Molecular Genetics: Eukaryotic Protein Synthesis

The start codon is the sequence of nucleotides that initiates protein synthesis. In this case, the start codon is AUG, which codes for the amino acid Methionine. Methionine is commonly used as the first amino acid in the majority of proteins.

The correct answer is "intiator methionine". The abbreviation "imet" is commonly used to represent "intiator methionine". This term refers to the methionine amino acid that serves as the starting point for protein synthesis in cells. It is called the initiator methionine because it is the first amino acid incorporated into a growing polypeptide chain during translation.

Polycistronic mRNA refers to a type of mRNA that contains multiple coding regions or open reading frames (ORFs), which can be translated into multiple different proteins. This type of mRNA is commonly found in prokaryotes and some viruses. In contrast, eukaryotes typically produce monocistronic mRNA, where each mRNA molecule encodes for only one protein. Therefore, the statement that polycistronic mRNA encodes for multiple different proteins is true.

Elongation is a stage in protein synthesis where amino acids are added to the growing polypeptide chain. GTP (guanosine triphosphate) is required for the elongation process as it provides the energy needed for the formation of peptide bonds between amino acids. GTP is hydrolyzed to GDP (guanosine diphosphate) during this process. Therefore, the statement "Elongation requires GTP" is true.

The triplet code AUG is actually the start codon for protein synthesis and codes for the amino acid methionine, not cysteine. Therefore, the statement that AUG is the triplet code for cysteine is false.

Scanning is the process by which the 40s subunit of a ribosome searches for the start codon in mRNA. The start codon (usually AUG) marks the beginning of a protein-coding sequence and signals the ribosome to initiate translation. Once the start codon is found, the ribosome assembles and begins synthesizing the protein.

Ribosomes are composed of two subunits, the large subunit and the small subunit. The large subunit is referred to as the 60s subunit, while the small subunit is referred to as the 40s subunit. Therefore, ribosomes are made of 60s + 40s subunits.

Ubiquitin tagging actually marks proteins for degradation by proteosomes, rather than preventing it. When a protein is tagged with ubiquitin molecules, it is recognized by the proteosomes and subsequently degraded. This process plays a crucial role in regulating protein levels and maintaining cellular homeostasis. Therefore, the correct answer is False.

The explanation for the given answer is that initiation in prokaryotes, which are simple single-celled organisms, requires only three factors, namely the RNA polymerase enzyme, the promoter sequence, and the initiation factors. On the other hand, eukaryotes, which are more complex organisms with a nucleus, require a total of 13 factors for initiation. These factors include several types of RNA polymerases, various transcription factors, and other proteins that are involved in the regulation and initiation of transcription. Therefore, it is true that initiation in prokaryotes requires only three factors, while eukaryotes use 13 factors.

The stop codons are UAG, UAA, and UGA. Stop codons are nucleotide sequences found in mRNA that signal the end of protein synthesis. When a ribosome encounters a stop codon, it releases the completed protein and detaches from the mRNA strand. UAG, UAA, and UGA are the three stop codons recognized by the ribosome, and they do not code for any amino acids.

The Shine-Dalgarno sequence is required during the initiation phase of prokaryotic translation. This sequence is found in the mRNA molecule and is complementary to the 16S rRNA in the small ribosomal subunit. It helps in positioning the ribosome correctly on the mRNA, ensuring accurate translation of the genetic code. This sequence is crucial for the initiation of protein synthesis in prokaryotes.

Streptomycin is a prokaryotic inhibitor because it specifically targets bacterial ribosomes and inhibits protein synthesis. It binds to the 30S subunit of the bacterial ribosome, preventing the initiation of protein synthesis and leading to the death of the bacterial cell. Streptomycin is commonly used as an antibiotic to treat bacterial infections, particularly those caused by gram-negative bacteria. It is not effective against eukaryotic cells, making it a selective inhibitor of prokaryotes. Cycloheximide, Ricin, and Abrin are not prokaryotic inhibitors and have different mechanisms of action.

The eukaryotic initiation phase requires three processes: removal of introns, addition of a 5' cap, and addition of a poly AAA tail. Removal of introns is necessary to remove non-coding regions from the pre-mRNA, allowing for the production of mature mRNA. The addition of a 5' cap protects the mRNA from degradation and helps in the initiation of translation. Lastly, the addition of a poly AAA tail at the 3' end of the mRNA stabilizes it and assists in the export of the mRNA from the nucleus.

Ricin is an Eukaryotic inhibitor because it is a protein toxin that inhibits protein synthesis in eukaryotic cells. It works by inactivating the ribosomes, which are responsible for protein production. This inhibition of protein synthesis leads to cell death. Ricin is derived from the castor bean plant and has been used as a biological weapon due to its high toxicity.

The initiation stage of protein synthesis makes promoting Eukaryotic genes in Prokaryotes difficult. During initiation, the RNA polymerase binds to the promoter region of DNA, which contains specific sequences that are recognized by the polymerase. In Eukaryotes, the promoter sequences are different from those in Prokaryotes, making it challenging for the RNA polymerase of Prokaryotes to recognize and bind to the Eukaryotic promoter. Therefore, the initiation stage becomes a barrier for promoting Eukaryotic genes in Prokaryotes.

The start codon is found in the Kozak sequence, which is a specific DNA sequence surrounding the start codon that helps in the recognition of the start site by the ribosome. It is the first codon in the scanning process, as it signals the ribosome to begin translation. The start codon codes for Methionine, which is the amino acid that initiates protein synthesis. It can be up to 1000 bases from the cap, referring to the 5' cap structure on mRNA, indicating that the start codon can be located quite far away from the mRNA cap.

The 5' Cap has multiple functions. It regulates nuclear export, preventing degradation by exonucleases, promotes translation, and promotes 5' intron excision. It does not serve as a tag for degradation or promote degradation by exonucleases, nor does it ligate exons.