Cell Biology PDF

cell What Is Biochemistry? Biochemistry is the scientific discipline that seeks to explain life at the molecular level. It uses the tools and terminology of chemistry to describe the various attributes of living organisms. Biochemistry offers answers to such fundamental questions as “Wha...

cell What Is Biochemistry? Biochemistry is the scientific discipline that seeks to explain life at the molecular level. It uses the tools and terminology of chemistry to describe the various attributes of living organisms. Biochemistry offers answers to such fundamental questions as “What are we made of?” and “How do we work?”  Biochemistry is also a practical science: It generates powerful techniques that underlie advances in other fields, such as genetics, cell biology, and immunology; it offers insights into the treatment of diseases such as cancer and diabetes; and it improves the efficiency of industries such as wastewater treatment, food production, and drug manufacturing.  Biochemistry focuses on the structures and functions of molecules. Interactions between molecules give rise to higher-order structures (for example, organelles), which may themselves be components of larger entities, leading ultimately to the entire organism.  Membranes All cells—and the various compartments inside eukaryotic cells are surrounded by membranes. Without membranes, a cell would be unable to retain essential resources. To begin to understand how membranes work, we will examine them as composite structures containing both lipids and proteins. The lipids that occur in biological membranes aggregate to form sheets that are impermeable to ions and other solutes. The key to this behavior is the hydrophobicity of the lipid molecules. Signal The nervous system works closely with the endocrine system to regulate an animal's internal physiological functions. The endocrine system is an interacting set of secretory cells, glands, and organs in different body regions that communicate using chemical signals. It responds to signals sent from the nervous system and blood-borne signals from other organs to regulate internal bodily functions.  The signals communicated by the nervous and endocrine systems differ greatly in their modes of transmission and in the times over which they act. The nervous system sends signals rapidly by action potentials running along nerve axons, and adjacent nerve cells communicate by means of neurotransmitters. In contrast, cells and glands of the endocrine system secrete chemical signals called hormones, which influence the actions of other cells in the body.  Whereas most hormones are released into the bloodstream, some others act locally. Circulating throughout the body, these hormones can influence distant target cells. As a result, endocrine communication is generally slower and more prolonged than the rapid and brief signals transmitted by nerve cells. Hormones bind to receptors on or in target cells.  Once bound, each hormone exerts a specific effect on those cells. Hormonal signals are amplified in a series of steps so that even a small amount of hormone can have dramatic effects on the body. Hormones can be grouped into two general classes: hydrophilic molecules, which cannot diffuse across the cell membrane, and hydrophobic molecules, which can. The hydrophilic hormones are peptide hormones and amine hormones, and the hydrophobic hormones are steroid hormones.