Compare globular and fibrous proteins
Globular proteins are generally soluble and physiological; fibrous proteins are generally insoluble and structural.
AS Level · Cambridge International Biology 9700, 2028–2030. These lessons explain syllabus concepts; self-checked practice does not measure practical competence or qualify as teacher-reviewed assessment.
Before you begin
- Recognise that biological molecules have structures that relate to their roles in cells and organisms.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which protein is a typical fibrous structural protein?
What you will learn
- State general solubility and role patterns for globular and fibrous proteins
- Use haemoglobin and collagen as contrasting examples
Compact globular proteins often act in physiology
Globular proteins fold into compact shapes and are generally soluble in water. Many have physiological roles such as transport, catalysis or immune function. Solubility allows many globular proteins to function in aqueous body fluids or cell contents.
Haemoglobin is a globular protein that transports oxygen. Enzymes and antibodies are other examples of physiological proteins, though their detailed structures are covered elsewhere.
Fibrous proteins provide structural support
Fibrous proteins have long, extended structures and are generally insoluble. Many provide mechanical support, strength or tensile resistance in tissues. Collagen is an example of a fibrous protein.
These are general patterns, not definitions without exceptions. Compare typical structure, solubility and role, and use a named example to support the distinction.
Pause and explain
Which description best matches a globular protein?
Worked example
A protein is long, insoluble and provides tensile strength in connective tissue. Classify it and compare with haemoglobin.
Show the worked solution
- Long and structural suggests fibrous.
- Haemoglobin is a soluble globular transport protein.
Answer The protein is consistent with collagen, a fibrous protein that is generally insoluble and has a structural role. Haemoglobin is globular, generally soluble and has a physiological transport role.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Compare globular and fibrous proteins by solubility and typical role.
Give me a hint
Give both patterns, not only examples.
Compare my reasoning
- Globular proteins are generally soluble and physiological.
- Fibrous proteins are generally insoluble and structural.
Globular proteins are generally soluble and have physiological roles. Fibrous proteins are generally insoluble and have structural roles. These are general patterns rather than absolute rules.
Look for these in your work
- Solubility patterns
- Role patterns
Classify haemoglobin and collagen and state one role for each.
Give me a hint
Use the typical examples.
Compare my reasoning
- Haemoglobin is globular and transports oxygen.
- Collagen is fibrous and provides structural support.
Haemoglobin is a globular protein with an oxygen-transport role. Collagen is a fibrous protein with a structural role, including providing tensile strength in connective tissues.
Look for these in your work
- Both classifications
- Roles stated
A student claims a fibrous protein dissolves easily because all proteins are soluble. Correct the statement.
Give me a hint
Contrast the general patterns.
Compare my reasoning
- Fibrous proteins are generally insoluble.
- Solubility patterns differ from globular proteins.
The general pattern is that fibrous proteins are generally insoluble and structural, whereas globular proteins are generally soluble and physiological. Individual conditions still matter.
Look for these in your work
- Generalisation corrected
- Contrast stated
Common mistakes
- Calling all globular proteins enzymes
- Saying every fibrous protein is completely insoluble in all conditions
- Swapping haemoglobin and collagen examples
What can you explain now?
Which protein is a typical fibrous structural protein?
Compare with the explanation
Collagen
Collagen is fibrous and structural.
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Make it stick
How do typical globular and fibrous proteins differ, and which examples illustrate each?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.