Gene Structure and Regulation PDF

2/11/24, 11:26 PM  3.3.5 Define Gene and Genome  Listen   3.3.5 Define Gene and Genome Gene Structure and Regulation A gene is a unit of DNA sequence that “encodes a specific functional product” (Buckingham, 2019). Most gene products are proteins. Some RNA transcripts of their encoding genes bec...

2/11/24, 11:26 PM  3.3.5 Define Gene and Genome  Listen   3.3.5 Define Gene and Genome Gene Structure and Regulation A gene is a unit of DNA sequence that “encodes a specific functional product” (Buckingham, 2019). Most gene products are proteins. Some RNA transcripts of their encoding genes become the functional products without translating into proteins. tRNA- and rRNA-coding genes are two familiar examples to you. A gene is more than the coding sequence; it also includes regulatory elements such as the promoter and enhancer regions, an initiation site, and a termination site necessary to produce the protein. Eukaryotic genes and prokaryotic genes differ in structure and regulation. The comparison table below summarizes the main differences. Genetic engineering techniques take advantage of the universality of the genetic code, often using bacterial cells to produce human proteins. On the other hand, molecular biologists also consider the differences in gene regulation and expression between prokaryotes and eukaryotes. Prokaryotic and Eukaryotic Gene Structure and Regulation in Comparison Prokaryotes Single-cell organisms lacking a nucleus e.g., bacteria 1. A single RNA polymerase produces mRNA, rRNA and tRNA 2. Prokaryotic RNA polymerase is simpler in structure 3. RNA splicing does not occur as there are no introns present 4. mRNAs are polycistronic - one mRNA can encode a variety of proteins by varying the start site 5. mRNAs do not have 5’ caps or poly-A tails 6. Transcription and translation are closely coupled; both occur in the cytoplasm. This allows organisms to respond quickly to sudden environmental changes. https://online.saskpolytech.ca/d2l/le/content/310889/viewContent/12772616/View 1/3 2/11/24, 11:26 PM 3.3.5 Define Gene and Genome 7. mRNAs are degraded quickly following translation; in fact, the 5’ ends of some molecules are degraded before the 3’ ends are synthesized Eukaryotes More complex single or multi-cellular organisms. e.g., animals, plants, fungi 1. Three separate RNA polymerases encode rRNA, tRNA and mRNA 2. RNA polymerases are more complex 3. A large portion of the gene is made up of non-coding sequences or introns 4. mRNAs are monocistronic – each mRNA produces only one type of protein 5. mRNAs have 5’ caps and poly-A tails - important signal sequences 6. Transcription occurs in the nucleus, while translation occurs in the cytoplasm. This allows for mRNA maturation 7. mRNA molecules have a longer half-life - often hours or days From Nucleotides to Genome Genome is a cell’s entire chromosomal DNA sequence (Green, 2022). In the case of RNA viruses, a genome is the whole RNA sequence in a viral particle. Since eukaryotic chromosomes are inside the nucleus, the DNA obtained from the cell nucleus is often called genomic DNA (gDNA). The prokaryotic gDNA refers to the DNA in the large circular chromosome. A mitochondrion contains its chromosome inside, separate from the chromosomes in the nucleus. The mitochondrial chromosome has a similar circular structure as the bacterial chromosome. In 2004, upon completing the Human Genome Project, scientists deciphered the entire human genome sequence (Rifai, 2018). The human genome contains approximately three billion base pairs. Interestingly, only 1.2% of the human genome are protein-encoding sequences. The first genome data in 2004 led to more discoveries about the commonality and diversity of human genetics. Reference(s) https://online.saskpolytech.ca/d2l/le/content/310889/viewContent/12772616/View 2/3 2/11/24, 11:26 PM 3.3.5 Define Gene and Genome Buckingham, L. (2019). Molecular diagnostics fundamentals, methods, & clinical applications (3rd ed.). F.A. Davis. Green, E. (2022, December 27). Genome. National Human Genome Research Institute. https://www.genome.gov/genetics-glossary/Genome Rifai, N. (2018). Tietz fundamentals of clinical chemistry and molecular diagnostics (8th ed.). Elsevier. https://online.saskpolytech.ca/d2l/le/content/310889/viewContent/12772616/View 3/3