins without the aid of enzymes" (lines 11-13). This provides a direct answer to the question.
Let's check the other options to be sure:

(A) The passage states that food chemists have known about this process for decades, but only recently have biologists recognized it can happen in the body (lines 19-22). It doesn't compare the speed of the process in food versus the body. This is not mentioned.
(B) The passage does not compare the ratio of glucose to protein required. This is not mentioned.
(C) This statement is a direct paraphrase of the definition given in lines 11-13: "without the aid of enzymes." This is true according to the passage.
(D) The passage mentions crystallin protein in the context of an experiment on cataracts (lines 48-49), not in relation to the speed of the process in food. This is not mentioned.
(E) The passage mentions that Amadori products "slowly dehydrate" (line 31) in the body, but it doesn't say that the process's effectiveness in food depends on environmental moisture. This is not mentioned.
Step 3: Final Answer:
The passage explicitly defines the process that discolors and toughens food as nonenzymatic glycosylation, which occurs "without the aid of enzymes."

Answer 3

Step 1: Understanding the Concept:
This question asks us to identify a characteristic of \textit{enzymatic} glycosylation, as described in the passage. The passage primarily discusses the nonenzymatic process, but it draws a contrast with the enzymatic one, so we must focus on that specific comparison.
Step 2: Detailed Explanation:
The passage makes a direct comparison between enzymatic and nonenzymatic glycosylation in lines 13-18. Let's examine that section closely: "When enzymes attach glucose to proteins (enzymatic glycosylation), they do so at a specific site on a specific protein molecule for a specific purpose. In contrast, the nonenzymatic process adds glucose haphazardly..." This sentence gives us a clear characteristic of the enzymatic process.
Now let's evaluate the options based on the passage:

(A) The formation of AGE's is described as a result of the \textit{nonenzymatic} process when proteins persist for months or years (lines 30-35).
(B) The Schiff base, part of the \textit{nonenzymatic} process, is described as unstable (line 27). The passage doesn't say this about the enzymatic process.
(C) The stiffening of tissues is linked to the cross-linking caused by AGE's, which result from the \textit{nonenzymatic} process (lines 41-44).
(D) This statement is a direct paraphrase of the description in lines 15-16: "at a specific site on a specific protein molecule for a specific purpose." This is the correct answer.
(E) The combination of amino and aldehyde groups to form Schiff bases is described as the beginning of the \textit{nonenzymatic} glycosylation process (lines 22-26).
Step 3: Final Answer:
The passage explicitly states that in enzymatic glycosylation, glucose is attached to proteins for a "specific purpose."

Answer 4

Step 1: Understanding the Concept:
This is a reading comprehension question that asks for a specific detail about "Amadori products." We need to locate the part of the passage that describes these products and identify a true statement about their origin or properties.
Step 2: Detailed Explanation:
Let's find the term "Amadori product" in the passage. It appears in the third paragraph. Lines 25-29 state: "The molecules combine, forming what is called a Schiff base within the protein. This combination is unstable and quickly rearranges itself into a stabler, but still reversible, substance known as an Amadori product." This sentence explicitly says that the Amadori product is formed from the rearrangement of a Schiff base. Now let's evaluate the options based on this information:

(A) The passage says Amadori products "slowly dehydrate" to become AGE's (line 31), not that they are more plentiful in a dehydrated environment.
(B) Amadori products are part of the \textit{nonenzymatic} glycosylation process, not the enzymatic one.
(C) They are formed from the combination of a glucose molecule and a protein molecule, so they are not composed "entirely of glucose."
(D) The passage directly states that the unstable Schiff base "rearranges itself into... an Amadori product." Therefore, they are derived from Schiff bases. This is correct.
(E) The passage states that Amadori products can rearrange to form AGE's (lines 30-35), not the other way around. AGE's are derived from Amadori products.
Step 3: Final Answer:
The passage clearly describes the formation of an Amadori product from the rearrangement of a Schiff base.

Answer 5

Step 1: Understanding the Concept:
This question asks about the function of a specific paragraph in the context of the entire passage. We need to understand how the third paragraph relates to the paragraphs that come before it.
Step 2: Detailed Explanation:
Let's summarize the paragraphs: - Paragraph 1 (and start of 2): Introduces the problem of aging tissues and proposes that nonenzymatic glycosylation might be a contributing cause. - Paragraph 2 (lines 11-18): Defines nonenzymatic glycosylation and contrasts it with the enzymatic process. - Paragraph 3 (lines 19-29): Starts with "This nonenzymatic glycosylation of certain proteins has been understood by food chemists..." and goes on to describe the initial chemical steps: "...begins when an aldehyde group (CHO) of glucose and an amino group (NH) of a protein are attracted... forming what is called a Schiff base... rearranges itself into... an Amadori product." The first two paragraphs introduce the concept of nonenzymatic glycosylation. The third paragraph starts to explain the chemical mechanism of this process in detail. Now let's evaluate the options:

(A) The third paragraph doesn't contradict anything; it explains the process in more detail.
(B) It's not a specific example, but rather a general description of the chemical steps.
(C) It doesn't explain an unsolved problem; it explains the known initial steps of the process.
(D) It doesn't evaluate the discoveries; it describes them.
(E) This is the most accurate description. The first two paragraphs introduce the process, and the third paragraph begins the "detailed description" of how it works chemically, starting with the formation of the Schiff base and the Amadori product.
Step 3: Final Answer:
The third paragraph serves to start a detailed, step-by-step chemical description of the nonenzymatic glycosylation process that was introduced more generally in the preceding paragraphs.

Answer 6

Step 1: Understanding the Concept:
This is an inference question. We need to identify which factor is the least important indicator of nonenzymatic glycosylation based on the information provided in the passage. This means we should first identify the factors that the passage tells us \textit{are} important. The one not mentioned or implied to be a secondary effect would be the least important determinant.
Step 2: Detailed Explanation:
Let's review the passage for factors related to nonenzymatic glycosylation:

Glucose exposure (A): The process is the attachment of glucose to proteins. Without glucose, it cannot happen. So, glucose exposure is essential.
Time (C): Lines 30-35 state that if a protein persists for "months or years," the process advances to form irreversible AGE's. So, the age of the proteins is very important.
Amino groups (D): Lines 22-25 state that the process begins when a glucose group and an "amino group (NH) of a protein" are attracted. The availability of amino groups is therefore a necessary prerequisite for the reaction to start.
Elasticity (E): Lines 41-44 link the cross-linking from this process to the "loss of elasticity characteristic of aging tissues." Therefore, a loss of elasticity is a strong sign that the process has occurred.
Color and spectrographic properties (B): Lines 35-37 mention that "Most AGE's are yellowish brown and fluorescent and have specific spectrographic properties." These properties are described as characteristics \textit{of} AGE's, which are the final products of the process. While they are an indicator that the process has reached its final stage, they are a result or a symptom, rather than a determinant of whether the process is \textit{likely to have taken place}. The other factors (A, C, D) are all prerequisites or contributing factors for the process to occur in the first place, and (E) is a primary physical consequence. The color is a secondary property of the end products. Therefore, it is arguably the least important factor in determining the likelihood of the process's occurrence compared to the essential ingredients (glucose, amino groups) and conditions (time).
Step 3: Final Answer:
The presence of glucose, amino groups, and long-lived proteins are all crucial factors for the process to occur. The loss of elasticity is a direct result. The color and spectrographic properties are secondary characteristics of the final end products, making them less fundamental in determining the likelihood of the process itself compared to the causal factors.

Answer 7

Step 1: Understanding the Concept:
This is an inference question based on a specific hypothesis mentioned in the passage. We need to combine the hypothesis with other information in the text to draw a logical conclusion.
Step 2: Detailed Explanation:
The hypothesis in lines 56-58 is that "nonenzymatic glycosylation of lens crystallins may contribute to cataract formation." This means that the process of nonenzymatic glycosylation is happening to the crystallin proteins in the eye's lens.
Now, let's look at what the passage says about the conditions required for the advanced stages of this process. Lines 30-35 state: "If a given protein persists in the body for months or years, some of its Amadori products slowly dehydrate and rearrange themselves... into... advanced glycosylation end products (AGE's)." The experiment on cataracts found that the cross-links had the color and fluorescence "characteristic of AGE's" (lines 55-56). Therefore, if the hypothesis is true, it means that AGE's have formed on the crystallin proteins. For AGE's to form, the proteins they are on must have persisted in the body for at least "months or years." Let's evaluate the options:

(A) The process causes a \textit{loss} of elasticity, not an increase.
(B) The passage doesn't provide information to compare the enzymatic response of crystallin proteins to others.
(C) The passage doesn't compare the susceptibility of crystallin to stiffening with that of other proteins.
(D) Since the crystallin proteins show evidence of AGE's, and AGE's only form on proteins that persist for "months or years," it can be inferred that these proteins are at least several months old. This is a sound logical deduction.
(E) The passage mentions dehydration as part of the process, but doesn't provide information to compare the moisture response of crystallin with other proteins.
Step 3: Final Answer:
If cataracts are caused by nonenzymatic glycosylation, it means AGEs have formed on crystallin proteins. According to the passage, AGE formation requires proteins to be in the body for months or years. Therefore, the crystallin proteins must be at least several months old.