functional anatomy of eukaryotic cells · © 2016 pearson education, inc. nucleoid • contains...

PowerPoint® Lecture Presentations prepared by Bradley W. Christian, McLennan Community College

C H A P T E R

© 2016 Pearson Education, Inc.

Functional Anatomy of Prokaryotic and Eukaryotic Cells

4


Comparing Prokaryotic and Eukaryotic Cells: An Overview

•  Prokaryote comes from the Greek words for prenucleus.

•  Eukaryote comes from the Greek words for true nucleus.


Comparing Prokaryotic and Eukaryotic Cells: An Overview

Prokaryote •  One circular chromosome,

not in a membrane •  No histones •  No organelles •  Bacteria: peptidoglycan

cell walls •  Archaea: pseudomurein

cell walls •  Divides by binary fission

Eukaryote •  Paired chromosomes,

in nuclear membrane •  Histones •  Organelles •  Polysaccharide cell walls,

when present •  Divides by mitosis


The Size, Shape, and Arrangement of Bacterial Cells

•  Average size: 0.2 to 2.0 µm diameter × 2 to 8 µm length

•  Most bacteria are monomorphic (single shape) •  A few are pleomorphic (many shapes)



•  Bacillus (rod-shaped) •  Coccus (spherical) •  Spiral

•  Vibrio •  Spirillum •  Spirochete

•  Star-shaped •  Rectangular


Figure 4.4 Spiral bacteria.


Figure 4.5a Star-shaped and rectangular prokaryotes.


Figure 4.5b Star-shaped and rectangular prokaryotes.



•  Pairs: diplococci, diplobacilli •  Clusters: staphylococci •  Chains: streptococci, streptobacilli •  Groups of four: tetrads •  Cubelike groups of eight: sarcinae


Plane of division

Diplococci

Streptococci

Tetrad

Sarcinae

Staphylococci

Figure 4.1 Arrangements of cocci.


Figure 4.2a-d Bacilli.


Figure 4.2b-c Bacilli.



•  Scientific name: Bacillus •  Shape: bacillus


Figure 4.3 Gram-stained Bacillus anthracis.


Figure 4.6 The Structure of a Prokaryotic Cell.


Glycocalyx

•  External to the cell wall •  Viscous and gelatinous •  Made of polysaccharide and/or polypeptide •  Two types

•  Capsule: neatly organized and firmly attached •  Slime layer: unorganized and loose


Glycocalyx

•  Contribute to virulence •  Capsules prevent phagocytosis •  Extracellular polymeric substance helps form biofilms


Figure 24.11 Streptococcus pneumoniae, the cause of pneumococcal pneumonia.

Capsules


Flagella

•  Filamentous appendages external of the cell •  Propel bacteria •  Made of protein flagellin


Flagella

•  Three parts: •  Filament: outermost region •  Hook: attaches to the filament •  Basal body: consists of rod and pairs of rings; anchors

flagellum to the cell wall and membrane


Gram- positive

Cell wall

Filament

Hook Basal body Peptidoglycan

Plasma membrane

Cytoplasm Parts and attachment of a flagellum of a gram-positive bacterium

Flagellum

Figure 4.8b The structure of a prokaryotic flagellum.


Flagellum Filament Gram-

negative

Hook Basal body Peptidoglycan Outer membrane

Cell wall

Plasma membrane

Cytoplasm Parts and attachment of a flagellum of a gram-negative bacterium

Figure 4.8a The structure of a prokaryotic flagellum.


Figure 4.7 Arrangements of bacterial flagella.


Flagella

•  Flagella allow bacteria to move toward or away from stimuli (taxis)

•  Flagella rotate to "run" or "tumble" •  Flagella proteins are H antigens and distinguish

among serovars (e.g., Escherichia coli O157:H7)


Figure 4.9a Flagella and bacterial motility.


Figure 4.9b Flagella and bacterial motility.


Axial Filaments

•  Also called endoflagella •  Found in spirochetes •  Anchored at one end of a cell •  Rotation causes cell to move like a corkscrew


A photomicrograph of the spirochete Leptospira, showing an axial filament

Axial filament

Figure 4.10a Axial filaments.


Axial filament Cell wall Outer sheath

A diagram of axial filaments wrapping around part of a spirochete

Figure 4.10b Axial filaments.


Fimbriae and Pili

•  Fimbriae •  Hairlike appendages that allow for attachment


Figure 4.11 Fimbriae.

Fimbriae


The Cell Wall

•  Prevents osmotic lysis and protects the cell membrane

•  Made of peptidoglycan (in bacteria) •  Contributes to pathogenicity


Capsule Cell wall

Inclusions

Cytoplasm

70S Ribosomes

Plasma membrane

Cell wall

Nucleoid containing DNA

Capsule

Figure 4.6 The Structure of a Prokaryotic Cell.


Composition and Characteristics

•  Peptidoglycan (backbone) •  Polymer of a repeating disaccharide in rows:

•  N-acetylglucosamine (NAG) •  N-acetylmuramic acid (NAM)

•  Rows are linked by polypeptides


Figure 4.12 N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) joined as in a peptidoglycan.


NAG

.

N-acetylglucosamine (NAG)

N-acetylmuramic acid (NAM)

Side-chain amino acid

Cross-bridge amino acid

NAM NAG

NAG Peptide bond

Structure of peptidoglycan in gram-positive bacteria

Carbohydrate "backbone"

Peptide cross-bridge

Tetrapeptide side chain

Figure 4.13a Bacterial cell walls.


Gram-Positive Cell Walls

•  Thick peptidoglycan •  Teichoic acids

•  Thin peptidoglycan •  Outer membrane •  Periplasmic space

Gram-Negative Cell Walls



•  Teichoic acids •  Lipoteichoic acid links cell wall to plasma membrane •  Wall teichoic acid links the peptidoglycan •  Carry a negative charge •  Regulate movement of cations (Na +, K+, Ca+)

•  Polysaccharides and teichoic acids provide antigenic specificity


Granular layer

Lipoteichoic acid

Peptidoglycan Wall teichoic acid

Cell wall

Plasma membrane

Protein

Figure 4.13b Bacterial cell walls.



•  Periplasm between the outer membrane and the plasma membrane contains peptidoglycan

•  Outer membrane made of polysaccharides, lipoproteins, and phospholipids



•  Protect from phagocytes and antibiotics •  Made of lipopolysaccharide (LPS)

•  O polysaccharide functions as antigen (e.g., E. coli O157:H7)

•  Lipid A is an endotoxin embedded in the top layer •  Porins (proteins) form channels through

membrane


Periplasm

Peptidoglycan Cell wall

Lipopolysaccharide Lipid A

Protein

Porin protein Lipoprotein

Phospholipid Outer membrane

Plasma membrane

Lipid A (endotoxin)

Core polysaccharide

O polysaccharide (antigenic)

Parts of the LPS

Core polysaccharide O polysaccharide

Figure 4.13c Bacterial cell walls.


Cell Walls and the Gram Stain Mechanism

•  Crystal violet-iodine crystals form inside cell •  Gram-positive

•  Alcohol dehydrates peptidoglycan •  CV-I crystals do not leave

•  Gram-negative •  Alcohol dissolves outer membrane and leaves holes in

peptidoglycan •  CV-I washes out; cells are colorless •  Safranin added to stain cells


Table 4.1 Some Comparative Characteristics of Gram-Positive and Gram-Negative Bacteria

Gram-Positive Gram-Negative


•  4-rings in basal body of flagella

•  Produce endotoxins and exotoxins

•  Low susceptibility to penicillin


•  2-rings in basal body of flagella

•  Produce exotoxins •  High susceptibility to

penicillin •  Disrupted by lysozyme



Atypical Cell Walls

•  Acid-fast cell walls •  Like gram-positive cell walls •  Waxy lipid (mycolic acid) bound to peptidoglycan •  Mycobacterium tuberculosis •  Nocardia •  Stain with carbolfuchsin


Figure 24.7 Mycobacterium tuberculosis.

Corded growth


Atypical Cell Walls

•  Mycoplasmas •  Lack cell walls •  Sterols in plasma membrane

•  Archaea •  Wall-less, or •  Walls of pseudomurein (lack NAM and D-amino acids)


Damage to the Cell Wall

•  Lysozyme hydrolyzes bonds in peptidoglycan •  Penicillin inhibits peptide bridges in peptidoglycan •  Protoplast is a wall-less gram-positive cell •  Spheroplast is a wall-less gram-negative cell

•  Protoplasts and spheroplasts are susceptible to osmotic lysis

•  L forms are wall-less cells that swell into irregular shapes


The Plasma (Cytoplasmic) Membrane

•  Phospholipid bilayer that encloses the cytoplasm •  Peripheral proteins on the membrane surface •  Integral and transmembrane proteins penetrate

the membrane


Lipid bilayer of plasma membrane Peptidoglycan Outer membrane

Plasma membrane of cell

Figure 4.14a Plasma membrane.


Outside

Pore Peripheral protein

Polar head

Nonpolar fatty acid tails Polar head

Peripheral protein

Integral proteins

Inside

Lipid bilayer

Lipid bilayer of plasma membrane

Figure 4.14b Plasma membrane.


Structure

•  Fluid mosaic model •  Membrane is as viscous as olive oil •  Proteins move freely for various functions •  Phospholipids rotate and move laterally •  Self-sealing


Functions

•  The plasma membrane's selective permeability allows the passage of some molecules, but not others •  Large molecules cannot pass (ie.proteins) •  Smaller molecules and substances that are solulble in

lipids can pass ie. H2O, CO2, nonpolar organic molcls. •  Contain enzymes for ATP production •  Some membranes have photosynthetic pigments

on foldings called chromatophores


Chromatophores

Figure 4.15 Chromatophores. - Rhodospirillum


The Movement of Materials across Membranes

•  Passive processes: substances move from high concentration to low concentration; no energy expended

•  Active processes: substances move from low concentration to high concentration; energy expended


Passive Processes

•  Simple diffusion: movement of a solute from an area of high concentration to an area of low concentration ie. H2O

•  Continues until molecules reach equilibrium


Outside

Plasma membrane

Inside

Simple diffusion through the lipid bilayer

Figure 4.17a Passive processes.


Passive Processes

•  Facilitated diffusion: solute combines with a transporter protein in the membrane

•  Transports ions and larger molecules across a membrane with the concentration gradient •  Usually inorganic molecules too hydrophilic to pass

through the interior of the lipid bilayer. •  Common in prokaryotes; non specific.


Nonspecific transporter

Facilitated diffusion through a nonspecific transporter

Facilitated diffusion through a specific transporter

Transported substance Specific

transporter

Glucose

Figure 4.17b-c Passive processes.


Extracellular enzymes •  When a molecule is too large to be taken in,

bacteria degrades the molecule into manegable subunits •  Proteins into amino acids (proteases) •  Polysaccharides into monosaccharides (lactase,

cellulase, maltase)


Passive Processes

•  Osmosis: the movement of water across a selectively permeable membrane from an area of high water to an area of lower water concentration

•  Through lipid layer •  Aquaporins (water channels)


Aquaporin (rapid transport of water)

Osmosis through the lipid bilayer (left) and an aquaporin (right)

Figure 4.17d Passive processes.


Passive Processes

•  Osmotic pressure: the pressure needed to stop the movement of water across the membrane


Glass tube

Rubber stopper

Rubber band

Sucrose molecule

Cellophane sack

Water molecule

At beginning of osmotic pressure experiment

At equilibrium

Figure 4.18a-b The principle of osmosis.


Passive Processes

•  Isotonic solution: solute concentrations equal inside and outside of cell; water is at equilibrium

•  Hypotonic solution: solute concentration is lower outside than inside the cell; water moves into cell

•  Hypertonic solution: solute concentration is higher outside of cell than inside; water moves out of cell


Cytoplasm Solute Plasma membrane

Cell wall

Isotonic solution. No net movement of water occurs.

Water Hypotonic solution. Water moves into the cell. If the cell wall is strong, it contains the swelling. If the cell wall is weak or damaged, the cell bursts (osmotic lysis).

Hypertonic solution. Water moves out of the cell, causing its cytoplasm to shrink (plasmolysis).

Figure 4.18c-e The principle of osmosis.


Active Processes

•  Active transport: requires a transporter protein and ATP; goes against gradient

•  Group translocation: requires a transporter protein and phosphoenolpyruvic acid (PEP); substance is altered as it crosses the membrane


Cytoplasm

•  Semitransparent elastic substance inside plasma membrane

•  80% water •  Major structures

•  Nucleoid •  Ribosomes •  Reserve deposits called inclusions


Nucleoid

•  Contains single long double stranded DNA called Bacterial Chromosome

•  Up to 20% of the cell is the nucleoid (when actively growing).

•  Plasmids – extrachromosomal DNA. •  Replicate independently of bacterial chromosome •  Contain 5-100 genes •  Not crucial for survival in normal conditions, but may

contain genes that give advantage to cell ie. Antibiotic resistance.

•  Can exchange plasmids sexually with other bacteria (same species usually).


Ribosomes

•  Protein synthesis •  70S = 50S + 30S

•  Made up of proteins and ribosomal RNA (rRNA). •  Antibiotics like streptomycin and gentamicin attach to

the 30S subuint. •  Erythromycin and chloramphenicol attach to the 50S

subunit to interfere with protein synthesis.


Inclusions

•  Metachromatic granules – inorganic phosphate storage

•  Polysaccharide granules – store glycogen and starch

•  Lipid incuisons •  Sulfur granules •  Carboxysomes – contains the enzyme ribulose

1,5-diphosphate carboxylase (CO2 fixation) •  Nitrifying bacteria and cyanobacteria

•  Gas vacuoles •  Magnetosomes (iron oxide inclusions)


Endospores

•  Some gram-positives like Clostridium and Bacillus form resting cells when nutrients are depleted •  Clostridium tetani, C.perfringes, B. anthracis

•  Heat, desication, exposure to chemicals •  40 mya endospore germinated •  Process is called sporulation •  Germination can be caused by high heat or

“germinants”. •  Important to food industry and from a clinical point

of view.


Magnetosomes

IN PLANT CELL ONLY

Vacuole

Cell wall

Chloroplast

Centrosome:

IN ANIMAL CELL ONLY

Pericentriolar material Centriole

Lysosome

Basal body

Flagellum

Idealized illustration of a composite eukaryotic cell, half plant and half animal

Peroxisome

IN PLANT AND ANIMAL CELLS

Nucleus

Nucleolus

Rough endoplasmic reticulum

Smooth endoplasmic reticulum

Microtubule

Microfilament

Mitochondrion

Plasma membrane

Ribosome

Cytoplasm

Golgi complex

Figure 4.22a Eukaryotic cells showing typical structures.

functional anatomy of eukaryotic cells · © 2016 pearson education, inc. nucleoid • contains...

Documents