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Which of the following is not an example of post-translational modification?
Polyadenylation is an example of post-transcriptional modification. This process involves adding large repeats of adenine bases to the 3' end of mRNA molecules, known as the poly-A tail.
Myristoylation is the process of adding myristate (a fatty acid) to a protein, alkylation is the process of adding an alkyl group, and ubiquination is the process of adding a molecule of ubiquitin (a small protein often used to signal degradation).
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In which of the following organelles does the initial linkage of a sugar for post-translation modification N-linked glycosylation most commonly occur?
Two of the more common types of glycosylation, N-linked and O-linked, occur at different points and in different places in the cell. N-linked glycosylation takes place in the lumen of the endoplasmic reticulum, while O-linked glycosylation takes place in the Golgi body.
The other options, the mitochondria and the nucleus, are not involved in these post-translational modifications.
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Please complete the following statement:
"The addition of a CH3CO group to the N-terminus of a protein is the most common form of protein modification. This chemical modification is called ________."
This question requires knowing either that CH3CO is an acetyl group, or that acetylation is the most common protein modification. Each of the other modifications described are biologically occurring modifications, but acetylation was the correct answer for the given statement.
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In prokaryotes what site on the mRNA does the ribosome bind to initiate translation?
The Shine-Dalgarno sequence is the ribosomal binding site in in prokaryotic mRNA that is located around 8 bases upstream of the start codon.
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The 5' cap on eukaryotic mRNA molecules is recognized by which of the following proteins?
The 5' cap is recognized by the important translation factor eIF4e. Once bound, eIF4e helps transport the mRNA molecule to the ribosome and facilitates bonding to the ribosomal machinery.
The 3' poly-A tail is recognized by PABP. RNA polymerase is involved in transcription, not translation. The 40s ribosomal subunit is recruited by the initiation complex (including eIF4e, PABP, and various other translation factors).
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When conducting a stain of chromosomes, certain regions along the chromosome will stain more darkly than the rest. This is due to the fact that these regions are more tightly condensed. What is the functional outcome of having one region more condensed (heterochromatin) than the rest (euchromatin)?
Heterochromatin often contains simple, repetitive sequences, and although it cannot be said that it is completely void of coding sequences, it is not typically transcribed. The tight wrapping prevents polymerase from accessing the strand, and euchromatin typically contains the regions that get transcribed. Thus, heterochromatin is though to contain repressed or inactive genes.
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Small GTPases are important molecular switches and signaling pathways. What proteins are responsible for promoting the activation of these small GTPases?
The correct answer is guanine nucleotide exchange factors. In order to activate small GTPases and subsequently stimulate downstream pathways, guanine nucleotide exchange factors bind inactive GTPases and cause the release of guanine diphosphate (GDP). This allows guanine triphosphate (GTP) to bind and active the GTPase.
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Which of the level of protein structure is incorrectly matched to its description?
Primary structure of a protein is determined by covalent peptide bonds, and corresponds to the linear sequence of amino acids before structures begin to form. Secondary structure results from hydrogen bonding between the amino acid backbones to form alpha-helices and beta-sheets. Tertiary structure is formed when functional groups of the amino acids interact, either by hydrogen bonding, hydrophobic interactions, or disulfide bridge formation. Tertiary structure is associated with the three-dimensional structure of a single polypeptide chain. Quaternary structure forms when multiple polypeptide chains interact to build a multi-subunit structure.
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Which of the following proteins are likely to contain leucine zipper domains?
Leucine zippers are domains that allow for the binding of DNA. The question is essentially asking, "which of these proteins are capable of binding DNA?"
Proteases cleave proteins, lipases hydrolyze lipids, and transmembrane proteins interact with membranes. Transcription factors are the only given proteins that bind DNA and, therefore, are much more likely to contain leucine zipper domains than the other options.
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Which protein structure involves the binding of multiple polypeptides?
The structures of a protein increase in complexity all the way up to quaternary structure. Primary structure is based on the amino acid sequence of the protein, while secondary and tertiary structures are based on intermolecular attractions between the amino acids in the polypeptide. Quaternary structure is only seen when a functional protein complex is composed of two or more polypeptides bound together.
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Disulfide bonds in proteins are categorized under which structure class?
The correct answer is more than one of these. Primary structure is defined as a succession of amino acids joined by peptide bonds. Secondary structure introduces dimensionality to a protein via hydrogen bonding to produce two predominant structures, alpha helices and beta-pleated sheets. Tertiary structures cause further protein folding by disulfide bonds between cysteines, Van der Waal interactions, and hydrophobic interactions. Quaternary structures involve multiple amino acid chains folding together, and utilize the same types of bonds as tertiary structures.
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To which of the following structures in a typical molecule of tRNA is an amino acid attached?
Amino acids are attached to the CCA tail of a tRNA. These are found at the 3' end of tRNA molecules and are important for recognition by aminoacyl tRNA synthetases (enzymes that actually attach the amino acids to the tRNA). The anticodon loop, as the name suggests, contains the anticodon, which will be important during translation for recognizing mRNA sequences. The D-loop and the variable loop are other portions of the tRNA that are important for maintaining structure and recognition.
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Chloramphenicol prevents protein translation by which of the following mechanisms?
Tetracycline blocks the binding of aminoacyl tRNA to the A site of the ribosome.
Cyclohexamide blocks the translocation reaction on ribosomes.
Rifamycin blocks the initiation of RNA chains by binding to RNA polymerase.
Chloramphenicol blocks the pepidyl transferase reaction on the ribosome.
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During translation, which site in the ribosome allows for tRNA moelcules to enter the complex?
The ribosomal complex has three sites where tRNA moelcules can be oriented during the process of translation: the A site, the P site, and the E site. During polypeptide elongation, a tRNA with an attached amino acid will enter at the A site. It will then move to the P site, now holding the growing polypeptide chain. All tRNAs no longer holding an amino acid will exit the ribosome at the E site.
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On which of the following molecules could you find an anticodon?
In order to make sure that the proper amino acid is added to the growing polypeptide chain, an anticodon found on the tRNA carrying the amino acid must be a match for the codon found on the mRNA.
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Which of the following most accurately describes the chronological order of ribosome biogenesis in eukaryotes?
Ribosomal proteins are translated in the cytoplasm and rRNA genes are transcribed in the nucleolus. Following protein translation, these proteins enter the nucleus through nuclear pores and localize to the nucleolus. Here, transcribed rRNA associates with the ribosomal proteins to form the 60S and 40S eukaryotic ribosomal subunits. Prokaryotes have 50S and 30S subunits. The ribosomal subunits then translocate to the cytoplasm where they join together to form fully functional ribosomes.
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How many ribosomal binding sites are there and what are their functions?
The correct answer is there are three sites. A site binds aminoacyl-tRNA, P site binds peptidyl-tRNA, E site binds free tRNA before ribosomal exit.
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Which of the following is not a type of RNA?
mRNA, tRNA, and rRNA are the most commonly recognized types of RNA, though there are several more divisions. Messenger RNA (mRNA) is the product of gene transcription and is used to carry genetic information to ribosomes for translation. Transfer RNA (tRNA) is used to transport amino acid residues to active ribosomes during translation and contains anticodon sequences to bind to mRNA. Ribosomal RNA (rRNA) forms part of the ribosomes structure.
Though cRNA is not a class of RNA molecule, complementary DNA (cDNA) is used to store and analyze genomes. cDNA is the non-coding complement to the template strand used for transcription, and can be used to analyze genetic sequences.
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Which of the following processes is not a type of RNA processing carried out by eukaryotes?
Processing of pre-mRNA occurs in the nucleus. After transcription, three crucial modification take place. A 7-methylguanosine molecule is added to the 5' end to form a cap. Polyadenylation is added to the 3' end to create a poly-A tail. Introns are spliced out by spliceosomes, removing the non-coding regions of the RNA. The final product after modifications is considered a mature mRNA; prior to this, the transcript is known as heteronuclear RNA (htRNA).
Nucleotide excision repair is a method of proofreading after DNA replication to reduce the frequency of mutation.
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What are snRNPs (small nuclear ribonucleic particles)?
snRNPs are RNA protein complexes that combine with pre-mRNA and other proteins to form a spliceosome. Spliceosomes remove introns from pre-mRNA. After final modifications, the spliced pre-mRNA is considered mature mRNA and can be exported to the cytoplasm for translation.
mRNA is an RNA molecule that conveys genetic material from DNA to the ribosome. tRNA is an RNA molecule that serves as the link between the nucleotide sequence of nucleic acids and the amino acid sequence of proteins. rRNA is the RNA component of the ribosome that is essential for protein synthesis in all living organisms.
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