Episode 38 is our second listener’s choice recAP from Instagram topic requests.
Episode 38 is our second listener’s choice recAP from Instagram topic requests. Pedigrees are used to study the pattern of inheritance of a particular trait through several generations in a family (1:20). Signal transduction pathways link signal reception of a ligand with a cellular response through phosphorylation (2:38). Cellular respiration oxidizes glucose to form ATP (3:30). Eukaryotic gene regulation occurs throughout the central dogma (4:50). Successful FRQ writing involves intentional application of your words (5:44).
The Question of the Day asks (7:14) “What is a prokaryote cluster of genes called when it has a single promoter? ”
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Hi and welcome to the APsolute Recap: Biology Edition. Today’s episode will recap multiple topics - it’ our second Listener’s Choice Episode.
Before we get started we wanted to say a huge THANK YOU to all those students and teachers that have followed along these past few months. We started podcasting in late February, and weren’t sure if anyone would listen. Today concludes week 12, episode 38, and over 19,000 downloads. Best of luck to everyone taking the AP Exam. We hope your experience this year has encouraged you to stay curious and maybe even pursue a future in science.
Lets Zoom out:
There are a lot of topics to review today! Thanks to our Instagram followers who wrote in with requests. We are going to recap pedigrees, signal transduction, cellular respiration, gene regulation, and FRQ strategies.
Lets Zoom in:
Our first recap topic comes to us from listener Cami. She wants to know how to tell the inheritance pattern of a pedigree. Remember, pedigrees are used to study the pattern of inheritance of a particular trait through several generations in a family. Usually this trait is some sort of disorder, but it doesn’t have to be. Google the royal family pedigree of hemophilia. It's intense - all traced back to Queen Victoria! When analyzing a pedigree, you are trying to determine if it is an autosomal trait (carried on chromosomes 1-22) or if its sex linked (chromosme 23). You also want to deduce if the disorder is dominant or recessive. Pedigrees will not confirm the pattern of inheritance, but they can disprove others through the process of elimination. If the trait is dominant, one of the parents has to have it. Dominant traits cannot skip a generation. If the trait is recessive, a child can have it while their parents don’t - since they can be heterozygous.Start with recessive first, and look for flaws in logic. If you start to see a pattern of an unaffected mom and a disproportionate amount of affected sons - might be sex linked recessive. Autosomal traits tend to have an equal distribution of affected sons and daughters. If even one parent to child interaction doesn’t work, then you have the wrong inheritance pattern.
Our next recap topic is signal transduction requested by Ana. Signal transduction pathways link signal reception of a ligand with a cellular response. Like a game of dominos, one molecular interaction will trigger the next, passing and often tweaking the message along the way. Many signal transduction pathways include protein modification and phosphorylation cascades, acting like an on/off switch. The phosphate added to the process will typically come from a molecule of ATP, temporarily activating each protein in the pathway. The transfer of the phosphate is catalyzed by an enzyme called kinase, Signals are often amplified during each step of the relay - in this way, even a small amount of ligand can have a significant cellular effect. This will involve the use of secondary messengers, such as calcium or cyclic AMP.
LIstener Trisha wants a recap of Cellular respiration - but the specifics. Follower Davian agees - asking for glycolysis and the Krebs cycle. There are a lot of steps, but follow the carbons and the energy. First is glycolysis in the cytosol, where 6 carbon glucose is broken down into two, 3 carbon pyruvates, also forming ATP and NADH. Next is pyruvate oxidation in the mitochondrial matrix, where pyruvate loses a carbon to carbon dioxide, becoming a two carbon molecule known as Acetyl CoA and forming more NADH. After that is the Krebs, or Citric Acid Cycle, also in the matrix. This process completes the oxidation of glucose, forming additional ATP, NADH, and CO2 as well as FADH2. The molecules of NADH and FADH2 formed up to this point will carry electrons to the final step of cellular respiration. Oxidative phosphorylation, also known as the electron transport chain, occurs in the inner mitochondrial membrane. As electrons move down the chain, energy is generated to actively pump hydrogen ions into the intramembranous space. This builds up an electrochemical gradient, where hydrogens will flow back into the matrix through ATP synthase - forming ATP. Electrons exit the chain and team up with oxygen and hydrogen forming water.
User JiamincJ wrote in about gene regulation, asking for a recap of eukaryotes specifically. Eukaryotic gene expression involves many steps, and almost all of them can be regulated. Different genes are regulated at different points, but it is most common at the transcription level. Some chromatin is more tightly wrapped around histones, making the genes inaccessible. Specific transcription factor proteins can bind to genes - actively promoting or repressing transcription through their interaction with RNA polymerase. Let’s assume the mRNA transcript is made - there are multiple levels of regulation there too. You can modify the capping and poly A tail or splice out different introns. And so you can get different transcripts from the same pre-mRNA molecule. Prokaryotes don’t have as many levels of regulation since transcription and translation often occur simultaneously.
Multiple users asked for FRQ practice. I would encourage you to look at the FRQs and scoring guys that have been published by the College Board. More specifically, they have released a 2020 sample that follows the exact formatting you can expect on May 18th. A few last minute tips - read the questions carefully, paying special attention to the action verbs (descrie, explain, justify etc.). You won’t earn points for restating the question nor will you earn this points for factual googled knowledge. Answer the question you know the most about first! There are no rules that you have to go in order. The 2020 exams are designed so that you are also unlikely to finish all parts of every question. (Don’t worry, you can still get a 5, even if you don’t answer each part). Develop your ideas as completely as possible, but avoid repeating the same information. Avoiding using buzz words! Everything you write should have intention and link specifically back to the FRQ prompt.
To recap….Pedigrees show inheritance patterns. Signal transduction involves phosphorylation cascades. Cellular respiration oxidizes glucose to form ATP. Gene regulation occurs throughout the central dogma. And successful FRQ writing involves intentional application of your words.
Good luck on the AP Exam May 18th! Please keep in touch to let us know how it went for you. The APsolute recAP is working on developing other AP content and preparation courses for the summer. Stay tuned!
Today’s Question of the day is about gene regulation.
Question. What is a prokaryote cluster of genes called when it has a single promoter?