Fibrous Protein Flashcards
Which amino acid is called secondary amino acid, why?
Proline because it forms a cyclic ring
Why do fibrous proteins have low solubility in water
Because they play a structural integrity role in tissue/create barriers
3 most common fibrous proteins
Collagen, elastin and keratin
Which is the most abundant protein in the body
Collagen (present in all tissues and organs)
Function of collagen
Provides framework that gives the tissue their form and structural strength
Collagen characteristics of following organ/tissue
- Tendons
- Bone
- Skin
- Cornea
~these are all what type of collagen
- Bundled in tight parallel fibers that provide great strength
- Fibers arranged at angle to each other to resist mechanical shear (meshwork)
- Loosely woven, flexible fibers
- Nearly crystalline; transparent
~Type I collagen meaning they form fibrils (in tissues that run long distances)
Collagen that forms sheets would be
Network forming (forms mesh to work as a barrier)
Function of fibril-associated collagen (FACTs)
Attach two different collagen fibers
Structure of collagen
What keeps it tight
Triple helix (braided)
Hydrogen bond which is added by hydroxylation, without this it would become loose (like a braid without a hair tie)
Amino acid sequence of collagen
Gly-X-Y
X= usually proline
Y= often hydroxyproline or hydroxylysine
~needs glycine because it is the smallest AA
- Hydroxyproline involved in
2. Hydroxylysine is site of
- Hydrogen bond formation to stabilize the triple helix
2. Site of attachment of carbohydrate moieties (usually glucose and galactose)
Synthesis of collagen:
What is necessary to start synthesis of a pro-alpha-chain
Signal sequence (acts as GPS) - directs growing polypeptide chain into cisternae of rER ~signal sequence is cleaved in ER to yield pro-alpha-chain
Synthesis of collagen:
Without signal sequence what would happen
Protein will be translated but will be present outside of the lumen (needs to be inside to continue process)
Synthesis of collagen:
What happens in the rER
This process requires what 3 things
What two enzymes catalyze this reaction
Post-translational hydroxylation of proline and lysine
Molecular oxygen, vitamin C (ascorbic acid), and ferrous iron
Prolyl and lysyl hydroxylase
What has to happen in order for collagen to form triple helix
Collagen has to be hydroxylated
Vitamin C deficiency leads to?
Symptoms
Scurvy (bleeding gums and bleeding joints)
~need vitamin c for prolyl and lysyl hydroxylase
Synthesis of collagen:
What happens to hydroxylysine residues?
They need to be modified by glycosylation with glucose or galactose
Synthesis of collagen
For pro alpha chains to form procollagen what needs to happen
How does the winding of triple helix happen (what direction)
Carboxy terminal end folds and forms disulfide bonds
From carboxyl to amino terminus
Synthesis of collagen
The completed triple helix goes to where
Golgi apparatus to be secreted out of cell via secretory vesicles
Synthesis of collagen
What happens when the triple helix leaves the cell
What happens if this does not happen
~this step happens where in the cell
N and C procollagen peptidases remove the terminal propeptides to release the triple helix tropocollagen molecule
Collagen will be soluble in water
~ECM (not within the cell)
Synthesis of collagen
How are the collagen fibrils formed
Individual tropocollagen molecules associate together
Synthesis of collagen
What enzyme matures the collagen fibers
What does it do
Lysyl oxidase
Forms cross links (makes it stronger)
~this also happens outside of cell
Function of collagenase
Cleave intact collagen fibers into smaller fragments for degradation in lysosome so that old collagen can be replaced by new collagen
Ehlers Danlos Syndrome
- Symptoms
- Deficient in?
- What else can lead to this syndrome?
- Stretchy skin and hyper-extendible joints (contortionists)
- Lysylhydroxylase, procollagen peptidases (collagen processing enzymes)(cannot form cross links)
- Replacement of glycine with another amino acids (rare)
Osteogenesis imperfecta
- AKA
- Caused by
- Other symptoms
- Brittle bone syndrome
- Glycine replaced
- Retarded wound healing, humpback spine, blue scleras, bones break easily
Main difference between collagen and elastin
Their function; synthesis is similar
Function of elastin
Where is elastin found in the body
Gives tissues and organs ability to stretch without tearing
Lungs, walls of large blood vessels, elastic ligaments, and skin
- Elastin forms desmosine which results in
- Formed from ?
- What enzyme is required for this process
- Extensively interconnected, rubbery network (gives elastin its elastic properties)
- Formed from 3 allysines and 1 lysine
- Lysyloxidase
Elastin is degraded by?
Where is this enzyme mostly found
Function
Elastase
WBCs (specifically neutrophils)
Main function is neutrophils will release elastase to degrade debris in lung tissue
Alpha 1-antitrypsin
- What does it inhibit
- Deficiency in this will lead to
- What is required to bind this to target proteases?
- Main function
- Proteolytic enzymes that hydrolyze and destroy proteins
- Emphysema
- Alpha 1-AT methionine
- Protects lung alveoli from damage from elastase
Lysyloxidase is __ containing
Copper
A 30 year old woman presents with progressive dyspnea. She denies smoking, her fmhx reveals that her sister has similar problems. Which etiology explains the patients symptoms?
Defect in alpha 1 antitrypsin
