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ANPS 019 09/07/12 Beneyto Summary of Transport Processes Passive Processes 1. Simple Diffusion 2. Osmosis 3. Facilitated Diffusion ‘Carrier mediated’ Active Transport Energy required: consumed ATP Independent of concentration gradients o Moves substance ‘uphill’ or from area of low concentration to are of high concentration Types of active transport include o Primary active transport; ex. Ion pumps o Secondary active transport; ex. Nutrients Primary Active Transport: The Sodium Potassium Exchange Pump Critical to cell function; creates ionic difference across cell membrane Membrane Enzyme: sodium-potassium ATPase Requires ATP Moves 3 sodium ions out, 2 potassium ions in Pump, Not channel (antiporter) Secondary Active Transport Transporter does not require energy, but the gradient for solute movement is created by energy use elsewhere in cell As long as the sodium-potassium ATPase is actively pumping sodium OUT, all of the transporters here will take advantage of sodium pushing back IN to move other substances through the membrane. Vesicular Transport: material moves into or out of cells in membrane-bound vesicles Exocytosis is ejection of materials from the cell o Fusion of a cytoplasmic vesicle with the plasma membrane o “loose” contents of vesicle are released into extracellular fluid o vesicle membrane now part of plasma membrane Endocytosis is movement of material into the cell o Pinocytosis o Receptor mediated endocytosis (coated vesicles) o Phagocytosis Pinocytosis = ‘cell drinking’ Cell ‘drinks in’ extracellular fluid Not specific as to what comes in: no receptors involved Process: o Formation of vesicle; fluid and dissolved solutes in vesicle; fusion of lysosome and vesicle; digestion by lysosmal enzymes; digested solutes in cell Receptor-Mediated Endocytosis Allows the cell to select specific large molecules from the extracellular fluid and bring them into the cell. Specificity comes from special membrane proteins clustered together that bind particular substance (ie:iron) Extracellular substance bind to membrane receptor Membrane pinches in forming cytoplasmic vesicle with substance bound on inside Vesicle fused with lysosome; enzymes remove ligand from receptor Vesicle returns to surface and reinserts into plasma membrane, again exposing receptors to extracellular fluid. The active and passive transport properties of a cell leave an uneven distribution of solutes across the membrane. Of special importance is the difference in ion concentrations across the cell membrane o Creates a difference in the electrical potential between the inside and outside of the cell- the transmembrane potential o Key to nerve and muscle function Two different states of DNA for two main nuclear events Chromosome appear just prior to mitosis, division of the nuclear material during cell division. The rest of the time, DNA is in the lose, dispersed form called chromatin, where small areas of the DNA can be exposed for the process of protein synthesis Review (DNA) DNA has a pair of nucleotide chains The chains spiral around one another (Double helix) Weak hydrogen bonds holding the two chains together can be easily broke to ‘unzip’ the spiral and expose bases on each strand. The Cell Cycle For most of a cell’s life, when the cell is in G0 and G1 stages, the DNA is in chromatin form. These are times of protein synthesis, making different proteins that determine the cell’s activities During the S phase of the cell cycle, the DNA is copied in it entirety in preparation for cell division. Both ‘daughter cells’ will have a complete set of identical DNA. G1: Normal cell functions plus cell growth, duplication of organelles, protein synthesis (8 or more hours) S: DNA replication, synthesis of histones (6 to 8 hours) G2: Protein synthesis (2 to 5 hours) Mitosis: Prophase, Metaphase, Anaphase, Telophase, Cytokinesis (1 to 3 hours) G0: Specialized cell functions (indefinite period) DNA Replication during Cell Division The nucleus contains the DNA and a chemical soup which includes both DNA and RNA nucleotides. In DNA replication, DNA nucleotides will be taken from the nuceloplasm and linked together under the direction of an enzyme called DNA polymerase to create new DNA strands. Chromosomes A gene is a small segment on a chromosome which codes for a unique protein Therefore, a gene codes for a sequence of amino acids Exceptions: Ribosomal RNA (rRNA) & transfer RNA (tRNA) Overview of Protein Synthesis 1. A particular sequence of DNA is unwrapped 2. A copy of one of the strands is made with RNA bases (transcription) 3. The copy leaves the nucleus and finds a ribosome in the cytoplasm 4. The copy is ‘read’ and a string of amino acids is formed using the RNA code (translation) 5. The new protein is sent elsewhere in the cell for immediate use of final adjustments The process of transcription leads to the creation of a strand of messenger RNA (mRNA) containing a code of bases complementary to one segment of one DNA strand. Transcription: making a copy of one strand of the DNA into RNA (think Transcribe) Translation: converting a nucleotide sequence into an amino acid sequence (think Translate) There are 3 kinds of RNA involved in the process 1. Ribosomal RNA – combined with proteins to make ribosomes 2. Messenger RNA – the message strand that carries the code for a protein from the DNA into the cytoplasm 3. Transfer RNA – Cytoplasmic RNA strand folded into cloverleaf; binds an amino acid at one end.