1. Topic 8 From Gene …to Protein Biology 1001 October 17, 2005

2. IIIA. Details of Transcription 5’- GCCAGGCTAAACTA -3’DNA coding strand 3’- CGGTCCGATTTGAT -5’DNA template strand 5’- GCCAGG …-3’RNA synthesis 3’- CGGTCCGATTTGAT -5’ 5’- GCCAGGCUAAACUA -3’ messenger RNA (mRNA)  RNA is similar to DNA except that it is always single-stranded, the sugar has a 2’-OH group, and the nitrogenous bases are A, C, G, & Uracil  Messenger RNA is transcribed or “copied” from a DNA template according to the base pairing rules, except that U pairs with A  The mRNA sequence is the same as the DNA coding strand sequence, except that there are Us instead of As

3. Figure 17.7 -Transcription has three stages initiation, elongation and termination

4. IIIB. Translation – the Basic Concept  Translation is the synthesis of a polypeptide under the direction of the mRNA  The nucleotide sequence of the mRNA is converted to the amino acid sequence of a polypeptide  The site at which this occurs is in the cell is the ribosome  Amino acids are carried to the growing polypeptide chain by tRNA molecules Figure 17.13

5. Figure 17.14 – The structure of transfer RNA Figure 17.16 – The anatomy of a ribosome

6. IIIC. Features of Gene Expression in Eukaryotes  Transcription occurs in the nucleus, translation in the cytoplasm  Transcription initially results in a pre-mRNA or primary transcript which undergoes RNA processing before being translated  The ribosomal subunits (rRNA & proteins) are assembled in the nucleolus Figure 17.26

7. IV. The Genetic Code  Four nucleotides need to specify 20 amino acids, so the genetic code is a triplet code  4 1 = 4, 4 2 = 16, 4 3 = 64  A codon is a sequence of three nucleotides that specifies a particular amino acid; 3 of the 64 possible codons function as stop signals and one (AUG) codes for the amino acid methionine & functions as a start signal  The code is read from the mRNA which is transcribed from the template strand of DNA  The code is degenerate – it is redundant but not ambiguous  The sequence needs to be read in non-overlapping tandem groups of three and in the correct reading frame  The code is nearly universal

8. IV. The Genetic Code Figure 17.4 Figure 17.5

9. V. The Effect of Mutation on Protein Function Mutation – a change in the genetic material Point mutation – a change in just one nucleotide (base) pair A substitution of one nucleotide pair for another produces silent, missense, or nonsense mutations An indel (insertion or deletion of a base pair) produces a frameshift mutation Mutations are either spontaneous errors during DNA replication or caused by mutagens – physical or chemical agents that interact with and damage DNA  Egs. Physical – UV, X-rays  Egs. Chemical – base analogs, intercalating agentsbase analogsintercalating agents

10. Figure 17.24 Base-pair substitution Silent

11. Review Videos of Transcription and Translation (These animations are intended to aid your conceptual understanding. I won’t test you on the content unless I mentioned it elsewhere in Topic 8)