RNA processing

Question 1

Alternative Polyadenylation Sites

Answer 1

Tissue specific choice of polyadenylation sites leads to alternative splicing, and tissue-specific expression of one of two alternative gene products

ex: Calcitonin is a hormone that causes increased calcium and phosphate incorporation into bone

different sitr of polyedenylation==>

Calcitonin Gene- Related Peptide (CGRP) inducesvasodilatation and may be a neurotransmitter or neuromodulator (in brain)

splicing gets rid of introns and produces 2 different proteins based on these polyAsites (vary from tissue to tissue)

allows us to get more proteins from fewer genes

Question 2

beta-thalassemia

Answer 2

Hemoglobin is a tetramer of two a and two b chains (a2b2).
Deficiency of any one of these chains leads to thalassemias (for example: b chain deficiency leads to (b-thalassemia).
Deficiency of b means: very little or no a2b2 and some a4. a-globin gets degraded in the absence of b .
Formation of a4 and degradation of RBCs.
Splicing defects are responsible for b-thalassemia.

Autosomal recessive disease.
Phenotype depends on the amount of b-globin produced.
b-thalassemia major: b0-Thalassemia (both alleles mutated).
b-thalassemia minor (Asymptomatic heterozygote):
b0 Heterozygote (one normal and one mutant allele)
b+ Heterozygote (one normal allele, and a mutant allele producing some normal globin).

Question 3

Spinal Muscular Atrophy

Answer 3

Autosomal recessive genetic disorder (5q13).
Affected individuals have altered control of muscle movement
Loss of motor neurons in spinal cord and part of the brain.

Molecular cause: mutations in SMN1 (survival motor neuron)–> doesn’t produce proteins.
Tandem duplication of SMN1 gave rise to SMN2 version.–>4 copies of the SMN2 gene because 2 alleles
SMN2 has a silent mutation in one of the exons that occurred naturally during duplication. The mutation leads to exon skipping.

normal protein produced by
SMN2 is not adequate