PDQ PHYSIOLOGY excretory vesicles L )=c Nucleolus ∴O 1-1 Elements of a typical n is the pathway of protein synthesis destination which can be membrane, or an exocytotic vesicle. ansfers occur by successive formation, delivery, and reception of transport vesicles Nuclear membrane. This is a double layer of phospholipids. The space between the layers is contiguous with the rough endoplasmic reticulum (see Figure 1-1),and the inner and outer membranes fuse together at various points and form nuclear pores, whose diameter(30 to 100 nm) permits unhindered exchange of ions, mRNA, ribosomes, and small proteins(up to 5 kilodaltons [kDa)) Nucleolus. The nucleoli, more than one of which may be present within a nucleus, consist of ribosomal rna and are the loci of rna processing and ribosome synthesis. They are not surrounded by a membrane Chromatin. This is a specific arrangement of DNA and the protein family called histones in approximately equal proportions. Its physical rrangement is in repeating units of one DNA molecule and eight histone molecules. It exists, for much of the cell cycle, as long, loosely coiled strands but condenses at cyclic intervals into well-defined chromosomes. These are the functional subunits of chromatinNuclear membrane. This is a double layer of phospholipids. The space between the layers is contiguous with the rough endoplasmic reticulum (see Figure 1–1), and the inner and outer membranes fuse together at various points and form nuclear pores, whose diameter (30 to 100 nm) permits unhindered exchange of ions, mRNA, ribosomes, and small proteins (up to 5 kilodaltons [kDa]). Nucleolus. The nucleoli, more than one of which may be present within a nucleus, consist of ribosomal RNA and are the loci of RNA processing and ribosome synthesis. They are not surrounded by a membrane. Chromatin. This is a specific arrangement of DNA and the protein family called histones in approximately equal proportions. Its physical arrangement is in repeating units of one DNA molecule and eight histone molecules. It exists, for much of the cell cycle, as long, loosely coiled strands but condenses at cyclic intervals into well-defined chromosomes. These are the functional subunits of chromatin. 2 PDQ PHYSIOLOGY Golgi apparatus Rough endoplasmic reticulum Nucleolus Nucleus Mitochondrion Smooth endoplasmic reticulum Peroxisome Lysosome Lysosome Ciliae Secretory vesicles cis trans Figure 1–1 Elements of a typical human cell. Also shown is the pathway of protein synthesis from rough endoplasmic reticulum to cis-Golgi, to medial Golgi, to trans-Golgi and from there to its final destination, which can be a lysosome, the plasma membrane, or an exocytotic vesicle. These transfers occur by successive formation, delivery, and reception of transport vesicles