Molecular Biology Practice Test

The mRNA cap is involved in several important functions, including protecting the mRNA from degradation, enhancing the translatability of the mRNA, enhancing the splicing of the mRNA, and enhancing the transport of the mRNA to the cytoplasm. However, it does not directly help regulate the expression of the mRNA from the promoter. This is typically done through other mechanisms such as transcription factors and enhancers.

Helicase is the enzyme used in the unwinding of DNA. It plays a crucial role in DNA replication and transcription by breaking the hydrogen bonds between the DNA strands, allowing the double helix to separate and unwind. This unwinding is necessary for the DNA to be accessible for replication or transcription processes. Helicase acts as a molecular motor, moving along the DNA strands and separating them in a process called DNA unwinding. Once the helicase unwinds the DNA, other enzymes can then bind to the separated strands and carry out their respective functions.

The correct order for RNA Cap synthesis is as follows: first, the terminal phosphate is removed from the pre-mRNA (2). Then, a capping GMP is added to the pre-mRNA (3). Next, N7 of the capping guanine is methylated (1). Finally, the 2'-O-methyl group of the penultimate nucleotide is methylated (4).

The addition of poly (A) to mRNA is indeed important for its translatability. Poly (A) is a tail of adenine nucleotides that is added to the 3' end of mRNA molecules. This poly (A) tail helps in stabilizing the mRNA molecule, protecting it from degradation. It also plays a crucial role in the initiation of translation, as it interacts with various proteins involved in translation initiation. Additionally, the poly (A) tail enhances the efficiency of mRNA export from the nucleus to the cytoplasm. Therefore, the addition of poly (A) to mRNA is essential for its stability and efficient translation, making the statement true.

DNA polymerase I is not required for mammalian cell polyadenylation of pre-mRNA. Polyadenylation is the process of adding a poly(A) tail to the 3' end of the mRNA molecule. PAP (poly(A) polymerase), CPSF (cleavage and polyadenylation specificity factor), PABII (poly(A)-binding protein II), and RNA polymerase II are all involved in this process. However, DNA polymerase I is not directly involved in polyadenylation. It is primarily responsible for DNA replication and repair, not mRNA processing.

Snurps, also known as snRNPs, are a type of small nuclear ribonucleoproteins that play a crucial role in the processing of pre-mRNA molecules. These molecules are composed of both RNA and protein components. The RNA component of snurps is responsible for binding to specific sequences in the pre-mRNA, while the protein component helps in stabilizing the structure and facilitating the splicing process. Therefore, the correct answer is RNA and protein.

The statement is false because capped mRNA is actually more stable than uncapped mRNA. The cap structure at the 5' end of capped mRNA provides protection against degradation by exonucleases. This cap structure also plays a crucial role in the initiation of translation by facilitating the binding of the mRNA to the ribosome. Therefore, capped mRNA is generally more stable and has a longer half-life compared to uncapped mRNA.

Pre-mRNA, which is the initial transcript of a gene, undergoes several modifications before it can become mature mRNA. One of these modifications is cleavage, where specific sections of the pre-mRNA molecule are removed. This cleavage is necessary to remove non-coding regions and join the coding regions together. After cleavage, the pre-mRNA is polyadenylated, which involves the addition of a poly-A tail at the 3' end. Therefore, the statement that pre-mRNA must be cleaved before it is polyadenylated is true.

Termination codons are specific sequences of nucleotides in mRNA that signal the termination of protein synthesis. In this case, the termination codons are UAG, UAA, and UGA. These codons do not code for any amino acids and instead signal the ribosome to stop translation. Therefore, when one of these codons is encountered during protein synthesis, the ribosome releases the newly synthesized protein and the process is terminated.

EF-Tu is a protein that plays a crucial role in protein synthesis. It acts as a molecular escort, facilitating the delivery of aminoacyl-tRNA molecules to the ribosome during translation. Aminoacyl-tRNA molecules carry the correct amino acids that correspond to the codons on the mRNA template. EF-Tu binds to aminoacyl-tRNA and helps to bring it to the ribosome, ensuring accurate and efficient protein synthesis. Therefore, the function of EF-Tu is to escort aminoacyl-tRNA to the ribosome.

During transcription, the pre-mRNA molecule is synthesized by RNA polymerase. However, the pre-mRNA molecule is not immediately ready for translation into a protein. It undergoes a series of modifications known as pre-mRNA processing. These modifications include the addition of a 5' cap, the addition of a poly-A tail, and the removal of introns through a process called splicing. These modifications are necessary for the stability and functionality of the mRNA molecule. Therefore, it can be concluded that pre-mRNA processing begins during transcription.

Experiments conducted with yeast as a model organism have provided evidence that supports the idea that cleavage of the poly (A) tail is indeed necessary for transcription termination. This means that the process of cutting off the poly (A) tail is crucial in order to properly end the transcription of genetic information. Therefore, the statement "Experiments using yeast as a model have shown that cleavage of the poly (A) tail is necessary for transcription termination" is true.

The correct answer is spliceosome. The spliceosome is a complex of proteins and small nuclear ribonucleoproteins (snRNPs) that is responsible for removing introns and joining exons in pre-mRNA during the process of mRNA splicing. It plays a crucial role in the maturation of mRNA molecules before they can be translated into proteins. The other options, ribosome, nucleolus, hnRNA, and R-loop, are not directly involved in mRNA splicing.

The 5' cap of mRNA plays a crucial role in the translatability of the mRNA. It helps in the recognition and binding of the mRNA to the ribosome during translation. Additionally, the 5' cap protects the mRNA from degradation and enhances its stability. Therefore, the presence of the 5' cap positively affects the translatability of the mRNA.

Poly(A) tails are actually added to the 3' end of the mRNA molecule. This modification, known as polyadenylation, involves the addition of a string of adenine nucleotides to the mRNA molecule. The poly(A) tail helps protect the mRNA from degradation and is also involved in the export of the mRNA from the nucleus to the cytoplasm.

The correct answer is that the capping of the pre-mRNA occurs before the mRNA reaches a chain length of 30 nt. This means that the capping process, which involves the addition of a modified guanine nucleotide to the 5' end of the mRNA, takes place early in the transcription process before the mRNA molecule has grown to a certain length. This capping is important for the stability and efficient processing of the mRNA molecule.

Polyadenylation is a crucial step in mRNA processing that involves the addition of a poly(A) tail to the 3' end of the mRNA molecule. This poly(A) tail plays a vital role in the efficient transport of mRNA out of the nucleus. It helps to protect the mRNA from degradation, aids in the binding of mRNA to transport proteins, and is involved in the recognition and export of mRNA through nuclear pores. Therefore, polyadenylation is indeed required for the efficient transport of mRNA out of the nucleus, making the given statement false.

The genetic code is not an overlapping code. In an overlapping code, a single nucleotide can be a part of multiple codons, leading to ambiguity in decoding the genetic information. However, in the genetic code, each nucleotide is read in a continuous, non-overlapping manner to form codons, which are then translated into specific amino acids. Therefore, the statement that the genetic code is an overlapping code is not true.

Genomic sequence information can be applied to study the evolution, function, and structure of genomes, as well as proteomics. By analyzing the sequence of DNA or RNA, scientists can gain insights into how genomes have evolved over time, understand the functions of different genes and non-coding regions, explore the structural organization of genomes, and investigate the relationship between genomic sequences and the proteins they encode. Therefore, all of the choices mentioned in the question are correct applications of genomic sequence information.

DNA polymerase I is not required for mammalian cell polyadenylation of pre-mRNA. Polyadenylation is the process of adding a poly(A) tail to the 3' end of the mRNA molecule. PAP (Poly(A) Polymerase), CPSF (Cleavage and Polyadenylation Specificity Factor), and PABII (Poly(A)-Binding Protein II) are all involved in this process. DNA polymerase I, on the other hand, is primarily involved in DNA replication and repair, and not in mRNA processing. Therefore, it is not required for mammalian cell polyadenylation.

The correct answer is GU-AG because it matches the consensus sequence for splicing signals. In splicing, the GU dinucleotide is found at the 5' end of the intron, while the AG dinucleotide is found at the 3' end. These dinucleotides are important for the recognition and cleavage of the intron during RNA splicing. Therefore, GU-AG is the correct answer as it follows the pattern of the splicing signal consensus sequence.

SnRNA U1 is a small nuclear RNA that plays a crucial role in pre-mRNA splicing. It is primarily located in the nucleus, where it forms a complex with other proteins called snRNPs. However, in order to carry out its function, snRNA U1 needs to be exported to the cytoplasm where mRNA translation occurs. To facilitate this export, snRNA U1 receives a 5' Cap modification, which helps in its transportation from the nucleus to the cytoplasm. Therefore, the correct answer is "export to the cytoplasm."

The three naturally occurring stop codons are UAG, UAA, and UGA. These codons signal the end of protein synthesis during translation. When a ribosome encounters one of these codons, it releases the newly synthesized protein and disassembles. UAG, UAA, and UGA are recognized by release factors, which cause the termination of translation. These stop codons do not code for any amino acids and are essential for the accurate and efficient synthesis of proteins.

Based on the electron micrograph results from the R-looping experiment, it can be concluded that the gene contains two introns. The presence of two loops in the electron micrograph indicates that there are two regions of single-stranded DNA where the mRNA has hybridized with the DNA template. These regions correspond to the introns in the gene. Therefore, the presence of two loops suggests that the gene contains two introns.

The catalytic center of the spliceosome is a complex composed of Mg2+, U2 and U6 snRNP, and the branch point region of the intron. These components work together to catalyze the splicing reaction, which involves removing the intron and joining the exons together. The Mg2+ ions facilitate the chemical reactions by stabilizing the transition state, while the U2 and U6 snRNPs play a role in recognizing the splice sites and positioning the intron for cleavage. The branch point region of the intron is also essential for proper splicing, as it helps to define the splice sites and guide the splicing machinery to the correct location.

Translation is the process by which ribosomes read the genetic message carried by mRNA and use it to synthesize proteins. This process involves the decoding of the nucleotide sequence of mRNA into a specific amino acid sequence, which then forms a protein. This definition accurately describes the process of translation and distinguishes it from other cellular processes such as transcription or post-translational modifications.

The correct answer is AAUAAA. This sequence, known as the polyadenylation signal motif, is commonly found in the mRNA of mammalian cells. It plays a crucial role in the process of polyadenylation, where a string of adenine nucleotides (poly-A tail) is added to the mRNA molecule. This poly-A tail helps in stabilizing the mRNA and facilitating its export from the nucleus to the cytoplasm for translation into proteins.

eIF2 is involved in binding tRNA to the ribosome.

The correct order is (3,2,1). During the elongation phase of translation, the process begins with EF-Tu, bound to GTP, delivering an aminoacyl-tRNA to the ribosomal A site. Once the aminoacyl-tRNA is correctly positioned, peptidyl transferase catalyzes the formation of a peptide bond between the existing peptide in the P site and the new amino acid in the A site, extending the growing polypeptide chain. Subsequently, EF-G, also bound to GTP, facilitates the translocation of the peptidyl-tRNA from the A site to the P site, effectively moving the ribosome along the mRNA and making the A site available for the next aminoacyl-tRNA, thus continuing the cycle of elongation.

R-looping experiments were useful in determining the existence of introns in the adenovirus genome. R-looping is a technique that involves the formation of RNA-DNA hybrids, where the RNA molecule hybridizes with the DNA template. This technique allows for the identification and mapping of introns, as the RNA molecule will form loops where the introns are present. Therefore, R-looping experiments provide valuable evidence for the existence of introns in the adenovirus genome.

U4: base pairs with 3' splice site of mRNA is the mismatched snRNP and its function. The correct function of U4 snRNP is to base pair with U6 snRNA to form a complex that prevents U6 from pairing with the 5' splice site. This complex is essential for the regulation of splicing and the removal of introns from mRNA.

The snRNA U1 functions in the nucleus, but it receives a 5' Cap to enhance its export to the cytoplasm. This suggests that the snRNA U1 is needed in the cytoplasm for some cellular processes or interactions. The 5' Cap modification helps facilitate its transport from the nucleus to the cytoplasm, where it can carry out its functions.

The correct order for prokaryotic translation initiation is as follows:

1) Binding of IF1, IF2, and GTP to the 30 S subunit.
2) Binding of IF3 to the 30S subunit.
3) Formation of the 30S initiation complex.
4) Binding of the 50S subunit and loss of IF1 and IF3.
5) Formation of the 70S initiation complex by dissociation of IF2 and GTP hydrolysis.
6) Dissociation of the 70S ribosome.

This order ensures that the correct components are bound to the ribosome and that the initiation complex is formed before the 50S subunit binds and the 70S ribosome is fully assembled.

mRNA is transcribed in the nucleus and then transported to the cytoplasm for translation. Once in the cytoplasm, the poly(A) tail of the mRNA is gradually shortened by enzymatic degradation. When the poly(A) tail is completely lost, the mRNA is targeted for degradation by exonucleases. Therefore, an mRNA that loses its poly(A) tail is not imported back into the nucleus. Hence, the correct answer is False.

The statement is false because the poly(A) tail can be removed from mRNA through enzymatic processes. One such process is called deadenylation, which involves the enzymatic removal of the poly(A) tail. Additionally, the poly(A) tail can also be shortened through other mechanisms such as mRNA decay pathways. Therefore, it is not accurate to say that the poly(A) tail is very difficult to remove once it is added to the mRNA.

The Shine-Dalgarno sequence is a short nucleotide sequence found in mRNA molecules. It is involved in the initiation of protein translation in prokaryotes. This sequence interacts with the complementary sequence in the 16S rRNA of the 30S ribosome, allowing the ribosome to bind to the mRNA and start protein synthesis. Therefore, the Shine-Dalgarno sequence can be found in mRNA.

The correct order of prokaryotic translation initiation steps is as follows: (1) Binding of IF3 to the 30S subunit (2) Binding of IF1, IF2, and GTP to the 30S subunit (3) Formation of the 30S initiation complex (4) Dissociation of the 70S ribosome (5) Binding of the 50S subunit and loss of IF1 and IF3 (6) Formation of the 70S initiation complex by dissociation of IF2 and GTP hydrolysis.

U1 is the correct answer because it is the first snRNP (small nuclear ribonucleoprotein particle) to bind during the assembly stage of the spliceosome cycle. The spliceosome is responsible for removing introns from pre-mRNA, and U1 snRNP recognizes the 5' splice site at the beginning of the intron. It forms a base pairing interaction with the 5' splice site, marking the start of the splicing process.

EF-Tu is a protein that plays a crucial role in protein synthesis. It acts as a molecular escort, binding to aminoacyl-tRNA and delivering it to the ribosome during translation. This process ensures that the correct amino acid is added to the growing protein chain. Without EF-Tu, the accuracy and efficiency of protein synthesis would be compromised. Therefore, the correct answer is "escort aminoacyl-tRNA to the ribosome".

The correct answer is "Splicing intermediate." Spliceosomal lariat refers to the structure formed during the splicing process of pre-mRNA molecules. It is a loop-like structure that is formed when the intron is removed and the exons are joined together. This intermediate structure plays a crucial role in removing the non-coding regions (introns) and joining the coding regions (exons) to produce the mature mRNA molecule. Therefore, the term "splicing intermediate" accurately describes the spliceosomal lariat.

The mRNA cap has several functions, including protecting the mRNA from degradation, enhancing translatability, enhancing transport to the cytoplasm, and enhancing splicing. However, it does not directly regulate the expression of the mRNA from the promoter. This function is typically carried out by transcription factors and other regulatory elements.

The direction of translation refers to the process by which a protein is synthesized from an mRNA template. The mRNA is read in the 3' to 5' direction, while the protein is made in the N to C direction. This means that the amino acids are added to the growing polypeptide chain starting from the N-terminus and progressing towards the C-terminus. Therefore, the correct answer is that protein is made in the N to C direction, starting from the N-terminus.

Bovine spongiform encephalitis is caused by a misfolded protein called a prion. Prions are abnormal proteins that can cause other proteins to misfold, leading to the accumulation of misfolded proteins in the brain. This accumulation damages brain cells and causes the symptoms of the disease. Sickle cell anemia, diabetes, Burkett's Lymphoma, and HIV-AIDS are not caused by misfolded proteins.

Proteomics is useful because it encompasses the study of all proteins in a cell, tissue, or organism. This includes not only the proteins that are encoded by genes, but also noncoding RNAs and transcripts of unknown functions. Additionally, proteomics allows for the study of various processes such as splicing of transcripts, degradation of mRNAs, and post-translational modifications. Therefore, all of these factors make proteomics a valuable tool in understanding the complex workings of biological systems.

The U2 snRNP binds to the spliceosome and requires ATP.

IF3 is the correct answer because it prevents reassociation of the 70s ribosome by binding to the free 30s subunit. This initiation factor acts as a dissociation factor, preventing the 30s subunit from reattaching to the 50s subunit after translation is complete. By binding to the free 30s subunit, IF3 helps to ensure that the ribosome remains in a dissociated state and ready for the next round of translation.

Eukaryotic translation initiation factor 6 (eIF6) binds to the 40s subunit and inhibits re-association of the 40s and 60s subunits.

The genetic code is the set of rules by which information encoded within DNA or mRNA sequences is translated into proteins. It is characterized by non-overlapping codons, meaning that each codon consists of three nucleotides and is read in a continuous sequence. There are no gaps between codons, as they are read one after another. The genetic code also exhibits wobbles, which refers to the flexibility in base pairing at the third position of the codon, allowing some variation in the amino acid that is encoded. However, the genetic code is not absolutely universal, as there are some variations and exceptions found in certain organisms or organelles.

Paralogs are homologous genes within the same species that have evolved through gene duplication. Therefore, it is incorrect to state that the gene for Huntington's disease has a paralog in bacteria, as bacteria and humans are different species.

The estimated total number of genes in the human genome is believed to be between 20,000 and 25,000. This estimate is based on ongoing research and advancements in genomic sequencing techniques. It is important to note that this number is not fixed and may vary slightly as new discoveries are made.