Q-1. Which of the following is/are extracellular matrix protein?
a) Collagen
b) Laminin
c) Fibronectin
d) Integrin
e) Elastin
Answer: a, b, c and e
Explanation:
Extracellular matrix protein:
Structural proteins: Collagen, elastin and fibrillin
Specialized proteins: Fibronectin and laminin
Ptroteo-glycans
Important point:
Integrins are the part of the cell membrane that mediates cellular attachment to extracellular matrix.
Q-2. All of the following are extracellular proteins except (AIIMS MAY 2002)
a) Laminin
b) Integrin
c) Collagen
d) Fibronectin
Answer: Integrin
Explanation:
See above explanation.
Q-3. The structural proteins are involved in maintaining the shape of a cell of in the formation of matrices in the body. The shape of these proteins is
a) Globular
b) Fibrous
c) Stretch of beads
d) Planar
Answer: Fibrous
Explanation:
Collagen is the most abundant of the fibrous proteins that constitute more than 25% of the protein mass in the human body.
Other prominent fibrous proteins include keratin and myosin.
These fibrous proteins represent a primary source of structural strength for cells (i.e., the cytoskeleton) and tissues.
Q-4. The collagen triple helix structure is not found in:
a) Cytoplasm
b) Golgi apparatus
c) Lumen of endoplasmic reticulum
d) Intracellular vesicles
Answer: Cytoplasm.
Explanation:
Synthesis of collagen: RER-> GB-> Intra-cellular secretory vesicles-> Extra-cellular space
Collagen is the major insoluble fibrous protein in the extracellular matrix and in connective tissue.
Q-5. 40 mm gap between two fibers of tropo-collagen which help in maintaining bone structure; is filled by (AIIMS Nov 2006)
a) Fe++
b) Hydroxyapatite
c) Carbohydrate
d) Mg++
Answer: Hydroxyapatite
Explanation:
Collagen is composed largely of the amino acids glycine, proline, and hydroxy-proline, which together account for more than 50% of the amino acid composition.
Tropo-collagen is the subunit of collagen fibrils formed of three polypeptides.
Each of the three chains forms a left-handed helical poly-proline II type helix with three residues per turn. There is a 40 nm gap, also called the “Hole Zone”, between the ends of each of these units.
These “Hole Zones” are critical in mineralization, as they appear to be the site of mineral nucleation for hydroxy-apatite crystals. The crystals appear to grow and proliferate from this area.
Q-6. Most abundant collagen in body is
a) Type I
b) Type II
c) Type III
d) Type IV
Answer: Type I
Explanation:
Collagen Type I:
This is the most abundant collagen of the human body.
It contains two chains called alpha-1 and one chain called alpha-2.
It is present in skin, cornea, bone, tendon, blood vessels.
Q-7. Collagen of which type is found in hyaline cartilage
a) Type I
b) Type II
c) Type III
d) Type IV
Answer: Type II
Explanation:
Type of collagen:
Fibril Forming Collagens:
Collagens Type I- Bone, Tendon, Skin, Cornea and Blood Vessels
Collagens Type II- Cartilage, Inter-vertebral Disk, Vitrous Body
Collagens Type III-Blood Vessels and Fetal skin
Network Forming Collagens:
Collagens Type IV- Basement membrane
Collagens Type VII- Beneath stratified squamous epithelia
Fibril Associated Collagens:
Collagens Type IX- Cartilage
Collagens Type XII- Tendon, Ligament
Q-8. Collagen of which type is found in hyaline cartilage (AIIMS Nov 2007)
a) Type I
b) Type II
c) Type III
d) Type IV
Answer: Type II
Explanation:
See above explanation.
Q-9. Which amino acid is not present in collagen?
a) Proline
b) Lysine
c) Glycine
d) Desmosine
Answer: Desmosine
Explanation:
Desmosine (DES) and Iso-Desmosine (IDES) are two unusual, tetra-functional, pyridinium ring-containing amino acids involved in elastin cross-linking.
Desmosine, a cross-linking amino acid of elastin, is an attractive biomarker for diagnosis of chronic obstructive pulmonary disease (COPD).
Q-10. Regarding proteoglycans false is
a) Chondroitin sulfate is a proteoglycan
b) They hold less amount of water
c) They are made up of sugar and amino acids
d) They carry charge
Answer: They hold less amount of water
Explanation:
Proteoglycans are glycosylated proteins which have covalently attached highly anionic glycosaminoglycans.
The major biological function of proteoglycans derives from the physicochemical characteristics of the glycosaminoglycan component of the molecule, which provides hydration and swelling pressure to the tissue enabling it to withstand compressional forces.
Crack PGMEE: On a Mission to Re-imagine Medical Education
Q-11. Muco-polysaccharide hyaluronic acid occurs maximally at
a) Lens
b) Vitreous humor
c) Retina
d) Cornea
Answer: Vitreous humor
Explanation:
Distribution of various Glycosaminoglycans:
Hyaluronic acid- Synovial fluid, vitreous humor, cartilage and loose connective tissue
Chondroitin sulfate- Cartilage, bone, cornea
Keratan sulfate I- Cornea
Keratan sulfate II- Loose connective tissue
Q-12. Viscosity in synovial fluid depends upon
a) N-acetyl galactosamine
b) N-acetyl glucosamine
c) Hyaluronic acid
d) Glucuronic acid
Answer: Hyaluronic acid
Explanation:
Normal synovial fluid contains hyaluronan (hyaluronic acid), a polymer of disaccharides composed of D-glucuronic acid and D-N-acetyl glucosamine joined by glycosidic bonds.
Hyaluronan is synthesized by the synovial membrane and secreted into the joint cavity to increase the viscosity and elasticity of articular cartilages and to lubricate the surfaces between synovium and cartilage.
Hyaluronic acid is especially high in concentration in embryonic tissue and is thought to play an important role in permitting cell migration during morphogenesis and wound repair.
The high concentration of hyaluronic acid and chondroitin sulfates present in cartilage contribute to its compressibility.
Q-13. Basement membrane degeneration is mediated by
a) Metalloproteinases
b) Oxidases
c) Elastases
d) Hydroxylases
Answer: Metalloproteinases
Explanation:
Degradation of collagen and other ECM proteins is achieved by a family of matrix metallo-proteinases which are dependent on Zinc ions for their activity.
Q-14. Bio-mineralization is seen in
a) Pinna
b) Molluscs shell
c) Hooves of cattle
d) Nails
Answer: Molluscs shell
Explanation:
Bio-mineralization is the process by which living organisms produce minerals. Bio-mineralization processes often lead to the hardening or stiffening of the mineralized materials.
The mollusc shell is a biogenic composite material that has been the subject of much interest in materials science because of its unusual properties and its model character for bio-mineralization.
Q-15. RBC membrane is maintained by (AIIMS May 2002)
a) Spectrin
b) Laminin
c) Collagen
d) Elastin
Answer: Spectrin
Explanation:
The shape, flexibility and the strength of RBC membrane is maintained by:
Spectrin (Most important)
Ankyrin
Protein 4.1
The deficiency of any one of the membrane skeletal proteins can cause hereditary spherocytosis.
Q-16. Biological role of metallothioneins is to sequester harmful metal ions. These bind: (AIIMS May 2004)
a) Cd++, Cu++ & Zn++
b) AI+++, Hg++ & NH4+
c) Pt++, As+++ & PO4–
d) Fe+++, Na+ & K+
Answer: Cd++, Cu++ & Zn++
Explanation:
Metallothioneins are the group of the small proteins found in the cytosol of the cells, particularly of liver, kidney and intestine.
They have a high content of cysteine and can bind copper, zinc, cadmium and mercury.
The SH groups of cysteine are involved in binding of metals.