in this video we're going to talk about transcription and translation and here is just a basic overview of these two processes transcription is the process by which dna gets converted into mrna also known as messenger rna and translation is the process of converting the information stored in messenger rna and using it to build a protein now if you recall which organ now is used to make proteins what would you say the answer is the ribosome the ribosome is the site at which proteins are manufactured in the cell so we're going to talk about that shortly but let's go over transcription first before we talk about translation transcription occurs in three steps initiation elongation and termination now during initiation rna polymerase binds to the promoter region of dna now what is the promoter region the promoter region is basically a short sequence of dna and eukaryotic dna it's t a t a double a also known as the tata box now this sequence is located 25 nucleotides upstream of the site where transcription begins the next thing that rna polymerase does is it causes the two dna strands to separate and during elongation it begins to add nucleotides to the growing mrna strand that we see here thus rna polymerase synthesizes mrna starting from the five prime end going to the three prime end however rna polymerase it reads the dna strand in the three to the five prime direction now there's two strands that you need to be familiar with the first one the one that's used to synthesize mrna is called the template strand or the anti-sense strand so that's the one in which rna polymerase is active upon the other one which is not used this is called the non-template strand also known as the sense strand some textbooks will call it the coding strand because its sequence matches up with rna except the fact that uracil is found in rna but thymine is found in dna now during the last step of transcription which is the termination step the rna polymerase molecule the mrna strand they all separate from the dna template strand now in this step the poly a polymerase enzyme it caps the three end of the mrna strand and this is known as the poly a tail now also during the beginning of transcription the five end is also capped and the reason for this is to protect the mrna strand from being degraded by certain enzymes at the end of the termination step during transcription dna has been used to create a pre messenger rna strand now this particular strand has something known as introns and exons introns are basically longer sequences of nucleotides that do not code for anything so these they must be removed in a process known as rna splicing now the exons those are shorter sequences of nucleotides and they're going to be used to synthesize proteins and so the exons remain but the introns they must be removed and so now we have a completed messenger rna strand now let's work on a practice problem let's say if you're given a sequence of nucleotides on a dna strand and you're asked to write the correspondence sequence on an mrna strand what would it be feel free to pause the video and try it so if we're reading the dna strand from the three to five direction we're gonna have to write the corresponding mrna sequence in the five to three direction so what letter corresponds to g it's important to know that g always corresponds to c and vice versa c corresponds to g now what letter corresponds to a a usually corresponds to t but there's no t in rna instead a is going to correspond to u for uracil but t in dna corresponds to a in rna and so if we continue everything else is going to be u c a u a u g c and so this is the mrna strand that corresponds to the nucleotide sequence in dna listed above now let's talk about translation which is the process of taking the information stored on an mrna strand and using it to construct a protein so once the mrna strand is synthesized in the nucleus it leaves the nucleus and enters the cytosol where it interacts with a free ribosome or one that is attached to the rough er now within the ribosome it's going to interact with a trna molecule or a transfer rna molecule now let's focus on the sequence of nucleotides on the mrna strand notice that they're separated in sets of three each set of three nucleotides represents a codon which matches up with another three nucleotides on the trna molecule known as an anticodon and each codon matches up with a specific amino acid and so that's how the information stored in the mrna strand can be used to construct a specific protein we're going to talk more about this later in this video translation like transcription occurs in three steps initiation elongation and termination so here in this picture we have a ribosome which is composed of two subunits the small subunit and the large subunit and the ribosome has three active sites the e site the p site and the a site now during initiation we have the start codon a u g which corresponds to the anticodon uac now that particular trna molecule has the methionine amino acid attached to it and this trna molecule it enters the ribosome at the p site also known as the peptidocyte where the peptide bonds are formed now during the second step of translation that is during elongation another trna molecule enters the a site so i'm just gonna draw it here and during that process a covalent bond will form between the two amino acids that we see here highlighted by the red circles now as the process continues the trna molecule in the p site will move to the e site and as it does so it's going to lose an amino acid and so what's going to happen is we're going to have a growing chain of amino acids that will leave or extend out of the ribosome so make sure you understand that that the trna molecules they enter the a site and then they exit from the east site and in the process the amino acids are being joined together so over time this polypeptide chain is going to grow creating a protein the last step of translation the termination step begins when a stop codon is read now there are three stop codons that you need to be familiar with the first one is uaa and then the second one is uag and the third one is u g a now these stop codons also known as nonsense codons they don't code for any specific trna molecule instead when these are read at the a site they cause a release factor to enter the a site which causes the small and a large ribosomal subunits to basically disassemble so this is where translation ends and the protein it leaves the ribosome where it eventually goes to the goji body for further processing and modification at the golgi body the proteins undergo folding where they form a specific shape to perform a specific function and that's basically it for this video hopefully it gave you a good overview of transcription and translation so that's all i got thanks for watching