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

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

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Amoeba in Motion

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Ciliates and Flagellates

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Cytoskeleton

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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.

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Fig. 6-21

VesicleATP

Receptor for motor protein

Microtubuleof cytoskeleton

Motor protein (ATP powered)

(a)

Microtubule Vesicles

(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 6-1

10 µm 10 µm 10 µm

Column of tubulin dimers

Tubulin dimer

Actin subunit

25 nm

7 nm

Keratin proteins

Fibrous subunit (keratins coiled together)

8–12 nm

Table 6-1a10 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 (keratinscoiled 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


Fig. 6-22Centrosome

Microtubule

Centrioles

0.25 µm

Longitudinal section of one centriole

Microtubules Cross sectionof the other centriole

Cilia and Flagella

• Microtubules control the beating of cilia and flagella

• Cilia and flagella differ in their beating patterns


Fig. 6-23

5 µm

Direction of swimming

(a) Motion of flagella

Direction of organism’s movement

Power stroke Recovery stroke

(b) Motion of cilia15 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


Fig. 6-24

0.1 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 microtubuleRadial 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


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

1 3

2

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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


Fig, 6-27a

Muscle cell

Actin filament

Myosin filamentMyosin arm

(a) Myosin motors in muscle cell contraction

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Actin – Myosin Interaction

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• actin and myosin drive amoeboid movement

• Pseudopodia (cellular extensions)

• extend and contract through the reversible assembly and contraction of actin subunits into microfilaments


Fig. 6-27bcCortex (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


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Cyclosis in Elodea

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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


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


• 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


Fig. 6-28

Secondary cell wall

Primary cell wall

Middle lamella

Central vacuoleCytosol

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


Fig. 6-30

EXTRACELLULAR FLUIDCollagen

Fibronectin

Plasmamembrane

Micro-filaments

CYTOPLASM

Integrins

Proteoglycancomplex

Polysaccharidemolecule

Carbo-hydrates

Coreprotein

Proteoglycanmolecule

Proteoglycan complex

Fig. 6-30a

Collagen

Fibronectin

Plasma membrane


Integrins

CYTOPLASMMicro-filaments

EXTRACELLULAR FLUID

Fig. 6-30b

Polysaccharide molecule

Carbo-hydrates

Core protein

Proteoglycan molecule


• Functions of the Extracellular matrix (ECM):

– Support

– Adhesion

– Movement

– Regulation


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 junctionsCopyright © 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


Fig. 6-31

Interior of cell

Interior of cell

0.5 µm Plasmodesmata Plasma 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


Fig. 6-32

Tight junction

0.5 µm

1 µmDesmosome

Gap junction

Extracellularmatrix

0.1 µm

Plasma membranesof adjacent cells

Spacebetweencells

Gapjunctions

Desmosome

Intermediatefilaments

Tight junction

Tight junctions preventfluid from movingacross a layer of cells

Fig. 6-32aTight junctions prevent fluid from moving across a layer of cells

Tight junction

Intermediate filaments

Desmosome

Gap junctions

Extracellular matrixSpace

between cells

Plasma membranes of adjacent cells

Fig. 6-32b

Tight junction

0.5 µm

Fig. 6-32c

Desmosome1 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


Fig. 6-33

5 µ

m

Fig. 6-UN1Cell Component Structure Function

Houses chromosomes, made ofchromatin (DNA, the geneticmaterial, and proteins); containsnucleoli, where ribosomalsubunits are made. Poresregulate entry and exit ofmaterials.

Nucleus

(ER)

Concept 6.3 The eukaryotic cell’s geneticinstructions are housed inthe nucleus and carried outby the ribosomes

Ribosome

Concept 6.4 Endoplasmic reticulum The endomembrane systemregulates protein traffic andperforms metabolic functionsin the cell

(Nuclearenvelope)

Concept 6.5 Mitochondria and chloro-plasts change energy fromone form to another

Golgi apparatus

Lysosome

Vacuole

Mitochondrion

Chloroplast

Peroxisome

Two subunits made of ribo-somal RNA and proteins; can befree in cytosol or bound to ER

Extensive network ofmembrane-bound tubules andsacs; membrane separateslumen from cytosol;continuous withthe nuclear envelope.

Membranous sac of hydrolyticenzymes (in animal cells)

Large membrane-boundedvesicle in plants

Bounded by doublemembrane;inner membrane hasinfoldings (cristae)

Typically two membranesaround fluid stroma, whichcontains membranous thylakoidsstacked into grana (in plants)

Specialized metaboliccompartment bounded by asingle membrane

Protein synthesis

Smooth ER: synthesis oflipids, metabolism of carbohy-drates, Ca2+ storage, detoxifica-tion of drugs and poisons

Rough ER: Aids in synthesis ofsecretory and other proteins frombound ribosomes; addscarbohydrates to glycoproteins;produces new membrane

Modification of proteins, carbo-hydrates on proteins, and phos-pholipids; synthesis of manypolysaccharides; sorting of Golgiproducts, which are then released in vesicles.

Breakdown of ingested substances,cell macromolecules, and damagedorganelles for recycling

Digestion, storage, wastedisposal, water balance, cellgrowth, and protection

Cellular respiration

Photosynthesis

Contains enzymes that transferhydrogen to water, producinghydrogen peroxide (H2O2) as aby-product, which is convertedto water by other enzymesin the peroxisome

Stacks of flattenedmembranoussacs; has polarity(cis and transfaces)

Surrounded by nuclearenvelope (double membrane)perforated by nuclear pores.The nuclear envelope iscontinuous with theendoplasmic reticulum (ER).

Fig. 6-UN1a

Cell Component Structure Function

Concept 6.3 The eukaryotic cell’s geneticinstructions are housed inthe nucleus and carried outby the ribosomes

Nucleus Surrounded by nuclearenvelope (double membrane)perforated by nuclear pores.The nuclear envelope iscontinuous with theendoplasmic reticulum (ER).

(ER)

Houses chromosomes, made ofchromatin (DNA, the geneticmaterial, and proteins); containsnucleoli, where ribosomalsubunits are made. Poresregulate entry and exit osmaterials.

Ribosome Two subunits made of ribo-somal RNA and proteins; can befree in cytosol or bound to ER

Protein synthesis

Fig. 6-UN1b

Cell Component Structure Function

Concept 6.4 The endomembrane systemregulates protein traffic andperforms metabolic functionsin the cell

Endoplasmic reticulum

(Nuclearenvelope)

Golgi apparatus

Lysosome

Vacuole Large membrane-boundedvesicle in plants

Membranous sac of hydrolyticenzymes (in animal cells)

Stacks of flattenedmembranoussacs; has polarity(cis and transfaces)

Extensive network ofmembrane-bound tubules andsacs; membrane separateslumen from cytosol;continuous withthe nuclear envelope.

Smooth ER: synthesis oflipids, metabolism of carbohy-drates, Ca2+ storage, detoxifica-tion of drugs and poisons

Rough ER: Aids in sythesis ofsecretory and other proteinsfrom bound ribosomes; addscarbohydrates to glycoproteins;produces new membrane

Modification of proteins, carbo-hydrates on proteins, and phos-pholipids; synthesis of manypolysaccharides; sorting ofGolgi products, which are thenreleased in vesicles.

Breakdown of ingested sub-stances cell macromolecules, and damaged organelles for recycling

Digestion, storage, wastedisposal, water balance, cellgrowth, and protection

Fig. 6-UN1c

Cell Component

Concept 6.5Mitochondria and chloro-plasts change energy fromone form to another

Mitochondrion

Chloroplast

Peroxisome

Structure Function

Bounded by doublemembrane;inner membrane hasinfoldings (cristae)

Typically two membranesaround fluid stroma, whichcontains membranous thylakoidsstacked into grana (in plants)

Specialized metaboliccompartment bounded by asingle membrane

Cellular respiration

Photosynthesis

Contains enzymes that transferhydrogen to water, producinghydrogen peroxide (H2O2) as aby-product, which is convertedto water by other enzymesin 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


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 junctionsCopyright © 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

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

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