Question

please answer all 6 questions

Question 27 3 pts TRBP is a protein important for the formation of the RISC complex. Which of the following would you expect in cells with null mutations in TRBP? o Reduced siRNA-mediated mRNA degradation o Increased miRNA-mediated translational repression o Increased deadenylase-mediated mRNA degradation o Reduced proteasome-mediated protein degradation D Question 28 3 pts A protein that binds to the 3' UTR of a VEGF mRNA and promotes deadenylation and uncapping is likely to: o Reduce VEGF transcription o Promote degradation of VEGF mRNA at the 5' and 3' ends o Promote VEGF ubiquitylation and degradation o Change VEGF RNA splicing from exon 8a to exon 8b Question 29 3 pts Which of the following is true of prokaryotes and not eukaryotes, and also allows prokaryotic transcription to be regulated by attenuation? o Transcription and translation occur simultaneously o Transcription does not require regulation at locations far from the promoter o mRNA must be transported from the nucleus to the cytoplasm o mRNA must be transported outside of the cell. Question 30 3 pts In a cancer genomes database, you find multiple mutations in the BMV gene in several types of cancers. The majority of these cancer-associated mutations are heterozygous (having also one wild type allele), and expression of these mutant versions of BMV in normal cells causes them to divide in the absence of extracellular signals. What type of gene is the mutant BMV most likely to be? o Oncogene o Tumor suppressor o Proto-oncogene

Answer 1

Question 27:

TRBP gene encodes for the TRBP protein which is required for the formation of the RISC (RNA-induced silencing complex). RISC is a ribonucleoprotein complex that incorporates one strand of the small interfering RNA (siRNA) or micro RNA (miRNA). This strand is used as a template that is used to recognize the complementary mRNA. On recognizing the complementary RNA, it cleaves the mRNA by the activity of the enzyme RNase. This is especially important for the protection against viruses that have double-stranded RNA as the genetic material.

A null mutation is defined as the mutation in the gene which prevents the transcription and translation of the gene into the mRNA and protein respectively. Thus, when there is a null mutation in the TRBP gene, the TRBP protein will not be produced. When the TRBP protein is not produced, the RISC will not be formed. This leads to the inability of the RISC to use either the siRNA or miRNA as a template to recognize and destroy the mRNA.

Thus, the correct option is Option (a) - reduced miRNA mediated mRNA degradation.

Question 28:

Vascular Endothelial Growth Factor (VEGF) is a mitogen essential for angiogenesis. The 3'UTR (untranslated region)

Question 29:

In bacteria, transcription and translation occur simultaneously. Attenuation in prokaryotes occurs because of this reason that the two processes occur simultaneously. Attenuation results in the premature termination of transcription. Attenuation is a regulatory mechanism in bacteria and it prevents the unnecessary gene expression which involves the use of energy.

Thus, the correct option is Option (a) - transcription and translation occur simultaneously.

Question 30:

Humans are diploid organisms, which means that there are two copies of each chromosome, one inherited from the paternal side and the other inherited from the maternal side. Humans have two alleles at each genetic locus, where one allele is inherited from each parent. An allele is defined as the variant form of a gene. When there is the mutation in any one the alleles of the protooncogene, it gets converted to an oncogene. An oncogene is capable of inducing cell differentiation and proliferation even in the absence of extracellular signals. this leads to the enhanced division of the cells leading to the formation of a tumor.

However, in the case of the tumor suppressor genes, a mutation in both the alleles is required for the loss of function of the tumor suppressor gene. The loss of function mutation is also responsible for the activation of the oncogenes to protooncogenes.

Thus, the mutation in the BMV gene is heterozygous, i.e., it also has one wild type allele. Hence, it can be said that the correct option is Option (c) - protooncogene.

Question 31:

Ras is responsible for the intracellular signaling. The functions of Ras are:

a. Restriction point is the point in the cell cycle beyond which the mitogens are not required to complete the cell cycle. Restriction point (R point) can be termed a the commitment point. The transition from the G1 phase to the S phase is initiated and maintained by the growth factors. The Ras pathway determines the transcription of Cyclin D1. This Cyclin D1-Cdk 6 complex is phosphorylated by the ERK for the transition to take place. Thus, if the Ras is mutated, then ERK will not be activated and hence, the entire cell cycle will be stopped at the R point.

b. MAPK/ERK pathway (also known as the Ras-Raf-MEK-ERK pathway) is the protein chain inside the cell. It is a cascade reaction and thus if one of the proteins gets mutated, the entire process gets stuck. thus if their si a mutation in the RAs, there will be no phosphorylation of the downstream proteins and MAPk will never be phosphorylated.

c. The Ras needs to be activated by the removal of GDP so that Ras can bind GTP and become active. The active Ras then activates the protein kinase activity of RAF kinase. However, if Ras is mutated, then it will not be activated and hence it will not bind and activate Raf.

d. Only when the phosphorylation of the downstream proteins of the MAPK cascade takes place (i.e., of Raf, MEK, and ERK) will the phosphorylation of the proteins involved in cell cycle proliferation take place. When the complex of Cyclin D with Cdk 6 is phosphorylated by ERK, the transition from the G1 to the S phase takes place. Normally the hypophosphorylated Retinoblastoma protein (Rb) binds to E2F and prevents the expression of the S phase genes - thus the cell cycle does not progress from G1 to s phase. however, the hyperphosphorylation of Rb destabilizes it and causes the release of E2f and the expression of the S phase entry genes. Thus, Rb will be hyperphosphorylated only when the ERK is phosphorylated. Thus, if there is a mutation in the Ras, then Rb will not be phosphorylated.

Thus the applicable options are -

Option (a) - the cell cycle will be arrested at the restriction point

Option (b) - MAPK will never be phosphorylated