641. Cholesterol is essential for normal membrane functions because it
A. plugs up the cardiac arteries of older men
B. cannot be made by higher organisms
C. keeps membranes fluid.
D. spans the thickness of the bilayer

642. The model that is now known to be correct for the structure of biological membrane is
A. Fluid mosaic model
B. Page’s model
C. Lac Operon model
D. Lock and Key model

643. In Fluid mosaic model, the biological membrane can be viewed as
A. two dimensional solutions of oriented lipids and globular proteins
B. three dimensional solutions of oriented lipids and globular proteins
C. two dimensional solutions of oriented lipids and carbohydrate
D. three dimensional solutions of oriented lipids and carbohydrate

644. Membrane lipids are
A. hydrophilic
B. hydrophobic
C. ampiphillic
D. none of these

645. Pinocytosis occurs in
A. all eukaryotic cells
B. all prokaryotic cells
C. mitochondria of all cells
D. none of these

646. Exocytosis is the secretion of proteins
A. out of the cell across the plasma membrane into the extracellular space
B. out of the cell across the plasma membrane into the intracellular space
C. is the uptake of macromolecules from the extracellular space into the cell across the plasma membrane
D. is the uptake of macromolecules from the intracellular space into the cell across the plasma membrane

647. The membrane proteins that catalyze active transport reactions differ from soluble enzymes as
A. they are permanently changed during the reaction
B. the substrates of the reaction are all outside the cell
C. they do not enhance the rates of reaction
D. the products of the reaction move in a specific direction

648. The movement of molecules across a membrane by passive transport does not require
A. an input of metabolic energy
B. internal energy
C. vibrational energy
D. none of these

649. Peptidoglycan is a complex consisting of
A. oligo-saccharide and protein
B. polysaccharide and protein
C. mono-saccharide and protein
D. aminoacid and carbohydrate

650. The mesosomes may be the sites of
A. DNA replication and specialized enzymatic reactions
B. RNA replications and specialized enzymatic reactions
C. RNA replications and specialized cyclic reactions
D. None of the above

651. Which of the following is correct?
A. Peroxisomes have a single boundary membrane
B. Peroxisomes contain enzymes that degrade fatty acids and amino acids
C. The byproduct of given reactions in (b) is toxic to cells
D. All of the above

652. The smooth endoplasmic reticulum (SER) is the site of
A. phospholipid synthesis
B. amino acid synthesis
C. carbohydrate synthesis
D. protein synthesis

653. Lysozymes are found in
A. plant cells
B. animal cells
C. microbial cells
D. all of these

654. Biological membranes are like water beds because
A. they are always moving
B. they (normally) do not leak their contents
C. the membrane is thin compared to the enclosed volume
D. all of the above

655. The plasma membrane is a selectively permeable barrier due to presence of specific transport
A. proteins
B. amino acids
C. carbohydrates
D. none of these

656. Which type of molecule spans the membrane, from its inner to outer surface according to the Fluid mosaic model of cell membranes?
A. Cholesterol
B. Phospholipid
C. Protein
D. Carbohydrate

657. In membranes, lipids are
A. glycerophospholipids
B. sphingolipids
C. sterols
D. all of these

658. Which of the following is not found in membranes?
A. Glycoproteins
B. Glycolipids
C. Nucleic acids
D. Phospholipids

659. Because DNA is a highly charged polyanion, its stability to heat denaturation
A. does not depend on hydrophobic interactions
B. increases with increasing salt
C. is independent of G – C content
D. decreases with increasing salt

660. The sugar in RNA is __________ , the sugar in DNA is __________
A. deoxyribose, ribose
B. ribose, deoxyribose
C. ribose, phosphate
D. ribose, uracil

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