Everything is connected and the evidence is overwhelming. You are in the Domain Eukarya, Kingdom animalia.
Everything is connected and the evidence is overwhelming. You are in the Domain Eukarya, Kingdom animalia – but the common ancestor of all eukaryotes was the OG with membrane bound organelles (1:02), linear chromosomes (2:47) and genes that contain introns(4:51). Each piece of structural and process evidence on the molecular and cellular level supports the common ancestry of all eukaryotes.
The Question of the Day asks (7:25) Collectively, what is a stack of thylakoids called?
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Hi and welcome to the APsolute RecAP: Biology Edition. Today’s episode will recap common ancestry.
Let’s zoom out:
Unit 7 – Natural Selection
Topic – 7.7
Big idea – Evolution
Your mother was a lobed finned fish! Everybody is descended from somebody, and although it’s been several million years since you shared fish characteristics, there is evidence of common ancestry hidden deep down within every cell structure and molecular process. And not just with fish but with cacti, mushrooms and amoebas too! So more specifically for this episode, your mother was a eukaryote.
Let’s zoom in:
Today we are going to focus primarily on eukaryotes – you remember eukaryotes right? What you don’t? Quick recap – Eukaryotes are organisms found within the domain Eukarya and include the kingdoms of protists, fungi, plants, and animals. Within this broad range of diverse organisms, there are several commonalities. Each are composed of one or more eukaryotic cells, which contain a nucleus and membrane bound organelles. This is in contrast to prokaryotes (domains bacteria and archaea) whose cells lack a nucleus and membrane bound organelles.
Membrane bound organelles! I’m sure you’ve heard that phase so many times that it's almost lost meaning, Which organelles are we referring to exactly? These are the cellular structures which are primarily composed of a phospholipid bilayer, bent and folded into specific shapes for each of their specific functions. From this commonality, we get the “endomembrane system” a fancy term for a group of organelles which can interact seamlessly with the help of vesicles, It includes the endoplasmic reticulum (smooth and rough) and golgi apparatus. You’ll also find the chloroplasts and mitochondria surrounded by membranes, two in fact! Get a refresh on the endosymbiosis theory with episode 34. And the purpose of all these membrane bound organelles? – compartmentalization! Structural and functional cellular evidence provides support for the common ancestry of all eukaryotes.
Next up – the organization of DNA. As previously mentioned – all eukaryotic cells store DNA within the nucleus. Enclosed by a nuclear envelope (or membrane) made of… you guessed it – a bilayer of phospholipids! But it’s not just the location of DNA which unifies all eukaryotes together, its organizational method as well. Eukaryotes contain multiple linear chromosomes of DNA wrapped around histones. These chromosomes range greatly in size and quantity from organism to organism. For example, humans have 46 homologous pairs, dogs 78, fruit fly 8 and the Venus fly trap 32.. No matter the quantity, eukaryotes replicate their DNA during the S phase of the cell cycle using familiar enzymes (topoisomerase, helicase, DNA polymerase etc.) at multiple origin sites. This is in contrast to prokaryotic DNA organization which has a singular circular chromosome with one origin site of replication.
Lastly, what type of information do the genes contain? Well that all depends on which sections are spliced out before expression! Yes, the central dogma is a large piece of molecular evidence for common ancestry. In eukaryotes, the flow of information from DNA, to RNA to proteins occurs distinctly and in separate cellular locations. The pre-mRNA transcript produced in the nucleus contains exons, sections of the genetic code which will be expressed following translation- and introns, interrupting sequences to be removed. One process of gene regulation that occurs within eukaryotes is called alternative splicing. This means that different introns are removed from the mRNA transcript from one gene to the next, resulting in varying protein products from the same genetic code. You won’t find introns in prokaryotes since transcription and translation occur simultaneously with the same mRNA molecule.
Time for unit connections. Unit 2 – Cell structure and function. Don’t you remember that ribosomes are found in all organisms? This greatly reflects the interconnectedness of life. Unit 5 – Heredity. The enduring understanding here is that living things are linked by lines of descent from common ancestors. This is further reinforced since fundamental processes are shared and conserved across the tree of life. We’ve already mentioned this earlier in unit 7, but recall vestigial structures, nucleotide sequences and amino acid sequences – all evidence of common ancestry. Everybody’s using the same genetic code! Ok what about the exam? It is suggested that you practice predicting changes to a system based on a visual, concept, process or model. You’ll want to review phylogenetic trees, character chart tables, and cell structure diagrams as well.
To recap…
Everything is connected and the evidence is overwhelming. You are in the Domain Eukarya, Kingdom animalia – but the common ancestor of all eukaryotes was the OG with membrane bound organelles, linear chromosomes and genes that contain introns. Each piece of structural and process evidence on the molecular and cellular level supports the common ancestry of all eukaryotes.
Coming up next on the Apsolute RecAP Biology Edition – Continuing Evolution
Today’s question of the day is about chloroplasts
Question: Collectively, what is a stack of thylakoids called?