It has been demonstrated that the levels of monoamine metabolites in CSF varies with polymorphism of serotonin transporter protein.
Which of the following components of genetic apparatus is responsible for such polymorphisms?
A. Polymorphism refers to variations in the genome at a particular locus noted in a general, apparently healthy population. Polymorphisms occur at a fairly high frequency in the general population. When the polymorphism occurs in more than 1% of a population, it can be considered as useful for genetic linkage analysis. ABO blood groups are a good example of polymorphism expressed in the protein products of genes. Restriction fragment length polymorphisms are those variations that create or destroy the sites at which restriction enzymes act on a DNA molecule, rendering differences in the final ‘restricted’ or cleaved DNA when these enzymes are applied in vitro. If these polymorphisms are due to changes in a single nucleotide in a sequence, they are called SNPs or single nucleotide polymorphisms. SNPs seem to be one of the most common genetic variations and various SNP genotyping methods are being increasingly employed to study polymorphisms. Polymorphisms arise originally out of mutations but are maintained in populations due to factors such as founder effect, genetic drift, and natural selection. Note that most polymorphisms occur in non-coding regions (that is introns), as coding sequences (or exons) on mutation often produce disease phenotypes. Serotonin transporter polymorphisms have been identified in the promoter region, which is a non-coding part of DNA (5HTTLPR–5HT transporter linked promoter region). 5HTTLPR can be a short or long variant. In those with a short variant, the serotonin transporter expression is low; the short variant is speculated to be associated with a higher incidence of affective disorders, anxiety, and PTSD. But the evidence is inconclusive as most studies are case–control design with significant heterogeneity. In addition, structural brain changes in the form of gray matter volume reduction in areas important for emotional processing, such as the amygdala, have been noted in subjects with the short variant of the promoter region. An altered number of chromosomes is termed aneuploidy.
In the diagnosis of HIV, following a positive ELISA test, western blotting could be used to confirm the diagnosis.
Which of the following cellular components is separated by electrophoresis for western blotting?
A. Molecular analysis techniques include Southern, northern, and western blotting. Western blotting is used in protein analysis, for example to detect HIV antibodies. Northern blotting is used in RNA analysis, while Southern blotting is used in the analysis of DNA. Southern blotting was named after its founder, Professor Edwin Southern; the other names were given to differentiate among the various blotting techniques.
Genetic information in an organism is inherited equally from parents of both sexes. An exception to this is seen in:
C. Mitochondrial DNA is wholly inherited from the ovum. The sperm has no mitochondria in its ‘head’; the ‘head’ is made of nuclear material and the acrosomal cap. The ‘body’ of sperm have many mitochondria which provide energy to propel the ‘tail’. The ‘body’ and ‘tail’ are shed on entry of sperm into the ovum. Hence the mitochondria of an embryo are completely maternally derived. This is important in clinical genetics as mitochondrial DNA abnormalities result in various diseases, such as MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and recurrent stroke syndrome) and Leber hereditary optic neuropathy. These diseases are purely maternally inherited. Mitochondrial DNA codes for 13 proteins involved in the respiratory chain in addition to 22 tRNAs and two ribosomal RNAs.
Microtubule-associated protein tau undergoes several post-translational modifications and aggregates into paired helical filaments in Alzheimer’s disease.
These modifications of tau include all of the following except:
E. Amino acid activation is an important step in the translation of mRNA to proteins. As tRNAs enter the cytoplasm after release from the nucleus where they are synthesized, they are attached to specific amino acids according to the codon sequences. This is an energy-dependent process called amino acid activation. The energy stored in such activated amino acids is used in making peptide bonds during protein translation. Translation takes place in the cytoplasm on ribosomes, where specific mRNAs are involved. Translation includes three steps—initiation, elongation, and termination. The ribosome contains two sites—peptidyl P site where methioninecontaining tRNA initially binds and aminoacyl A site where each new incoming tRNAs with activated amino acids can bind. In the elongation step amino acids are added one by one in a string-like fashion to produce proteins. Chain termination is signalled by one of three codons— UAA, UGA, or UAG. Following this protein synthesis (or sometimes simultaneously at one end of long proteins), post-translational modifications take place to transport the synthesized proteins to appropriate cellular sites. These modifications take place in endoplasmic reticulum and golgi bodies. This includes covalent modifications, protein folding, and tagging with signal peptides to dispatch to appropriate cellular destinations. Glycosylation, proteolysis, phosphorylation, gamma carboxylation, prenylation, ubiquitation, polyamination, and nitration are some of the recognized post-translational modifications. This process is essential in tagging wrongly folded or aberrant proteins to enter lysosomes for destruction.
Which one of the following refers to the synthesis of RNA molecules from DNA?
C. Transcription refers to the synthesis of RNA from DNA. Translation refers to the production of proteins from RNA. Replication refers to the production of new DNA copies from template copies of DNA. Splicing refers to the removal of non-coding sequences of RNA following transcription. DNA contains both coding and non-coding sequences. To synthesize proteins, the code contained in exons (coding sequences) are required. The heterogeneous nuclear RNA, which contains both coding exons and non-coding introns, undergoes splicing by spliceosomes within the nucleus to produce mature mRNA. Modification refers to the posttranslational changes in a protein molecule before it becomes functionally active.
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