Ch. 14 RNA & Protein Synthesis DNA - Deoxy - ribonucleic Acid - Double - stranded - A, G, C, T( thymine) - A - T, C - G - 1 type - Deoxyribose sugar (missing an oxygen RNA - Ribonucleic Acid - Single stranded - A, G, C, U (Uracil) - A - G, C - G - 3 types (mRNA, tRNA, rRNA) - Ribose sugar( no missing oxygen) 3 types of RNA 1) mRNA (messenger RNA) - Copy the genetic information of DNA and carries to ribosome 2) tRNA ( transfer RNA) - Transfer amino acid to make proteins 3) rRNA (ribosomal RNA) - Make up ribosomes 1.Transcription ( DNA - mRNA) - DNA is copied into RNA because DNA cannot leave the nucleus - Occurs inside the nucleus Steps of Transcription 1) DNA molecule unwinds by the helicase( enzyme) 2) An enzyme called RNA polymerase makes mRNA, a copy of DNA, using the base - pairing rule 3) mRNA leaves the nucleus and travels to the ribosome for protein synthesis 2. mRNA modification - Occurs before mRNA leaves the nucleus after transcription - During the transcription, introns are cleaved and removed, while exons combine to form useful mRNA . ONly exons exit the nucleus - I nitial mRNA - introns (noncoding region = junk DNA) cleaved - exons (coding region = code for AA) combine - final mRNA. 3. Translation / Protein Synthesis (mRNA -> Protein) - Translate the DNA codes on mRNA to make protein - Occurs in ribosomes - Each protein is made up of amino acids - mRNA is translated in base triplets called codon which represents an amino acid ( 3 nitrogen bases on mRNA ( 1 codon) = 1 amino acid - Use genetic code table to determine which amino acid each codon represents Steps of Translation 1) mRNA leaves nucleus and travels to ribosome 2) tRNA carries its specific amino acid and arrives at the ribosome when mRNA contains a START codon (AUG) 3) tRNA’s anticodon base - pair with mRNA’s codon and releases its amino acid 4) Amino acids form peptide bonds to combine 5) tRNs continue moving down the mRNA strand and transferring amino acids until STOP codon is reached 6) Ribosome releases mRNA and the protein is also released. Anticodon Vs. Codon - tRNA has anticodon that matches codon on mRNA Analogy ( Transcription and Translation) - DNA = Original text - RNA = an image captured on the negative - tRNA = a photograph of the original text - Protein = text in new language Genetic Code - All living things have same genetic code - Ex: ACC in human codes for same amino acid as in ACC in you dog or an oak tree - Different DNA sequence -> different a.a sequence -> distinct protein - The presence / absence of different proteins determines the physical traits of a living things Why can a codon not be one or two nitrogen bases long? - Not enough combinations to convert all 20 amino acids - 1 nitrogen bases long = 4^1 = 4 amino acids - 2 nitrogen bases long = 4^2 = 16 amino acids - 3 nitrogen bases long = 4^3 = 64 amino acids - Having more than one codons (especially the this letter of a codon) for each amino acid minimized a mistake in transcription/ translation Function of Proteins 1) Transport (hemoglobin) 2) Internal define (immunological protein such as antibodies) 3) Catalysts( enzymes) 4) Structural (collagen in skin, hair) 5) Regulation ( hormones) 6) Movement (muscles, cytoskeleton) Protein Folding - Amino acid sequence determines how proteins fold because of some a.a. Are attracted to each other and some repel - How proteins get folded determine its 3-D shape and its function Mutation - Any change in DNA sequence - m utations in reproductive cells are inheritable, but mutations in body cells are not - Must mutations - harmful because changes to the DNA sequence can change the amino acid sequence - A mutation may change the way the protein folds due to a change in amino acid sequence, and prevent it from carrying out its usual function - Occasionally, a mutation can be beneficial. - The mutation may produce a new or more efficient protein that improve the survival of the organism ( bacteria and viruses) What causes mutation? mutagens! - Radiation (UV, nuclear, gamma, X- rays), chemicals, high temperature
