Unit 3.1: Protein Synthesis DNA  RNA  Protein

1. Unit 3.1: Protein SynthesisDNA  RNA  Protein

2. Vocabulary: Transcription: DNA  mRNA; process in which a small section of DNA is copied onto a messenger RNA molecule. Translation: mRNA  protein; process in which the codons on an mRNA molecule are translated into amino acids. Codon: a three-nucleotide sequence that codes for a particular amino acid; found on mRNA Anticodon: a three-nucleotide sequence that is complementary to a codon; found on tRNA mRNA: “messenger” RNA; carries a copy of the DNA transcript from the nucleus to the cytoplasm rRNA: “ribosomal” RNA; makes the subunits of a ribosome tRNA: “transfer” RNA; brings amino acids to ribosome where they join to become a protein

3. I. Structure of Nucleic Acids • Discovery of DNA’s structure: • Rosalind Franklin: made X-ray crystallography images of DNA - 1953 • James Watson, Francis Crick interpreted R. Franklin’s image to decode structure of DNA - 1953

4. Structure of DNA: • DNA isa double helix, a twisted ‘ladder’ • Sides of ladder: sugar (deoxyribose); phosphate groups • Rungs of ladder: nitrogenous bases held together by hydrogen bonds • Purines: Adenine, Guanine • Double-ring bases • Pyrimidines: Thymine, Cytosine • Single-ring bases

5. Purines: G, A Pyrimidines: C,T • Chargaff’s Base-Pairing Rules: • Erwin Chargaff found that in any sample of DNA, the amount of guanine always equaled the amount of cytosine, and the amount of adenine always equaled the amount of thymine • %G = %C and %A = %T • G always pairs with C • Forms 3 hydrogen bonds • G ≠T, bonds don’t match • A always pairs with T • Forms 2 hydrogen bonds • A ≠ C, bonds don’t match • A purine always pairs with a pyrimidine • Keeps “rungs” same size • If 2 purines, too wide • If 2 pyrimidines, too narrow

6. Structure of RNA: • Differs from DNA in 3 ways: • Single-stranded: one-half of a ladder, one-half of a zipper • Sugar is Ribose, not Deoxyribose • Uses uracil in place of thymine • A with U; G with C • Like a disposable copy of DNA

7. II. Protein Synthesis • DNA is a “recipe” for how to make a protein. But the monomers of DNA are _______________, and the monomers of proteins are _______ _____; so how can one “code” for the other? • Codon: 3 nucleotide bases that code for a particular amino acid • So DNA code is a recipe written with three letter words (codons): • Ex: the big dog ate his fat cat and ran

8. Codons are universal: all life on Earth uses the same code • Ex: the codon for threonine is ACG whether you are bacteria, plant, animal, or virus • (This is evidence that all life evolved from a single life form.) • 64 possible combinations!: • Different codons can code for same amino acid, but one codon cannot code 2 different amino acids • Ex: AGU = Serine; AGC also = Serine; but AGC ≠ Leucine

9. Amino Acids are based on the CODONS of mRNA, not the anticodons of tRNA!

10. 3 Types of RNA required: • messenger RNA (mRNA): • Carries copy of DNA from nucleus to cytoplasm • ribosomal RNA (rRNA): • Makes up the two subunits of ribosomes • transfer RNA (tRNA): • Bring amino acids to the ribosome where they form peptide bonds

11. transfer RNA (tRNA): carries amino acids to the ribosome according to the mRNA code • messenger RNA (mRNA): a copy of the DNA message, made in the nucleus ribosomal RNA (rRNA): makes up the two subunits of a ribosome

12. Transcription: DNA  mRNA • Occurs in nucleus in eukaryotes • Part of one DNA strand is “written across” (transcribed) to mRNA • “trans-” = across; “script-” = to write • mRNA serves as a “messenger”; carries a copy of the DNA message to a ribosome in the cytoplasm • If DNA is the cookbook that stays in the cupboard (nucleus), mRNA is a “recipe card” that goes to the mixer (ribosome)

13. Base-pairing rules define the mRNA sequence: • DNA ‘G’ pairs up with ‘C’ on mRNA strand • DNA ‘C’ pairs up with ‘G’ on mRNA strand • DNA ‘T’ pairs up with ‘A’ on mRNA strand, • But DNA ‘A’ pairs up with ‘U’ on mRNA strand b/c there is no ‘T’ in RNA • Ex: DNA ‘GCT’ = mRNA codon of ‘CGA’ • Ex: DNA ‘TCA’ = mRNA codon of ‘AGU’ • if DNA is: CGT ATT GCT GCA CAA TTG mRNA: ___ ___ ___ ___ ___ ___

14. Translation: mRNA  Protein • Occurs on ribosomes in cytoplasm, ER • mRNA transcript is “translated” into a protein • mRNA binds to ribosome • tRNA brings amino acids to ribosome: • Anticodons on tRNA match up to codon on mRNA • Protein elongates until a “stop” codon is reached • When “stop” codon is reached, protein is complete and is released from the ribosome.

15. GGC CAG UGA AUG AUC UAC Met Pro Val Thr Tyr If mRNA is AUG CCG GUC ACU UAC UAG then tRNA is

16. Warm-up answers for this unit: