Collagen, Keratin, Elastin Flashcards
What are the four levels in the hierarchical structure of collagen?
Alpha chains made of amino acids (L=1 nm) -> tropocollagen (L=300 nm, D=1.5 nm) -> fibrils (L = 1 micron, D = 50-200 nm), fibers (L=10 micron, D=1 micron)
How many amino acids are used in collagen?
20 different ones
How many types of collagen are there? What are the most common ones and where are they found?
20 types of collagen
Type 1 - Most human tissues
Type 2 - cartilage
Type 3 - Blood vessel and repair sites
How prevalent is glycine in collagen? What role does it fulfil?
1 out of every 3-4 amino acids is glycine
It’s on the inside of the tropocollagen coil and it forms hydrogen bonds which stabilize tropocollagen (individual hydrogen bonds are weak but glycine allows for the formation of a lot of then and the arrangement allows for close packing)
What techniques are used to image collagen?
Optical microscopy
Confocal microscopy
Scanning electron microscopy (SEM)
Transmission electron microscopy (TEM)
X-ray diffraction
Atomic force microscopy (AFM)
What is tropocollagen?
Three left-handed alpha chains twisted in a right hand triple helix (“twisted rope structure”)
The helix is stabilized by hydrogen bonds and some covalent bonds
How does crystallinity change between vs within collagen fibrils?
Within the tropocollagen, it’s a crystal, between tropocollagen it’s amorphous
What mechanisms explain the mechanical response of tropocollagen?
Tropocollagen is rate-dependent
Energy dissipation occurs through (molecular rotation, H-bond rupture, and backbone stretching)
What is the structure of collagen fibrils?
The tropocollagen has a head and a tail region. The molecules assemble such that the head bonds with the tail which leaves a gap of 67 nm. The structure of the fibrils is periodic and displays the characteristic “D-period” of collagen
Why does collagen demonstrate a toe region during mechanical testing?
The toe region occurs due to straightening of the nanocrimps under load.
What were the results of a mechanical properties study done on a single collagen fibril using a MEMS loading stage and an optical microscope?
Stress-strain curve shows two stages with different stiffness
Device was not strong enough to break the fiber
Cyclic tests demonstrated damage accumulation
What did AFM testing of a single collagen fibril reveal?
Small viscoelastic effect but overall elastic
What animals produce keratin? What cells produce keratin in humans?
Most vertebrates have keratin; in humans, it’s produced by the epithelial cells on the outer skin
What are the two type of keratin? What are some examples of where they’re found?
Alpha keratin (aka mammalian keratin) - found in skin, hoof, whale baleen
Beta keratin (aka avian keratin) - claws, scales, feathers, beaks
What is the structure of keratin in skin?
Diffuse structure
The alpha keratin filaments are often curved and they’re cross-linked with a sulphur rich matrix
