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Chapter 3 - Cells: The living units (part a). Just as bricks and timbers are the structural units of a house, cells are the structural units of all living things, from one-celled “generalists” like amoebas to complex multicellular organisms such as humans, dogs, and trees. The human body has 50 to 100 trillion of these tiny building blocks. This chapter focuses on structures and functions shared by all cells.
Cells: The Living Units The cell is the smallest structural and functional living unit Organismal functions depend on individual and collective cell functions Biochemical activities of cells are dictated by their specific sub cellular structures called organelles Over 200 different types of human cells Types differ in size, shape, subcellular components, and functions Erythrocytes Fibroblasts Epithelial cells (a) Cells that connect body parts, form linings, or transport gases Skeletal Muscle cell Smooth muscle cells (b) Cells that move organs and body parts Macrophage Nerve cell (e) Cell that gathers information and control body functions Sperm (f) Cell of reproduction Fat cell (c) Cell that stores nutrients Copyright © 2010 Pearson Education, Inc (d) Cell that fights disease Figure 3.1 All cells have some common structures and functions Human cells have four basic parts: ◦Plasma membrane flexible outer boundary ◦Cytoplasm intracellular fluid ◦Organelles multiple functions ◦Nucleus control center Chromatin Nucleolus Nuclear envelope Nucleus Smooth endoplasmic reticulum Mitochondrion Cytosol Lysosome Centrioles Centrosome matrix Cytoskeletal elements • Microtubule • Intermediate filaments Copyright © 2010 Pearson Education, Inc Plasma membrane Rough endoplasmic reticulum Ribosomes Golgi apparatus Secretion being released from cell by exocytosis Peroxisome Figure 3.2 Bimolecular layer of lipids and proteins in a constantly changing fluid mosaic Plays a dynamic role in cellular activity Separates intracellular fluid (ICF) from extracellular fluid (ECF) ◦Interstitial fluid (IF) = ECF that surrounds cells Extracellular fluid (watery environment) Polar head of phospholipid molecule Cholesterol Glycolipid Glycoprotein Carbohydrate of glycocalyx Outwardfacing layer of phospholipids Integral proteins Filament of cytoskeleton Peripheral Bimolecular Inward-facing proteins lipid layer layer of containing phospholipids Nonpolar proteins tail of phospholipid Cytoplasm molecule (watery environment) Copyright © 2010 Pearson Education, Inc Figure 3.3 Phospholipids (lipid bilayer) ◦Phosphate heads: polar and hydrophilic ◦Fatty acid tails: nonpolar and hydrophobic (Review Fig. 2.16b) Transport Receptors for signal transduction Attachment to cytoskeleton and extracellular matrix Nonpolar lipidsoluble (hydrophobic) substances diffuse directly through the phospholipid bilayer Diffusion is the movement of solutes from a solution of higher concentration to that of a lower concentration PLAY Animation: Diffusion Extracellular fluid Lipidsoluble solutes Cytoplasm (a) Simple diffusion of fat-soluble molecules directly through the phospholipid bilayer Copyright © 2010 Pearson Education, Inc Figure 3.7a Certain lipophobic molecules (e.g., glucose, amino acids, and ions) use carrier proteins or channel proteins, both of which: ◦Exhibit specificity (selectivity) ◦Are saturable; rate is determined by number of carriers or channels ◦Can be regulated in terms of activity and quantity Transmembrane integral proteins transport specific polar molecules (e.g., sugars and amino acids) Binding of substrate causes shape change in carrier Lipid-insoluble solutes (such as sugars or amino acids) (b) Carrier-mediated facilitated diffusion via a protein carrier specific for one chemical; binding of substrate causes shape change in transport protein Copyright © 2010 Pearson Education, Inc Figure 3.7b Aqueous channels formed by transmembrane proteins selectively transport ions or water Two types: ◦Leakage channels Always open ◦Gated channels Controlled by chemical or electrical signals Small lipidinsoluble solutes (c) Channel-mediated facilitated diffusion through a channel protein; mostly ions selected on basis of size and charge Copyright © 2010 Pearson Education, Inc Figure 3.7c Movement of solvent (water) from a solution of low concentration to that of a higher concentration, across a selectively permeable membrane Water diffuses through plasma membranes: ◦Through the lipid bilayer ◦Through water channels called aquaporins (AQPs) Water molecules Lipid billayer Aquaporin (d) Osmosis, diffusion of a solvent such as water through a specific channel protein (aquaporin) or through the lipid bilayer Copyright © 2010 Pearson Education, Inc Figure 3.7d Water concentration is determined by solute concentration because solute particles displace water molecules Osmolarity: The measure of total concentration of solute particles When solutions of different osmolarity are separated by a membrane, osmosis occurs until equilibrium is reached (a) 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 H2O Solute Membrane Copyright © 2010 Pearson Education, Inc Solute molecules (sugar) Figure 3.8a (b) 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 Left compartment Right compartment Both solutions have identical osmolarity, but volume of the solution on the right is greater because only water is free to move H2O Membrane Copyright © 2010 Pearson Education, Inc Solute molecules (sugar) Figure 3.8b When osmosis occurs, water enters or leaves a cell Change in cell volume disrupts cell function PLAY Animation: Osmosis Tonicity: The ability of a solution to cause a cell to shrink or swell Isotonic: A solution with the same solute concentration as that of the cytosol Hypertonic: A solution having greater solute concentration than that of the cytosol Hypotonic: A solution having lesser solute concentration than that of the cytosol (a) Isotonic solutions Cells retain their normal size and shape in isotonic solutions (same solute/water concentration as inside cells; water moves in and out) Copyright © 2010 Pearson Education, Inc (b) Hypertonic solutions Cells lose water by osmosis and shrink in a hypertonic solution (contains a higher concentration of solutes than are present inside the cells) (c) Hypotonic solutions Cells take on water by osmosis until they become bloated and burst (lyse) in a hypotonic solution (contains a lower concentration of solutes than are present in cells) Figure 3.9 ... Over 200 different types of human cells Types differ in size, shape, subcellular components, and functions Erythrocytes Fibroblasts Epithelial cells (a) Cells that connect body parts, form... transport gases Skeletal Muscle cell Smooth muscle cells (b) Cells that move organs and body parts Macrophage Nerve cell (e) Cell that gathers information and control body functions Sperm (f) Cell of... Pearson Education, Inc (d) Cell that fights disease Figure 3.1 All cells have some common structures and functions Human cells have four basic parts: ◦Plasma membrane flexible outer boundary