Central Dogma and Gene Expression Worksheet

Worksheet – Central Dogma and Gene Expression Answer the questions below. It is recommended that you work with 2 to 3 of your classmates on these questions and that you review each others’ work to make sure your answers are complete and correct. Many of the answers will be found in your textbook, but you may also need to use other resources. Each student must turn in their completed worksheet answers individually. I. Compare how Bacteria, Archaea, and Eukaryotes differ on each of the following aspects of DNA replication: 1. How do the number and types of DNA polymerase differ between these three groups? Bacteria- ~5; Pol III, PolC, DnaEhs, DnaB, DnaD Archaea- ~5; Pol-A, Pol-B, Pol-C, Pol-D and Pol-E. Eukaryotes- ~15; Pol α-, Pol δ-, Pol ε-, Sld2, Sld3, Dpb 11, MCM2-7 etc. 2. How does the physical location in the cell of DNA replication differ between these three groups? Bacteria- Cytosol Archaea- Cytosol Eukaryotes- Nucleus 3. Are there differences between these three groups in the timing of when DNA replication occurs in cells? DNA replication in Bacteria- Continuous and bidirectional DNA replication in Archaea- Semi-discontinuous, Bidirectional DNA replication in Eukaryotes- Semi-discontinuous, Bidirectional For prokaryote, it continuously replicates DNA when the cells are growing. In eukaryote, it occurs in s-phase. 4. How does origin of replication differ in terms of number and location between these three groups? Bacteria- single; Origin recognition by DnaA Archaea- multiple; Origin recognition by Orc1*/Cdc1* Eukaryotes- multiple; Origin recognition by OrC* II. Discuss the following aspects of transcription: 1. What is meant by monocistronic or polycistronic? How do these differ between prokaryotes and eukaryotes? Monocistronic- mRNA that yields single type of protein after translation. All eukaryotic mRNA is monocistronic. Polycistronic - These mRNA encode several proteins, after translation. Prokaryotic mRNA is mostly polycistronic. 2. How does the half-life (amount of time before half of the copies of a molecule degrade) of prokaryotic mRNA compare to that of eukaryotic mRNA? What features contribute to the difference? Prokaryotic mRNA half life is about few seconds to one hour while eukaryotic mRNA half is about 20 minutes to less than 40 hours. 2. Prokaryotes do not have 5'cap. Although some of them have poly A tail, the feature supports mRNA degradation. 3. How does the physical location in the cell of transcription differ between prokaryotes and eukarotes? Prokaryotic mRNA- Immediate translation following the transcription of the mRNA. Eukaryotic mRNA- mRNA needs to be processed considerably before undergoing translation. Physical location of cell transcription in prokaryotes is in the Cytoplasm while in eukaryotes its in the Nucleus 4. What are introns? How do the genes of prokaryotes and eukaryotes differ in regard to introns and how are they removed from genes that have them? Intron is a segment of a DNA or RNA molecule which does not code for proteins and interrupts the sequence of genes. Prokaryotes don’t have introns while Eukaryotes do posses introns in between the exons, that are removed by the process of splicing before translation. III. Discuss the following aspects of translation: 1. How does the location and timing of transcription/translation differ between prokaryotes and eukaryotes? Prokaryotes- Transcription and translation in Cytosol Eukaryotes- Transcription occurs in nucleus while translation occurs in cytosol. 2. How do the types of ribosomes differ between prokaryotes and eukaryotes? In prokaryotes, ribosomes include three separate rRNA molecules, whereas in eukaryotes ribosomes include four separate rRNA molecules. Prokaryotes- 70s ribosome; Large 50s subunit and small 30s subunit Eukaryotes- 80s ribosome; Large 60s subunit and small 40s subunit 3. How does the first amino acid of the translated protein differ between bacteria, archaea, and eukaryotes? Bacteria- first amino acid of the translated protein is formyl-methionine (fMet) Archaea- first amino acid of the translated protein methionine Eukaryotes- first amino acid of the translated protein is formyl-methionine (fMet) IV. Gene Expression It is recommended that you divide the next question between members of a small group. Each person should answer the question for one type of gene expression regulation and then explain their answers to the rest of the group. All students will be responsible for this information on examinations. Provide the information below for each of the following types of gene expression regulation: 1. Repression, 2. Induction, 3. Positive Regulation. In repression, the cell is going to be making the message for a protein product all the time except in conditions where it needs to turn off that gene expression because it no longer needs that product. So in repression, the gene expression is typically on until turned off. Induction is the opposite. In induction, gene expression is turned off until the cell receives a signal that it needs the product of that gene. So gene expression in induction is typically off until the cell turns it on through induction of regulation The example we will use for positive regulation is catabolite activating protein. This is not an on/off situation but more about the level of production. So in positive regulation, you may have a gene whose expression has been induced but only at a low level. With positive regulation, when certain conditions are available in the cell it will turn that expression to a higher level. So positive regulation is a regulation of the level of gene expression and can increase that level of expression under certain conditions. A. Name an example operon. Example Operon: Lac operon B. Create a list or table of the major elements (sequences or regions, proteins, etc.) involved in this method of gene expression regulation. Mode of regulation: induction by the specific inducer that is Lactose List of the major elements involved in Lac operon:  CAP site  Promoter  Operator  lacZ gene encoding for Beta-glucosidase.  lacY gene encoding Permease.  lacZ gene encoding Transacetylase. C. Create a simplified diagram showing the sequence of events and interaction of elements for this method of gene expression regulation.