Cell Growth and Reproduction, and Protein Synthesis

Cell Growth and Reproduction Cell Life Cycle –Interphase G 1, S, G 2 DNA replication –Mitosis Prophase, Metaphase, Anaphase, Telophase Cytokinesis

Protein Synthesis Role of RNA –mRNA, tRNA, rRNA Transcription –Making mRNA complement –Editing mRNA Translation

DNA Synthesis

General Information One gene-one polypeptide hypothesis –Bridge RNA DNA  RNA  Protein Transcription –Synthesis of RNA under direction of DNA Translation –Actual synthesis of a polypeptide

DNA vs. RNA DNA –Sugar is deoxyribose –Nitrogenous bases A, G, C, and T RNA –Sugar is ribose –Nitrogenous bases A, G, C, and U –3 types mRNA rRNA tRNA

Transcription (Overview) Info is copied from DNA to RNA Copy = protein building instruction –mRNA Occurs in nucleus –mRNA then leaves nuclear envelope

Translation (Overview) Occurs in cytoplasm –On ribosomes Translation of mRNA into amino acid sequence

Triplet Code Gene  Protein based on triplet code Need mRNA first 3 nucleotide bases code for a single amino acid –Called a codon Must be read correctly –Ordering called the reading frame

Transcription RNA polymerase Three steps –Polymerase binding and initiation –Elongation –Termination

Polymerase Binding and Initiation Promoters –Initiation site for transcription Transcription factors –Aids polymerase in finding promoter region Polymerase –Separates two DNA strands

Elongation of RNA strand Polymerase separates double helix –Exposes DNA for transcription Transcription simultaneous

Termination of Transcription Termination site on DNA –RNA strand released –AATAAA site in eukaryotes mRNA editing –Introns must be removed spliceosomes

Translation tRNA –Transfers amino acids to a ribosome –Contains the anticodon –Builds polypeptide codon by codon Occurs on ribosomes –Contains rRNA –P site, A site, E site (not shown in the following pictures)

Translation Three stages –Chain initiation –Chain elongation –Chain termination Energy required for initiation and elongation (GTP)

Initiation mRNA, tRNA, and ribosomes come together GTP required to form initiation complex tRNA goes from A site to P site –A site ready for next tRNA

Elongation Amino acids added one by one Three step cycle –Codon recognition –Peptide bond formation –Translocation

Termination Termination codon –UAA, UAG, UGA Release factor in A site –Bond broken Between tRNA in P site and last amino acid of polypeptide chain –Polypeptide and tRNA free

Functional Protein Polypeptide coils and folds –3-D structure forms Some posttranslational modifications may be required