Cell Biology and Structure

Statement (a) is incorrect. They are thin-walled, not thick-walled, isodiametric cells with abundant protoplasm.

The endothelium is the thin layer of cells that lines the interior surface of blood vessels and lymphatic vessels.

Integrins are a family of transmembrane glycoprotein receptors that mediate cell-matrix. They are involved in the anchoring of cells to an extracellular matrix. They affect tumour progression, which has made them an appealing target for cancer therapy.

Cytoplasm is a jelly-like substance in the cell.

Clara cells: Bronchial cells secreting surfactant Macrophages, fibroblasts and melanocytes are of connective tissue origin.

The basal lamina is a layer of extracellular matrix on which epithelium sits and is secreted by the epithelial cells. It is often confused with the basement membrane, and sometimes used inconsistently in the literature.

These cells form gonads.

This pair is correct. Haploid cells are responsible for the production of ova.

Endoplasmic reticulum (ER) is the largest intracellular compartment with an extensive array of interconnecting membrane tubules and cisternae that extend throughout the cell including the nuclear envelope. The outer membrane of nuclear envelope is continuous with that of the ER.

Galactosyl transferase (GT) belongs to the glycosyl transferases. In several tissues and cell lines, the enzyme is localised by immunocytochemistry to the two to three trans cisternae of the Golgi complex and thus, may be considered as a specific membrane component of this type of endomembrane. As a consequence, it is the most common Golgi "marker" enzyme in cell fractionation studies.

Most of the cases receptor mediated endocytosis from plasma membrane involves clathrin-coated vesicles. Macromolecules bind to cell-surface receptors, accumulate in clathrin-coated pits and enter the cell as a receptor and ligand complexes in clathrin-coated vesicles. Clathrin consists of three copies each of heavy chain and light chain, forming a three-legged structure called a triskelion.

The fossil record shows that earliest eukaryotic cells evolved about 1.5 billion years ago. Details of the evolutionary path from prokaryotes to eukaryotes cannot be deduced from the fossil record alone, but morphological and biochemical comparison of modern organisms has suggested a reasonable sequence of events consistent with the fossil evidence.

Mitochondria are double membrane bound organelles. It has an outer membrane, an inner membrane and an inter-membrane space. The inner membrane is highly convoluted, forming folds called cristae.

Cell organelles are correctly matched with their functions. Mitochondria synthesise ATP by means of electron transport chain. SER is responsible for the synthesis of fatty acids whereas post translational modification of proteins occur in the lumens of RER. Lysosomes are responsible for autophagy, a process of self-digestion.

Proteins are synthesised by ribosomes associated with the cytoplasmic side of the membrane of rough endoplasmic reticulum (RER). Synthesised proteins enter into the membrane and lumen of RER by the process of co-translational translocation. Modification of proteins is also occurred in the lumen. Proteins destined to be secreted then follow the secretory pathway. On the other hand, SER is responsible for lipid biosynthesis, detoxification, etc.