Nuclei (yellow) and actin (red) Figure 4.6x

network of protein fibers THE CYTOSKELETON The cell’s internal skeleton helps organize its structure and activities network of protein fibers Figure 4.17A

Microfilaments of actin enable cells to change shape and move Intermediate filaments reinforce the cell and anchor certain organelles Microtubules give the cell rigidity provide anchors for organelles act as tracks for organelle movement

INTERMEDIATE FILAMENT Tubulin subunit Actin subunit Fibrous subunits 25 nm 7 nm 10 nm MICROFILAMENT INTERMEDIATE FILAMENT MICROTUBULE Figure 4.17B

How do cilia and flagella move? A cilia or flagellum is composed of a core of microtubules wrapped in plasma membrane Eukaryotes have “9+2” structure Cilia and flagella move when microtubules bend

Electron micrograph of sections: FLAGELLUM Electron micrograph of sections: Outer microtubule doublet Plasma membrane Flagellum Central microtubules Outer microtubule doublet Plasma membrane Basal body Basal body (structurally identical to centriole) Figure 4.18A

Slide 43

polar head P – cytosol nonpolar tails Phospholipid bilayer Figure: 05-01a-b Note: The nature of phospholipids (polar, nonpolar) gives a membrane its selective permeabiility.as far as hydrophobic and hydrophilic molecules. Caption: The essential building block of the cell’s plasma membrane is the phospholipid molecule, which has both a hydrophilic “head” that bonds with water, and hydrophobic “tails” that do not. Two layers of phospholipids sandwich together to form the plasma membrane. The phospholipids’ hydrophobic tails form the interior of the membrane, while their hydrophilic heads jut out toward the watery environments that exist both inside and outside of the cell. The bilayer forms a barrier to all but the smallest hydrophilic molecules, but hydrophobic molecules can pass through fairly freely. cytosol hydrophobic molecules hydrophilic molecules nonpolar tails Phospholipid bilayer

Cell surfaces protect, support, and join cells Surfaces allow exchange of signals and molecules. Plant cells connect by plasmodesmata

PLASMODESMATA Walls of two adjacent plant cells Vacuole Layers of one plant cell wall Cytoplasm Plasma membrane Figure 4.19A

Animal cells - extracellular matrix sticky layer of glycoproteins binds cells together in tissues can also protect and support cells

Tight junctions can bind cells together into leakproof sheets Anchoring junctions link animal cells Gap junctions allow substances to flow from cell to cell TIGHT JUNCTION ANCHORING JUNCTION GAP JUNCTION Plasma membranes of adjacent cells Extracellular matrix Figure 4.19B

Eukaryotic organelles fall into 4 functional groups 1. Manufacture and transport – dependent on network of membranes Nucleus Ribosomes Rough ER Smooth ER Golgi apparatus

2. Breakdown – all single-membrane sacs Lysosomes (in animals, some protists) Peroxisomes Vacuoles (plants)

3. Energy Processing – involves extensive membranes embedded with enzymes Chloroplasts Mitochondria

4. Support, Movement, Communication Cytoskeleton – includes cilia, flagella, filaments, microtubules Cell walls Extracellular matrix Cell junctions

Figure: 03-00CO Title: Cholesterol in blood. Caption: Our bodies cannot function without cholesterol, yet too much cholesterol can threaten our health by contributing to hard deposits (colored gray in this photo) that restrict the flow of blood through arteries. Inside our bodies, the cell membrane shoulders much of the task of keeping blood cholesterol levels within bounds.

What do these have in common? HIV infection Transplanted organs Communication between neurons Drug addiction Cystic fibrosis hypercholesteremia

Membranes organize the chemical activities of cells selectively permeable hold teams of enzymes   Cytoplasm Figure 5.10

Plasma membrane Contact between cell and environment Keeps useful materials inside and harmful stuff outside Allows transport, communication in both directions

Plasma membrane components Phospholipid bilayer Cholesterol Proteins Glycocalyx

polar head P – cytosol nonpolar tails Phospholipid bilayer Figure: 05-01a-b Note: The nature of phospholipids (polar, nonpolar) gives a membrane its selective permeabiility.as far as hydrophobic and hydrophilic molecules. Caption: The essential building block of the cell’s plasma membrane is the phospholipid molecule, which has both a hydrophilic “head” that bonds with water, and hydrophobic “tails” that do not. Two layers of phospholipids sandwich together to form the plasma membrane. The phospholipids’ hydrophobic tails form the interior of the membrane, while their hydrophilic heads jut out toward the watery environments that exist both inside and outside of the cell. The bilayer forms a barrier to all but the smallest hydrophilic molecules, but hydrophobic molecules can pass through fairly freely. cytosol hydrophobic molecules hydrophilic molecules nonpolar tails Phospholipid bilayer

Cholesterol blocks some small molecules, adds fluidity THE PLASMA MEMBRANE phospholipids cholesterol Figure: 05-02a Title: The plasma membrane. Caption: integral protein cytoskeleton peripheral protein Cholesterol blocks some small molecules, adds fluidity

Membrane Proteins span entire membrane or lie on either side Purposes Structural Support Recognition Communication Transport

Glycocalyx Composed of sugars protruding from lipids and proteins Functions Binding sites for proteins Lubricate cells. Stick cells down.

Many membrane proteins are enzymes Some proteins function as receptors for chemical messages from other cells The binding of a messenger to a receptor may trigger signal transduction Messenger molecule Receptor Activated molecule Figure 5.13 Enzyme activity Signal transduction

The plasma membrane of an animal cell Glycoprotein Carbohydrate (of glycoprotein) Fibers of the extracellular matrix Glycolipid Phospholipid Cholesterol Microfilaments of the cytoskeleton Proteins CYTOPLASM Figure 5.12

Diffusion and Gradients Diffusion = movement of molecules from region of higher to lower concentration. Osmosis = diffusion of water across a membrane

In passive transport, substances diffuse through membranes without work by the cell Molecule of dye Membrane EQUILIBRIUM EQUILIBRIUM Figure 5.14A & B

selectively permeable membrane H2O selectively permeable membrane free water molecule: can fit through pore sugar pore bound water molecules clustered around sugar: cannot fit through pore Figure: 03-03 Title: Osmosis. Caption: Free water molecules diffuse down their concentration gradient across a selectively permeable membrane, from a region of high water concentration to a region of lower water concentration. (b) selectively permeable membrane sugar molecule bag bursts water molecule pure water

Osmosis = diffusion of water across a membrane Hypotonic solution Hypertonic solution water travels from an area of higher concentration to an area of lower water concentration Selectively permeable membrane Solute molecule HYPOTONIC SOLUTION HYPERTONIC SOLUTION Water molecule Selectively permeable membrane Solute molecule with cluster of water molecules NET FLOW OF WATER Figure 5.15

Water balance between cells and their surroundings is crucial to organisms osmoregulation = control of water balance Osmosis causes cells to shrink in a hypertonic solution and swell in a hypotonic solution

hypertonic solution hypotonic solution 10 microns isotonic solution Figure: 03-05 Title: The effects of osmosis. Caption: Red blood cells are normally suspended in the fluid environment of the blood. (a) If red blood cells are immersed in an isotonic salt solution, which has the same concentration of dissolved substances as the blood cells do, there is no net movement of water across the plasma membrane. The red blood cells keep their characteristic dimpled disk shape. (b) A hypertonic solution, with too much salt, causes water to leave the cells, shriveling them up. (c) A hypotonic solution, with less salt than is in the cells, causes water to enter, and the cells swell. equal movement of water into and out of cells net water movement out of cells net water movement into cells

Passive transport = diffusion across membranes Small nonpolar molecules - simple diffusion Many molecules pass through protein pores by facilitated diffusion Solute molecule Transport protein Figure 5.17

Active transport transport proteins needed against a concentration gradient requires energy (ATP)

Active transport in two solutes across a membrane FLUID OUTSIDE CELL Phosphorylated transport protein Active transport in two solutes across a membrane Na+/K+ pump Protein shape change Transport protein First solute 1 First solute, inside cell, binds to protein 2 ATP transfers phosphate to protein 3 Protein releases solute outside cell Second solute 4 Second solute binds to protein 5 Phosphate detaches from protein 6 Protein releases second solute into cell Figure 5.18

Exocytosis and endocytosis transport large molecules exocytosis = vesicle fuses with the membrane and expels its contents FLUID OUTSIDE CELL CYTOPLASM Figure 5.19A

b Figure: 05-08b Title: Movement out of the cell. Caption: b. Micrograph of material being expelled from the cell through exocytosis. b

or the membrane may fold inward, trapping material from the outside (endocytosis) Figure 5.19B

Phagocytosis, “cell eating” —How the human immune system ingests whole bacteria or one-celled creatures eat. phagocytosis food particle 1 2 3 Figure: 03-07b Title: Two types of endocytosis. Caption: (b) Pseudopodia encircle an extracellular particle. The ends of the pseudopodia fuse, forming a large vesicle that contains the engulfed particle. particle enclosed in vesicle

pinocytosis (extracellular fluid) 2 vesicle containing extracellular Figure: 03-07a Title: Two types of endocytosis. Caption: (a) To capture drops of liquid, a dimple in the plasma membrane deepens and eventually pinches off as a fluid-filled vesicle, which contains a random sampling of the extracellular fluid. vesicle containing extracellular fluid (cytoplasm)

extracellular fluid plasma membrane cytosol vesicle coated pit receptors captured molecules vesicle Figure: 05-09a-c Title: Three types of endocytosis. Caption: a. In pinocytosis, the plasma membrane invaginates to create a kind of harbor. The harbor then encloses completely, pinches off as a vesicle, and moves into the cell's cytoplasm, carrying with it whatever material was enclosed. b. In receptor-mediated endocytosis, many receptors bind to molecules. Then, while holding on to the molecules, the receptors migrate laterally through the cell, forming an invagination called a coated pit. The coated pit pinches off, delivering its receptor - held molecules into the cytoplasm. c. In phagocytosis, food particles - or perhaps whole organisms (such as bacteria)-are taken in by means of "false feet" or pseudopodia that surround the material. Pseudopodia then fuse together, forming a vesicle that moves into the cell's interior with its catch enclosed. bacterium pseudopodium vesicle

Receptor-mediated endocytosis

Cholesterol can accumulate in the blood if membranes lack cholesterol receptors Phospholipid outer layer LDL PARTICLE Receptor protein Protein Cholesterol Plasma membrane Vesicle CYTOPLASM Figure 5.20

Figure: 03-00CO Title: Cholesterol in blood. Caption: Our bodies cannot function without cholesterol, yet too much cholesterol can threaten our health by contributing to hard deposits (colored gray in this photo) that restrict the flow of blood through arteries. Inside our bodies, the cell membrane shoulders much of the task of keeping blood cholesterol levels within bounds.

What do these have in common? HIV infection Transplanted organs Communication between neurons Drug addiction Cystic fibrosis hypercholesteremia