Episode 81 will recap multiple topics - it’ our third Listener’s Choice Episode. Cladograms are branching diagrams that show common ancestry among groups of organisms.
Episode 81 will recap multiple topics - it’ our third Listener’s Choice Episode. Cladograms are branching diagrams that show common ancestry among groups of organisms. (0:46) Cellular respiration and photosynthesis are energy conversion processes - focus on what goes in, what comes out, where, and why. (2:07) Cell signaling involves reception, transduction and response. (3:22) DNA replication is semiconservative and involves several enzymes. (5:38) And the central dogma has information flow from DNA to RNA to protein. (7:05)
The Question of the Day asks (9:13) Which DNA strand is synthesized faster - leading or lagging?
Thank you for listening to The APsolute RecAP: Biology Edition!
(AP is a registered trademark of the College Board and is not affiliated with The APsolute RecAP. Copyright 2021 - The APsolute RecAP, LLC. All rights reserved.)
Website:
EMAIL:
Follow Us:
Hi and welcome to the APsolute Recap: Biology Edition. Today’s episode will recap multiple topics - it’ our third Listener’s Choice Episode.
Zoom out:
There are alot of topics to review today! Thanks to our Instagram followers who wrote in with requests. We are going to recap cladograms, gene expression, cell signaling, cellular respiration, photosynthesis, and DNA replication.
Let’s Zoom in:
First topic request comes from listener Samantha - who wants to know a few tips on constructing cladograms. This is found in Unit 7 Natural Selection. A cladogram is a branching diagram that attempts to show evolutionary relationships between organisms. They are not ALL ENCOMPASSING, meaning they can only be constructed based on available data presented. Cladograms show ancestral relationships, with the branching point or node of separation representing the most recent common ancestor. Organisms adjacent and connected to the same node are often called sister taxa. Be careful, just because two organisms are physically adjacent on a diagram, does not mean they are more closely related. Follow the lines back to a node - where two connect, you have a common ancestor, shared derived characteristics, and relatedness. All nodes can pivot, which can cause the organisms on top of it to swap places on the chart. If tasked to create a cladogram, always start with the least related organism first (has the least amount of + signs in a character table, or greatest differences in amino acids etc.). This is your outgroup or basal taxa. Then, see if you can cluster other organisms in the table by most similarities.
Cellular Respiration and photosynthesis can be very overwhelming processes to digest - and listener Siddhant B would like a breakdown. First of all - deep breath. You do not need to know every step of each process in great detail. Focus on what goes in, what comes out and what each molecule's role is in the process. It is likely that the college board would even provide you with simplified diagrams of each process for you to apply your knowledge to. Also, find the commonalities to each process - they are essentially bookends or mirror images of the same energy transduction story. Light energy is captured, transferred through ATP and NADPH and stored in sugars during photosynthesis. Energy is released from sugar, transferred through NADH and FADH2 and stored as ATP in cellular respiration. Water splits to donate electrons to the ETC in thylakoid membranes whereas electrons leaving the ETC in the cristae join with oxygen and hydrogen to form water. Carbon dioxide enters the calvin cycle and is reduced into sugars whereas pyruvate is gradually oxidized in the Krebs cycle, with carbon dioxide released.
Listener Alanna B wants a recap of cell signaling. Three steps: Reception, transduction, response. Ligands (the signaling molecules) bind to an extracellular receptor if polar, large or charged and an intracellular receptor if nonpolar and small. Ligands binding to receptors is often temporary, and can be triggered to dissociate with the end of a signal transduction pathway. Many signal transduction pathways include protein modification and phosphorylation cascades. The phosphate added to the process will typically come from a molecule of ATP, temporarily activating each protein in the pathway. Signals are often amplified (or turned up) 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 cyclic AMP or calcium. Lastly, response. Possibilities are endless but some examples include cell growth, secretion of molecules, gene expression or function. This could ultimately modify the physical expression, phenotype, or even end in apoptosis, programmed cell death.
Diana R would like a review of DNA Replication, so let’s go through the enzymes. First - Topoisomerase. This enzymes relaxes the DNA supercoiling so that hydrogen bonds are more easily accessible. Next, the enzyme helicase separates the DNA strands, breaking the hydrogen bonds between nitrogenous base pairs and forming a replication fork. Now that the nitrogenous bases are exposed, semi-conservative replication can begin. A short RNA primer is added to the template strands - indicating and supplying a replication starting point for our next enzyme, DNA polymerase. DNA polymerase reads the template strand 3’ to 5’ direction and synthesizes the new strand 5’ to 3’, laying down new complementary nucleotides and proofreading its own work as it goes! On the leading strand, this synthesis is continuous in one piece as DNA polymerase follows in the same direction that helicase unwinds. But remember - DNA strands are antiparallel. So DNA polymerase is synthesizing away from the direction of helicase on the lagging strand in Okazaki fragments. The last enzyme is ligase which seals any gaps left behind by the now removed RNA primers and ensures that fragments are joined on the lagging strand.
Lastly, gene expression - a recap request by listener Zarin M. Time for the CENTRAL DOGMA! DNA, transcribed into mRNA, and translated into protein. RNA polymerase reads the gene 3’ to 5’ and synthesizes an mRNA strand 5’ to 3’. The mRNA transcript is produced following Chargaff’s rules of complementary base pairs with one exception. Guanine is still complementary to Cytosine, but there is no Thymine in a molecule of RNA. Adenine will instead pair with a different pyrimidine, called Uracil.
If this transcription is for a prokaryote, translation occurs simultaneously. In eukaryotes, there’s a bit of processing that occurs. mRNA gets a 3’ polyA tail, 5’ mG cap and introns are removed. Out to a ribosome for translation. In short, rRNA (or ribosomal RNA) reads three nucleotides of mRNA at a time, called codons. These codons correlate to one specific amino acid, which is brought over by tRNA. For example the mRNA codon UCG encodes for the amino acid Serine. This amino acid, among others, is then transferred to the growing polypeptide chain and the process is continued until a stop codon is reached. Don’t worry, the codon chart is provided for you with the question on the exam.
To recap……
Cladograms are branching diagrams that show common ancestry among groups of organisms. Cellular respiration and photosynthesis are energy conversion processes - focus on what goes in, what comes out, where, and why. Cell signaling involves reception, transduction and response. DNA replication is semiconservative and involves several enzymes. And the central dogma has information flow from DNA to RNA to protein.
Coming up next on the Apsolute RecAP Biology Edition: Our final episode of season 2! Testing Strategies
Today’s question of the day is about DNA Replication.
Question of the day: Which DNA strand is synthesized faster - leading or lagging?