PDQ PHYSIOLOGY lined cisternae. It is a polarized structure, with a cis side close to the rough ER(see Figure 1-1)and a trans side at the distal end from the rough ER The sacs lying between the cis and trans sacs are termed medial golgi. The cis-Golgi receives transport vesicles from the rough ER, and the trans-Golgi releases other vesicles to their final destination(see Figure 1-1) The Golgi apparatus is a major site of membrane formation. It is here that proteins are modified, sorted, and accumulated in distinct vesicles whose ultimate destination is the plasma membrane, lysosomes, or exocy totic storage granules. Lysosomes are membrane lined and assume a variety of shapes. Primary lysosomes have just budded off from the Golgi apparatus and tend to be herical. They are filled with enzymes that are capable of digesting pro- teins, carbohydrates, lipids, nucleic acids, and other biologic material. Their digestive function follows fusion with vesicles that have enclosed the target Peroxisomes Peroxisomes resemble lysosomes in structure(single phospholipid bilayer membrane)but differ in their point of origin(they bud off the smooth ER) and they contain mostly the peroxidases and hydrolases that are required for metabolism of free oxygen radicals or the oxidation of lipids, amino acids, ethanol, and so on. Mitochondria These are elongated structures, surrounded by two phospholipid bilayers that generally do not touch( Figure 1-3). Their number in a cell is closely corre- 一 L5 Figure 1-2 Ribosomes are the sites of protein assembly ( translation) in accordance with the print camied from nuclear DNA by mRNA. Amino acid constituents of the protein the 3'end of the mRNA. When a protein molecule has been assembled, the two subunits oflined cisternae. It is a polarized structure, with a cis side close to the rough ER (see Figure 1–1) and a trans side at the distal end from the rough ER. The sacs lying between the cis and trans sacs are termed medial Golgi. The cis-Golgi receives transport vesicles from the rough ER, and the trans-Golgi releases other vesicles to their final destination (see Figure 1–1). The Golgi apparatus is a major site of membrane formation. It is here that proteins are modified, sorted, and accumulated in distinct vesicles whose ultimate destination is the plasma membrane, lysosomes, or exocy￾totic storage granules. Lysosomes Lysosomes are membrane lined and assume a variety of shapes. Primary lysosomes have just budded off from the Golgi apparatus and tend to be spherical. They are filled with enzymes that are capable of digesting pro￾teins, carbohydrates, lipids, nucleic acids, and other biologic material. Their digestive function follows fusion with vesicles that have enclosed the target. Peroxisomes Peroxisomes resemble lysosomes in structure (single phospholipid bilayer membrane) but differ in their point of origin (they bud off the smooth ER), and they contain mostly the peroxidases and hydrolases that are required for metabolism of free oxygen radicals or the oxidation of lipids, amino acids, ethanol, and so on. Mitochondria These are elongated structures, surrounded by two phospholipid bilayers that generally do not touch (Figure 1–3). Their number in a cell is closely corre- 4 PDQ PHYSIOLOGY AA4 AA2 AA1 A G C U GC UUU A A A C A G G U C U U U AA A AA3 tRNA for AA1 is leaving AA4 + tRNA are arriving Ribosome A G C UUU U G C AAA A C G C UG U U U AAA Ribosome AA1 AA2 AA4 AA3 AA5 AA6 AA7 AA8 AA9 3' 5' 3' 5' movement of ribosome assembled and growing protein mRNA Figure 1–2 Ribosomes are the sites of protein assembly (translation) in accordance with the blueprint carried from nuclear DNA by mRNA. Amino acid constituents of the protein are selected by the appropriateness of the base coding carried by the attached transfer RNA (tRNA). After each amino acid is joined to the preceding one the ribosome advances one codon toward the 3 end of the mRNA. When a protein molecule has been assembled, the two subunits of the ribosome dissociate.