How are cells able to move? List some different techniques of cell locomotion.

Amoeba in Motion

Ciliates and Flagellates

Cytoskeleton

Actin Microfilaments two gently twisted strands of actin subunits – long but only 7nm in diameter – maintain shape of the cell – bearing tension (pull) rather than resistance (push) – instrumental in major changes of cell shape such as Pseudopodia muscle contractions cleavage that occurs during cell division.

Tubulin - Microtubules The microtubule subunits wind around in a continuously growing strand and can be added to lengthen the hollow tube that is formed – 25nm in diameter – Hollow tube part is 15 nm in diameter used in cell motility by flagella and cilia Maintains the shape of a cell by resisting compression used to move around items inside the cell, such as organelles or chromosomes during cell division.

Dividing newt lung cell seen under a light microscope and colored using fluorescent dyes: chromosomes in blue, intermediate filaments in red, and spindle fibers (bundled microtubules assembled for cell division) in green.microtubules

Fig Vesicle ATP Receptor for motor protein Microtubule of cytoskeleton Motor protein (ATP powered) (a) MicrotubuleVesicles (b) 0.25 µm

Intermediate Filaments Keratin protein fibers – arranged in cords of differing diameters of 8-12nm (depending on the function in the cell) Serve as permanent structures, unlike the microtubules and microfilaments – part of a permanent scaffolding – serve to maintain rigid cell shape – anchor organelles in fixed positions when necessary the nucleus is fixed in a position with rigid intermediate filaments

Name the three types of structures which make up the cytoskeleton. – Microtubules – Microfilaments – Intermediate filaments

Describe the differences in size between microtubules, microfilaments and intermediate filaments.

Components of the Cytoskeleton – Microtubules are the thickest of the three components of the cytoskeleton – Microfilaments, also called actin filaments, are the thinnest components – Intermediate filaments are fibers with diameters in a middle range Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Table µm Column of tubulin dimers Tubulin dimer Actin subunit  25 nm 7 nm Keratin proteins Fibrous subunit (keratins coiled together) 8–12 nm

Table 6-1a 10 µm Column of tubulin dimers Tubulin dimer   25 nm

Table 6-1b Actin subunit 10 µm 7 nm

Table 6-1c 5 µm Keratin proteins Fibrous subunit (keratins coiled together) 8–12 nm

Centrosomes and Centrioles In many cells, microtubules grow out from a centrosome near the nucleus The centrosome is a “microtubule-organizing center” In animal cells, the centrosome has a pair of centrioles, each with nine triplets of microtubules arranged in a ring Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig Centrosome Microtubule Centrioles 0.25 µm Longitudinal section of one centriole Microtubules Cross section of the other centriole

Cilia and Flagella Microtubules control the beating of cilia and flagella Cilia and flagella differ in their beating patterns Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig µm Direction of swimming (a) Motion of flagella Direction of organism’s movement Power strokeRecovery stroke (b) Motion of cilia 15 µm

Cilia and flagella share a common ultrastructure: – A core of microtubules sheathed by the plasma membrane – A basal body that anchors the cilium or flagellum – A motor protein called dynein, which drives the bending movements of a cilium or flagellum Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig µm Triplet (c) Cross section of basal body (a)Longitudinal section of cilium 0.5 µm Plasma membrane Basal body Microtubules (b)Cross section of cilium Plasma membrane Outer microtubule doublet Dynein proteins Central microtubule Radial spoke Protein cross- linking outer doublets 0.1 µm

How dynein “walking” moves flagella and cilia: − Dynein arms alternately grab, move, and release the outer microtubules – Protein cross-links limit sliding – Forces exerted by dynein arms cause doublets to curve, bending the cilium or flagellum Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 6-25a Microtubule doublets Dynein protein (a) Effect of unrestrained dynein movement ATP

Fig. 6-25b Cross-linking proteins inside outer doublets Anchorage in cell ATP (b) Effect of cross-linking proteins (c) Wavelike motion 13 2

alef0 Hypothesis of Flagellar Beating

Microfilaments that function in cellular motility contain the protein myosin in addition to actin In muscle cells, thousands of actin filaments are arranged parallel to one another Thicker filaments composed of myosin interdigitate with the thinner actin fibers Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig, 6-27a Muscle cell Actin filament Myosin filament Myosin arm (a) Myosin motors in muscle cell contraction

Actin – Myosin Interaction

actin and myosin drive amoeboid movement Pseudopodia (cellular extensions) extend and contract through the reversible assembly and contraction of actin subunits into microfilaments Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 6-27bc Cortex (outer cytoplasm): gel with actin network Inner cytoplasm: sol with actin subunits Extending pseudopodium (b) Amoeboid movement Nonmoving cortical cytoplasm (gel) Chloroplast Cell wall Streaming cytoplasm (sol) Parallel actin filaments (c) Cytoplasmic streaming in plant cells Vacuole

Cytoplasmic streaming – a circular flow of cytoplasm within cells – speeds distribution of materials within the cell – In plant cells, actin-myosin interactions and sol-gel transformations drive cytoplasmic streaming Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Cyclosis in Elodea

Extracellular components and connections between cells help coordinate cellular activities Most cells synthesize and secrete materials that are external to the plasma membrane These extracellular structures include: – Cell walls of plants – The extracellular matrix (ECM) of animal cells – Intercellular junctions Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Cell Walls of Plants cell wall – an extracellular structure that distinguishes plant cells from animal cells – Prokaryotes, fungi, and some protists also have cell walls – protects the plant cell, maintains its shape, and prevents excessive uptake of water – Plant cell walls are made of cellulose fibers embedded in other polysaccharides and protein Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Plant cell walls may have multiple layers: – Primary cell wall: relatively thin and flexible – Middle lamella: thin layer between primary walls of adjacent cells – Secondary cell wall (in some cells): added between the plasma membrane and the primary cell wall Plasmodesmata are channels between adjacent plant cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig Secondary cell wall Primary cell wall Middle lamella Central vacuole Cytosol Plasma membrane Plant cell walls Plasmodesmata 1 µm

The Extracellular Matrix (ECM) of Animal Cells Animal cells lack cell walls but – covered by an elaborate extracellular matrix (ECM) – made up of glycoproteins such as collagen, proteoglycans, and fibronectin bind to receptor proteins in the plasma membrane called integrins Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig EXTRACELLULAR FLUID Collagen Fibronectin Plasma membrane Micro- filaments CYTOPLASM Integrins Proteoglycan complex Polysaccharide molecule Carbo- hydrates Core protein Proteoglycan molecule Proteoglycan complex

Fig. 6-30a Collagen Fibronectin Plasma membrane Proteoglycan complex Integrins CYTOPLASM Micro- filaments EXTRACELLULAR FLUID

Fig. 6-30b Polysaccharide molecule Carbo- hydrates Core protein Proteoglycan molecule Proteoglycan complex

Functions of the Extracellular matrix (ECM): – Support – Adhesion – Movement – Regulation Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Intercellular Junctions Neighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contact Intercellular junctions facilitate this contact There are several types of intercellular junctions – Plasmodesmata – Tight junctions – Desmosomes – Gap junctions Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Plasmodesmata in Plant Cells Plasmodesmata – channels that perforate plant cell walls – water and small solutes (and sometimes proteins and RNA) can pass from cell to cell Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig Interior of cell 0.5 µm PlasmodesmataPlasma membranes Cell walls

Tight Junctions, Desmosomes, and Gap Junctions in Animal Cells At tight junctions – membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid Desmosomes – (anchoring junctions) fasten cells together into strong sheets Gap junctions – (communicating junctions) provide cytoplasmic channels between adjacent cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig Tight junction 0.5 µm 1 µm Desmosome Gap junction Extracellular matrix 0.1 µm Plasma membranes of adjacent cells Space between cells Gap junctions Desmosome Intermediate filaments Tight junction Tight junctions prevent fluid from moving across a layer of cells

Fig. 6-32a Tight junctions prevent fluid from moving across a layer of cells Tight junction Intermediate filaments Desmosome Gap junctions Extracellular matrix Space between cells Plasma membranes of adjacent cells

Fig. 6-32b Tight junction 0.5 µm

Fig. 6-32c Desmosome 1 µm

Fig. 6-32d Gap junction 0.1 µm

The Cell: A Living Unit Greater Than the Sum of Its Parts Cells rely on the integration of structures and organelles in order to function For example, a macrophage’s ability to destroy bacteria involves the whole cell, coordinating components such as the cytoskeleton, lysosomes, and plasma membrane Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig µm

Fig. 6-UN1 Cell Component Structure Function Houses chromosomes, made of chromatin (DNA, the genetic material, and proteins); contains nucleoli, where ribosomal subunits are made. Pores regulate entry and exit of materials. Nucleus (ER) Concept 6.3 The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes Ribosome Concept 6.4 Endoplasmic reticulum The endomembrane system regulates protein traffic and performs metabolic functions in the cell (Nuclear envelope) Concept 6.5 Mitochondria and chloro- plasts change energy from one form to another Golgi apparatus Lysosome Vacuole Mitochondrion Chloroplast Peroxisome Two subunits made of ribo- somal RNA and proteins; can be free in cytosol or bound to ER Extensive network of membrane-bound tubules and sacs; membrane separates lumen from cytosol; continuous with the nuclear envelope. Membranous sac of hydrolytic enzymes (in animal cells) Large membrane-bounded vesicle in plants Bounded by double membrane; inner membrane has infoldings (cristae) Typically two membranes around fluid stroma, which contains membranous thylakoids stacked into grana (in plants) Specialized metabolic compartment bounded by a single membrane Protein synthesis Smooth ER: synthesis of lipids, metabolism of carbohy- drates, Ca 2+ storage, detoxifica- tion of drugs and poisons Rough ER: Aids in synthesis of secretory and other proteins from bound ribosomes; adds carbohydrates to glycoproteins; produces new membrane Modification of proteins, carbo- hydrates on proteins, and phos- pholipids; synthesis of many polysaccharides; sorting of Golgi products, which are then released in vesicles. Breakdown of ingested substances, cell macromolecules, and damaged organelles for recycling Digestion, storage, waste disposal, water balance, cell growth, and protection Cellular respiration Photosynthesis Contains enzymes that transfer hydrogen to water, producing hydrogen peroxide (H 2 O 2 ) as a by-product, which is converted to water by other enzymes in the peroxisome Stacks of flattened membranous sacs; has polarity (cis and trans faces) Surrounded by nuclear envelope (double membrane) perforated by nuclear pores. The nuclear envelope is continuous with the endoplasmic reticulum (ER).

Fig. 6-UN1a Cell Component Structure Function Concept 6.3 The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes Nucleus Surrounded by nuclear envelope (double membrane) perforated by nuclear pores. The nuclear envelope is continuous with the endoplasmic reticulum (ER). (ER) Houses chromosomes, made of chromatin (DNA, the genetic material, and proteins); contains nucleoli, where ribosomal subunits are made. Pores regulate entry and exit os materials. Ribosome Two subunits made of ribo- somal RNA and proteins; can be free in cytosol or bound to ER Protein synthesis

Fig. 6-UN1b Cell Component Structure Function Concept 6.4 The endomembrane system regulates protein traffic and performs metabolic functions in the cell Endoplasmic reticulum (Nuclear envelope) Golgi apparatus Lysosome Vacuole Large membrane-bounded vesicle in plants Membranous sac of hydrolytic enzymes (in animal cells) Stacks of flattened membranous sacs; has polarity (cis and trans faces) Extensive network of membrane-bound tubules and sacs; membrane separates lumen from cytosol; continuous with the nuclear envelope. Smooth ER: synthesis of lipids, metabolism of carbohy- drates, Ca 2+ storage, detoxifica- tion of drugs and poisons Rough ER: Aids in sythesis of secretory and other proteins from bound ribosomes; adds carbohydrates to glycoproteins; produces new membrane Modification of proteins, carbo- hydrates on proteins, and phos- pholipids; synthesis of many polysaccharides; sorting of Golgi products, which are then released in vesicles. Breakdown of ingested sub- stances cell macromolecules, and damaged organelles for recycling Digestion, storage, waste disposal, water balance, cell growth, and protection

Fig. 6-UN1c Cell Component Concept 6.5 Mitochondria and chloro- plasts change energy from one form to another Mitochondrion Chloroplast Peroxisome Structure Function Bounded by double membrane; inner membrane has infoldings (cristae) Typically two membranes around fluid stroma, which contains membranous thylakoids stacked into grana (in plants ) Specialized metabolic compartment bounded by a single membrane Cellular respiration Photosynthesis Contains enzymes that transfer hydrogen to water, producing hydrogen peroxide (H 2 O 2 ) as a by-product, which is converted to water by other enzymes in the peroxisome

You should now be able to: 1.Distinguish between the following pairs of terms: magnification and resolution; prokaryotic and eukaryotic cell; free and bound ribosomes; smooth and rough ER 2.Describe the structure and function of the components of the endomembrane system 3.Briefly explain the role of mitochondria, chloroplasts, and peroxisomes 4.Describe the functions of the cytoskeleton Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

5.Compare the structure and functions of microtubules, microfilaments, and intermediate filaments 6.Explain how the ultrastructure of cilia and flagella relate to their functions 7.Describe the structure of a plant cell wall 8.Describe the structure and roles of the extracellular matrix in animal cells 9.Describe four different intercellular junctions Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

How might cells from various parts of the body differ in the number and types of cellular organelles they contain due to their specific function?

stomach cell – rough ER for secretion muscle cell – mitochondria for ATP liver storage cell – vacuoles for storage Liver detoxification cell – peroxisomes and smooth ER to break down toxins Adipose cell – vacuoles for storage white blood cell – lysosomes to break down engulfed pathogens mesophyll cell—plant leaf cell – chloroplasts for photosynthesis potato cell – vacuoles for starch storage

Recycling Cells are wonderful at recycling! – the endomembrane system cycles phospholipids – lysosomes, peroxisomes and the smooth ER break down macromolecules to component parts and reassemble them – the cytoskeleton constant flow of assembling and de-assembling subunits

Why are cells so efficient at recycling? Limited resources limited energy efficiency