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Chapter 3: Cells (The Living Units)
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Identified the cell organelle now named the
Camillo Golgi ( ) Identified the cell organelle now named the “Golgi Body” and he worked extensively in research helping to define the field of neurobiology. Dr. Golgi received Nobel Prize in 1906.
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Figure 3.2 Structure of the generalized cell.
Chromatin Nuclear envelope Nucleolus Nucleus Smooth endoplasmic reticulum Plasma membrane Mitochondrion Cytosol Lysosome Centrioles Centrosome matrix Rough endoplasmic reticulum Ribosomes Golgi apparatus Secretion being released from cell by exocytosis Cytoskeletal elements • Microtubule • Intermediate filaments Peroxisome
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(a) Cells that connect body parts, form linings, or transport gases
Figure 3.1 Cell diversity. Erythrocytes Fibroblasts Epithelial cells (a) Cells that connect body parts, form linings, or transport gases Nerve cell Skeletal Muscle cell Smooth muscle cells (e) Cell that gathers information and control body functions (b) Cells that move organs and body parts Sperm Macrophage (f) Cell of reproduction Fat cell (c) Cell that stores nutrients (d) Cell that fights disease
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Extracellular fluid (watery environment) Cholesterol Polar head of
Figure 3.3 Structure of the plasma membrane according to the fluid mosaic model. Extracellular fluid (watery environment) Cholesterol Polar head of phospholipid molecule Glycolipid Glycoprotein Carbohydrate of glycocalyx Outward- facing layer of phospholipids Integral proteins Filament of cytoskeleton Inward-facing layer of phospholipids Bimolecular lipid layer containing proteins Peripheral proteins Nonpolar tail of phospholipid molecule Cytoplasm (watery environment)
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Figure 3.4a Membrane proteins perform many tasks.
(a) 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.
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Figure 3.4b Membrane proteins perform many tasks.
(b) Receptors for signal transduction Signal A membrane protein exposed to the outside of the cell may have a binding site with a specific shape that fits the shape of a chemical messenger, such as a hormone. The external signal may cause a change in shape in the protein that initiates a chain of chemical reactions in the cell. Receptor
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Figure 3.4c Membrane proteins perform many tasks.
(c) Attachment to the cytoskeleton and extracellular matrix (ECM) Elements of the cytoskeleton (cell’s internal supports) and the extracellular matrix (fibers and other substances outside the cell) may be anchored to membrane proteins, which help maintain cell shape and fix the location of certain membrane proteins. Others play a role in cell movement or bind adjacent cells together.
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Figure 3.4d Membrane proteins perform many tasks.
(d) Enzymatic activity Enzymes A protein built into the membrane may be an enzyme with its active site exposed to substances in the adjacent solution. In some cases, several enzymes in a membrane act as a team that catalyzes sequential steps of a metabolic pathway as indicated (left to right) here.
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Figure 3.4e Membrane proteins perform many tasks.
(e) Intercellular joining Membrane proteins of adjacent cells may be hooked together in various kinds of intercellular junctions. Some membrane proteins (CAMs) of this group provide temporary binding sites that guide cell migration and other cell-to-cell interactions. CAMs
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Figure 3.4f Membrane proteins perform many tasks.
(f) Cell-cell recognition Some glycoproteins (proteins bonded to short chains of sugars) serve as identification tags that are specifically recognized by other cells. Glycoprotein
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Figure 3.5 Cell junctions. Plasma membranes of adjacent cells Microvilli Intercellular space Basement membrane Intercellular space Intercellular space Plaque Channel between cells (connexon) Interlocking junctional proteins Intercellular space Intermediate filament (keratin) Linker glycoproteins (cadherins) (a) Tight junctions: Impermeable junctions prevent molecules from passing through the intercellular space. (b) Desmosomes: Anchoring junctions bind adjacent cells together and help form an internal tension-reducing network of fibers. (c) Gap junctions: Communicating junctions allow ions and small molecules to pass from one cell to the next for intercellular communication.
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Figure 3.6 Diffusion.
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Figure 3.7 Diffusion through the plasma membrane.
Extracellular fluid Lipid-insoluble solutes (such as sugars or amino acids) Small lipid- insoluble solutes Water molecules Lipid- soluble solutes Lipid billayer Aquaporin Cytoplasm (a) Simple diffusion of fat-soluble molecules directly through the phospholipid bilayer (b) Carrier-mediated facilitated diffusion via a protein carrier specific for one chemical; binding of substrate causes shape change in transport protein (c) Channel-mediated facilitated diffusion through a channel protein; mostly ions selected on basis of size and charge (d) Osmosis, diffusion of a solvent such as water through a specific channel protein (aquaporin) or through the lipid bilayer
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Solute and water molecules move down their concentration gradients
Figure 3.8a Influence of membrane permeability on diffusion and osmosis. (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 Solute molecules (sugar) Membrane
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(b) Membrane permeable to water, impermeable to solutes
Figure 3.8b Influence of membrane permeability on diffusion and osmosis. (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. Both solutions have identical osmolarity, but volume of the solution on the right is greater because only water is free to move Left compartment Right compartment H2O Solute molecules (sugar) Membrane
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Figure 3.9 The effect of solutions of varying tonicities on living red blood cells.
(a) Isotonic solutions (b) Hypertonic solutions (c) 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 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 solutes than are present in cells).
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Figure 3.10 Primary Active Transport: The Na+-K+ Pump
Extracellular fluid Na+ Na+–K+ pump ATP-binding site K+ Na+ bound Cytoplasm 1 Cytoplasmic Na+ binds to pump protein. P ATP K+ released ADP K+ is released from the pump protein and Na+ sites are ready to bind Na+ again. The cycle repeats. 6 2 Binding of Na+ promotes phosphorylation of the protein by ATP. Na+ released K+ bound P Pi K+ K+ binding triggers release of the phosphate. Pump protein returns to its original conformation. 5 Phosphorylation causes the protein to change shape, expelling Na+ to the outside. 3 P 4 Extracellular K+ binds to pump protein.
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Figure 3.12 Events of endocytosis mediated by protein-coated pits.
Coated pit ingests substance. 1 Extracellular fluid Plasma membrane Protein coat (typically clathrin) Cytoplasm 2 Protein- coated vesicle detaches. Coat proteins detach and are recycled to plasma membrane. 3 Transport vesicle Endosome Uncoated endocytic vesicle Uncoated vesicle fuses with a sorting vesicle called an endosome. 4 Transport vesicle containing membrane components moves to the plasma membrane for recycling. 5 Lysosome 6 Fused vesicle may (a) fuse with lysosome for digestion of its contents, or (b) deliver its contents to the plasma membrane on the opposite side of the cell (transcytosis). (b) (a)
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Overview of Endocytosis (This diagram is not in your textbook.)
Extracellular fluid Cytoplasm Extracellular fluid Extracellular fluid Cytoplasm Plasma membrane Clathrin- coated pit Bacterium or other particle Recycling of membrane and receptors (if present) to plasma membrane 1 Clathrin protein Ingested substance Exocytosis of vesicle contents Pseudopod Clathrin (b) Phagocytosis protein Endosome Uncoated vesicle Detachment of clathrin- coated vesicle 3 Transcytosis Membrane receptor 2 Clathrin- coated vesicle To lysosome for digestion and release of contents Uncoating Plasma membrane Uncoated vesicle fusing with endosome Clathrin protein (a) Clathrin-mediated endocytosis (c) Receptor-mediated endocytosis
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Figure 3.13a Comparison of three types of endocytosis.
Phagocytosis The cell engulfs a large particle by forming pro- jecting pseudopods (“false feet”) around it and en- closing it within a membrane sac called a phagosome. The phagosome is combined with a lysosome. Undigested contents remain in the vesicle (now called a residual body) or are ejected by exocytosis. Vesicle may or may not be protein- coated but has receptors capable of binding to microorganisms or solid particles. Phagosome
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Figure 3.13b Comparison of three types of endocytosis.
Pinocytosis The cell “gulps” drops of extracellular fluid containing solutes into tiny vesicles. No receptors are used, so the process is nonspecific. Most vesicles are protein-coated. Vesicle
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Figure 3.13c Comparison of three types of endocytosis.
Receptor-mediated endocytosis Extracellular substances bind to specific receptor proteins in regions of coated pits, enabling the cell to ingest and concentrate specific substances (ligands) in protein-coated vesicles. Ligands may simply be released inside the cell, or combined with a lysosome to digest contents. Receptors are recycled to the plasma membrane in vesicles. Vesicle Receptor recycled to plasma membrane
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The Process of Exocytosis (This is not in your textbook).
Extracellular fluid Plasma membrane SNARE Vesicle SNARE Molecules to be secreted Secretory vesicle Cytoplasm (a) (b)
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i>Clicker Question #1:
Which of the following would be considered true for facilitated diffusion? The movement of materials is along (or with) the concentration gradient. The process may use a channel protein. An example of facilitated diffusion is seen in the sodium-potassium pump. Two of the above are correct. All of the above are correct.
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The process of exocytosis The membrane- bound vesicle migrates to the
Figure 3.14a Exocytosis. Plasma membrane SNARE (t-SNARE) The process of exocytosis Extracellular fluid Fusion pore formed Secretory vesicle The membrane- bound vesicle migrates to the plasma membrane. 1 Vesicle SNARE (v-SNARE) The vesicle and plasma membrane fuse and a pore opens up. 3 Molecule to be secreted Cytoplasm There, proteins at the vesicle surface (v-SNAREs) bind with t-SNAREs (plasma membrane proteins). 2 Vesicle contents are released to the cell exterior. 4 Fused v- and t-SNAREs
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Figure 3.14b Exocytosis.
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Outer mitochondrial membrane Ribosome Mitochondrial DNA Inner
Figure Mitochondrion. Outer mitochondrial membrane Ribosome Mitochondrial DNA Inner mitochondrial membrane (a) Cristae Matrix (c) Enzymes (b)
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Figure 3.18 The endoplasmic reticulum.
Smooth ER Nuclear envelope Rough ER Ribosomes Diagrammatic view of smooth and rough ER (b) Electron micrograph of smooth and rough ER (10,000x)
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Figure 3.19 Golgi apparatus.
New vesicles forming Cis face— “receiving” side of Golgi apparatus Transport vesicle from rough ER Cisternae New vesicles forming Transport vesicle from trans face Trans face— “shipping” side of Golgi apparatus Secretory vesicle Golgi apparatus Transport vesicle from the Golgi apparatus (a) Many vesicles in the process of pinching off from the membranous Golgi apparatus. (b) Electron micrograph of the Golgi apparatus (90,000x)
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destined for exocytosis Secretion by exocytosis Extracellular fluid
Figure The sequence of events from protein synthesis on the rough ER to the final distribution of those proteins. Protein- containing vesicles pinch off rough ER and migrate to fuse with membranes of Golgi apparatus. 1 Rough ER ER membrane Phagosome Plasma mem- brane Proteins in cisterna Pathway C: Lysosome containing acid hydrolase enzymes Proteins are modified within the Golgi compartments. 2 Vesicle becomes lysosome Proteins are then packaged within different vesicle types, depending on their ultimate destination. 3 Secretory vesicle Golgi apparatus Pathway B: Vesicle membrane to be incorporated into plasma membrane Pathway A: Vesicle contents destined for exocytosis Secretion by exocytosis Extracellular fluid
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Light areas are regions where materials are being digested.
Figure Electron micrograph of a cell containing lysosomes (12,000x). Lysosomes Light areas are regions where materials are being digested.
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Figure 3.22 The endomembrane system.
Nucleus Nuclear envelope Smooth ER Rough ER Vesicle Golgi apparatus Plasma membrane Transport vesicle Lysosome
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Figure 3.23 Cytoskeletal elements support the cell and help to generate movement.
(a) Microfilaments (b) Intermediate filaments (c) Microtubules Strands made of spherical protein subunits called actins Tough, insoluble protein fibers constructed like woven ropes Hollow tubes of spherical protein subunits called tubulins Tubulin subunits Fibrous subunits Actin subunit 25 nm 7 nm 10 nm Microfilaments form the blue network surrounding the pink nucleus in this photo. Intermediate filaments form the purple batlike network in this photo. Microtubules appear as gold networks surrounding the cells’ pink nuclei in this photo.
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Centrosome matrix Centrioles (a) Microtubules (b)
Figure Centrioles. Centrosome matrix Centrioles (a) Microtubules (b)
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Figure 3.26 Structure of a cilium.
Outer microtubule doublet Dynein arms The doublets also have attached motor proteins, the dynein arms. Central microtubule Cross-linking proteins inside outer doublets The outer microtubule doublets and the two central microtubules are held together by cross-linking proteins and radial spokes. Radial spoke TEM A cross section through the cilium shows the “9 + 2” arrangement of microtubules. Microtubules Cross-linking proteins inside outer doublets Radial spoke Plasma membrane Plasma membrane Cilium Triplet Basal body TEM TEM A longitudinal section of a cilium shows microtubules running the length of the structure. Basal body (centriole) A cross section through the basal body. The nine outer doublets of a cilium extend into a basal body where each doublet joins another microtubule to form a ring of nine triplets.
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Figure 3.27 Ciliary function.
Power, or propulsive, stroke Recovery stroke, when cilium is returning to its initial position 1 2 3 4 5 6 7 (a) Phases of ciliary motion. Layer of mucus Cell surface (b) Traveling wave created by the activity of many cilia acting together propels mucus across cell surfaces.
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Surface of nuclear envelope.
Figure The nucleus. Surface of nuclear envelope. Fracture line of outer membrane Nuclear envelope Nuclear pores Nucleus Chromatin (condensed) Nucleolus Nuclear pore complexes. Each pore is ringed by protein particles. Nuclear lamina. The netlike lamina composed of intermediate filaments formed by lamins lines the inner surface of the nuclear envelope. Cisternae of rough ER (a) (b)
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Figure 3.30 Chromatin and chromosome structure.
DNA double helix (2-nm diameter) 1 Histones Chromatin (“beads on a string”) structure with nucleosomes 2 Linker DNA Nucleosome (10-nm diameter; eight histone proteins wrapped by two winds of the DNA double helix) (a) Tight helical fiber (30-nm diameter) 3 Looped domain structure (300-nm diameter) 4 Chromatid (700-nm diameter) 5 Metaphase chromosome (at midpoint of cell division) (b)
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S Growth and DNA synthesis
Figure The cell cycle. G1 checkpoint (restriction point) S Growth and DNA synthesis G2 Growth and final preparations for division G1 Growth M G2 checkpoint
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Interphase Early Prophase Late Prophase Figure 3.33 Mitosis (1 of 2)
Centrosomes (each has 2 centrioles) Early mitotic spindle Spindle pole Polar microtubule Plasma membrane Fragments of nuclear envelope Aster Chromatin Nucleolus Centromere Nuclear envelope Chromosome consisting of two sister chromatids Kinetochore Kinetochore microtubule Interphase Early Prophase Late Prophase
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Telophase and Cytokinesis Metaphase Anaphase Nucleolus forming Nuclear
Figure Mitosis (2 of 2) Telophase and Cytokinesis Metaphase Anaphase Nucleolus forming Nuclear envelope forming Spindle Contractile ring at cleavage furrow Metaphase plate Daughter chromosomes Metaphase Anaphase Telophase
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Cell Metabolism Characteristics
Cofactors & coenzymes
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Cell Metabolism Characteristics
Aerobic & Anaerobic Respiration
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Cell Metabolism Characteristics
Pathways used in breakdown of Carbohydrates, Lipids, Fats
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