Proteins: Structure and Types

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the main protein found in hair, nails, and the outer layer of skin?

Elastin

Gliadine

Collagen

α-Keratin (correct)

What is the function of vitamin C in collagen synthesis?

Converting keratin into collagen

Converting proline into hydroxyproline (correct)

Breaking down collagen into gelatin

Converting glycine into proline

What is the approximate percentage of collagen that constitutes collagen I?

95%

60%

90% (correct)

50%

What is the repeating sequence found in collagen?

–Gly-X-Y- Signup and view all the answers

What is the result of heating collagen with water or dilute HCl?

Collagen is converted into gelatin Signup and view all the answers

What is the main characteristic of scleroproteins?

They are structural proteins Signup and view all the answers

What is the disease caused by a deficiency of vitamin C?

Scurvy Signup and view all the answers

What is the percentage of glycine in the collagen structure?

⅓ Signup and view all the answers

What is the main characteristic of fibrous proteins?

They are insoluble in water and highly cross-linked Signup and view all the answers

What is the function of keratins in the human body?

They are structural proteins that make up hair, fur, nails, and skin Signup and view all the answers

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 Signup and view all the answers

What is the main difference between myoglobin and hemoglobin?

Myoglobin has a higher affinity for oxygen than hemoglobin Signup and view all the answers

What is the name of the globular protein that stores oxygen in muscles?

Myoglobin Signup and view all the answers

What is the characteristic of globular proteins in terms of their secondary structure?

They have a complex mixture of secondary structures Signup and view all the answers

What is the term used to describe a protein that consists of two or more peptide chains?

Oligomer Signup and view all the answers

What is the function of hemoglobin in the human body?

It transports oxygen in the blood Signup and view all the answers

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 Signup and view all the answers

What is the main role of α1-antitrypsin in the lungs?

To inhibit elastase and prevent destruction of elastin Signup and view all the answers

What is the main characteristic of elastin that allows it to function properly?

It is composed of 4 polypeptide chains (tetramer) Signup and view all the answers

What is the main consequence of elastin deficiency in the lungs?

Loss of elasticity of the lung, leading to emphysema Signup and view all the answers

What is the main function of collagen type I?

To form normal bone formation in babies Signup and view all the answers

What is the main characteristic of collagen that distinguishes it from elastin?

It is rich in hydroxyproline and hydroxylysine Signup and view all the answers

What is the main consequence of a deficiency in collagen synthesis?

Bleeding, loosing of teeth, and swollen gum Signup and view all the answers

What is the main difference between phosphoproteins and lipoproteins?

Phosphoproteins are conjugated with phosphate group, while lipoproteins are conjugated with lipids Signup and view all the answers

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