Structural proteins Flashcards
Three distinct groups of fibrous proteins
Coiled coil alpha helices- keratin and myosin
triple helix collagen
beta sheets in amyloid fibers and silks
what is Gly-X-Y?
The three amino acids that form the repeating amino acid sequence that form collagen. Glycine, X is usually proline and Y is usually hydroxyproline
Collagen quaternary structure
three, right handed alpha helical polypeptide chains wrapped around each other to aggregate into one with a left hand turn
Why is glycine always present?
Small enough R group to fit in the centre of the triple helix
Formation of collagen stages
- Synthesised as pro-collagen by the fibroblasts with few extra amino acids at the terminals
- Extra amino acids formed of few glycines, so no helical structure and high cysteine- high disulfide bridges forming globular ends- align the chains
- Procollagen enzymes cleave extra amino acids, forming tropocollagen
Collagen adaptations
Ends of parallel molecules are staggered to prevent a weak spot forming.
Crosslinks between adjacent chains- hydrogen bonding via hydroxyproline and NH/CO of glycine residues.
Why is hydroxyproline so important?
Can form extra hydrogen bonds providing more stability,
Where is collagen found?
Tendons and ligaments
What is a histone?
Globular protein containing chromatin
Histone structure
October of two of each: H2A, H2B, H3 and H4 that has DNA wound round it, forming a nucleosome
Cationic surface purpose
Neutralises DNA phosphates
a disease that affects collagen
Ehlers-Danlos Syndrome
explain Ehlers-Danlos syndrome
defect in collagen which leads to very elastic skin, hyper mobility, heart problems, leaky valves
proline function in triple helix
produces a kink, facilitating the alpha helix shape
