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chapter2 - IPHY 3430 Human Physiology Fall 2007 REVIEW...

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IPHY 3430 – Human Physiology Fall 2007 REVIEW TOPICS & STUDY QUESTIONS – Chapter 2: Cellular Physiology Lecture Summary 1. A typical cell within the human body contains cytoplasm (various organelles and cytosol) and a nucleus (DNA and nucleolus), bound by the plasma membrane. The plasma membrane is selectively permeable, meaning that certain substances may cross while others cannot. The plasma membrane separates two fluid compartments – the extracellular fluid (ECF) outside the cell and the intracellular fluid (ICF) inside the cell. 2. The genetic code of the nuclear DNA is transcribed into mRNA. mRNA is exported from the nucleus into the cytoplasm where it is translated to form peptide chains. DNA and RNA are composed of nucleotides while peptides (and proteins) are composed of amino acids. Proteins that remain in the cell are translated on free ribosomes in the cytoplasm. Proteins destined for release from the cell (secretory proteins) or those associated with the plasma membrane (integral membrane proteins such as ion channels) are translated on ribosomes on the surface of the rough endoplasmic reticulum (rER). The peptide chain is modified within the rER, giving rise to the protein product of gene expression. The protein is released in a transport vesicle from the rER via exocytosis. The vesicle may fuse with the membrane of the smooth ER (sER), allowing the protein to enter the sER for additional modifications. Modified proteins also emerge from the sER in transport vesicles. Following ER modification, transport vesicles containing the protein fuse with another membranous structure, the Golgi Complex. Further processing of the protein occurs in the Golgi and the final protein product is released from the Golgi in a secretory vesicle. Two types of secretory vesicles, lysosomes and peroxisomes, remain in the cell as organelles and function in intracellular digestion and free radical defense, respectively. Other vesicles, containing proteins such as neurotransmitters or peptide hormones are tagged with surface markers that aid in directing their release from the cell. 3. Cytoskeletal elements, such as microfilaments, microtubules, and intermediate filaments are also found in the cytoplasm and provide structural support and/or function in cell transport. Mitochondria are organelles bound by a lipid bilayer membrane and are involved in cellular energetics. The Citric Acid (Krebs) Cycle occurs within the mitochondrial matrix. The majority of ATP synthesis occurs within the mitochondria due to the presence of the Electron Transport System (or Electron Transport Chain, ETC). Cytochromes of the ETC are proteins embedded within the inner mitochondrial membrane. Oxidation-reduction reactions between the cytochromes establish a proton gradient across the inner membrane. This gradient drives ATP synthesis. The ETC operates only in the presence of oxygen because oxygen serves as the final electron acceptor, combining with two electrons and two protons to form a molecule of water. Some tissues, such as skeletal muscle, can catabolize glucose for a limited time in the absence of oxygen (glycolysis, anaerobic respiration).
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