AP BIOLOGY

Detailed explanation-1: -The genes that encode ribosomal proteins are transcribed outside of the nucleolus by RNA polymerase II, yielding mRNAs that are translated on cytoplasmic ribosomes. The ribosomal proteins are then transported from the cytoplasm to the nucleolus, where they are assembled with rRNAs to form preribosomal particles.

Detailed explanation-2: -rough endoplasmic reticulum (RER), series of connected flattened sacs, part of a continuous membrane organelle within the cytoplasm of eukaryotic cells, that plays a central role in the synthesis of proteins.

Detailed explanation-3: -Proteins are made at the ribosome. In the cytoplasm, ribosomes attach to messenger RNA (mRNA). They read the nucleotides in groups of three called codons. Each codon codes for a specific amino acid.

Detailed explanation-4: -Proteins synthesized by the rough ER include the prominent milk protein casein, and whey proteins. These proteins are packaged into secretory vesicles or large micelles and travel through the Golgi network before fusing with the plasma membrane, releasing their contents into milk ducts.

Detailed explanation-5: -Plasma membrane and lysosomal proteins also travel from the rough ER to the Golgi and then to their final destinations. Still other proteins travel through the initial steps of the secretory pathway but are then retained and function within either the ER or the Golgi apparatus.