Anatomy & Physiology

Anatomy & Physiology Study Guide The nucleus contains DNA and enzymes essential for controlling cellular activities: • The nucleus is the control center of cellular operations. It is surrounded by a nuclear envelope. • The nucleus controls the cell by directing the synthesis of specific proteins using information stored in chromosomes. The chromosome structure consists of DNA bound to proteins called histones. • The cell’s information storage system is the genetic code. DNA controls protein synthesis, cell structure, and cell function: • Transcription is the production of RNA from a DNA template. After transcription, a strand of messenger RNA (mRNA) carries instructions from the nucleus of the cytoplasm. • The DNA of the nucleus has both direct and indirect control over protein synthesis. Diffusion is a passive transport mechanism facilitating membrane passage: • The permeability of a barrier, such as the plasma membrane, is an indication of the barrier’s effectiveness. Nothing can pass through an impermeable barrier; anything can pass through a freely permeable barrier. Plasma membranes are selectively permeable. • Diffusion is the net movement of material from an area of higher concentration to an area of lower concentration. Diffusion occurs until the concentration gradient is eliminated. • Osmosis is the net flow of water across a membrane in response to differences in osmotic pressure. • Tonicity describes the effects of osmotic solutions on cells. A solution that does not cause an osmotic flow is isotonic. A solution that causes water to flow into a cell is hypotonic. A solution that causes water to flow out of a cell is hypertonic. Carrier-mediated and vesicular transport mechanisms facilitate membrane passage: • Carrier-mediated transport involves the binding and transporting of specific ions by integral proteins. Cotransport moves two substances in the same direction; counter transport moves them in opposite directions. • In facilitated diffusion, compounds are transported across a membrane after binding to a receptor site within the channel of a carrier protein. • In vesicular transport, materials move into or out of the cell in membranous vesicles. Movement into the cell is accomplished through endocytosis. This active process can take three forms: receptor-mediated endocytosis, pinocytosis, or phagocytosis. The ejection of materials from the cytoplasm is accomplished by exocytosis. The transmembrane potential results from the unequal distribution of ions across the plasma membrane: • The potential difference, measured in volts, between the two sides of a plasma membrane is the transmembrane potential. The transmembrane potential is the cell’s resting potential.

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