*2.3.1 Cleavage of signal peptides*

In most cases, the signal peptide is cleaved from the nascent polypeptide chain upon leaving the endoplasmic reticulum by a protease (signal peptidase) located on the inner surface of the membrane. The cleavage usually occurs in the C-terminal region, which allows further processes such as folding and assembly of the protein [46].

#### *2.3.2 Protein folding and assembly*

In order to have a three-dimensional structure and function, all proteins must undergo protein folding. With few exceptions, protein folding and assembly occur in the lumen of the endoplasmic reticulum and contribute to protein stability and efficient

#### **Figure 4.**

*Synthesis of fatty acids and oils in intracellular organelles during the seed filling period after fertilization. 1: FAD enzymes, 2: hydroxylase enzymes, 3: elongase complex enzymes, FAD: fatty acid desaturases, Glc-6-P: glucose-6 phosphate, PEP: phosphoenol pyruvate, OAA: oxaloacetate, ACP: acyl carrier protein, CoA: coenzyme A, FAT: fatty acyl thioesterase [1].*

transport [1, 45–49]. Many plant vacuolar proteins, including storage proteins are oligomers, most of which are oligomerized in the endoplasmic reticulum. Chaperone proteins in the endoplasmic reticulum promote proper folding of polypeptides, and protein disulfide isomerase (PDI) forms disulfide bonds within and/or between peptides using the -SH groups of cysteines. The function of chaperones depends on their ability to recognize a variety of nascent polypeptides that do not share unique similarities, while accurately discriminating between properly folded and unfolded structures [50].
