Ribosome 核糖体

1、Just a quick overview of what were going to coverlWhat ribosome is and what its subunits arelThe purpose of ribosomelThe process of protein synthesis, including:lDNA to mRNA (transcription)lmRNA to protein (translation)lInitiationlElongationlEnd of translationJust a quick overview of what were going

2、 to coverlStructures of the two ribosome subunitslThe larger subunitlThe smaller subunitlRNAs relation to their structureWhat is ribosome?lRibosome - protein synthesizer consisting of two subunitslLarger one, “50S”, is upper picture. Smaller is “30S”(They look the same size here because of space res

3、trictions.)50S and 30S?lRelated to their respective sizes. Numbers actually measures of how quickly each subunit sinks to the bottom of a container of liquid when spun in a centrifugelOne subunit smaller than other, but both are larger than average proteinA couple more nifty picturesl50S (left) and

4、30S. This time you can see them from different angles, through different style of pictureSo whats the purpose of ribosome?lRibosome basically a protein factory. Subunits each have role in making of proteinslTo understand exactly what each subunit does, its necessary to walk through protein synthesis

5、 step by stepProtein synthesislProcess starts from DNA through “transcription”l“Translation” is where ribosome comes in. Translation occurs when protein formed from code on mRNAlRibosome carries out the translation of the nucleotide tripletsProtein synthesislChart - visual image of transcription and

6、 translation in protein synthesizinglDNA and RNA have nucleotides that determine kind of proteinl3 nucleotides = 1 amino acid of a proteinRibosome and RNAlmRNA with code for proteins located at 30S subunitltRNAs responsible for carrying amino acids to mRNA. Each tRNA has own nucleotide triplet which

7、 binds to matching triplet on mRNA, ex., tRNA with code AAA (triple adenine) would match up with mRNA that has code UUU (triple uracil)Initiation:The first phase of translationlTranslation begins when mRNA attaches to the 30SltRNA comes and binds to mRNA where nucleotide code matcheslThis triggers 5

8、0S binding to 30S. 50S is where all tRNAs will bind. Now we move on to elongationElongation:The second phaselTwo binding sites on 50S: A site and P site, which aid in continuing translationlFirst tRNA connected at A site. Now moves to P site as another tRNA approacheslSecond tRNA binds to A siteElon

9、gation (continued)lPeptide bond forms between amino acids of tRNAs (methionine and proline)lFirst tRNA now detached from its amino acid, and it leaves ribosome. Second tRNA still has proline and methionine attachedElongation (continued)lThe tRNA left now moves to P site. Ribosome ready to accept ano

10、ther tRNA and continue processlEach tRNA adds another amino acid to growing peptide chain (thus “elongation”)lEventually process has to finish, howeverEnd of translationlRibosome was moving along nucleotide triplets one by onelRibosome reaches “stop codon,” peptide chain finished. Last tRNA leaves r

11、ibosome, leaving behind completed peptide chainEnd of translation (continued)lRibosome separates from mRNAlRibosome subunits also separate, and will remain this way until another mRNA comes along to restart the processStill awake?Its Pop Quiz Time!lHeres a little quiz on what weve covered so far, ju

12、st to keep your brain alert.lFirst questionlWhat are the two subunits of ribosome known as, and which is which?lAnswer: 50S (the larger one) and 30S (the smaller one)Another questionl(This ones multiple choice!)lThe process of converting code on the mRNA into a protein is called?lA. TransitionlB. Tr

13、ansductionlC. TranslationlD. TranscriptionAnd nowlThats the end of the quiz (whew)!lAny questions so far?lOkay, thats taken care of. And now, without further ado, we move on toStructures of the subunitsl50S and 30S besides difference in size, also have somewhat different structureslBoth are rather c

14、omplicated, since theyre much larger than average proteinlWell cover structure of 50S firstThe 50S subunitlThis part of ribosome contains site where new peptide bonds are formed when proteins are synthesizedlmRNA would be located horizontally in groove across middlelTo help with protein synthesis, s

15、ubunit uses adenine RNA nucleotide, shown by green dot in centerThe 50S subunitlThis part of ribosome contains site where new peptide bonds are formed when proteins are synthesizedlmRNA would be located horizontally in groove across middlelTo help with protein synthesis, subunit uses adenine RNA nuc

16、leotide, shown by green dot in centerThe 50S subunitl50S made of two RNA strands: a long one, shown in an orangey color, and shorter one, shown in yellowlBlue things in the picture are a few of many proteins that have bound to ribosomes surfacelMany of proteins have long tails that go inside ribosom

17、e and keep the RNA strands in placeA bit more on 50Sl50S is quite rigid, folded and packed so well that its virtually immobile within its structurelContrasts with structure of 30S, which well now move toThe 30S subunitlUnlike 50S, 30S is fairly flexiblelIt needs to have movable regions because, when

18、 it shifts from one mRNA nucleotide triplet to another, movement is necessary to aid this processl30S controls flow of information during protein synthesisThe 30S subunitl30S finds an mRNA and then makes sure that each tRNA is matched up correctly on mRNAlIts been suggested that mRNA enters through

19、small hole in 30S (shown here in center of left side)The 30S subunitl30S finds an mRNA and then makes sure that each tRNA is matched up correctly on mRNAlIts been suggested that mRNA enters through small hole in 30S (shown here in center of left side)The 30S subunitlmRNA then extends up into the pla

20、ce where translation occurs, located in cleft between top part, “head”, and bottom part, “body”Structure and RNAlRecently discovered - about two-thirds of ribosomes mass made up of RNAlMost important functions of ribosome performed by RNA. This has been found because of atomic knowledge of structure

21、s of 50S and 30S and their assemblage into 70S(One might logically think it to be 80S, but it really isnt)ConcludinglAlthough a good amount of progress has been made in figuring out structures of 50S and 30S, there is probably still a lot that hasnt been deciphered yetlIts somewhat difficult to find

22、 out structures because, as mentioned earlier, theyre relatively large. Hopefully more will be discovered about them in the futureGuess whatIts Quiz Time again!lThis is the last one, I promise. Its a piece of cake anywaywell, if you were paying attention, that is.lRibosome is primarily made up of?lA. DNAlB. RNAlC. ProteinslGlad thats over, huh? Now to summarize what we coveredTo summarizelRib