My AP Biology Thoughts  Unit 6 Gene Expression and RegulationWelcome to My AP Biology Thoughts podcast, my name is Shriya Karthikvatsan and I am your host for episode #110 called Unit 6: Gene Expression and Regulation. Today we will be discussing the mechanisms used by cells to increase or decrease the production of specific gene types, and how this fits into the overarching unit.  Segment 1: Introduction to Gene Expression and RegulationWe will begin by going over a few helpful terms and ideas to provide context for the topic of gene expression and regulation which is a pretty broad topic as a whole A gene consists of a string of DNA hidden in a cell’s nucleus, and what we will unpack is how it knows when to express itself and cause the production of a string of amino acids called a protein The overall process is that a string of DNA is expressed to make RNA Then, something called mRNA is translated from nucleic acid coding to protein coding to form a protein  In terms of regulation, genes can’t control an organism on their own so they must interact with and respond to the organism’s environment  Some genes are always “on” regardless of environmental conditions, and these genes are among the most important elements of the genome because they control the ability of DNA to replicate, express itself, repair itself, and perform protein synthesis Overall, regulated genes are needed occasionally and get turned “on” or “off”  Regulation differs between prokaryotes and eukaryotes because in prokaryotes, most regulatory proteins are negative and turn genes off  In eukaryotes, cell-cell differences are determined by expression of different sets of genes This means that an undifferentiated fertilized egg looks and acts quite different from a skin cell, a neuron, or a muscle cell because of differences in the genes each cell expresses  In the next segment we will go into further detail of the specific processes involved in expression and regulation 

Segment 2: More About Gene Expression and RegulationGene expression begins with transcription which makes mRNA and the overall process is the same in both prokaryotes and eukaryotes  Prokaryotes lack a nuclear envelope, and eukaryotes use an extra step called RNA processing where RNA is edited and introns are edited out and exons are spliced together It is catalyzed by RNA polymerase which separates DNA strands and links RNA nucleotides at the 3’ end (side notes: prokaryotes have 1 type of polymerase and eukaryotes have 3) Transcription is initiated when RNA polymerase binds to a promoter and unwinds the DNA strands Initiation site and a small sequence after are recognized by transcription factors which are proteins that bind to promoter and guide RNA polymerase to bind to TATA box  Then, mRNA carries the genetic code and mRNA itself is a series of codons In eukaryotes, mRNA processing works by the 5’ end getting a GTP cap and the 3’ end getting a poly-A tail  Also, a splicesome complex of SnRNPs + a protein work together to cut out the introns (intruding codons) and splice the exons (expressed codons) together Following transcription, translation occurs in the ribosome after mRNA brings the genetic code and it is when tRNA brings the amino acid and the ribosome is able to be completely assembled Translation is initiated by a small subunit of the ribosome which binds to a recognition site on the mRNA and an anticodon of tRNA initiator binds to a start codon The next part of translation is elongation in which the anticodon of the next tRNA binds to a codon at the A site and the polypeptide bonds the 2nd amino acid onto the 1st amino acid (this process repeats until a stop codon is reached) Finally, termination is when the stop codon reaches the A site and a release factor frees the tRNA from the P site and disconnects the polypeptide causing everything to separate After translation, the protein is modified