What do cells consist of?

Cells consist of many components. The plasma membrane, a continuous double layer of phospholipid molecules, constitutes the boundary between the cell and its external environment. In addition to lipids, the plasma membrane has protein components. The structure as a whole is selective permeable. The plasma membrane contains receptors that selectively receive nerve and hormone signals and transmit them to the interior of the cell. Direct cell-to-cell interactions can occur through specialized regions of plasma membrane known as junctions.

Exterior to the plasma membrane of most plant and bacteria is a cell wall, a cell product made largely complex of polysaccharides. The cytoplasm is the water-rich matrix within a cell that contains and surrounds the other cellular contents. Nucleus is the membrane-bounded structures contained within the cytoplasm of eucaryotes are referred to as organelles. DNA, combined with protein, is organized inside the nucleus into structural units called chromosomes, which usually occur in identical pairs. Genes contain the coded instructions for the assembly of polypeptides and larger proteins. The nucleus is surrounded by an envelope of two concentric membranes. The nucleus also contains a specialized region, the nucleolus, where nucleoprotein particles are assembled

What are ribosomes?

Ribosomes are the "factories" where the instructions encoded in the DNA of the nucleus are translated to make proteins. Among the other membranous structures are extensive membrane systems that make up the smooth and rough endoplasmic reticulum. The rough endoplasmic reticulum is one of the sites of protein synthesis in the cytoplasm. Similar in appearance to and perhaps continuous with the endoplasmic reticulum is a region of smooth, stacked membranous sacks known as Golgi apparatus. The apparatus modifies proteins after they are synthesized and packaged on the rough endoplasmic reticulum-by linking them with sugars or other molecules.

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What are cells composed of?	\|	What are lysosomes? What are mitochondria?

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