Introduction
1. Stem cells are unspecialized cells that have the ability to replicate themselves and generate specialized cells.
2. The interaction and number of cells is important to the organism. 2.1 The Components of Cells
1. Biologists recognize three broad varieties, or domains, of cells based on cellular complexity. The three domains are the Eubacteria (the more common forms of bacteria), the Archaea (the extreme bacteria), and the Eukarya (higher cells).
2. The Archaea and Eubacteria are similar in that they are single-celled organisms, but they differ in certain features of their RNA and membranes. These cells lack nuclei and other organelles and therefore are categorized as prokaryotes.
3. Eukaryotic cells are complex, with abundant and diverse organelles that compartmentalize biochemical reactions. Human cells are therefore eukaryotic.
4. All three domains use ribosomes for protein synthesis. Chemical Constituents of Cells
1. Cells are constructed from numerous small molecules and macromolecules.
2. The building blocks of cells include carbohydrates (sugars and starches), proteins, lipids (fats and oils), and nucleic acids.
3. Enzymes are proteins that catalyze the multitude of biochemical reactions that occur in the cell. Organelles
1. Organelles represent the compartments (and unique microenvironments) in the cell and are involved in a variety of functions (division of labor).
2. The nucleus (the storehouse of the majority of DNA in the cell) has a double membrane and nuclear pores, which allow movement of biomolecules into and out of the nucleus.
3. The outer layer of the cell is the plasma membrane, which encloses an area called the cytoplasm.
4. The rough endoplasmic reticulum (ER), smooth ER, and Golgi body function as a membrane network for the synthesis of proteins and lipids that are targeted for delivery to the plasma membrane, organelles, or for secretion.
5. In response to biochemical signals, information from genes is copied into messenger RNA (mRNA). mRNA and transfer RNA (tRNA) direct the manufacture of proteins in the ER for secretion. Compounds for secretion enter into vesicles along the ER, and leave the cell via the Golgi apparatus and the plasma membrane.
6. The Golgi apparatus is a processing center that attaches sugars to biomolecules, forming either glycoproteins or glycolipids.
7. Lysosomes contain enzymes that degrade cellular debris.
8. Peroxisomes house enzymes that detoxify certain substances, break down lipids, and synthesize bile acids.
9. A mitochondrion has a double membrane whose inner folds carry enzymes that catalyze reactions that extract energy from nutrients. This energy is stored in the chemical bonds of ATP. The Plasma Membrane
1. The plasma membrane forms a selective barrier to monitor the movement of molecules in and out of the cell.
2. The cell membrane is composed of a bilayer of phospholipids and the underlying cytoskeleton (microtubules and microfilaments).
3. The proteins (or glycoproteins) residing in the cell membrane function as enzymes, signal transduction receptors, transport proteins, and cell adhesion proteins. The Cytoskeleton
1. The major cytoskeleton components include microtubules (tubulin), microfilaments (actin), and intermediate filaments (various families of intermediate filament proteins).
2. Microtubules serve as the foundation of cilia and flagella.
3. Microfilaments provide cell strength and anchoring.
4. Intermediate filaments provide an inner framework for a cell.
3. Spherocytosis is a heredity defect in the cytoskeleton of the red blood cell. An abnormal cytoskeletal protein, ankyrin, lies beneath the cell membrane, and causes the red blood cells to balloon out, blocking narrow blood vessels in organs. 2.2 Cell Division and Death
1. Mitosis occurs in somatic cells, providing new cells for an organism.
2. Apoptosis is programmed cell death, and is a necessary component of development. The Cell Cycle
1. The cell cycle consists of interphase, when a cell is not dividing, and mitosis.
2. During interphase, proteins, lipids, and carbohydrates are produced in the G1 phase; DNA and proteins are made during S phase; and more proteins are produced in G2. Cells in G0 phase do not replicate their DNA or divide.
3. During S phase chromosomes are replicated. Each replicated chromosome has two sister chromatids attached at their centromeres.
4. In mitotic prophase, replicated chromosomes condense, a spindle forms, and the nuclear membrane breaks down. In metaphase, chromosomes align down the center of the cell (equator or metaphase plate). In anaphase, centromeres part, one chromatid from each pair pulled to opposite ends of the cell. In telophase, the cell pinches in the middle (cytokinesis), and the two new cells separate.
5. The cell cycle is tightly controlled and regulated at several "checkpoints."
6. A cellular clock that limits the number of divisions is based on shrinking telomeres.
7. Crowding, hormones, and growth factors are extracellular influences on mitosis.
8. Within cells, kinases and cyclins activate the genes whose products carry out mitosis. Apoptosis
1. Mitosis (cell division) and apoptosis (cell death) are continuous processes that occur in a series of steps and are both initiated by signals in the extracellular environment.
2. The balance between cell division and death maintains tissues in growth, development, and repair.
3. In prenatal development coordination of these processes sculpts body form. After birth, mitosis and apoptosis protect and maintain the body.
4. Disruption of the balance between cell division and cell death can lead to cancer or other disorders. 2.3 Cell-Cell Interactions
Signal Transduction
1. In signal transduction, molecules on the plasma membrane assess, transmit and amplify incoming messages.
2. The process involves proteins on the plasma membrane and in the cytoplasm.
3. Neurofibromatosis type I (NF1) is caused by faulty signal transduction. Nerve cells beneath the skin inappropriately transmit a growth factor signal, triggering cell division. A tumor forms. Cell Adhesion
1. Cell adhesion is a precise sequence of interactions between cell surface proteins that join cells.
2. In inflammation, cell adhesion molecules (CAMs) guide white blood cells to injury sites.
3. Leukocyte-adhesion deficiency and cancer are disorders that can result from abnormal cell adhesion. 2.4 Stem Cells and Cell Specialization
1. Stem cells and progenitor cells renew tissues by replacing cells lost to apoptosis, injury, disease or growth.
2. Stem cells and progenitor cells are described in terms of development potential. They may be either totipotent or pluripotent
3. The zygote or fertilized egg is totipotent, capable of producing any cell type.
4. Cells of the early embryo are pluripotent, meaning they can differentiate into some but not all types of cells.
5. Later in development, pluripotent stem cells give rise to progenitor cells that are committed to a particular pathway.
6. Stem cells are non-specialized cells that retain the potential to differentiate and enable a tissue to grow or repair itself.
7. Regenerative medicine uses stem cells to replace or rejuvenate injured or diseased tissue.
8. Embryonic stem cells (ES) are derived from 5 day old blastocysts (embryos).
9. Somatic cell nuclear transfer (SCNT), or "therapeutic cloning" generates genetically identical cells for use in treating diseases. |
