Biochemistry-Connective Tissue Disorders Flashcards
What are the two major components of the extra-cellular matrix?
Collagen and proteoglycans
What special cells would you expect to find in extra cellular skin tissue? Bone?
Fibroblasts and Macrophages. Osteocytes/osteoclasts/osteoblasts are found in bone.
What connective tissues are used in the body to give tissue strength?
Elastin (gives elasticity due to hydrophobic region), collagen (hard strength) and laminin (adhesion molecule).
What clinical signs will you observe in someone who is deficient in laminin?
Blistering. Laminin is responsible for anchoring of epithelial cells to the extra-cellular matrix.
What gives cartilage its strength and elasticity, respectively?
Strength = collagen Elasticity = elastin
What protein classification does collagen fall into?
Fibrous glycoproteins. It is made of 3 polypeptide chains wound together to form a triple-helix with varying amounts of carbohydrate.
How would you use proper nomenclature to describe a three-chain a2b structure made up of type I collagen? How do the other collagen types differ from type I?
The other collagen types are homotrimers
What type of collagen makes up 90% of our body’s collagen? Where is it found?
Type I. It is found in skin, bone, tendons, cornea, soft tissue and scars. It also has the least amount of carbohydrate.
What is the main type of collagen made by chondrocytes in cartilage?
Type II. It has about 10% carbohydrate
What type of collagen is very important in hollow organs and blood vessels? Where is it not found?
Type III. It is not found in bone or tendons unless there is scarring.
What type of collagen is not fiber-forming, forms a mesh and is responsible for adhesion in basement membranes?
Type IV. Has the highest carbohydrate content and utilizes disulfide bonds.
How are fibrillar collagens genetically similar?
They all contain 42 exons with varying intron length. They all have a central encoding region that generates a 1014 AA stretch with repeating [Gly-X-Y] units
What are the primary amino acids found in fibrillar collagen? How is this beneficial to collagen strength and stability?
Glycine, Proline and Hydroxyproline. Glycine is found in the middle of the helix because it is small. Glycines and prolines hydrogen bond for increased strength.
Which way do the helices go in collagen? How is this beneficial to collagen strength and stability?
Left-handed helical strands coiled in a right-handed super-helix. If you try to pull the helix out, the left-handed helices will counteract the right-handed super helix
In a study of someone’s tissue who has a collagen disorder, it is found that their collagen is only stable at a temperature below 27* C. What could be different about their collagen?
They may be missing hydroxyproline. The hydroxyl group on the outer surface of collagen is what allows for stability at higher temperatures.
How is collagen formed from preprocollagen?
Procollagen is formed after signal peptides are removed in the ER. Procollagen wraps up to form three domains: globular N & C domains at the ends, a triple helical domain and a non-triple helical domain. Proline and lysine are hydroxylated. Procollagen is secreted. Extracellularly, amino and carboxyl-procollagen peptidases cleave the globular ends to form tropocollagen. Tropocollagen then assembles into fibrils and the lysyl oxidase stabilizes the fibrils via lysine residue cross-linkages.
What condition is a consequence of a loss of collagen strength due to defective amino-procollagen peptidases?
Ehlers-Danlos type VII
What enzyme deficiency can cause a type of Ehlers-Danlos due to instability of intermolecular cross-linking in collagen fibrils?
Lysyl oxidase
What is needed for preservation of prolyl/lysyl hydroxylase?
Ascorbic acid. Every once in a while prolyl/lysyl hydroxylase will oxidize alpha-ketoglutarate instead of proline/lysine which causes Fe2+ to become Fe3+. Ascorbic acid reduces the Fe3+ and protects the enzyme from destruction and it can continue hydroxylating proline/lysine residues.
A patient comes to your clinic complaining of poor wound healing after a simple appendectomy. Physical exam shows easily bruised skin, hyperextensible skin and joint hypermobility. What is your diagnosis?
The patient has Ehlers-Danlos type I connective tissue disorder
A patient comes to visit you complaining of hearing loss. While taking this patient’s history, you find that he had lots of bone fractures as a child. You also note bluish sclera in your physical exam. His mother has a similar condition. What is connective tissue is mutated in this patient?
This is a mild case of autosomal dominant type I osteogenesis imperfecta. This results from a decrease in the amount of type I collagen.
What is the biochemical mechanism responsible for the lethal type II form of osteogenesis imperfecta?
Glycine substitutions in the collagen helix that destabilizes the collagen.
Development of what specific enzyme makes malignant melanoma a highly metastatic cancer?
Type IV collagenases eat through basal lamina and allow for tumor spread
What inorganic ion plays a role in defense against newly developed tumor cells?
Zn2+. Matrix metalloproteases (collagenases) release endostatin when they degrade collagen. Endostatin plays a role in the prevention of angiogenesis and thus prevents blood supply to tumors.
What were proteoglycans formerly known as?
Mucopolysaccharides
Why are most structural polysaccharides linked via beta linkages?
It creates a tighter linkage so digestive enzymes can’t chop it up.
What makes up the proteoglycans in higher mammals?
Uronic acid + “osamine” with beta 1,3 and beta 1,4 linkages
How do engineer mimic the structure of our extracellular ground substance when building bridges?
They use steel (collagen) for tensile strength and concrete (proteoglycans) for resilience.
What are the different glycosaminoglycans?
Why do glycosaminoglycans make great molecules for smooth articulation of joint surfaces?
They have a high negative charge that makes them highly hydrated and great for lubrication.
How is hyaluronic acid different from the other glycosaminoglycans?
It does not have sulfer and does not covalently bond with molecules in the ECM
What is the difference between heparan sulfate and heparin?
Heparin has much more iduronic acid, sulfates and has a lower molecular weight. It is an anticoagulant where heparan sulfate is a glycosaminoglycan found in many connective tissues.
A 7 year old child sustains a tear to his cartilage during a soccer game. What proteoglycan will be laid down first in healing? What will be laid down thereafter?
Hyaluronic acid is usually laid down first, but does not covalently bind to anything. Chondroiton is the main proteoglycan of cartilage and has a core protein covalently bound to repeating disaccharides.
What transferases “leap frog” over eachother once the initial carbohydrates have been added to a serine/threonine in the protein in proteoglycan synthesis?
Transferases that add Glucuronic acid to N-acetylglucosamine and transferases that add N-acetylglucosamine to glucuronic acid.
How are sulfates transfered onto the polymer during proteoglycan synthesis?
PAPS
How does iduronic acid get into proteoglycan chains during synthesis?
Epimerases convert glucuronic acid to iduronic acid after glucuronic acid has already been incorporated into the chain.
How do chondrocytes recycle material for proteoglycan synthesis?
Every 100 days or so the proteoglycans are taken up by the chondrocytes and degraded by the lysosomes.
What is the biochemical basis of the different mucopolysaccharidoses?
Defect in degradation of proteoglycans. Degradation must go stepwise otherwise these osmotically active polymers aggregate in the lysosomes and cause cell death.
A concerned mother brings her 6 month old baby in to see you with a concern of mental retardation. You note coarse facial features, skeletal abnormalities, corneal clouding and organomegaly. What proteoglycans are possibly accumulating in this child?
Dermatan and heparan sulfate due to alpha-L-iduronidase deficiency causing Hurler’s syndrome (MPS I)
Why do patients with Hurler’s syndrome typically have smaller stature? How can you confirm diagnosis of Hurler’s syndrome?
Premature closure of the growth plate due to early death of chondrocytes. In order to diagnose it you need to add alpha-L-iduronidase to a tissue sample and see if it fixes the chondrocytes.
