Transcript Power Point Cells

CELL STRUCTURE AND
FUNCTION
CHAPTER 3
Processes of Life
 Growth
 Reproduction
 Responsiveness
 Metabolism
Prokaryotes
 Do not have membrane surrounding their DNA; no
nucleus
 Lack various internal structures bound with
phospholipid membranes
 Small; ~1.0 µm in diameter
 Simple structure
 Comprised of bacteria and archaea
Eukaryotes
 Have membrane surrounding DNA; have nucleus
 Have internal membrane-bound organelles
 Are larger; 10-100 µm in diameter
 Have more complex structure
 Comprised of algae, protozoa, fungi, animals, and
plants
Comparing Prokaryotes and Eukaryotes
Figure 3.2a
Comparing Prokaryotes and Eukaryotes
Figure 3.2b
External Structures of Prokaryotic Cells
 Glycocalyces
 Flagella
 Fimbriae and pili
Glycocalyces
 Gelatinous, sticky substance surrounding the outside
of the cell
 Composed of polysaccharides, polypeptides, or both
 Two types
 Capsule
 Slime layer
Capsule
 Composed of organized repeating units of organic
chemicals
 Firmly attached to cell surface
 Protects cells from drying out
 May prevent bacteria from being recognized and
destroyed by host
Example of Capsule
Figure 3.4a
Slime Layer
 Loosely attached to cell surface
 Water soluble
 Protects cells from drying out
 Sticky layer that allows prokaryotes to attach to
surfaces
Example of Slime Layer
Figure 3.4b
Flagella
 Are responsible for movement
 Have long structures that extend beyond cell surface
 Not all prokaryotes have flagella
Bacterial Flagella Structure
 Composed of filament, hook, and basal body
 Flagellin protein (filament) is deposited in a helix at
the lengthening tip
 Base of filament inserts into hook
 Basal body anchors filament and hook to cell wall by
a rod and a series of either two or four rings of integral
proteins
 Filament capable of rotating 360º
Bacterial Flagella Structure
Figure 3.5a
Bacterial Flagella Structure
Figure 3.5b
Arrangements of Bacterial Flagella
Figure 3.6a
Arrangements of Bacterial Flagella
Figure 3.6b
Arrangements of Bacterial Flagella
Figure 3.6c
Function of Bacterial Flagella
 Rotation propels bacterium through environment
 Rotation can be clockwise or counterclockwise;
reversible
 Bacteria move in response to stimuli (taxis)
 Runs – movements of cell in single direction for some
time due to counterclockwise flagellar rotation;
increase with favorable stimuli (positive chemotaxis,
positive phototaxis)
 Tumbles – abrupt, random, changes in direction due to
clockwise flagellar rotation; increase with unfavorable
stimuli (negative chemotaxis, negative phototaxis)
Bacterial Movement
Fimbriae and Pili
 Nonmotile extensions
 Fimbriae
 Sticky, proteinaceous, bristlelike projections
 Used by bacteria to adhere to one another, to hosts, and
to substances in environment
 May be hundreds per cell and are shorter than flagella
 Serve an important function in biofilms
Fimbriae Versus Flagella
Figure 3.9
Pili
 Long hollow tubules composed of pilin
 Longer than fimbriae but shorter than flagella
 Bacteria typically only have one or two per cell
 Join two bacterial cells and mediate the transfer of
DNA from one cell to another (conjugation)
 Also known as conjugation pili or sex pili
Pilus Versus Fimbriae
Figure 3.10
Prokaryotic Cell Wall
 Provides structure and shape and protects cell from
osmotic forces
 Assists some cells in attaching to other cells or in
eluding antimicrobial drugs
 Animal cells do not have; can target cell wall of
bacteria with antibiotics
 Bacteria and archaea have different cell wall
chemistry
Bacterial Cell Wall
 Most have cell wall composed of peptidoglycan; a few
lack a cell wall entirely
 Peptidoglycan composed of sugars, NAG, and NAM
 Chains of NAG and NAM attached to other chains by
tetrapeptide crossbridges
 Bridges may be covalently bonded to one another
 Bridges may be held together by short connecting
chains of amino acids
 Scientists describe two basic types of bacterial cell
walls: gram-positive and gram-negative
Gram-Positive Cell Wall
 Relatively thick layer of peptidoglycan
 Contains unique polyalcohols called teichoic acids
 Some covalently linked to lipids, forming lipoteichoic
acids that anchor peptidoglycan to cell membrane
 Retains crystal violet dye in Gram staining procedure;
appear purple
 Acid-fast bacteria contain up to 60% mycolic acid;
helps cells survive desiccation
Gram-Negative 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
 Following Gram staining procedure, cells appear pink
LPS
 Union of lipid with sugar
 Also known as endotoxin
 Lipid portion known as lipid A
 Dead cells release lipid A when cell wall disintegrates
 May trigger fever, vasodilation, inflammation, shock,
and blood clotting
 Can be released when antimicrobial drugs kill bacteria
Periplasmic Space
 Located between outer membrane and cell membrane
 Contains peptidoglycan and periplasm
 Contains water, nutrients, and substances secreted by
the cell, such as digestive enzymes and proteins
involved in transport
Bacterial Cell Walls
Figure 3.13a
Bacterial Cell Walls
Figure 3.13b
Archael Cell Walls
 Do not have peptidoglycan
 Cell walls contain variety of specialized
polysaccharides and proteins
 Gram-positive archaea stain purple
 Gram-negative archaea stain pink
Prokaryotic Cytoplasmic Membrane
 Referred to as phospholipid bilayer; composed of
lipids and associated proteins
 Approximately half the membrane is composed of
proteins that act as recognition proteins, enzymes,
receptors, carriers, or channels
 Integral proteins
 Peripheral proteins
 Glycoproteins
 Fluid mosaic model describes current understanding
of membrane structure
Phospholipid Bilayer of Cytoplasmic
Membrane
Figure 3.14
Cytoplasmic Membrane Function
 Controls passage of substances into and out of the cell;
selectively permeable
 Harvests light energy in photosynthetic prokaryotes
Control of Substances Across Cytoplasmic
Membrane
 Naturally impermeable to most substances
 Proteins allow substances to cross membrane
 Occurs by passive or active processes
 Maintains a concentration gradient and electrical
gradient
 Chemicals concentrated on one side of the membrane
or the other
 Voltage exists across the membrane
Passive Processes of Transport
 Diffusion
 Facilitated diffusion
 Osmosis
 Isotonic solution
 Hypertonic solution
 Hypotonic solution
Effects of Solutions on Organisms
Figure 3.18
Active Processes of Transport
 Active Transport
 Utilizes permease proteins and expends ATP
 Uniport
 Antiport
 Symport
 Group Translocation
 Substance chemically modified during transport
Cytoplasm of Prokaryotes
 Cytosol – liquid portion of cytoplasm
 Inclusions – may include reserve deposits of
chemicals
 Ribosomes – sites of protein synthesis
 Cytoskeleton – plays a role in forming the cell’s basic
shape
 Some bacterial cells produce dormant form called
endospore
External Structure of Eukaryotic Cells
 Glycocalyces
 Never as organized as prokaryotic capsules
 Helps anchor animal cells to each other
 Strengthens cell surface
 Provides protection against dehydration
 Function in cell-to-cell recognition and
communication
Eukaryotic Cell Walls
 Fungi, algae, plants, and some protozoa have cell
walls but no glycocalyx
 Composed of various polysaccharides
 Cellulose found in plant cell walls
 Fungal cell walls composed of cellulose, chitin, and/or
glucomannan
 Algal cell walls composed of cellulose, proteins, agar,
carrageenan, silicates, algin, calcium carbonate, or a
combination of these
Eukaryotic Cytoplasmic Membrane
 All eukaryotic cells have cytoplasmic membrane
 Is a fluid mosaic of phospholipids and proteins
 Contains steroid lipids to help maintain fluidity
 Controls movement into and out of cell
 Uses diffusion, facilitated diffusion, osmosis, and
active transport
 Performs endocytosis; phagocytosis if solid substance
and pinocytosis if liquid substance
 Exocytosis enables substances to be exported from cell
Cytoplasm of Eukaryotes – Nonmembranous
Organelles
 Flagella
 Cilia
 Ribosomes
 Cytoskeleton
 Centrioles and centrosome
Flagella
 Shaft composed of tubulin arranged form
microtubules
 “9 + 2” arrangement of microtubules in all flagellated
eukaryotes
 Filaments anchored to cell by basal body; no hook
 Basal body has “9 + 0” arrangement of microtubules
 May be single or multiple; generally found at one pole
of cell
 Do not rotate, but undulate rhythmically
Cilia
 Shorter and more numerous than flagella
 Composed of tubulin in “9 + 2” and “9 + 0”
arrangements
 Coordinated beating propels cells through their
environment
 Also used to move substances past the surface of the
cell
Eukaryotic Flagella
Figure 3.27a
Eukaryotic Cilia
Figure 3.27c
Eukaryotic Flagella and Cilia
Figure 3.27b
Ribosomes
 Larger than prokaryotic ribosomes (80S versus 70S)
 Composed of 60S and 40S subunits
Cytoskeleton
 Extensive
 Functions
 Anchor organelles
 Cytoplasmic streaming and movement of organelles
 Movement during endocytosis and amoeboid action
 Produce basic shape of the cell
 Made up of tubulin microtubules, actin
microfilaments, and intermediate filaments composed
of various proteins
Centrioles and Centrosome
 Centrioles play a role in mitosis, cytokinesis, and in
formation of flagella and cilia
 Centrioles composed of “9 + 0” arrangement of
microtubules
 Centrosome – region of cytoplasm where centrioles
are found
Cytoplasm of Eukaryotes – Membranous
Organelles
 Nucleus
 Endoplasmic reticulum
 Golgi body
 Lysosomes, peroxisomes, vacuoles, and vesicles
 Mitochondria
 Chloroplasts
Nucleus
 Often largest organelle in cell
 Contains most of the cell’s DNA
 Semiliquid portion called nucleoplasm
 One or more nucleoli present in nucleoplasm; RNA
synthesized in nucleoli
 Nucleoplasm contains chromatin – masses of DNA
associated with histones
 Surrounded by double membrane composed of two
phospholipid bilayers – nuclear envelope
 Nuclear envelope contains nuclear pores
Endoplasmic Reticulum
 Netlike arrangement of flattened, hollow tubules
continuous with nuclear envelope
 Functions as transport system
 Two forms
 Smooth endoplasmic reticulum (SER) – plays role in
lipid synthesis
 Rough endoplasmic reticulum (RER) – ribosomes
attached to its outer surface; transports proteins
produced by ribosomes
Rough and Smooth Endoplasmic Reticulum
Figure 3.32
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 all eukaryotic cells contain Golgi bodies
Golgi Body
Figure 3.33
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
Mitochondria
 Have two membranes composed of phospholipid
bilayer
 Produce most of cell’s ATP
 Interior matrix contains 70S ribosomes and circular
molecule of DNA
Chloroplasts
 Light-harvesting structures found in photosynthetic
eukaryotes
 Have two phospholipid bilayer membranes and DNA
 Have 70S ribosomes
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; retained
portion of DNA, ribosomes, and cytoplasmic
membranes
 Larger cell became dependent on parasites for aerobic
ATP production
 Aerobic prokaryotes evolved into mitochondria
 Similar scenario for origin of chloroplasts