Chapter 3 Cell Structure and Function 6/27/111MDufilho.

Chapter 3

Cell Structure and Function

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Processes of Life

What is the difference between a living thing and a non living thing?

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Figure 3.1 Examples of types of cells-overview

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How are these cells similar?

Prokaryote Eukaryote

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External Structures of Bacterial Cells

• Two Types of Glycocalyces– Capsule

– Composed of organized repeating units of organic chemicals

– Firmly attached to cell surface– May prevent bacteria from being recognized by host

– Slime layer– Loosely attached to cell surface– Water soluble– Sticky layer allows prokaryotes to attach to surfaces

© 2012 Pearson Education Inc.

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Figure 3.5 Glycocalyces-overview

Glycocalyx(capsule)

Glycocalyx(slime layer)

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• Flagella– Are responsible for movement

– Have long structures that extend beyond cell surface

– Are not present on all bacteria


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Figure 3.6 Proximal structure of bacterial flagella-overview

Filament

Directionof rotationduring run

Peptidoglycanlayer (cell wall)

Cytoplasmicmembrane

Cytoplasm

Rod

Protein rings

Gram Gram

Filament

Outerproteinrings

Rod

Integral protein

Innerproteinrings

Integralprotein

Basalbody

Cytoplasm

Outer membrane

Peptidoglycanlayer

Cytoplasmicmembrane

Cellwall

Ho

o

k

Ho

o

k

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ANIMATION Flagella: Movement

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Figure 3.7 Micrographs of basic arrangements of bacterial flagella-overview

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Figure 3.8 Axial filament-overview

Axial filament

Endoflagellarotate Axial filament

rotates aroundcell

Outermembrane

Cytoplasmicmembrane

Axial filamentSpirochetecorkscrewsand movesforward

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Figure 3.10 Fimbriae

Flagellum Fimbria

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Figure 3.11 Pili

Conjugation pilus

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Bacterial Cell Walls

• Bacterial Cell Walls– Provide structure and shape and protect cell from

osmotic forces– Assist some cells in attaching to other cells or in

resisting antimicrobial drugs– Can target cell wall of bacteria with antibiotics– Give bacterial cells characteristic shapes– Composed of peptidoglycan– Scientists describe two basic types of bacterial cell

walls, Gram-positive and Gram-negative


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Figure 3.13 Comparison of the structures of glucose, NAG, and NAM-overview

Glucose N-acetylglucosamineNAG

N-acetylmuramic acidNAM

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• Gram-Positive Bacterial Cell Walls– Relatively thick layer of peptidoglycan

– Contain unique polyalcohols called teichoic acids and lipotechoic acid – have a negative charge

– Appear purple following Gram staining procedure

– Up to 60% mycolic acid in acid-fast bacteria helps cells survive desiccation


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Figure 3.15a Comparison of cell walls of Gram-positive and Gram-negative bacteria

Gram-positive cell wall

Peptidoglycan layer(cell wall)

Cytoplasmic membrane

Teichoic acid

Lipoteichoic acid

Integralprotein

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• Gram-Negative Bacterial Cell Walls– Have only a thin layer of peptidoglycan

– Bilayer membrane outside the peptidoglycan contains phospholipids, proteins, and lipopolysaccharide (LPS)

– May be impediment to the treatment of disease

– Appear pink following Gram staining procedure


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Figure 3.15b Comparison of cell walls of Gram-positive and Gram-negative bacteria

Gram-negative cell wall

Outermembraneof cell wall

Peptidoglycanlayer of cell wall

Cytoplasmicmembrane

Lipopolysaccharide(LPS)

Porin

Porin(sectioned)

Periplasmic space

Phospholipid layers

Integralproteins

n

Corepolysaccharide

O side chain(varies Inlength andcomposition)

Lipid A(embeddedin outermembrane)

Fatty acid

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Bacterial Cytoplasmic Membranes

• Structure– Referred to as phospholipid bilayer

– Composed of lipids and associated proteins– Fluid mosaic model describes current

understanding of membrane structure


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Figure 3.16 The structure of a prokaryotic cytoplasmic membrane: a phospholipid bilayer

Head, whichcontains phosphate(hydrophilic)

Tail(hydrophobic)

Phospholipid

Phospholipidbilayer

Integral proteinPeripheral protein

Integralprotein

Cytoplasm

Integralproteins

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Bacterial Cytoplasmic Membranes

Remember the Functions???

What are they???


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Cytoplasm of Bacteria

• Cytosol – Liquid portion of cytoplasm• Inclusions – May include reserve deposits of

chemicals• Endospores – Unique structures produced by

some bacteria that are a defensive strategy against unfavorable conditions


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Figure 3.23 Granules of PHB in the bacterium Azotobacter chroococcum

Polyhydroxybutyrate

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Figure 3.24 The formation of an endospore-overview

DNA is replicated.

DNA aligns alongthe cell’s long axis.

Cytoplasmic membraneinvaginates to formforespore.

Cytoplasmic membranegrows and engulfsforespore within a second membrane.Vegetative cell’s DNAdisintegrates.

Cell wallCytoplasmicmembrane

DNA

Vegetative cell

Forespore

Firstmembrane

Second membrane

A cortex of calcium anddipicolinic acid isdeposited betweenthe membranes.

Spore coat formsaround endospore.

Endospore matures:completion of spore coatand increase in resistanceto heat and chemicals byunknown process.

Endospore is released fromoriginal cell.

Cortex

Spore coat

Outerspore coat

Endospore

Outerspore coat

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Cytoplasm of Bacteria

• Nonmembranous Organelles

– Ribosomes – Sites of protein synthesis

– Cytoskeleton – Plays a role in forming the cell’s basic shape


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Endosymbiotic Theory

• Mitochondria and chloroplasts have 70S ribosomes, circular DNA, and two membranes. Why????


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Chapter 3 Cell Structure and Function 6/27/111MDufilho.

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Transcript of Chapter 3 Cell Structure and Function 6/27/111MDufilho.