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The Human Cell

The Human Cell

Cells are the very essence of life. Cells may be defined as the basic living, structural, and functional units of the human body. They vary greatly in size, chemical composition, and function, but each one is a remarkable miniaturization of human life. Cells move, grow, ingest food and excrete wastes, react to their environment, and even reproduce. This chapter provides a brief review of the basics of a cell, including cellular components, communication, energy, and transport. An overview of the natural life span of a typical cell is provided because of its importance in nutrition and disease.
The Human Cell

multicellular organisms

Cells of all multicellular organisms are called eukaryotic cells (from the Greek eu, meaning “true,” and karyon, “nucleus”). Eukaryotic cells evolved from simpler, more primitive cells called prokaryotic cells (from the Greek meaning “before nucleus”).The major distinguishing feature between the two cell types is that eukaryotic cells possess a defined nucleus, whereas prokary-otic cells do not. Also, eukaryotic cells are larger and much more complex structurally and functionally than their ancestors.

cell specialization

Specialization among cells is a necessity for the living, breathing human, but cells in general have certain basic similarities. All human cells have a plasma membrane and a nucleus (or have had a nucleus), and most contain an endoplasmic reticulum, Golgi apparatus, and mitochondria. Considering the relationship between the normal functioning of a typical cell and the health of the total organism the human being brings to mind the old rule: “A chain is only as strong as its weakest link.”

Components/Parts of the human cell

Cell membrane or plasma membrane

Cells are surrounded by a phospholipid bilayer that contains embedded proteins, carbohydrates, and lipids. Membrane proteins act as receptors sensitive to external stimuli and channels that regulate the movement of substances into and out of the cell

Golgi apparatus

The Golgi apparatus is a series of membrane sacks that process and package proteins after they leave the rough endoplasmic reticulum.

Lysosome

Contains digestive enzymes that break up proteins, lipids, and nucleic acids. They also remove and recycle waste products.

Cytoplasm

The cytoplasm is the gel-like substance inside cells. Cytoplasm contains cell organelles, protein, electrolytes, and other molecules.

Nucleus

The nucleus contains the DNA in the cell. Molecules of DNA provide coded instructions used for protein synthesis.

Mitochondrion

Organelles that produce most of the energy (ATP) used by cells.

Rough endoplasmic reticulum

A series of membrane sacks that contain ribosomes that build and process proteins.

Smooth endoplasmic reticulum

Region of the endoplasmic reticulum involved in lipid synthesis. Smooth endoplasmic reticula do not have ribosomes and are not involved in protein synthesis.

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