Fibrous and Globular Proteins

Biological Molecules

Fibrous proteins

- Structural sheets or strands (e.g. collagen, keratin)
- Organized into polypeptide chains of long fibers/ sheets due to lots of amino acids with hydrophobic R groups (simple primary structure)
- Rope like structure
- Insoluble in water
- Very tough physically, may be stretchy

Globular proteins

- Metabolic roles in the body (e.g. enzymes, antibodies)
- Complex tertiary structure maintained by bonding
- Chains folded in compact, ball shape, formed when the hydrophobic R groups in tertiary group fold away from water
- Water soluble
- Essential for regulating many processes

Globular proteins vs Fibrous proteins

Insulin

- Globular protein hormone
- Involved in the regulation of blood glucose concentration
- Hormones transported in the blood \= soluble
- Fit specific receptor on cell surface membrane \= specific shape

Haemoglobin

- Quaternary globular protein
- 4 polypeptide chains and 2 alpha and 2 beta subunits
- subunits have iron-containing prosthetic heam group which binds reversible to oxygen (how it transports oxygen)
- soluble

Catalase

- Enzyme that increases reaction rate
- Iron react with hydrogen peroxide to seed up breakdowns
- Stops hydrogen peroxide ( damaging bioproduct of metabolism if allowed to accumulate)
-Quaternary protein with 4 haem prosthetic groups

Keratin

- A group of fibrous proteins in skin, hair and nails
- Larger proportion if sulfur containing amino acids \= strong disulfide bonds
- The amount of disulfide bonds determines flexibility

Elastin

- Fibrous protein in elastic fibers
- In walls of blood vessels and alveoli
- Quaternary protein made of many insoluble linked tropoelastins
\= large, insoluble and stable cross link structure
- Tropoelastins contain alternating hydrophobic and lysin rich areas \= can stretch and recoil
- Formed when multiple tropoelastins aggregate via interaction between hydrophobic areas
- Gives strength and elasticity to skin, tissues and organs

Collagen

- Fibrous protein that gives the skin form and strength
- Made up of 3 polypeptides wound in a long, strong rope like structure
- Every 3rd amino acid is a glycine, the small size allows 3 protein molecules to form closely packed triple helix
- Many hydrogen bonds form between chains \= long quaternary proteins with staggered ends , allows proteins to join end and form tropocollagen crosslink (strong)
- Proline and hydroxyl proline R groups repel each other \= stability
- In ligaments and tendons \= fibers aggregate onto larger bundles
- In skin \= fibers form a mesh resistant from tearing

Protein misfolding

- When proteins misfold \= cause disease
- If mutation happens alternative amino acid could be inserted into chains or cut chain short (effects how protein folds and might not function properly)

Protein modelling software

- Used to examine the folding of protein
- See how they work and how they can be changed to aid us
- Huge amount of info can be processed and seen quickly
- Can predict changes in viruses to produce vaccines and medicines
- However, is no proof that the model is accurate