thank you okay so for today's lesson what we're going to be looking at is uh we are covering RNA which is the libel nucleic acids now if you remember DNA nucleotides are monomers and when they're joined together they make the polymer known as DNA right so um it's the same for armanas what do I mean by that what I mean by that is how many nucleotides which are monomers so let's look at RNA nucleotides how many nucleotides um over here if you remember the pentose sugar is called a ribose sugar where at Carbon number two they have the oh groups and there are four types of bases in RNA nucleotides adenine guanine cytosine all unicel they don't have thymine and they also have the phosphate groups each of them have different which have labeled in green so RNA nucleotides when they are joined together they will become the polymer known as RNA ribonucleic acid it's as simple as that so A molecule of RNA is usually a single stranded nucleic acid made up of RNA nucleotides and the Albany nucleotides are joined together by phosphodiester bonds which I've labeled over there for you now what we have to look at is the three types of RNA that can exist the first type of RNA that can exist is known as the messenger RNA also known as the MRNA in the exam you can just use the word mRNA it's fine small Amia by the way small M and uppercase rnas um you don't have to write out the whole entire sentence uh you don't have to write out the whole messenger RNA that's fine and just like the DNA they do have some similarities in which they have the five Prime to three Prime with the exception that RNA is single standard DNA is double standard and the nuclei the RNA nucleotides are joined together by phosphodiester bonds generally speaking messenger rnas are linear shaped and here's where it becomes important every triplet or three bases on the Mr and a are referred to as something called as a codon okay now what do I mean by that let's just throw it out again as you can see here I'm highlighting every three bases on the MRNA and each of the triplet base refers to as one codon now why is this important we will talk about we will explain that later but what we have to know now is every three bases on the MRNA equals to one codon that's basically it the number of codons can be variable in the MRNA in this case the MRNA has six codons because it has 18 bases in total so as a question if an mRNA has 210 nucleotides which is 210 bases then how many codons are there well one codon equals to three bases so 210 bases divided by 3 will equal to 70 codons that's just basically it now the second type of RNA that we're going to be looking at is something called Transfer RNA now if we were to draw out the linear shape of Transfer RNA you will notice something very interesting it looks quite similar to mRNA but at the three prime end which I've highlighted the bases are fixed the bases are c c and a now some students may be wondering do I need to memorize that um I don't think you have to actually memorize that if you want to go for it but that is not the important part I mean that's not the important part of the transfer RNA so the difference between mRNA and TRNA is the fact that the transfer RNA can fold within itself okay and what do I mean by that the changes basically false and forms a kind of 3D structure you can still see the CCA all right if you notice I'm also highlighting a green color area three bases in the green color area I'll explain why that is so now this three-dimensional shape is quite confusing so what we do is we like to represent trnas in a two-dimensional drawing and that two-dimensional drawing is the one that you'll often see in the textbook five primantly Prime still made up of a single chain all right and you can still see the base CCA at the end of the three prime and we will call this shape the Clover shape why is it a clover because it looks a bit like a four leaf clover right which is which is a particular type of plant it's a very unique leaf so the part where I've highlighted in green are referred to as something called anticodons now in mRNA they can have many codons but in TRNA it only has one anticodon now some students will be like hey but there are so many other bases you did not highlight I don't care okay in TRNA they only have one anticodon which is that very particular specific triplet base that I've highlighted in green again I've also labeled that for you so that is important to know and their significance will be important later and another very important thing to also know about trnas are they can fold within themselves by forming hydrogen bonds so if I zoom in into this TRNA and if I put BC on one side the other side it forms a complementary base spelling with guanin okay within its own Chain by the way and it has three hydrogen bonds if one side has adenine the other side has uracil so just like polypeptide chains can fold within themselves are trns can also fold within themselves as well so if cgas on one side gcus on the other side and if uug is on one side AAC is on the other side and they form hydrogen bonds now another very important thing to also know is at the pre-prime end where the base CCA is located they will the TRNA will attach to a a specific amino acid more to be elaborated on that later but for now this is just what you have to know about the structure of the TRNA molecule I will not talk about the functions yet and last but not least the third type of rnas referred to as ribosomal RNA still a single chain made up of RNA nucleotides joined together by phosphodiester bonds and their function is very simple you have one rrna which is the longer one and another rrna at the bottom which is the shorter one they both coil within themselves and form a 3D structure add together some proteins and what do you get you get a ribosome because if you remember when we looked at chapter one and when we described the structure of the ribosome the ribosome is actually made up of rrnas and proteins joined together and the ribosome has two parts a small subunit and a large subunit the large subunit is made up of a longer rrna and the shorter ribosome is made up of sorry the smaller subunit is made up of the uh shorter rrna enzyme proteins as well so if a question were to ask you what is the ribosome made out of you just have to say rrnas and some proteins do you have to know the names of the proteins no you don't have to that's basically it