BIOLOGY Case study (4 Marks)

Structures of the bacterial ribosome have provided a framework for understanding universal mechanisms of protein synthesis. However, the eukaryotic ribosome is much larger than it is in bacteria, and its activity is fundamentally different in many key ways. All ribosomes are composed of two subunits, both of which are built from RNA and protein. Bacterial ribosomes, for example of Escherichia coli, contain a small subunit (SSU) composed of one 16S ribosomal RNA (rRNA) and 21 ribosomal proteins (r-proteins) and a large subunit (LSU) containing 5S and 23S rRNAs and 33 rproteins. In contrast to their bacterial counterparts, eukaryotic ribosomes are much larger and more complex, containing additional rRNA in the form of so-called expansion segments (ES) as well as many additional r-proteins and r-protein extensions.

(1).Ribosomes are present in
(a) Eukaryotes only
(b) Eukaryotes and prokaryotes
(c) Prokaryotes only
(d) Eukaryotes, prokaryotes and viruses

(2) In 70S ribosomes, ‘S’ stands for
(a) SI unit (b) Solubility factor (c) Svedberg unit (d) all of these

(3) 80 S ribosomes occur in
(a) Eukaryotic cells of animals
(b) Eukaryotic cells of animals and plants
(c) Both Eukaryotic cells and prokaryotic cells
(d) all of these

(4) Ribosomes are made up of
(a) RNA only (b) RNA and proteins (c) RNA, DNA and proteins (d) Nucleic acids, proteins and lipids

(5) Polysomes are
(a) multiple units of ribosomes
(b) attachment of many ribosomes to a common mRNA
(c) attachment of many mRNA to a common ribosome
(d) lysosomal aggregations

Cell membrane, also called plasma membrane, thin membrane that surrounds every living cell, delimiting the cell from the environment around it. Enclosed by this cell membrane are the cell’s constituents, large, water-soluble, highly charged molecules such as proteins, nucleic acids, carbohydrates, and substances involved in cellular metabolism. Cell membranes are composed primarily of fatty-acid based lipids and proteins. Membrane lipids are principally of two types, phospholipids and sterols (generally cholesterol). Both types share the defining characteristic of lipids—they dissolve readily in organic solvents—but in addition they both have a region that is attracted to and soluble in water.

(1).Plasma membrane is made up of
(a) A protein, a lipid and a cellulose layer
(b) Bimolecular lipid layer surrounded by protein layers
(c) A protein layer between two lipid layers
(d) A lipid layer between two protein layers

(2) Fluid mosaic model of cell was put forward by –
(a) Danielli and Dawson
(b) Singer and Nicolson
(c) Garner and Allard
(d) Watson and Crick

(3) Which of the following statements best describes the chemical composition of
plasma-membrane?
(a) Plasma membrane is composed of two layers—one layer of phospholipids and one layer
of proteins.
(b) Plasma membrane is composed of equal numbers of phospholipids, proteins, and
carbohydrates.
(c) Plasma membrane is bilayers of proteins with associated lipids and carbohydrates.
(d) Plasma membrane is bilayers of phospholipids with associated proteins and
carbohydrates.

(4) Most abundant lipid in the cell membrane is
(a) phospholipids (b) cerebrosides (c) glycolipids (d) None of these