Download Lecture 1 Part I Nordström 13.9.

6/9/2016
PowerPoint® Lecture
Presentations prepared by
Mindy Miller-Kittrell,
North Carolina State University
CHAPTER
3
Cell Structure
and Function
© 2015 Pearson Education, Ltd.
Prokaryotic and Eukaryotic Cells: An Overview
I. Prokaryotes
• Include bacteria and archaea
• Have a simple structure
• Lack nucleus
• Lack various membrane-bound internal structures
• Are typically 1.0 µm in diameter or smaller
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Figure 3.2 Typical prokaryotic cell.
Inclusions
Ribosome
Cytoplasm
Nucleoid
Glycocalyx
Flagellum
Cell wall
Cytoplasmic membrane
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Prokaryotic and Eukaryotic Cells: An Overview
II. Eukaryotes
• Have nucleus
• Have internal membrane-bound organelles
• Are typically 10–100 µm in diameter
• Have more complex structure
• Include algae, protozoa, fungi, animals, and plants
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Figure 3.3 Typical eukaryotic cell.
Nuclear envelope
Nuclear pore
Nucleolus
Lysosome
Mitochondrion
Centriole
Secretory vesicle
Golgi body
Cilium
Transport vesicles
Ribosomes
Rough endoplasmic
reticulum
Smooth endoplasmic
reticulum
Cytoplasmic
membrane
Cytoskeleton
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Figure 3.4 Approximate size of various types of cells.
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1. External Structures of Bacterial Cells
1.1. Glycocalyx
• Gelatinous, sticky substance surrounding the outside of
the cell
• Composed of polysaccharides, polypeptides, or both
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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 as biofilms
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Figure 3.5 Glycocalyces.
Glycocalyx
(capsule)
Glycocalyx
(slime layer)
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External Structures of Bacterial Cells
1.2. Flagella
• Are responsible for movement
• Have long structures that extend beyond cell surface
• Are not present on all bacteria
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External Structures of Bacterial Cells
• Flagella
• Structure
• Composed of filament, hook, and basal body
• Basal body anchors the filament and hook to cell wall
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Figure 3.6 Proximal structure of bacterial flagella.
Filament
Direction
of rotation
during run
Rod
Peptidoglycan
layer (cell wall)
Protein rings
Cytoplasmic
membrane
Cytoplasm
Filament
Outer
protein
rings
Outer
membrane
Rod
Gram +
Gram –
Basal
body
Peptidoglycan
layer
Integral
protein
Inner
protein
rings
Cell
wall
Cytoplasmic
membrane
Cytoplasm
Integral
protein
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Figure 3.7 Micrographs of basic arrangements of bacterial flagella.
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Figure 3.8 Axial filament.
Endoflagella
rotate
Axial filament
Axial filament
rotates around
cell
Outer
membrane
Cytoplasmic
membrane
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Spirochete
corkscrews
and moves
forward
Axial filament
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External Structures of Bacterial Cells
• Flagella
• Function
• Rotation propels bacterium through environment
• Rotation reversible; can be counterclockwise or clockwise
• Bacteria move in response to stimuli (taxis)
• Runs
• Tumbles
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External Structures of Bacterial Cells
1.3. Fimbriae and Pili
• Fimbriae
• Sticky, bristlelike projections
• Used by bacteria to adhere to one another and to
substances in environment
• Shorter than flagella
• Serve an important function in biofilms
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Figure 3.10 Fimbriae.
Flagellum Fimbria
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External Structures of Prokaryotic Cells
• Pili
• Special type of fimbria
• Also known as conjugation pili
• Longer than fimbriae but shorter than flagella
• Bacteria typically have only one or two per cell
• Transfer DNA from one cell to another (conjugation)
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Figure 3.11 Pili.
Pilus
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2. 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 3.12 Bacterial shapes and arrangements.
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Figure 3.13 Comparison of the structures of glucose, NAG, and NAM.
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Figure 3.14 Possible structure of peptidoglycan.
Sugar
chain
Tetrapeptide
(amino acid)
crossbridge
Connecting chain
of amino acids
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Bacterial Cell Walls
2.1. Gram-Positive Bacterial Cell Walls
• Relatively thick layer of peptidoglycan
• Contain unique polyalcohols called teichoic acids
• Appear purple following Gram staining procedure
• Presence of 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.
Peptidoglycan layer
(cell wall)
Cytoplasmic
membrane
Gram-positive cell wall
Lipoteichoic acid
Teichoic acid
Integral
protein
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Prokaryotic Cell Walls
2.2. Gram-Negative Bacterial Cell Walls
• Have only a thin layer of peptidoglycan
• Bilayer membrane outside the peptidoglycan contains
phospholipids, proteins, and lipopolysaccharide (LPS)
• Lipid A portion of LPS can cause fever, vasodilation,
inflammation, shock, and blood clotting
• May impede 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.
Porin
Outer
membrane
of cell wall
Porin
(sectioned)
Peptidoglycan
layer of cell wall
Gram-negative cell wall
Periplasmic space
Cytoplasmic
membrane
Phospholipid layers
Lipopolysaccharide
(LPS) layer, containing
lipid A
Integral
proteins
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Prokaryotic Cell Walls
2.3. Bacteria Without Cell Walls
• A few bacteria lack cell walls
• Often mistaken for viruses because of small size and
lack of cell wall
• Have other features of prokaryotic cells, such as
ribosomes
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3. Bacterial Cytoplasmic Membranes
• Structure
• Referred to as phospholipid bilayer
• Composed of lipids and associated proteins
• Integral proteins
• Peripheral 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, which
contains phosphate
(hydrophilic)
Phospholipid
Tail
(hydrophobic)
Integral
proteins
Cytoplasm
Integral
protein
Phospholipid
bilayer
Peripheral protein
Integral protein
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Bacterial Cytoplasmic Membranes
• Function
• Control passage of substances into and out of the cell
• Energy storage
• Harvest light energy in photosynthetic bacteria
• Selectively permeable
• Naturally impermeable to most substances
• Proteins allow substances to cross membrane
• Maintain concentration and electrical gradient
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Figure 3.17 Electrical potential of a cytoplasmic membrane.
Na+
Cl–
Cell exterior (extracellular fluid)
–30
mV
Cytoplasmic membrane
Integral
protein
Protein
DNA
Protein
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Cell interior (cytoplasm)
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Bacterial Cytoplasmic Membranes
• Function
• Passive processes
• Diffusion
• Facilitated diffusion
• Osmosis
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Figure 3.18 Passive processes of movement across a cytoplasmic membrane.
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Figure 3.19 Osmosis, the diffusion of water across a semipermeable membrane.
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Figure 3.20 Effects of isotonic, hypertonic, and hypotonic solutions on cells.
Cells without a wall
(e.g., mycoplasmas,
animal cells)
H2 O
H2 O
H2 O
Cell wall
Cells with a wall
(e.g., plants, fungal
and bacterial cells)
Cell wall
Cell membrane
Isotonic
solution
H2 O
H2 O
H2 O
Cell membrane
Hypertonic
solution
Hypotonic
solution
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Prokaryotic Cytoplasmic Membranes
• Function
• Active processes
• Active transport
• Group translocation
• Substance is chemically modified during transport
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Figure 3.21 Mechanisms of active transport.
Extracellular fluid
Uniport
Cytoplasmic
membrane
ATP
ATP
ADP
ADP
P
P
Symport
Cytoplasm
Uniport
Antiport
Coupled transport:
uniport and symport
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Figure 3.22 Group translocation.
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Cytoplasm of Bacteria
• Cytosol
• Liquid portion of cytoplasm
• Mostly water
• Contains cell's DNA in region called the nucleoid
• Inclusions
• May include reserve deposits of chemicals
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Figure 3.23 Granules of PHB in the bacterium Azotobacter chroococcum.
Polyhydroxybutyrate
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• Endospores
• Unique structures produced by some bacteria
• Defensive strategy against unfavorable conditions
• Vegetative cells transform into endospores when
nutrients are limited
• Resistant to extreme conditions such as heat, radiation,
chemicals
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Cytoplasm of Prokaryotes
• Nonmembranous Organelles
• Ribosomes
• Sites of protein synthesis
• Composed of polypeptides and ribosomal RNA
• 70S ribosome composed of smaller 30S and 50S subunits
• Many antibacterial drugs act on bacterial ribosomes
without affecting larger eukaryotic ribosomes
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Cytoplasm of Prokaryotes
• Nonmembranous Organelles
• Cytoskeleton
• Composed of three or four types of protein fibers
• Can play different roles in the cell
• Cell division
• Cell shape
• Segregation of DNA molecules
• Movement through the environment
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III. External Structures of Archaea
• Glycocalyces
• Function in the formation of biofilms
• Adhere cells to one another and inanimate objects
• Flagella
• Consist of basal body, hook, and filament
• Numerous differences from bacterial flagella
• Fimbriae and Hami
• Many archaea have fimbriae
• Some make fimbria-like structures called hami
• Function to attach archaea to surfaces
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Figure 3.26 Archaeal hami.
Hamus
Grappling
hook
Prickles
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Archaeal Cell Walls and Cytoplasmic
Membranes
• Most archaea have cell walls
• Do not have peptidoglycan
• Contain variety of specialized polysaccharides and
proteins
• All archaea have cytoplasmic membranes
• Maintain electrical and chemical gradients
• Control import and export of substances from the cell
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Figure 3.27 Representative shapes of archaea.
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Cytoplasm of Archaea
• Archaeal cytoplasm similar to bacterial cytoplasm
• 70S ribosomes
• Fibrous cytoskeleton
• Circular DNA
• Archaeal cytoplasm also differs from bacterial cytoplasm
• Different ribosomal proteins
• Different metabolic enzymes to make RNA
• Genetic code more similar to that of eukaryotes
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(II). External Structure of Eukaryotic Cells
1. Glycocalyces
• Not as organized as prokaryotic capsules
• Help anchor animal cells to each other
• Strengthen cell surface
• Provide protection against dehydration
• Function in cell-to-cell recognition and communication
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Eukaryotic Cell Walls and Cytoplasmic
Membranes
• Fungi, algae, plants, and some protozoa have cell
walls
• Composed of various polysaccharides
• Cellulose is found in plant cell walls
• Fungal cell walls are composed of cellulose, chitin,
and/or glucomannan
• Algal cell walls are composed of a variety of
polysaccharides
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Eukaryotic Cell Walls and Cytoplasmic
Membranes
• All eukaryotic cells have cytoplasmic membrane
• Are a fluid mosaic of phospholipids and proteins
• Contain steroid lipids to help maintain fluidity
• Contain regions of lipids and proteins called
membrane rafts
• Localize signaling, protein sorting, and movement
• Control movement into and out of cell
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Figure 3.30 Endocytosis.
Pseudopod
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2. Flagella
• Structure and arrangement
• Differ structurally and functionally from prokaryotic flagella
• Within the cytoplasmic membrane
• Shaft composed of tubulin arranged to form microtubules
• Filaments anchored to cell by basal body; no hook
• May be single or multiple; generally found at one pole of cell
• Function
• Do not rotate but undulate rhythmically
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Figure 3.31a-b Eukaryotic flagella and cilia.
Flagellum
Cilia
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3. Cilia
• Shorter and more numerous than flagella
• Coordinated beating propels cells through their
environment
• Also used to move substances past the surface of the
cell
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Cytoplasm of Eukaryotes
4. Other Nonmembranous Organelles
• 4.1. Ribosomes
• Larger than prokaryotic ribosomes (80S versus 70S)
• Composed of 60S and 40S subunits
• 4.2. Cytoskeleton
• Extensive network of fibers and tubules
• Anchors organelles
• Produces basic shape of the cell
• Made up of tubulin microtubules, actin microfilaments, and
intermediate filaments
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Cytoplasm of Eukaryotes
• Other Nonmembranous Organelles
• 4.3. Centrioles and centrosome
• Centrioles are composed of nine triplets of microtubules
• Located in region of cytoplasm called centrosome
• Not found in all eukaryotic cells
• Centrosomes play a role in mitosis, cytokinesis, and
formation of flagella and cilia
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Cytoplasm of Eukaryotes
5. Membranous Organelles
• 5.1. Nucleus
• Often largest organelle in cell
• Contains most of the cell's DNA
• Semiliquid portion is called nucleoplasm
• Contains chromatin
• RNA synthesized in nucleoli present in nucleoplasm
• Surrounded by nuclear envelope
• Contains nuclear pores
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Figure 3.35 Eukaryotic nucleus.
Nucleolus
Nucleoplasm
Chromatin
Nuclear envelope
Two phospholipid
bilayers
Nuclear pores
Rough ER
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Cytoplasm of Eukaryotes
• Membranous Organelles
• 5.2. Endoplasmic reticulum
• Netlike arrangement of flattened, hollow tubules
continuous with nuclear envelope
• Functions as transport system
• Two forms
• Smooth endoplasmic reticulum (SER)
• Rough endoplasmic reticulum (RER)
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Figure 3.36 Endoplasmic reticulum.
Membrane-bound
ribosomes
Mitochondrion
Free ribosome
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Smooth endoplasmic
reticulum (SER)
Rough endoplasmic
reticulum (RER)
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Cytoplasm of Eukaryotes
• Membranous Organelles
• 5.3. Golgi body
• Receives, processes, and packages large molecules for
export from cell
• Packages molecules in secretory vesicles that fuse with
cytoplasmic membrane
• Composed of flattened hollow sacs surrounded by
phospholipid bilayer
• Not in all eukaryotic cells
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Figure 3.37 Golgi body.
Secretory vesicles
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Vesicles
arriving
from ER
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Cytoplasm of Eukaryotes
• Membranous Organelles
• 5.4. Lysosomes, peroxisomes, vacuoles, and vesicles
• Store and transfer chemicals within cells
• May store nutrients in cell
• Lysosomes contain catabolic enzymes
• Peroxisomes contain enzymes that degrade poisonous
wastes
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Figure 3.39 The roles of vesicles in endocytosis and exocytosis.
Endocytosis
(phagocytosis)
Bacterium
Phagosome
(food vesicle)
Vesicle
fuses with a
lysosome
Smooth
endoplasmic
reticulum
(SER)
Transport
vesicle
Lysosome
Phagolysosome
Golgi body
Secretory
vesicle
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Exocytosis
(elimination, secretion)
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Cytoplasm of Eukaryotes
• Membranous Organelles
• 5.5. Mitochondria
• Have two membranes composed of phospholipid bilayer
• Produce most of cell's ATP
• Interior matrix contains 70S ribosomes and circular
molecule of DNA
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Figure 3.40 Mitochondrion.
Outer membrane
Inner membrane
Crista
Matrix
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Ribosomes
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Cytoplasm of Eukaryotes
• Membranous Organelles
• 5.6. Chloroplasts
• Light-harvesting structures found in photosynthetic
eukaryotes
• Use light energy to produce ATP
• Have two phospholipid bilayer membranes and DNA
• Have 70S ribosomes
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Figure 3.41 Chloroplast.
Granum
Stroma
Thylakoid
space
Thylakoid
Inner bilayer
membrane
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Outer bilayer
membrane
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Cytoplasm of Eukaryotes
• Endosymbiotic Theory
• Eukaryotes formed from union of small aerobic prokaryotes
with larger anaerobic prokaryotes
• Smaller prokaryotes became internal parasites
• Parasites lost ability to exist independently
• Larger cell became dependent on parasites for
metabolism
• Aerobic prokaryotes evolved into mitochondria
• Similar scenario for origin of chloroplasts
• Theory is not universally accepted
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