Biology Answer Note #5

Question 1 A cell that needs to produce large amounts of proteins to work in the cytoplasm of that cell would need Question 9 options: a. An extensive smooth endoplasmic reticulum b. A large number of free ribosomes c. An extensive golgi apparatus d. An extensive rough endoplasmic reticulum Answer The correct answer for this question would be option a. An extensive smooth endoplasmic reticulum. The smooth endoplasmic reticulum (SER) plays a crucial role in protein production in eukaryotic cells. It is a membranous network in the cytoplasm that lacks ribosomes and is responsible for the synthesis, modification, and packaging of various biomolecules, including proteins. In order to understand why the SER is necessary for the production of large amounts of proteins, it is important to first understand its structure and functions. The SER is composed of a system of interconnected tubules and vesicles that span through the cytoplasm. Its main function is to synthesize lipids, including phospholipids and cholesterol, which are needed for the formation of cell membranes. Additionally, the SER is involved in detoxification processes and the storage of calcium ions. However, one of the most important functions of the SER is its role in protein production. The process of protein synthesis occurs in two main stages: transcription and translation. Transcription, which takes place in the cell nucleus, involves the synthesis of messenger RNA (mRNA) from DNA. The mRNA then travels to the cytoplasm where it is translated by ribosomes on the surface of the rough endoplasmic reticulum (RER). Although the RER is responsible for the translation of most proteins, the SER also plays a significant role. The SER contains ribosomes as well, but these are free, meaning they are not attached to its surface. These free ribosomes produce proteins that are used in the cytoplasm, rather than being exported outside of the cell. As a result, cells that require a high rate of protein production to carry out their functions would need a large amount of free ribosomes in the cytoplasm, which can be found in an extensive smooth endoplasmic reticulum. Furthermore, the SER also modifies and packages proteins, preparing them for transportation to other parts of the cell, such as the Golgi apparatus. Therefore, in order for a cell to efficiently produce and transport large quantities of proteins, it would require not only a large number of free ribosomes but also a well-developed SER. Question 2 Guanine makes up 14% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be Adenine? Question 11 options: a. 36% b. 14% c. 72% d. 8% Answer Based on the information given, we can determine that the remaining 86% of the nucleotides in this sample of DNA must be made up of the other three nitrogenous bases: Adenine, Thymine, and Cytosine. Therefore, the percentage of Adenine in this sample would be approximately 86% divided by 3, which equals approximately 28.67%. However, since Thymine and Cytosine each make up half of the remaining 86%, we can estimate that Adenine makes up roughly half of the remaining 86%. Therefore, the approximate percentage of Adenine in this sample of DNA is 43%. Question 3 The sequence above is an mRNA strand that is in the cytoplasm ready to translated by a ribosome. If the gene that codes for this mRNA mutated so that the codon in the red box became CUG instead of AUG. What effect would it have when the mutated mRNA was translated? Question 14 options: a. There would be a protein with just 4 amino acids made b. There would be a protein with just 5 amino acids made c. The mutated mRNA could not be translated d. There would a protein with just 3 amino acids made Answer The mutation in the gene sequence will result in a change in the mRNA sequence, which will ultimately affect the translation process. The change of the codon from AUG to CUG will lead to a different amino acid being inserted into the growing polypeptide chain during translation. To fully understand the impact of this mutation, we need to understand the process of translation and the role of the AUG codon. Translation is the process by which the genetic information in the mRNA sequence is decoded into a specific amino acid sequence, thereby forming a polypeptide chain. This process occurs in the cytoplasm, where ribosomes act as the site of translation. The codon AUG serves as the start codon for translation and is responsible for initiating the process. It codes for the amino acid methionine, which is usually the first amino acid in a polypeptide chain. However, with the mutation in the gene sequence, the start codon has changed to CUG, which codes for the amino acid leucine. This change in the start codon will cause a shift in the reading frame of the mRNA, resulting in a completely different amino acid sequence being produced. As a result, the polypeptide chain will be shorter, as the mutation has caused a premature stop codon in the sequence. Therefore, the correct answer to the question is d. There would be a protein with just 3 amino acids made. In conclusion, this mutation in the gene sequence would have a significant impact on the translation process, leading to the production of a shorter polypeptide chain with a different amino acid sequence. This can potentially result in a non-functional or altered protein, which can have serious implications on the functioning of the organism. Additional calculations: If we consider the reading frame to be shifted by 1 nucleotide, the mutated mRNA sequence would code for the amino acids leucine, proline, and histidine (CUG-CCU-CAU). This would result in a polypeptide chain with a length of 3 amino acids. Question 4 Proteins are synthesized during the process of ________. Question 16 options: a. Translation b. DNA replication c. Transcription d. mRNA processing Answer Translation is a process in molecular biology that specifically involves the synthesis of proteins from an RNA template. It occurs in the cytoplasm of the cell and is a crucial step in the central dogma of biology, which describes the flow of genetic information from DNA to RNA to protein. During translation, the sequence of nucleotides in a messenger RNA (mRNA) molecule is decoded into a sequence of amino acids, the building blocks of proteins. Useful sources for understanding the process of translation include biology textbooks, peer-reviewed journal articles, and online resources such as Khan Academy and Albert.io. It is important for a university-level student to carefully review and critically assess multiple sources to ensure the accuracy and validity of the information presented. Additionally, understanding the underlying mechanisms and biochemical processes involved in translation, such as the ribosome and tRNA binding, can aid in understanding the step-by-step breakdown of protein synthesis. Question 5 Epigenetic phenomena involve DNA methylation and ________. Question 19 options: a. genetic mutation b. gene inversions c. histone acetylation d. chromosomal rearrangements Answer Epigenetic phenomena involve DNA methylation and histone acetylation. These are two distinct mechanisms that play crucial roles in the regulation of gene expression. DNA methylation is a process in which methyl groups are added to specific regions of DNA, leading to changes in gene activity. This process primarily occurs on cytosine bases within the DNA sequence and is carried out by enzymes called DNA methyltransferases (DNMTs). It is an essential mechanism for regulating gene expression during development and cell differentiation, as well as in response to environmental cues. On the other hand, histone acetylation is a modification of the proteins called histones that are associated with DNA in the nucleus of cells. The addition of acetyl groups to histones alters their structure, allowing for easier access to the DNA and ultimately influencing gene expression. This process is carried out by enzymes called histone acetyltransferases (HATs) and histone deacetylases (HDACs). Both DNA methylation and histone acetylation play critical roles in epigenetic regulation and are closely interconnected. They work together to control gene expression and determine which genes are turned on or off in a particular cell at a specific time. Biology textbooks, such as "Molecular Biology of the Cell" by Bruce Alberts et al. and "Essentials of Biology" by Sylvia Mader, provide comprehensive explanations of epigenetic mechanisms and their significance in gene regulation. Additionally, scientific articles like "Epigenetics in Human Disease" by Manel Esteller and "The Role of DNA Methylation in Cancer" by Maria Esteller are highly informative sources on the topic. In terms of calculations, no specific numerical computations are needed to understand the concept of DNA methylation and histone acetylation. However, studying their specific patterns and levels in different cell types can involve statistical analysis and various bioinformatics tools. In conclusion, DNA methylation and histone acetylation are two key epigenetic mechanisms that work together to regulate gene expression. These molecular processes are crucial for proper development and functioning of cells and can also contribute to the development of diseases.