24 Questions
What is the main protein found in hair, nails, and the outer layer of skin?
α-Keratin
What is the function of vitamin C in collagen synthesis?
Converting proline into hydroxyproline
What is the approximate percentage of collagen that constitutes collagen I?
90%
What is the repeating sequence found in collagen?
–Gly-X-Y-
What is the result of heating collagen with water or dilute HCl?
Collagen is converted into gelatin
What is the main characteristic of scleroproteins?
They are structural proteins
What is the disease caused by a deficiency of vitamin C?
Scurvy
What is the percentage of glycine in the collagen structure?
⅓
What is the main characteristic of fibrous proteins?
They are insoluble in water and highly cross-linked
What is the function of keratins in the human body?
They are structural proteins that make up hair, fur, nails, and skin
What is the term used to describe the assembly of two or more peptide chains held together by non-covalent interactions or covalent cross-linkages?
Quaternary structure
What is the main difference between myoglobin and hemoglobin?
Myoglobin has a higher affinity for oxygen than hemoglobin
What is the name of the globular protein that stores oxygen in muscles?
Myoglobin
What is the characteristic of globular proteins in terms of their secondary structure?
They have a complex mixture of secondary structures
What is the term used to describe a protein that consists of two or more peptide chains?
Oligomer
What is the function of hemoglobin in the human body?
It transports oxygen in the blood
What is the main consequence of a genetic deficiency or mutation in the gene that synthesizes collagen type I?
Abnormal bone formation in babies and frequent bone fracture in children
What is the main role of α1-antitrypsin in the lungs?
To inhibit elastase and prevent destruction of elastin
What is the main characteristic of elastin that allows it to function properly?
It is composed of 4 polypeptide chains (tetramer)
What is the main consequence of elastin deficiency in the lungs?
Loss of elasticity of the lung, leading to emphysema
What is the main function of collagen type I?
To form normal bone formation in babies
What is the main characteristic of collagen that distinguishes it from elastin?
It is rich in hydroxyproline and hydroxylysine
What is the main consequence of a deficiency in collagen synthesis?
Bleeding, loosing of teeth, and swollen gum
What is the main difference between phosphoproteins and lipoproteins?
Phosphoproteins are conjugated with phosphate group, while lipoproteins are conjugated with lipids
Study Notes
Proteins Classification
- Globins: basic proteins rich in histidine amino acid, present combined with heme to form hemoglobin of RBCs
- Histones: basic proteins rich in histidine amino acid, present combined with DNA
- Gliadines: proteins present in cereals
- Scleroproteins: structural proteins, not digested, include keratin, collagen, and elastin
Scleroproteins
- Keratin:
- Protein found in hair, nails, enamel of teeth, and outer layer of skin
- α-helical polypeptide chain, rich in cysteine and hydrophobic (non-polar) amino acids, so it is water insoluble
- Collagen:
- Protein of connective tissues found in bone, teeth, cartilage, tendons, skin, and blood vessels
- Most important protein in mammals, forming about 30% of total body proteins
- 20+ types of collagens, with collagen I being the most common (about 90% of cell collagens)
- Structure: three helical polypeptide chains (trimeric) twisted around each other forming a triplet-helix molecule
- Composition: ⅓ glycine, 10% proline, 10% hydroxyproline, and 1% hydroxylysine
- Insoluble in all solvents and not digested
- Collagen Diseases:
- Scurvy: disease due to deficiency of vitamin C, which is important for conversion of proline into hydroxyproline and lysine into hydroxylysine
- Osteogenesis Imperfecta (OI): inherited disease resulting from genetic deficiency or mutation in collagen type I gene, leading to abnormal bone formation and frequent bone fracture
- Elastin:
- Present in walls of large blood vessels (such as aorta), lungs, elastic ligaments, skin, and cartilage
- Composition: 4 polypeptide chains (tetramer), rich in glycine and proline, but low in hydroxyproline and absence of hydroxylysine
- Elastic fiber that can be stretched to several times its normal length
- Disease: Emphysema, resulting from deficiency of α1-antitrypsin, leading to degradation of lung and destruction of lung elasticity
Fibrous and Globular Proteins
- Fibrous proteins:
- Much of the polypeptide chain is parallel to a single axis
- Often mechanically strong and highly cross-linked
- Usually insoluble
- Examples: keratins
- Globular proteins:
- Compact protein structure
- Soluble in water (or in lipid bilayers)
- Secondary structure is a complex mixture of α-helix, β-sheet, and loop structures
- Quaternary structure is held together by noncovalent forces
- Functions in all aspects of metabolism (enzymes, transport, hormones, etc.)
Quaternary Structure of Protein
- When a protein consists of two or more peptide chains held together by non-covalent interaction or covalent cross-linkage
- The assembly is called an oligomer, with each peptide chain being a monomer or subunit
- Each subunit has its own tertiary structure
Conjugated Proteins
- On hydrolysis, they give a protein part and a non-protein part
- Subclassified into:
- Phosphoproteins: proteins conjugated with phosphate group, attached to OH group of serine or threonine
- Lipoproteins: proteins conjugated with lipids
This quiz covers the basic structure and types of proteins, including globins, histones, gliadines, and scleroproteins.
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