Q-151. Which type of RNA has the highest percentage of modified base?
A. mRNA
B. tRNA
C. rRNA
D. snRNA
Answer: tRNA
Explanation:
There are more than 100 other naturally occurring modified nucleosides. The greatest structural diversity of modifications can be found in tRNA, while pseudo-uridine and nucleosides with 2′-O-methylribose often present in rRNA are the most common.
However, it is notable that, in ribosomal RNA, many of the post-transcriptional modifications occur in highly functional regions, such as the peptidyl transferase center and the subunit interface, implying that they are important for normal function.
Q-152. During phagocytosis, the metabolic process called respiratory burst involves the activation of
a) Oxidase
b) Hydrolase
c) Peroxidase
d) Dehydrogenase
Answer: Oxidase
Explanation:
The biochemical mechanism of microbial killing and degradation following phagocytosis is called respiratory burst.
This is accomplished largely by oxygen dependent mechanisms through generation of reactive oxygen intermediate.
It is due to rapid activation of NADPH oxidase.
Q-153. The ligand-receptor complex dissociates in the endosome because
a) Of its large size
b) The vesicle loses its clathrin coat
c) Of the acidic pH of the vesicle
d) Of the basic pH of the vesicle
Answer: Of the acidic pH of the vesicle
Explanation:
Endocytosed cell-surface receptors dissociate from their ligands within late endosomes.
The acidic pH of late endosomes causes most receptors and ligands to dissociate.
Q-154. The specialized mammalian tissue/ organ in which fuel oxidation serves not to produce ATP but of generate heat is
a) Adrenal gland
b) Skeletal muscle
c) Brown adipose tissue
d) Heart
Answer: Brown adipose tissue
Explanation:
Brown fat is more abundant in infant but is present in adult as well, is located between scapulas, at the nape of the nick, along the great vessels in thorax and abdomen.
In brown fat depot, fat cells as well blood vessels have extensive sympathetic innervation.
Brown fat cells contain several small droplets of fat in contrast to ordinary lipocytes.
Brown fat cells also contain many mitochondria that contain a unique protein called uncoupling protein 1 (UCP1).
UCP1 functions to dissipate the proton motive force that is normally used to drive the synthesis of cellular ATP.
As a consequence of UCP1 action, the energy in the mitochondrial electrochemical gradient is released in the form of heat.
Q-155. The human plasma lipoprotein containing the highest percentage of triacylglycerol by weight is
a) VLDL
b) Chylomicrons
c) HDL
d) LDL
Answer: Chylomicrons
Explanation:
Triacylglycerol content of lipoproteins:
Chylomicron: 90 %
VLDL: 60 %
LDL: 8 %
HDL: 5 %
Q-156. Which one of the following can be a homologous substitution for iso-leucine in a protein sequence?
a) Methionine
b) Aspartic acid
c) Valine
d) Arginine
Answer: Valine
Explanation:
Valine is homologous substitution for iso-leucine in a protein sequence.
Valine and iso-leucine are amino acids with aliphatic side chain.
Q-157. Proteins are linear polymers of amino acids. They fold into compact structures. Sometimes these folded structures associate to form homo or hetero dimmers. Which one of the following refers to this associated form
a) Denatured state
b) Molecular aggregation
c) Precipitation
d) Quaternary structure
Answer: Quaternary structure
Explanation:
Quaternary structure defines the polypeptide composition of a protein and, for an oligomeric protein, the spatial relationships between its protomers or subunits.
Important points:
Monomeric proteins consist of a single polypeptide chain. Dimeric proteins contain two polypeptide chains.
Homo-dimers contain two copies of the same polypeptide chain, while in a hetero-dimer the polypeptides differ.
Q-158. The comparison of the amino acid sequence of cytochrome C from different species shows many variations. Most of these variations are found
a) Randomly
b) Only in helical regions
c) Only in strand regions
d) Mainly in loop regions
Answer: Randomly
Explanation:
Cytochrome-c consists of a chain of 112 amino acids, 19 of which occur in exactly the same sequential order positions in all organisms.
Differences in the identity and positions of the remaining 93 amino acids are considered to be the result of mutational substitution during the course of evolution.
Q-159. There are more than 300 variants of human hemoglobin gene. Among these only a few are fatal. Hence the most important factor to be conserved in a protein for its function is the
a) Amino acid sequence
b) Ligand binding residues
c) Structure
d) Environment
Answer: Ligand binding residues
Explanation:
Ligand binding is most important factor with regard to conservation of protein function.
As long as the ligand binding residues are preserved, function of hemoglobin will essentially be preserved.
Q-160. 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.