It’s the battle of the nucleic acids in Episode 32! DNA may have all the information, but RNA does all the work.
It’s the battle of the nucleic acids in Episode 32! DNA may have all the information, but RNA does all the work. DNA and RNA are made of nucleotide monomers (1:05). DNA and RNA nucleotides differ in their pentose sugar (1:55) and pyrimidine base ( 3:00). DNA forms an antiparallel double helix (3:50) compared to the single strand RNA (5:05), forming mRNA, rRNA and tRNA.
The Question of the Day asks (6:44) “Nucleic acids are one of two biological molecules that contain the element nitrogen. What is the other?”
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Hi and welcome to the APsolute Recap: Biology Edition.
Today’s episode will recap DNA vs. RNA
Lets Zoom out:
Unit 6 - Gene Expression and Regulation
Topic - 6.1
Big Idea: Information Storage and Transmission
Genetic information is transmitted from one generation to the next through DNA or RNA. Each is a nucleic acid polymer made of nucleotide monomers. This episode will compare and contrast the two polymers in structure, location and function.
Let the battle begin.
Lets Zoom in:
First - structure. Both DNA and RNA are made of nucleotide monomers. A nucleotide is made of a phosphate group, sugar and nitrogenous base joined by covalent bonds. Imagine their arrangement like a typical drawing a toddler would make - where the sugar is a house, the phosphate above the house is the sun, and the nitrogenous base next to the house is the garage.
The nucleotide sugar is a pentose ring, five sided, with each carbon designated as 1’, 2’ and so on. This numbering of carbons on the pentose rings gives DNA directionality. This will be important when discussing orientation during processes such as replication, transcription and translation. The difference between DNA and RNA sugars occurs at the 2’ carbon. RNA has ribose, which contains a hydroxyl group (or -OH) at the 2’ carbon. DNA has deoxyribose, which is missing the oxygen at the 2’ carbon. Get it? De-oxy. Scientists are not too creative when naming molecules - which does help when it comes to understanding the properties of each.
The nucleotide phosphate group (PO4) is covalently bound to the 5’ carbon of the pentose sugar within a nucleotide and to the 3’ carbon of an adjacent nucleotide. Alternating sugars and phosphates form the backbone of each nucleic acid. The phosphate group has a negative charge - which is why DNA samples migrate toward the cathode side during electrophoresis. Phosphate groups are the same in RNA and DNA
The last part of a nucleotide is the nitrogenous base which encodes the genetic information. The nitrogenous base is arranged perpendicular to the backbone and covalently bonded to the pentose sugar at the 1’ carbon. There are five different types of nitrogenous bases grouped into two categories. The purines are double ringed nitrogenous bases - and include Guanine and Adenine. These are found in both DNA and RNA molecules. The pyrimidines are single ringed nitrogenous bases and include cytosine, thymine and uracil. Cytosine is common to both nucleic acids, whereas Thymine is only in DNA and Uracil is only in RNA. This is why you have to “swap” out base pairs during the process of transcription from DNA to mRNA. Adenine will always bond with Thymine or Uracil with two hydrogen bonds and Guanine will always bond with Cytosine with three hydrogen bonds. Listen to episode 17 for a purine/pyrimidine memory hack.
Location location location. Nucleus vs. Cytoplasm. DNA forms an antiparallel double helix, that coils and condenses into chromosomes when preparing for cellular division.
In a ladder analogy, the sugars and phosphates form the sides while the nitrogenous bases face inwards (the rungs of the ladder) and join through hydrogen bonds. DNA wraps around proteins called histones much like beads on a string. This loosest form is referred to as chromatin and is found during most of the cell cycle. Histone condensing as well as methylation strongly coorleate to gene expression and epigenetics. You need to be able to access the nitrogenous bases and the information they contain in order to transcribe and translate - kind of hard to do if DNA remains tightly coiled. Prokaryotes typically have circular chromosomes in the cytoplasm while eukaryotic organisms typically have multiple linear chromosomes in a nucleus. The mapped organization of eukaryotic chromosomes is called a karyotype. These diagrams group homologous pairs by size and banding pattern. Both prokaryotes and eukaryotes can also contain plasmids - small extra chromosomal DNA molecules that serve a variety of functions for the cell.
In contrast, RNA typically forms a single helix. But this is an oversimplification. While DNA is all comfy and protected in the nucleus - RNA is out there in the cytoplasm doing the grunt work - in three forms. mRNA or messenger RNA is a single strand produced by RNA polymerase during the process of transcription. It is a short piece of genetic information, that is spliced, capped and tailed on its way out of a nuclear pore. mRNA transcripts do not have a long shelf life. rRNA, or ribosomal RNA is larger and composed of two subunits. The mRNA transcript is thread though the ribosomal halves for translation. It looks like a hamburger - with mRNA as the burger and rRNA as the bun. rRNA reads the mRNA transcript in codons, three base pairs at a time. Ribosomes are so important in their role of producing proteins that they can be found in all cells - either in the cytoplasm or studded on the Endoplasmic reticulum (hence - rough ER). Finally tRNA, or transfer RNA. tRNA is conveniently shaped like a T, with an amino acid at one end and an anticodon at the other. The anticodon will temporarily bind to the mRNA transcript codon within the ribosome. All three types of RNA working together for translation, making our proteins. Listen to Episode 20 on the central Dogma for the full recap.
To recap….
DNA might have the info, but RNA makes it happen. Double helix vs single, deoxyribose vs. ribose, thymine vs uracil.
Today’s Question of the day is about biological molecules.
Question “Nucleic acids are one of two biological molecules that contain the element nitrogen. What is the other?”
Coming up next on the Apsolute RecAP Biology Edition: Biotechnology