AQA · A-Level · Biology
Course version: 7402 · Version from Sept 2016
The importance of maintaining a stable core temperature and stable blood…
Full specification wording
Principles of homeostasis and negative feedback (A-level only): The importance of maintaining a stable core temperature and stable blood pH in relation to enzyme activity.
Enzymes are globular proteins whose tertiary structure creates a complementary active site.
Checked against the AQA 7402 specification (opens in a new tab) on .
- Point 2 of 6
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Enzymes are globular proteins whose tertiary structure creates a complementary active site. Raising temperature increases the kinetic energy of enzyme and substrate molecules, so more successful collisions form enzyme-substrate complexes and the rate rises. Above the optimum, increased vibration breaks hydrogen and ionic bonds in the tertiary structure; the active site changes shape, substrate is no longer complementary and the enzyme is denatured. This denaturation is usually irreversible. Blood pH is maintained near 7.4 because a change in hydrogen ion concentration alters the ionic and hydrogen bonding that holds the tertiary structure, again altering active site shape. Outside the narrow pH range, metabolic reactions slow or stop. Core temperature and blood pH are therefore homeostatic variables kept within narrow limits by negative feedback.
What earns the marks
- Enzymes are globular proteins; the tertiary structure forms an active site complementary to a specific substrate.
- Raising temperature increases kinetic energy, so more enzyme-substrate complexes form and the rate of reaction rises.
- Above the optimum temperature, hydrogen and ionic bonds break, the tertiary structure and active site change shape, and the enzyme is denatured; this is usually irreversible.
- A change in blood pH alters hydrogen ion concentration, disrupting ionic and hydrogen bonds in the tertiary structure and altering the active site.
- Normal blood pH is approximately 7.4; deviation slows or stops metabolic reactions because fewer enzyme-substrate complexes form.
- Core temperature and blood pH are homeostatic variables maintained within narrow limits by negative feedback.
Common mistakes and how to put them right
Writing that the active site is on the substrate.
Put it right: The active site is a region of the enzyme formed by its tertiary structure.
Claiming denaturation breaks peptide bonds.
Put it right: Denaturation disrupts hydrogen and ionic bonds that maintain tertiary structure; peptide bonds in the primary structure remain intact.
Explaining pH effects without linking them to bond disruption.
Put it right: State that pH changes alter ionic and hydrogen bonding, changing tertiary structure and active site shape.
Describing denaturation as reversible.
Put it right: Denaturation of an enzyme is usually irreversible because the tertiary structure cannot reform.
Exam tips
- Use the three-step chain: bonds break, tertiary structure changes, active site no longer complementary to the substrate.
- When discussing human metabolism, state that normal blood pH is approximately 7.4 and explain that deviation alters enzyme active sites.
- Link temperature and pH answers to the same underlying mechanism: disruption of bonds maintaining tertiary structure.
Try the lesson
The start of the Principles of homeostasis and negative feedback (A-level only): The importance of maintaining a stable core temperature and stable blood pH in relation to enzyme activity. lesson, made from checked teaching notes for this specification point.
Have a go first
A mammal maintains a stable core temperature of approximately 37 °C. Which statement best explains why this stability is important for enzyme-controlled reactions?
Listen
Enzymes are globular proteins whose tertiary structure creates a complementary active site. Raising temperature increases the kinetic energy of enzyme and substrate molecules, so more successful collisions form enzyme-substrate complexes and the rate rises. Above the optimum, increased vibration breaks hydrogen and ionic bonds in the tertiary structure; the active site changes shape, substrate is no longer complementary and the enzyme is denatured. This denaturation is usually irreversible. Blood pH is maintained near 7.4 because a change in hydrogen ion concentration alters the ionic and hydrogen bonding that holds the tertiary structure, again altering active site shape. Outside the narrow pH range, metabolic reactions slow or stop. Core temperature and blood pH are therefore homeostatic variables kept within narrow limits by negative feedback. A strong answer earns marks for these points. Enzymes are globular proteins; the tertiary structure forms an active site complementary to a specific substrate. Raising temperature increases kinetic energy, so more enzyme-substrate complexes form and the rate of reaction rises. Above the optimum temperature, hydrogen and ionic bonds break, the tertiary structure and active site change shape, and the enzyme is denatured; this is usually irreversible. A change in blood pH alters hydrogen ion concentration, disrupting ionic and hydrogen bonds in the tertiary structure and altering the active site. A common slip: Writing that the active site is on the substrate. Instead, the active site is a region of the enzyme formed by its tertiary structure. Exam tip: Use the three-step chain: bonds break, tertiary structure changes, active site no longer complementary to the substrate.
Key words
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Tertiary structure and active site complementarity
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Kinetic energy and collision frequency
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Denaturation by temperature and pH change
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Homeostatic control of core temperature and blood pH
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See every definition
- Tertiary structure and active site complementarity
- Enzymes are globular proteins whose tertiary structure creates an active site complementary to a specific substrate.
- Kinetic energy and collision frequency
- Raising temperature increases the kinetic energy of enzyme and substrate molecules, so more successful collisions form enzyme-substrate complexes and the rate rises.
- Denaturation by temperature and pH change
- Increased vibration or altered hydrogen ion concentration breaks hydrogen and ionic bonds in the tertiary structure, the active site changes shape, substrate is no longer complementary and the enzyme is denatured.
- Homeostatic control of core temperature and blood pH
- Core temperature and blood pH are homeostatic variables kept within narrow limits by negative feedback.
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