PowerPoint ® Lecture Slides prepared by Karen Dunbar Kareiva Ivy Tech Community College © Annie Leibovitz/Contact Press Images Chapter 3 Part A Cells: The Living Units © 2016 Pearson Education, Inc.

Why This Matters Understanding the structure of the body’s cells explains why the permeability of the plasma membrane can affect treatment © 2016 Pearson Education, Inc.

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 © 2016 Pearson Education, Inc.

3.1 Cells: The Living Units Cell diversity –Over 200 different types of human cells –Types differ in size, shape, and subcellular components; these differences lead to differences in functions © 2016 Pearson Education, Inc.

Figure 3.1 Cell diversity. Erythrocytes Fibroblasts Epithelial cells Skeletal muscle cell Smooth muscle cells Nerve cell Macrophage Fat cell Sperm Cell of reproduction Cell that stores nutrients Cells that connect body parts, form linings, or transport gases Cells that move organs and body parts Cell that gathers information and controls body functions Cell that fights disease © 2016 Pearson Education, Inc.

3.1 Cells: The Living Units 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 © 2016 Pearson Education, Inc.

Figure 3.2 Structure of the generalized cell. Chromatin Smooth endoplasmic reticulum Nucleolus Mitochondrion Lysosome Centrioles Centrosome matrix Peroxisome Secretion being released from cell by exocytosis Golgi apparatus Ribosomes Rough endoplasmic reticulum Nuclear envelope Nucleus Plasma membrane Cytoplasm Cytoskeletal elements Microtubule Intermediate filaments © 2016 Pearson Education, Inc.

Extracellular Materials Substances found outside cells Classes of extracellular materials include: –Extracellular fluids (body fluids), such as: Interstitial fluid: cells are submersed (bathed) in this fluid Blood plasma: fluid of the blood Cerebrospinal fluid: fluid surrounding nervous system organs –Cellular secretions (e.g., saliva, mucus) –Extracellular matrix: substance that acts as glue to hold cells together © 2016 Pearson Education, Inc.

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” © 2016 Pearson Education, Inc.

3.2 Structure of Plasma Membrane Consists of membrane lipids that form a flexible lipid bilayer Specialized membrane proteins float through this fluid membrane, resulting in constantly changing patterns –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 © 2016 Pearson Education, Inc.

Figure 3.3 The plasma membrane. Extracellular fluid (watery environment outside cell) Cholesterol Glycolipid Glycoprotein Polar head of phospholipid molecule Nonpolar tail of phospholipid molecule Glycocalyx (carbohydrates) Lipid bilayer containing proteins Outward-facing layer of phospholipids Inward-facing layer of phospholipids Filament of cytoskeleton Peripheral proteins Integral proteins Cytoplasm (watery environment inside cell) Functions of the Plasma Membrane: Mechanical barrier: Separates two of the body’s fluid compartments. Selective permeability: Determines manner in which substances enter or exit the cell. Electrochemical gradient: Generates and helps to maintain the electrochemical gradient required for muscle and neuron function. Communication: Allows cell-to-cell recognition (e.g., of egg by sperm) and interaction. Cell signaling: Plasma membrane proteins interact with specific chemical messengers and relay messages to the cell interior. © 2016 Pearson Education, Inc.

Membrane Lipids Lipid bilayer is made up of: –75% phospholipids, which consist of two parts: Phosphate heads: are polar (charged), so are hydrophilic (water-loving) Fatty acid tails: are nonpolar (no charge), so are hydrophobic (water-hating) –5% glycolipids Lipids with sugar groups on outer membrane surface –20% cholesterol Increases membrane stability © 2016 Pearson Education, Inc.

Membrane Proteins Allow cell communication with environment Make up about 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 © 2016 Pearson Education, Inc.

Membrane Proteins (cont.) 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 © 2016 Pearson Education, Inc.

Membrane Proteins (cont.) Peripheral proteins –Loosely attached to integral proteins –Include filaments on intracellular surface used for plasma membrane support –Function as: Enzymes Motor proteins for shape change during cell division and muscle contraction Cell-to-cell connections © 2016 Pearson Education, Inc.

Figure 3.4 Membrane proteins perform many tasks. A protein (left) that spans the membrane may provide a hydrophilic channel across the mem­brane that is selective for a particular solute. Some transport proteins (right) hydro­lyze ATP as an energy source to actively pump substances across the membrane. A membrane protein exposed to the outside of the cell may have a binding site that fits the shape of a specific chemical messenger, such as a hormone. When bound, the chemical messenger may cause a change in shape in the protein that initiates a chain of chemical reactions in the cell. Ele­ments of the cytoskeleton (cell’s internal supports) and the extracellular matrix (fibers and other substances outside the cell) may anchor to membrane proteins, which helps main­tain cell shape and fix the location of certain membrane proteins. Others play a role in cell movement or bind adjacent cells together. A membrane protein may be an enzyme with its active site exposed to substances in the adjacent solution. A team of several enzymes in a membrane may catalyze sequential steps of a met­abolic pathway as indicated (left to right) here. Membrane proteins of adjacent cells may be hooked together in various kinds of intercellular junctions. Some membrane proteins (cell adhesion molecules or CAMs) of this group provide temporary binding sites that guide cell migration and other cell-to-cell interactions. Some glycoproteins (proteins bonded to short chains of sugars which help to make up the glycocalyx) serve as identification tags that are specifically recognized by other cells. Intercellular joining Cell-cell recognition Attachment to the cytoskeleton and extracellular matrix Receptors for signal transduction Transport Enzymatic activity Glycoprotein CAMs Enzymes ATP Signal Receptor © 2016 Pearson Education, Inc.

Figure 3.4a Membrane proteins perform many tasks. Transport A protein (left) that spans the membrane may provide a hydrophilic channel across the mem­brane that is selective for a particular solute. Some transport proteins (right) hydro­lyze ATP as an energy source to actively pump substances across the membrane. ATP © 2016 Pearson Education, Inc.

Figure 3.4b Membrane proteins perform many tasks. Receptors for signal transduction A membrane protein exposed to the outside of the cell may have a binding site that fits the shape of a specific chemical messenger, such as a hormone. When bound, the chemical messenger may cause a change in shape in the protein that initiates a chain of chemical reactions in the cell. Signal Receptor © 2016 Pearson Education, Inc.

Figure 3.4c Membrane proteins perform many tasks. Ele­ments of the cytoskeleton (cell’s internal supports) and the extracellular matrix (fibers and other substances outside the cell) may anchor to membrane proteins, which helps main­tain cell shape and fix the location of certain membrane proteins. Others play a role in cell movement or bind adjacent cells together. Attachment to the cytoskeleton and extracellular matrix © 2016 Pearson Education, Inc.

Figure 3.4d Membrane proteins perform many tasks. Enzymatic activity A membrane protein may be an enzyme with its active site exposed to substances in the adjacent solution. A team of several enzymes in a membrane may catalyze sequential steps of a met­abolic pathway as indicated (left to right) here. Enzymes © 2016 Pearson Education, Inc.

Figure 3.4e Membrane proteins perform many tasks. Intercellular joining Membrane proteins of adjacent cells may be hooked together in various kinds of intercellular junctions. Some membrane proteins (cell adhesion molecules or CAMs) of this group provide temporary binding sites that guide cell migration and other cell-to-cell interactions. CAMs © 2016 Pearson Education, Inc.

Figure 3.4f Membrane proteins perform many tasks. Cell-cell recognition Some glycoproteins (proteins bonded to short chains of sugars which help to make up the glycocalyx) serve as identification tags that are specifically recognized by other cells. Glycoprotein © 2016 Pearson Education, Inc.

Glycocalyx Consists of sugars (carbohydrates) sticking out of cell surface –Some sugars are attached to lipids (glycolipids) and some to proteins (glycoproteins) Every cell type has different patterns of this “sugar coating” –Functions as specific biological markers for cell- to-cell recognition –Allows immune system to recognize “self” vs. “nonself” © 2016 Pearson Education, Inc.

Clinical – Homeostatic Imbalance 3.1 Glycocalyx of some cancer cells can change so rapidly that the immune system cannot recognize the cell as being damaged. Mutated cell is not destroyed by immune system so it is able to replicate © 2016 Pearson Education, Inc.

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 © 2016 Pearson Education, Inc.

Cell Junctions (cont.) Tight junctions –Integral proteins on adjacent cells fuse to form an impermeable junction that encircles whole cell –Prevent fluids and most molecules from moving in between cells –Where might these be useful in body? © 2016 Pearson Education, Inc.

Figure 3.5a Cell junctions. Interlocking junctional proteins Intercellular space Basement membrane Microvilli Intercellular space Plasma membranes of adjacent cells Tight junctions: Impermeable junctions that form continuous seals around the cells prevent molecules from passing through the intercellular space. © 2016 Pearson Education, Inc.

Cell Junctions (cont.) Desmosomes –Rivet-like cell junction formed when linker proteins (cadherins) of neighboring cells interlock like the teeth of a zipper –Linker protein is anchored to its cell through thickened “button-like” areas on inside of plasma membrane called plaques –Keratin filaments connect plaques intercellularly for added anchoring strength –Desmosomes allow “give” between cells, reducing the possibility of tearing under tension –Where might these be useful in body? © 2016 Pearson Education, Inc.

Figure 3.5b Cell junctions. Plaque Intercellular space Linker proteins (cadherins) Intermediate filament (keratin) Microvilli Intercellular space Plasma membranes of adjacent cells Desmosomes: Anchoring junctions that bind adjacent cells together act like molecular “Velcro” and also help form an internal tension-reducing network of fibers. Basement membrane © 2016 Pearson Education, Inc.

Cell Junctions (cont.) Gap junctions –Transmembrane proteins (connexons) form tunnels that allow small molecules to pass from cell to cell –Used to spread ions, simple sugars, or other small molecules between cells –Allows electrical signals to be passed quickly from one cell to next cell Used in cardiac and smooth muscle cells © 2016 Pearson Education, Inc.

Figure 3.5c Cell junctions. Intercellular space Channel between cells (formed by connexons) Basement membrane Microvilli Intercellular space Plasma membranes of adjacent cells Gap junctions: Communicating junctions that allow ions and small molecules to pass are particularly important for communication in heart cells and embryonic cells. © 2016 Pearson Education, Inc.

How do substances move across the plasma membrane? Plasma membranes are selectively permeable –Some molecules pass through easily; some do not Two ways substances cross membrane –Passive processes: no energy required –Active processes: energy (ATP) required © 2016 Pearson Education, Inc.

3.3 Passive Membrane Transport Passive transport requires no energy Two types of passive transport –Diffusion Simple diffusion Carrier- and channel-mediated facilitated diffusion Osmosis –Filtration Type of transport that usually occurs across capillary walls © 2016 Pearson Education, Inc.

Diffusion 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 © 2016 Pearson Education, Inc.

Figure 3.6 Diffusion. Dye pelletDiffusion occurring Dye evenly distributed © 2016 Pearson Education, Inc.

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 © 2016 Pearson Education, Inc.

Clinical – Homeostatic Imbalance 3.2 If plasma membrane is severely damaged, substances diffuse freely into and out of cell, compromising concentration gradients Example: burn patients lose precious fluids, proteins, and ions that weep from damaged cells © 2016 Pearson Education, Inc.

Diffusion (cont.) Nonpolar, hydrophobic lipid core of plasma membrane blocks diffusion of most molecules Molecules that are able to passively diffuse through membrane include: –Lipid-soluble and nonpolar substances –Very small molecules that can pass through membrane or membrane channels –Larger molecules assisted by carrier molecules © 2016 Pearson Education, Inc.

Diffusion (cont.) Simple diffusion –Nonpolar lipid-soluble (hydrophobic) substances diffuse directly through phospholipid bilayer –Examples: oxygen, carbon dioxide, fat-soluble vitamins © 2016 Pearson Education, Inc.

Figure 3.7a Diffusion through the plasma membrane. Extracellular fluid Lipid- soluble solutes Cytoplasm Simple diffusion of fat-soluble molecules directly through the phospholipid bilayer © 2016 Pearson Education, Inc.

Diffusion (cont.) Facilitated diffusion –Certain hydrophobic molecules (e.g., glucose, amino acids, and ions) are transported passively down their concentration gradient by: Carrier-mediated facilitated diffusion –Substances bind to protein carriers Channel-mediated facilitated diffusion –Substances move through water-filled channels © 2016 Pearson Education, Inc.

Diffusion (cont.) Carrier-mediated 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 © 2016 Pearson Education, Inc.

Figure 3.7b Diffusion through the plasma membrane. Lipid-insoluble solutes (such as sugars or amino acids) Shape change releases solutes Carrier-mediated facilitated diffusion via protein carrier specific for one chemical; binding of substrate causes transport protein to change shape © 2016 Pearson Education, Inc.

Diffusion (cont.) Channel-mediated facilitated diffusion –Channels with aqueous-filled 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 © 2016 Pearson Education, Inc.

Figure 3.7c Diffusion through the plasma membrane. Small lipid- insoluble solutes Channel-mediated facilitated diffusion through a channel protein; mostly ions selected on basis of size and charge © 2016 Pearson Education, Inc.

Diffusion (cont.) 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) Through specific water channels called aquaporins (AQPs) –Flow occurs when water (or other solvent) concentration is different on the two sides of a membrane © 2016 Pearson Education, Inc.

Figure 3.7d Diffusion through the plasma membrane. Water molecules Lipid bilayer Aquaporin Osmosis, diffusion of a solvent such as water through a specific channel protein (aquaporin) or through the lipid bilayer © 2016 Pearson Education, Inc.

Diffusion (cont.) Osmolarity: measure of total concentration of solute particles Water concentration varies with number of solute particles because solute particles displace water molecules –When solute concentration goes up, water concentration goes down, and vice versa Water moves by osmosis from areas of low solute (high water) concentration to high areas of solute (low water) concentration © 2016 Pearson Education, Inc.

Diffusion (cont.) When solutions of different osmolarity are separated by a membrane permeable to all molecules, both solutes and water cross membrane until equilibrium is reached –Equilibrium: Same concentration of solutes and water molecules on both sides, with equal volume on both sides © 2016 Pearson Education, Inc.

Figure 3.8a Influence of membrane permeability on diffusion and osmosis. Membrane permeable to both solutes and water Solute and water molecules move down their concentration gradients in opposite directions. Fluid volume remains the same in both compartments. Left compartment: Solution with lower osmolarity Right compartment: Solution with greater osmolarity Both solutions have the same osmolarity: volume unchanged Solute molecules (sugar) Freely permeable membrane Solute H2OH2O © 2016 Pearson Education, Inc.

Diffusion (cont.) When solutions of different osmolarity are separated by a membrane that is permeable only to water, not solutes, osmosis will occur until equilibrium is reached –Same concentration of solutes and water molecules on both sides, with unequal volumes on both sides © 2016 Pearson Education, Inc.

Figure 3.8b Influence of membrane permeability on diffusion and osmosis. Membrane permeable to water, impermeable to solutes Solute molecules are prevented from moving but water moves by osmosis. Volume increases in the compartment with the higher osmolarity. H2OH2O Left compartment Right compartment Solute molecules (sugar) Selectively permeable membrane Both solutions have identical osmolarity, but volume of the solution on the right is greater because only water is free to move © 2016 Pearson Education, Inc.

Diffusion (cont.) Movement of water causes pressures: –Hydrostatic pressure: pressure of water inside cell pushing on membrane –Osmotic pressure: tendency of water to move into cell by osmosis The more solutes inside a cell, the higher the osmotic pressure © 2016 Pearson Education, Inc.

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 © 2016 Pearson Education, Inc.

Diffusion (cont.) Tonicity –Ability of a solution to change the shape or tone of cells by altering the cells’ internal water volume Isotonic solution has same osmolarity as inside the cell, so volume remains unchanged Hypertonic solution has higher osmolarity than inside cell, so water flows out of cell, resulting in cell shrinking –Shrinking is referred to as crenation Hypotonic solution has lower osmolarity than inside cell, so water flows into cell, resulting in cell swelling –Can lead to cell bursting, referred to as lysing © 2016 Pearson Education, Inc.

Figure 3.9 The effect of solutions of varying tonicities on living red blood cells. Isotonic solutions Hypertonic solutions Hypotonic solutions Cells retain their normal size and shape in isotonic solutions (same solute/water concentration as inside cells; water moves in and out). Cells lose water by osmosis and shrink in a hypertonic solution (contains a higher concentration of nonpenetrating solutes than are present inside the cells). Cells take on water by osmosis until they become bloated and burst (lyse) in a hypotonic solution (contains a lower concentration of nonpenetrating solutes than are present inside cells). © 2016 Pearson Education, Inc.

Clinical – Homeostatic Imbalance 3.3 Intravenous solutions of different tonicities can be given to patients suffering different ailments –Isotonic solutions are most commonly given when blood volume needs to be increased quickly –Hypertonic solutions are given to edematous (swollen) patients to pull water back into blood –Hypotonic solutions should not be given because they can result in dangerous lysing of red and white blood cells © 2016 Pearson Education, Inc.