Essentials of Anatomy & Physiology   3/e   Seeley/Stephens/Tate
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• Cells are highly organized units composed of living material.
• The nucleus contains genetic material, and cytoplasm is living material outside the nucleus.

Cell Membrane

• The cell membrane forms the outer boundary of the cell. It determines what enters and leaves the cell.
• The cell membrane is composed of a double layer of lipid molecules in which proteins float. The proteins function as membrane channels, carrier molecules, receptor molecules, enzymes, and structural components of the membrane.

Nucleus

• The nuclear envelope consists of two separate membranes with nuclear pores.
• DNA and associated proteins are found inside the nucleus as chromatin. DNA is the hereditary material of the cell and controls the activities of the cell.

Nucleoli and Ribosomes

• Nucleoli consist of RNA and proteins and are the sites of ribosomal subunit assembly.
• Ribosomes are the sites of protein synthesis.

Rough and Smooth Endoplasmic Reticulum

• Rough ER is ER with ribosomes attached. It is a major site of protein synthesis.
• Smooth ER does not have ribosomes attached and is a major site of lipid synthesis.

The Golgi Apparatus

• The Golgi apparatus is a series of closely packed membrane sacs that function to collect, modify, package, and distribute proteins and lipids produced by the ER.

Secretory Vesicles

• Secretory vesicles are membrane-bound sacs that carry substances from the Golgi apparatus to the cell membrane, where the vesicle contents are released.

Lysosomes

• Membrane-bound sacs containing enzymes are called lysosomes. Within the cell the lysosomes break down phagocytized material.

Mitochondria

• Mitochondria are the major sites of ATP production, which cells use as an energy source. Mitochondria carry out aerobic respiration (requires oxygen).

Cytoskeleton

• The cytoskeleton supports the cytoplasm and organelles and is involved with cell movements.
• The cytoskeleton is composed of microtubules, microfilaments, and intermediate filaments.

Cilia, Flagella, and Microvilli

• Cilia move substances over the surface of cells.
• Flagella are much longer than cilia and propel sperm cells.
• Microvilli increase the surface area of cells and aid in absorption.

Whole-Cell Activity

• The interactions between organelles must be considered for cell function to be fully understood.

Movement Through the Cell Membrane

• Lipid-soluble molecules pass through the cell membrane readily by dissolving in the lipid portion of the membrane.
• Small molecules can pass through membrane channels.
• Large molecules that are not lipid-soluble can be transported through the membrane by carrier molecules.
• Large molecules that are not lipid-soluble, particles, and cells can be transported across the membrane by vesicles.

Diffusion

• Diffusion is the movement of a solute from an area of higher concentration to an area of lower concentration within a solvent. At equilibrium, there is a uniform distribution of molecules.
• For a given distance, a concentration gradient is equal to the higher concentration minus the lower concentration of a solute in a solution.

Osmosis

• Osmosis is the diffusion of a solvent (water) across a selectively permeable membrane.
• Osmotic pressure is a measure of the tendency of water to move across the selectively permeable membrane.
• In a hypotonic solution, cells swell (and can undergo lysis); in an isotonic solution, cells neither swell nor shrink; and in a hypertonic solution, cells shrink and undergo crenation.

Filtration

• Filtration is the passage of a solution through a partition in response to a pressure difference. Some materials in the solution do not pass through the partition.

Mediated Transport Mechanisms

• Mediated transport is the movement of a substance across a membrane by means of a carrier molecule. The substances transported tend to be large, water-soluble molecules.
• Facilitated diffusion moves substances from a higher to a lower concentration and does not require energy in the form of ATP.
• Active transport can move substances from a lower to a higher concentration and requires ATP. An exchange pump is an active transport mechanism that moves two substances in opposite directions across the cell membrane.
• Secondary active-transport uses the power of one substance moving down its concentration gradient to move another substance into the cell.

Endocytosis and Exocytosis

• Endocytosis is the movement of materials into cells by the formation of a vesicle. Phagocytosis is the movement of solid material into cells by the formation of a vesicle. Pinocytosis is similar to phagocytosis, except that the material ingested is much smaller and is in solution.
• Exocytosis is the secretion of materials from cells by vesicle formation.

Cell Metabolism

• Aerobic respiration requires oxygen and produces carbon dioxide, water, and 36 to 38 ATP molecules from a molecule of glucose.
• Anaerobic respiration does not require oxygen and produces lactic acid and two ATP molecules from a molecule of glucose.

Protein Synthesis

• Cell activity is regulated by enzymes (proteins), and DNA controls enzyme production.

Transcription

• During transcription, the sequence of nucleotides in DNA (a gene) determines the sequence of nucleotides in mRNA; the mRNA moves through the nuclear pores to ribosomes.

Translation

• During translation the sequence of codons in mRNA is used at ribosomes to produce proteins. Anticodons of tRNA bind to the codons of mRNA, and the amino acids carried by tRNA are joined to form a protein.

Cell Division

Mitosis

• Cell division that occurs by mitosis produces new cells for growth and tissue repair.
• DNA replicates during interphase, the time between cell division.
• Mitosis is divided into four stages:
• Prophase-Each chromosome consists of two chromatids joined at the centromere.
• Metaphase-Chromosomes align at the center of the cell.
• Anaphase-Chromatids separate at the centromere and migrate to opposite poles.
• Telophase-The two new nuclei assume their normal structure, and cell division is completed, producing two new daughter cells.

Meiosis

• Meiosis results in the formation of gametes (sperm cells or oocytes). Gametes have half the number (haploid number) of chromosomes that other (diploid) body cells do.
• There are two cell divisions in meiosis. Each division has four stages similar to those in mitosis.
• During meiosis the processes of crossing over within tetrads and random distribution of chromosomes increase genetic variability.

Differentiation

• Differentiation, the process by which cells develop specialized structures and functions, results from the selective activation and inactivation of DNA.

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