1. ONE GENE – ONE POLYPEPTIDE HYPOTHESIS  It is known that genes control the synthesis of all proteins. Some proteins are enzymes, some are hormones.  As we know that, proteins are made up of polypetides- long chains of amino acids. Some proteins consist of two or more polypeptides linked and twisted around each other. Ex: hemoglobin

2. ONE GENE – ONE POLYPEPTIDE HYPOTHESIS It was found that the synthesis of each polypeptide is controlled by a different gene. Because of this fact, the one gene – one enzyme hypothesis was changed to one gene – one polypeptide hypothesis.

3. THE DNA CODE  There are 20 amino acids in the proteins of human. Therefore, there must be at least 20 different code to specify these amino acids.  There are 4 types of nucleotides in DNA to form the genetic code; Adenine (A) Guanine (G) Cytosine (C) Thymine (T)

4. THE DNA CODE using a two-letter code 4 2 = 16 different 2 letter code sequences can be madeand this is not enough. using a three-letter code 4 3 =64 different 3 – base sequences can bemade – more than needed. Each group of three bases on themRNA that specifies an amino acid iscalled a codon.

6. TYPES OF RNA: Messenger RNA (mRNA): It is found in cell nucleus. It is synthesized on DNA byRNA polymerase enzyme. This process iscalled transcription ( = the copying of a genetic message into a molecule of mRNA)  mRNA carries the genetic code (information) that is needed to sytnhesize apolypetide molecule from DNA to ribosome.

7. Each group of three bases on the mRNA thatspecifies an amino acid is called a codon. 1 codon Codes for the addition of 1amino acid to the polypeptidechain AUG Beginning codone UAA UGA UAG Stop codones

8. Transfer RNA (tRNA): It carries the amino acids from the cytoplasm to theribosomes.  Each tRNA is specific for an amino acid. So at least 20 different tRNA molecules must bepresent in the cells.  Anticodon is complement of a mRNA codon that is, tRNA anticodon binds with thespecific codon on the mRNA during proteinsynthesis.

9.  The codon, which anticodon matches,is the one thatspecifies the aminoacid that each tRNAcarries.  Thus, tRNA is a device for bringinga certain amino acidto a certain placespecified by mRNA.

12. Ribosomal RNA (rRNA):  It is formed in the nucleoli of the cell.  Ribosome is where a polypeptide is assembled during protein synthesis.  A ribosome consist of protein and rRNA. Ribosomal protein is synthesized in thecytoplasm and travels to nucleus. In the nucleolithe protein and the rRNA join to formribosomes. 60% rRNA + 40% protein ribosome

13. Ribosomal RNA

14. PROTEIN SYNTHESIS Some of the materials that are used inprotein synthesis are; DNA RNA Amino acids Ribosomes Enzymes ATP Some ions

15. During protein synthesis, a copy of thegene on a DNA that contains theinformation for building a po l ypeptide is built into an RNA molecule, which then carriesthe information to the ribosomes whereprot e ins are synthesized from the amino acid building blocks. PROTEIN SYNTHESIS

17. Protein synthesis has two phases: 1. Transcription in which the information onDNA is copied intomRNA 2. Translationin which themRNA molecule isused to arrangeamino acids withinthe polypeptide

18. Sites of Protein Synthesis  In prokaryotes transcription andtranslation takesplace in thecytoplasm.  While transcription continues,translation beginson the ribosomes.

19. Sites of Protein Synthesis  In eukaryotes transcription takesplace in the nucleus(also in mitochondriaand chloroplasts).  mRNA then moves to the cytoplasm throughthe nuclear pores andtranslation takes placein the cytoplasm.

20.  The first step in directing protein synthesis is to copy the DNA code for a polypeptide into amolecule of RNA. To copy the code, DNAstrands separate for a short time and serve astemplate for RNA.  The copying of a genetic message into a mRNA molecule is called transcription. 1. Transcription

21. Some of the Materials Used in Transcription MaterialWhat the material does Template strand of DNAProvides recipe for building the mRNA RNA nucleotidesBuilding blocks of RNA RNA polymeraseEnzyme that promotes construction of mRNA ATPProvides energy for forming bonds between RNA nucleotides

22. At the attachment site of the enzymeRNA polymerase, the DNA opens up, and as the RNApolymerase moves along the DNA molecule, the twostrands of the molecule separate.

23. Nucleotide building blocks are assembled into RNA in5 ' to 3 ' direction as the enzyme reads the template DNA strand in a 3 ' to 5‘ direction.

24. Note that the RNAstrand iscomplementary –notidentical- to thetemplate strand fromwhich it is transcribed;it is sequence ishowever, identical tothat of the inactive(untranscribed) DNAstrand, except for thereplacement ofthymine (T) by uracil(U).

25. A) Initiation 2. TransLATION B) ElongationC) Termination AUG UAA UGA UAG

26. Some of the Materials Used in Translation MaterialWhat material does RibosomeHolds and orients materials, promotes the formation of bonds between amino acids Amino acidsBuilding blocks of proteins mRNAProvides instructions for linking a.a into protein tRNABrings a.a to the ribosome and lines them up according to the information on mRNA EnzymesBind materials to the ribosome; bind a.a to the tRNA; initiate translation ATPProvides energy for the reactions

28. A) Initiation:

29. B) Elongation:

31. C) Termination:When the ribosome reaches a termination (stop) codonthe polypeptide is cleaved from the last tRNA is released fromthe P site. (UAA, UGA, UAG) @

34. Overview of transcription and translation

35.  The information flows from DNA to RNA to protein.  Replication of the DNA occurs only once in each cell cycle, during the S phase prior to mitosis or meiosis.  Transcription and translation, however, occur repeatedly throughout the interphase portion of the cellcycle.