Operons! Get your operons here! Episode 21 explains how the same DNA instructions can indicate Gene regulation begins with chromatin structure.
Operons! Get your operons here! Episode 21 explains how the same DNA instructions can indicate Gene regulation begins with chromatin structure (1:40). DNA has areas of regulatory sequences which control transcription (2:30). Don’t get lost in the promotor, regulator, activator lingo - but focus on the effect of molecules interacting with the DNA strand (4:00). Regulation can also occur through alternative splicing of an mRNA transcript (4:30). Melanie concludes by recapping the learning objectives from the CED (5:05)
The Question of the Day asks (6:48) “What is the effect of a nucleotide insertion or deletion?”
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Hi and welcome to the APsolute Recap: Biology Edition. Today’s episode will recap Gene Regulation
Lets Zoom out:
Unit 6 - Gene Expression and Regulation
Topic - 6.5 and 6.6
Big Idea: Information Storage and Transmission
DNA instructions are the same in all cells within an organism - but not all cells perform the same tasks! As the recipe for life, skin cells might read and express the instructions in Chapter 2 while muscle cells focus on Chapter 4. DNA isn’t organized into chapters, but rather into chromosomes and genes. There are several levels of regulation and control within a cell and organism to ensure that the correct genes are expressed at the right time.
Lets Zoom in:
Differences in the expression of genes account for some of the phenotypic differences between organisms. Location, location, location. The processes of transcription and translation occur in a specific sequence and in a specific place within a cell. For a full recap of the central dogma, check out Episode 20.
Recall that DNA is a double helix that coils around proteins called histones in eukaryotes. This chromatin exists in two forms. Euchromatin has histone acetylation causing less coiling. This loosening in chromatin structure enhances transcription because nitrogenous bases are more accessible. In contrast, heterochromatin is methylated and tightly packed. As a result, nitrogenous bases are less accessible and less likely to be transcribed.
Transcription is the process by which DNA is read and an mRNA strand is produced. This occurs in the nucleus of eukaryotic cells and in the cytoplasm of prokaryotes. DNA has stretches of regulatory sequences that interact with regulatory proteins to control transcription. Both prokaryotes and eukaryotes have groups of genes that work together for gene regulation.
In prokaryotes, groups of genes called operons are transcribed in a single mRNA molecule. This allows the cell to efficiently express sets of genes when products are needed at the same time. An operon consists of a promoter, operator, and one or more genes. RNA polymerase binds to the promoter while a repressor can bind to the operator. The lac operon is an example of an inducible operon, meaning that it is activated by the presence of a particular molecule. Other operons are repressible, meaning that their switch is on by default but can be turned off by a specific molecule.
In eukaryotes, groups of genes may be influenced by the same transcription factors to coordinate expression. DNA control elements in enhancers bind to specific transcription factors. Promoters are DNA sequences upstream of the transcription start site where RNA polymerase and transcription factors bind to initiate transcription. At times, physical bending of the DNA strand enables activators to control proteins at the promoter, initiating transcription. In contrast, negative regulatory molecules inhibit gene expression by binding to DNA and blocking transcription.
Promotor, regulator, activator - that's a lot to keep straight. The big take away is this: Genes turn on and off as proteins and molecular products physically bind to a DNA stand. Most of this binding occurs “upstream” or before the genetic sequence is read.
Regulation can also occur at the level of mRNA processing. Recall that in addition to a 3’ poly A tail and 5’ mG cap, small sections called introns must be spliced out of the primary mRNA transcript. Exons remain in mRNA to be translated and expressed. The sequences that classify as interrupting introns can change. And so, the same sequence of DNA can create two or more different mRNA transcripts through alternative splicing. In addition, mRNA molecules can be degraded after periods of time, affecting how many proteins can be made from it.
There are three primary learning objectives that the college board wants you to be able to explain. First, explain how the location of regulatory sequences relates to their function. Second, be ready to explain how the binding of transcription factors to promoter regions affects gene expression and/or the phenotype of the organism. Lastly, be able to explain the connection between regulation of gene expression and phenotypic differences in cells and organisms. It is likely that you will be asked to predict the effect of a transcription factor or regulator on transcription and translation in a new scenario.
To recap….
Gene regulation results in differential gene expression and influences cell products and function. Location matters for each step in DNA coiling, transcription, RNA processing, and translation. Some genes are consistently activated, while others are turned on by protein products.
Today’s Question of the day is about mutations.
Question:What is the effect of a nucleotide insertion or deletion?