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2.3.62 · Biological Molecules

Collagen — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions

5 min read 8 parts Lesson 21 of 25 1 quiz

📚 Cambridge AS & A Level Biology 9700 Hub / Topical Revision
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Lesson summary

2.3.6 Collagen — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Describe the structure of collagen and explain how it suits its structural role.Common protein — the most abundant structural protein in vertebrates.Tissues — tendons, cartilage, ligaments, bones, teeth,…

  • Triple helix
  • Each chain
  • Proline and hydroxyproline
  • Cross-links
  • Tensile strength
  • Flexibility

Section 1 of 8Where collagen is found

Where collagen is found
Common protein
  • Common protein the most abundant structural protein in vertebrates.
Tissues
  • Tissues tendons, cartilage, ligaments, bones, teeth, skin, blood vessel walls and the cornea.
Type
  • Type an insoluble fibrous protein.

Section 2 of 8Structure of a collagen molecule

Structure of a collagen molecule
Triple helix
  • Triple helix three polypeptide chains held together by hydrogen bonds (tropocollagen).
Each chain
  • Each chain about 1000 amino acids in a helix that is less tightly wound than an alpha-helix.
Glycine
  • Glycine almost every third amino acid is glycine, the smallest amino acid, which sits inside and lets the chains pack tightly.
Proline and hydroxyproline
  • Proline and hydroxyproline common amino acids whose R groups repel each other, adding stability.

Section 3 of 8From molecules to fibres

Cross-links
  • Cross-links covalent bonds link R groups of neighbouring triple helices.
Fibrils
  • Fibrils cross-linked molecules form fibrils with staggered ends.
  • The staggered ends give strength and the striated look in electron micrographs.
Fibres
  • Fibres many fibrils form collagen fibres, which line up with the forces they resist.

Section 4 of 8Function

Function
Tensile strength
  • Tensile strength many hydrogen bonds give great strength, so collagen withstands pulling forces without stretching or breaking.
Flexibility
  • Flexibility it is a flexible structural protein.
Insolubility
  • Insolubility the long molecules take too long to dissolve, so collagen is insoluble.

Section 5 of 8Collagen compared with haemoglobin

FeatureCollagenHaemoglobin
Polypeptide chains3 (triple helix)4
ShapeLong, thinSpherical
TypeFibrousGlobular
FunctionStructuralOxygen transport
Amino acid sequenceRepetitiveVariable
Prosthetic groupNoYes (haem)
SolubilityInsolubleSoluble

Section 6 of 8More from the specification

More from the specification
Primary and Secondary Protein Structures
  • The primary structure of a protein is the unique sequence of amino acids linked by covalent peptide bonds;
    • folding into secondary α-helices and β-pleated sheets is stabilized by hydrogen bonds.
Tertiary Structure Stabilizing Bonds
  • The three-dimensional tertiary structure of globular proteins is stabilized by four types of R-group interactions: hydrogen bonds, ionic bonds, hydrophobic interactions,
  • and covalent disulfide bridges.
Quaternary Structure and Fibrous Collagen
  • Collagen is a fibrous structural protein composed of three polypeptide chains wound into a tight triple helix, cross-linked by covalent bonds to provide immense tensile strength in tendons and skin.
Solubility and Hydrophobic Interactions
  • Globular proteins fold with hydrophobic non-polar R-groups buried in the interior and hydrophilic polar groups exposed to surrounding water, ensuring water solubility.
Secondary structure
  • Α-helix and β-pleated sheet held by backbone hydrogen bonds.
Quaternary structure
  • Arrangement of multiple polypeptide subunits.
Amine group
  • The –NH2 functional group.
Hydrophobic
  • Water-hating; non-polar and unable to dissolve in water.
Specific
  • Able to act on only one type of substrate.
Tertiary structure
  • 3D folding of a polypeptide held by R group interactions.
Primary structure
  • The sequence of amino acids in a polypeptide.
Hydrophobic interaction
  • A weak attraction between non-polar R groups.

Section 7 of 8Key terms

TermMeaning
CollagenAn insoluble fibrous protein forming connective tissue.
TropocollagenA collagen molecule made of a triple helix.
FibrilA bundle of cross-linked collagen molecules.
GlycineThe smallest amino acid, found at every third position in collagen.
Tensile strengthResistance to being pulled apart.
Connective tissueTissue such as tendon, cartilage and skin that supports the body.

Section 8 of 8Exam technique

1
Saying collagen is globular — it is fibrous and insoluble.
2
Saying collagen has an alpha-helix — its helices are less tightly wound.
3
Forgetting the cross-links and staggered ends — they give fibril strength.
4
Saying collagen has a prosthetic group — it does not.

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