AP BIOLOGY

Detailed explanation-1: -Ribosomes engaged in the synthesis of proteins that are destined for secretion are then targeted to the endoplasmic reticulum by a signal sequence at the amino terminus of the growing polypeptide chain.

Detailed explanation-2: -Synthesis of new proteins starts in the nucleus, where ribosomes get their instruction to begin the process. Sections of DNA (genes), encoding a specific protein, are copied over to messenger RNA (mRNA) strands in a process called transcription.

Detailed explanation-3: -The ribosomes, found within the rough endoplasmic reticulum or floating in the cytoplasm, are the main site of protein synthesis. The ribosome reads the mRNA and tRNA molecules add amino acid molecules, building chains of amino acid molecules called polypeptide chains.

Detailed explanation-4: -Most of the enzymes are protein molecules and are synthesized on the ribosomes.

Detailed explanation-5: -Therefore, rough ER is prominent in liver cells that secrete serum albumin, cells of the digestive system that secrete enzymes, endocrine cells that synthesize and secrete protein hormones (such as insulin) and in cells that create the proteins of the extracellular matrix.