Gene Expression“The Central Dogma” (transcription) (translation) DNA RNA Protein protein protein Fig.4.5
TRANSCRIPTION Transcription occurs in the nucleus. The genetic code of DNA is transcribed onto mRNA. mRNA enters the cytosol. Fig. 4.7 Fig. 4.10
Translation occurs in the cytosol. mRNA – messenger RNA rRNA – ribosomal RNA tRNA – transfer RNA TRANSLATION Fig. 4.7 Fig. 4.10
TRANSLATION polyribosome in cytosol Fig. 4.9 Fig. 1-21 G translation of secretory or membrane proteins at rough er
Post-translational Modification • occurs in rough ER and Golgi • deletion of amino acids • disulfide bond formation • glycosylation (addition of sugar groups) Fig. 19-4 G e.g., insulin preproinsulin = 130 a.a. proinsulin = 80 a.a. insulin = 51 a.a.
Post-translational Modification Sorting, Packaging, and Secretion Fig. 4.11
Glycosylation • occurs within the lumen of the Golgi (or ER) extracellular fluid cytosol Fig. 3.6 sugar groups on transmembrane glycoprotein Therefore, the sugar groups of glycoproteins and glycolipids are on the extracellular surface of the cell. Fig. 4.11