this video is about protein synthesis which uses a sequence of nucleotides to build polypeptides or proteins in a cell this is a key process that occurs in most cell types the topics in this key Concepts video are the role of DNA in protein synthesis transcription or building messenger RNA from a DNA template the role of RNA in Translation and the process of translation which is building a polypep tide using messenger RNA as a template these key concepts are some of the most important topics covered in the IB Biology course you may have heard the concept that DNA is the code of life the reason we say this is because DNA determines the cell structure and function by controlling the production of a vast array of proteins there are thousands of different types of proteins that have structural roles such as collagen in the skin and proteins that have functional roles like en enzymes such as lipases controlling metabolism or proteins involved in cell signaling such as neurotransmitters DNA codes for polypeptide chains that fold into proteins genes are specific sections of DNA that encode the information needed to produce polypeptides the building blocks of proteins however within a cell not all genes are actively utilized or expressed at all times some genes remain silenced meaning their information is not transcribed and translated into proteins this control over transcription initiation is a powerful means of determining which proteins are synthesized and which remain silent within the cell in order to maintain the structure and function of a protein it is essential the order of the DNA nucleotides is not altered when alterations occur in the DNA sequence a phenomenon known as a mutation arises mutations can lead to significant changes in the resulting structure and function of a protein in some cases a mutation might result in a protein with impaired function or no function at all alternatively IM mutation can lead to the creation of a protein with an entirely different function from its original intended role these changes in protein function due to mutations can have diverse effects on cellular processes potentially impacting an organism's Health development and ability to adapt to its environment DNA is protected from mutation in many ways some of the structural Protections in DNA is that it's double stranded which stabilizes the molecule DNA is also protected by the nuclear membrane isolating it from the metabolic activity in the cytool of the cell as well as DNA being wrapped around histone proteins DNA is also protected from mutagens and carcinogens that cause changes to DNA Through Repair mechanisms that can correct changes to DNA sequences so now that we understand the role of DNA let's see how a strand of messenger RNA is synthesized during transcription during transcription only the gene or specific section of DNA that contains the information needed to code for a particular polypeptide that will fold into a protein is transcribed into messenger RNA this ensures that only the relevant genetic instructions are transcribed and subsequently translated into a functional protein the non-coding region of DNA are not transcribed during this process transcription is the process by which an RNA molecule specifically messenger RNA or mRNA is synthesized using a DNA template it serves as a crucial bridge between the genetic information encoded in DNA and the actual synthesis of proteins during transcription the DNA sequence is transcribed into messenger RNA preserving the genetic code and enabling it to be trans transported from the nucleus to the ribosomes where translation occurs RNA polymerase is the enzyme responsible for catalyzing transcription it binds to the initiation point of a DNA segment that encodes a polypeptide then unwinds the DNA Helix to expose the template strand during this process RNA polymerases adds RNA nucleotides to the growing strand according to the complimentary base rule guanine and cytosine and Adine and uel connecting the paired bases via hydrogen bonds it's important to note that uel substitutes thyine during RNA synthesis this pairing involves hydrogen bonds Au forms two while GC forms three ensuring accurate complementary pairing between bases as RNA polymerase moves down the RNA it links RNA nucleotides together with calent bonds once the MRNA seg is transcribed it undergoes modifications and exits the nucleus through a nuclear pore to enter the cytoplasm so far we have seen RNA function as messenger RNA in the role of transcription in that form messenger RNA is long and linear whose function it is to carry the order of bases from DNA however RNA takes several different forms in the process of translation the first is R RNA or ribosomal RNA R RNA is a component of the ribosome which consists of a small and large subunit the third type of RNA is Transfer RNA or t RNA Transfer RNA is composed of an RNA strand coiled in on itself with three nucleo tide bases exposed at one end an amino acid attached at the other end the three bases that are exposed are called an anti-codon and are specific to the amino acid for instance this TR has three bases UAC which means it has the amino acid methionin or met attached to it if the three bases are GAA it will have the amino acid Lucine or L attached to it in the first stage of translation the MRNA attaches to the small subunit of a ribosome the large subunit will then attach which has binding sites for TRNA the MRNA is read in triplets or codon the first codon is a u so the complimentary bases on the TRNA or anti-codon would be UAC notice that the amino acid met is attached at the top the next codon on the MRNA is gu and the anti-codon on the TRNA must be c a notice that the amino acid attached to the TRNA is Val when when two molecules of TRNA are situated next to each other in the ribosome the ribosome will catalyze a calent peptide bond to form between them this is the start of the polypeptide chain when the ribosome moves down the first amino acid detaches from the first TRNA and that TRNA will leave the ribosome the ribosome moves down the length of messenger RNA one codon at a time leaving space for another molecule of TRNA to enter as this piece of TRNA enters the TRNA anti-codon will pair with the messenger RNA codon to bring the specific amino acid a peptide bond forms between amino acids and the polypeptide chain elongates this process continues until the polypeptide chain is complete the end of the polypeptide chain is signaled by a stop codon which leads to the release of the polypeptide now the free polypeptide is able to fold into a protein or be processed further in the endoplasmic reticulum in this video we saw how DNA codes for proteins by having a particular order of nucleotide bases which forms a template for messenger RNA we saw that transcription is the process of using DNA as a template to create a strand of mRNA using complimentary base pairing rules RNA polymerase catalyzes transcription by unwinding the DNA Helix and forming calent bonds between mRNA nucleotides finally we looked at translation the process of building a polypeptide we saw how this occurs at the ribosome where the triplet code in mRNA or codons is red and amino acids are added to the growing polypeptide chain one amino acid at a time