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RNA Synthesis or “Transcription”

RNA Synthesis or “Transcription”. Used in the process of protein synthesis!. RNA ( Ribonucleic acid). RNA is the nucleic acid that acts as a messenger between DNA and the ribosomes and carries out the process by which proteins are made from amino acids. How RNA is Different from DNA.

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RNA Synthesis or “Transcription”

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  1. RNA Synthesis or “Transcription” Used in the process of protein synthesis!

  2. RNA (Ribonucleic acid) • RNA is the nucleic acid that acts as a messenger between DNA and the ribosomes and carries out the process by which proteins are made from amino acids

  3. How RNA is Different from DNA • Single strand • Linear not helical • Contains uracil instead of thymine • Copy of 1 gene, not entire DNA strand (100’s of genes) • Formed in nucleus prior to protein synthesis • Initially in the nucleus BUT then migrates to cytoplasm via a nuclear pore and eventually attaches to a ribosome

  4. Transcription • The process by which a gene segment of DNA is copied into a complementary strand of RNA • The type of RNA formed in this way is called messenger RNA or mRNA • Occurs so that the information to make a protein can be taken from the nucleus to the ribosome where protein synthesis occurs

  5. There are two other types of RNA: • Transfer RNA (tRNA): carries amino acids (the building blocks of proteins) to the ribosome where they can be bonded together • Ribosomal RNA (rRNA) : small organelle (the ribosome) is made of this kind of rRNA and proteins. The ribosome supplies the site where the reaction to link amino acids together occurs.

  6. Lets take a closer look at the steps to make mRNA or transcription: • The enzyme RNA polymerase attaches to the DNA strand and unzips it at the gene to be copied - “unzipping” means that the H-bonds between nitrogenous bases are broken

  7. RNA nucleotides base pair with the exposed bases of the gene being copied - since 2 sides of the DNA strand are exposed, the side being copied is called the “sense” side, while the other uncopied side is called the “missense” side.

  8. Sugar-phosphate bonds form between RNA nucleotides • Hydrogen bonds break and mRNA is free to leave the nucleus (through a pore) and attach to ribosome in the cytoplasm (protein used in cell) or on RER (proteins used outside cell)

  9. Finally, the H-bonds reform between the DNA strands and the strands rezip. • http://www.youtube.com/watch?v=ztPkv7wc3yU&feature=related

  10. A sequence… • Can refer to either the order the nitrogenous bases come in on a DNA strand or mRNA strand OR the order of the amino acids in a polypeptide chain.

  11. The sequence of nitrogenous bases on an mRNA strand is read in a specific way… • Each group of 3 nucleotides codes for one amino acid • This group of 3 nucleotides is called a codon • There are 20 different amino acids that the bases code for

  12. Since there are 64 possible combinations of 3 nucleotides, each amino acid is coded for by more than one codon! • AUG is the “start” codon as it shows the ribosome where to start protein synthesis • There are 3 “stop” codons that signal the end of protein synthesis.

  13. Closer look at tRNA • This molecule “reads” the genetic code on the mRNA molecule and supplies the correct amino acids • One end holds the amino acid, the other contains the “anticodon” that matches up with the codon on the mRNA strand

  14. Anticodon… • Each tRNA molecule contains 3 nucleotides on one end • These nucleotides base pair with a codon on mRNA, ensuring that the appropriate amino acid is added to the polypeptide chain

  15. Practice! • Go to this site and play a couple of the games to practice the steps we’ve learned about DNA replication and protein synthesis so far… • http://mrhartog.blogspot.com/2009/01/transcription-game-httpwww.html • Homework: Complete part 3 of the notes!

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