Kin 290, Chapter 3, Week 3
Kin 290, Chapter 3, Week 3 Kin 290
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This 7 page Class Notes was uploaded by Leonard Carey on Monday April 11, 2016. The Class Notes belongs to Kin 290 at 1 MDSS-SGSLM-Langley AFB Advanced Education in General Dentistry 12 Months taught by Dr. Satern in Spring 2016. Since its upload, it has received 9 views. For similar materials see Anatomy & Physiology in Kinesiology at 1 MDSS-SGSLM-Langley AFB Advanced Education in General Dentistry 12 Months.
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Date Created: 04/11/16
Chapter 3 ActiChapter 3 Cells: The Living Units Why This Matters Understanding the structure of the body’s cells explains why the permeability of the plasma membrane can affect treatment 3.1 Cells: The Living Units Cell theory – A cell is the structural and functional unit of life – How well the entire organism functions depends on individual and combined activities of all of its cells – Structure and function are complementary Biochemical functions of cells are dictated by shape of cell and specific subcellular structures – Continuity of life has cellular basis Cells can arise only from other preexisting cells 3.1 Cells: The Living Units (Figure 3.1 – p. 61) Cell diversity – Over 200 different types of human cells – Types differ in size, shape, and subcellular components; these differences lead to differences in functions 3.1 Cells: The Living Units (Figure 3.2 – p. 62) Generalized Cell – All cells have some common structures and functions – Human cells have three basic parts: 1. Plasma membrane: flexible outer boundary 2. Cytoplasm: intracellular fluid containing organelles 3. Nucleus: DNA containing control center Part 1 Plasma Membrane Acts as an active barrier separating intracellular fluid (ICF) from extracellular fluid (ECF) Plays dynamic role in cellular activity by controlling what enters and what leaves cell Also known as the “cell membrane” 3.2 Structure of Plasma Membrane (Figure 3.3 – p. 64) Consists of membrane lipids that form a flexible lipid bilayer Specialized membrane proteins float through this fluid membrane, resulting in constantly changing patterns © 2016 Pearson Education, Inc. 1 Chapter 3 – Referred to as fluid mosaic (made up of many pieces) pattern Surface sugars form glycocalyx Membrane structures help to hold cells together through cell junctions Membrane Lipids Lipid bilayer is made up of: – 75% phospholipids, which consist of two parts: Phosphate heads: are polar (charged), so are hydrophilic (waterloving) Fatty acid tails: are nonpolar (no charge), so are hydrophobic (waterhating) – 5% glycolipids Lipids with sugar groups on outer membrane surface – 20% cholesterol Increases membrane stability Membrane Proteins Allow cell communication with environment Make up half the mass of plasma membrane Most have specialized membrane functions Some float freely, and some are tethered to intracellular structures Two types: – Integral proteins; peripheral proteins Membrane Proteins (cont.) (Figure 3.4a,c,e,f – p. 66) Integral proteins – Firmly inserted into membrane – Most are transmembrane proteins (span membrane) – Have both hydrophobic and hydrophilic regions Hydrophobic areas interact with lipid tails Hydrophilic areas interact with water – Function as transport proteins (channels and carriers), enzymes, or receptors Cell Junctions Some cells are “free” (not bound to any other cells) – Examples: blood cells, sperm cells Most cells are bound together to form tissues and organs Three ways cells can be bound to each other – Tight junctions – Desmosomes – Gap junctions How do substances move across the plasma membrane? Plasma membranes are selectively permeable © 2016 Pearson Education, Inc. 2 Chapter 3 – Some molecules pass through easily; some do not Two ways substances cross membrane – Passive processes: no energy required – Active processes: energy (ATP) required 3.3 Passive Membrane Transport Passive transport requires no energy Two types of passive transport – Diffusion Simple diffusion Carrier and channelmediated facilitated diffusion Osmosis – Filtration Type of transport that usually occurs across capillary walls Diffusion (Figure 3.6 – p. 68) Collisions between molecules in areas of high concentration cause them to be scattered into areas with less concentration – Difference is called concentration gradient – Diffusion is movement of molecules down their concentration gradients (from high to low) Energy is not required Speed of diffusion is influenced by size of molecule and temperature Diffusion (cont.) Molecules have natural drive to diffuse down concentration gradients that exist between extracellular and intracellular areas Plasma membranes stop diffusion and create concentration gradients by acting as selectively permeable barriers Diffusion (cont.) Nonpolar, hydrophobic lipid core of plasma membrane blocks diffusion of most molecules Molecules that are able to passively diffuse through membrane include: – Lipidsoluble and nonpolar substances – Very small molecules that can pass through membrane or membrane channels – Larger molecules assisted by carrier molecules Diffusion (cont.) Simple diffusion (Figure 3.7a – p. 69) – Nonpolar lipidsoluble (hydrophobic) substances diffuse directly through phospholipid bilayer © 2016 Pearson Education, Inc. 3 Chapter 3 – Examples: oxygen, carbon dioxide, fatsoluble vitamins Diffusion (cont.) Facilitated diffusion – Certain hydrophobic molecules (e.g., glucose, amino acids, and ions) are transported passively down their concentration gradient by: Carriermediated facilitated diffusion – Substances bind to protein carriers Channelmediated facilitated diffusion – Substances move through waterfilled channels Diffusion (cont.) (Figure 3.7b – p. 69) Carriermediated facilitated diffusion – Carriers are transmembrane integral proteins – Carriers transport specific polar molecules, such as sugars and amino acids, that are too large for membrane channels Example of specificity: glucose carriers will carry only glucose molecules, nothing else – Binding of molecule causes carrier to change shape, moving molecule in process – Binding is limited by number of carriers present Carriers are saturated when all are bound to molecules and are busy transporting Diffusion (cont.) (Figure 3.7c – p. 69) Channelmediated facilitated diffusion – Channels with aqueousfilled cores are formed by transmembrane proteins – Channels transport molecules such as ions or water (osmosis) down their concentration gradient Specificity based on pore size and/or charge Water channels are called aquaporins – Two types: Leakage channels – Always open Gated channels – Controlled by chemical or electrical signals Diffusion (cont.) (Figure 3.7d – p. 69) Osmosis – Movement of solvent, such as water, across a selectively permeable membrane – Water diffuses through plasma membranes Through lipid bilayer (even though water is polar, it is so small that some molecules can sneak past nonpolar phospholipid tails) © 2016 Pearson Education, Inc. 4 Chapter 3 Through specific water channels called aquaporins (AQPs) – Flow occurs when water (or other solvent) concentration is different on the two sides of a membrane Diffusion (cont.) A living cell has limits to how much water can enter it Water can also leave a cell, causing cell to shrink Change in cell volume can disrupt cell function, especially in neurons Table 3.1 – p. 73 3.4 Active Membrane Transport Two major active membrane transport processes – Active transport – Vesicular transport Both require ATP to move solutes across a plasma membrane for any of these reasons: – Solute is too large for channels, or – Solute is not lipid soluble, or – Solute is not able to move down concentration gradient Active Transport Requires carrier proteins (solute pumps) – Bind specifically and reversibly with substance being moved Moves solutes against their concentration gradient (from low to high) – This requires energy (ATP) Active Transport (cont.) Two types of active transport: – Primary active transport Required energy comes directly from ATP hydrolysis – Secondary active transport Required energy is obtained indirectly from ionic gradients created by primary active transport Active Transport (cont.) Primary active transport – Energy from hydrolysis of ATP causes change in shape of transport protein – Shape change causes solutes (ions) bound to protein to be pumped across membrane + + – Example of pumps: calcium, hydrogen (proton), Na K pumps © 2016 Pearson Education, Inc. 5 Chapter 3 Active Transport (cont.) (Table 3.2 top – p. 79) Sodiumpotassium pump – Most studied pump – Basically is an enzyme, called Na K ATPase, that pumps Na out of cell and K + back into cell – Located in all plasma membranes, but especially active in excitable cells (nerves and muscles) Active Transport (cont.) (Focus Figure 3.1 – p. 74) + Leakage channels located in membranes result in leaking of Na into the cell and leaking of K out of cell – Both travel down their concentration gradients + + + + Na K pump works as an antiporter that pumps Na out of cell and K back into cell against their concentration gradients Maintains electrochemical gradients, which involve both concentration and electrical charge of ions – Essential for functions of muscle and nerve tissues 3.5 Membrane Potential Resting membrane potential (RMP) – Electrical potential energy produced by separation of oppositely charged particles across plasma membrane in all cells Difference in electrical charge between two points is referred to as voltage Cells that have a charge are said to be polarized – Voltage occurs only at membrane surface Rest of cell and extracellular fluid are neutral Membrane voltages range from –50 to –100 mV in different cells (negative sign (–) indicates inside of cell is more negative relative to outside of cell) K is Key Player in RMP + + K diffuses out of cell through K leakage channels down its concentration gradient Negatively charged proteins cannot leave – As a result cytoplasmic side of cell membrane becomes more negative + K is then pulled back by the more negative interior because of its electrical gradient When drive for K to leave cell is balanced by its drive to stay, RMP is established – Most cells have an RMP around –90 mV Electrochemical gradient of K sets RMP + K is Key Player in RMP (cont.) (Figure 3.14 – p. 80) In many cells, Na also affects RMP – Na+ is also attracted to inside of cell because of negative charge © 2016 Pearson Education, Inc. 6 Chapter 3 + If Na enters cell, it can bring RMP up to –70 mV – Membrane is more permeable to K than Na , so K primary influence on RMP – Cl does not influence RMP because its concentration and electrical gradients are exactly balanced Active Transport Maintains Electrochemical Gradients RMP is maintained through action of the Na K pump, which continuously ejects 3Na + + out of cell and brings 2K back inside Steady state is maintained because rate of active pumping of Na out of cell equals the + rate of Na diffusion into cell Neuron and muscle cells “upset” this steady state RMP by intentionally opening gated + + Na and K channels © 2016 Pearson Education, Inc. 7