8.1 Introduction Secreted protein Figure 8. 1 Overview: proteins that are localized post-translationally are sma membrane prote in released into the cytosol after synthesis on free ribosomes. Some have signalS a Coated vesicle transport for targeting to organelles such as th nucleus or mitochondria. Proteins that are localized cotranslationally associate -gOLgi retention signal Cytosolic with the Er membrane during synthesis proteins WER retention signal so their ribosomes are " membrane M itochondrial signa bound". The proteins pass into the ■■■I endoplasmic reticulum, along to the Golgi, and then through the plasma Free" ribosome Membranous membrane, unless they have signals that bosomed cause retention at one of the steps on the pathway. They may also be directed Nuclear signal to other organelles, such as endosomes or lysosomes 请莘大 I Post-translational transport Co-translational transport E:aFigure 8.1 Overview: proteins that are localized post-translationally are released into the cytosol after synthesis on free ribosomes. Some have signals for targeting to organelles such as the nucleus or mitochondria. Proteins that are localized cotranslationally associate with the ER membrane during synthesis, so their ribosomes are "membrane￾bound". The proteins pass into the endoplasmic reticulum, along to the Golgi, and then through the plasma membrane, unless they have signals that cause retention at one of the steps on the pathway. They may also be directed to other organelles, such as endosomes or lysosomes. 8.1 Introduction