Presentation on theme: "RNA Synthesis or “Transcription”"— Presentation transcript:
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 strandLinear not helicalContains uracil instead of thymineCopy of 1 gene, not entire DNA strand (100’s of genes)Formed in nucleus prior to protein synthesisInitially in the nucleus BUT then migrates to cytoplasm via a nuclear pore and eventually attaches to a ribosome
4 TranscriptionThe process by which a gene segment of DNA is copied into a complementary strand of RNAThe type of RNA formed in this way is called messenger RNA or mRNAOccurs 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 togetherRibosomal 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.
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 acidThis group of 3 nucleotides is called a codonThere 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 synthesisThere are 3 “stop” codons that signal the end of protein synthesis.
13 Closer look at tRNAThis molecule “reads” the genetic code on the mRNA molecule and supplies the correct amino acidsOne 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…Homework: Complete part 3 of the notes!