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Prokaryotes
Do not have membrane surrounding their DNA
lack a nucleus Lack various internal structures
bound with phospholipid membranes
Are small, ~1.0 µm in diameter Have a simple structure Composed of bacteria and
archaea
Eukaryotes
Have membrane surrounding their DNA
Have a nucleus Have internal membrane-
bound organelles Are larger, 10-100 µm in
diameter Have more complex structure Composed of algae, protozoa,
fungi, animals, and plants
[INSERT FIGURE 3.1]
Structure
Referred to as phospholipid bilayer; composed of lipids and associated proteins
Approximately half 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
Membranes contain a hydrophilic and hydrophobic side
Composed of many different types of proteins
Proteins in the lipid bilayer move freely within the membrane
Thin pliable lipid and protein envelope
that defines a cell.
Phospholipid bilayer
Functions:
Regulates nutrient and water intake
Regulates waste removal Site of prokaryotic respiration Site of prokaryotic flagella
attachment Involved in the distribution of
genetic material during binary fission
Function Energy storage Harvest light energy in
photosynthetic prokaryotes Selectively permeable Naturally impermeable to most
substances Proteins allow substances to
cross membrane Occurs by passive or active
processes Maintain concentration and
electrical gradient Chemicals concentrated on
one side of the membrane or the other
Voltage exists across the membrane
Glycocalyces
Gelatinous, sticky substance surrounding the outside of the cell
Composed of polysaccharides, polypeptides, or both
Types of Glycocalyces
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
Polysaccharides or polypeptides in composition.
Surround the cell wall in some bacteria.
Function:
Protection from phagocytosisOsmotic barrierReservoir for nutrientsVirulence factor
Consist of polysaccharide fibers that extend form the bacterial surface
Functions:
ProtectionAttachmentAssociated with biofilms
Types of Glycocalyces
Slime layer Loosely attached to cell
surface Water soluble Protects cells from drying out Sticky layer that allows
prokaryotes to attach to surfaces
Flagella
Axial Filaments
Pili (Fimbriae)
Flagella
Structures of locomotion
Originate in the plasma membrane
In bacteria rotate like a propellar
Many different arrangements
Flagella Are responsible for
movement Have long structures that
extend beyond cell surface
Are not present on all prokaryotes
Flagella
Structure Composed of filament,
hook, and basal body Flagellin protein (filament)
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
Arrangements of Flagella
A.Monotrichous
B.Lophotrichous
C.Amphitrichous
D.Peritrichous
Axial filament (endoflagella)
Originates in the cell membrane and transverses the length of the cell in the periplasmic space.
As the endoflagella rotate to move the cell the characteristic shape is formed .
Endoflagella are associated with spirochetes.
Endoflagellum is also know as an axial filament.
Attached to the plasma embrane and transverses the entire cell.
Responsible for the spirochete morphology.
Flagella
Function Rotation propels bacterium
through environment Rotation reversible, can be
clockwise or counterclockwise Bacteria move in response to
stimuli (taxis) Runs Tumbles
Fimbriae and Pili Rod-like proteinaceous
extensions
Fimbriae
Hollow tubes that protrude from some bacteria
Compose of protein
• Fimbriae Sticky, bristlelike
projections Used by bacteria to
adhere to one another, to hosts, and to substances in environment
Shorter than flagella May be hundreds per cell Serve an important
function in biofilms Virulence factor
Pili Tubules composed of pilin Also known as conjugation pili Longer than fimbriae but shorter
than flagella Bacteria typically only have one
or two per cell Mediate the transfer of DNA
from one cell to another (conjugation)
Bacterial Conjugation
Transfer of plasmid DNA from a donor to a recipient.
Process strengthens the bacterial cell and alows for survival in a competitive environment.
1. poly-Beta-hydroxybutyric acid - stores lipids for use in plasma membrane
2. glycogen - stores starch like polymer of sugar for energy production
3. Polyphosphate granules (metachromatic granules) - storage for phosphates for plasma membrane and the formation of ATP from ADP.
4. Sulfur granules - stores sulfur which is necessary for the metabolic reactions in biosynthesis.
Mesosomes - invagination of the plasma membrane that increases the surfaces area of the plasma membrane during binary fission.
The mesosome also serves as a site for the attachment and distribution of genetic material during binary fission.
In prokaryotic cell division, called binary fission.
A diagram of the attachment of bacterial chromosomes, indicating the possible role of the mesosome (an inward fold of the cell membrane) in ensuring the distribution of the "chromosomes" in a dividing cell.
Upon attachment to the plasma membrane, the DNA replicates and reattaches at separate points. Continued growth of the cell gradually separates the chromosomes and allocates chromosome copies to the two daughter cells.
6. gas vacuoles - storage of metabolic gases such as methane or hydrogen gas. The gas vacuoles help in the buoyancy of the cell and aids in it motility.
7. ribosomes - responsible for the synthesis of proteins.
8. nucleoid material - the genetic material of bacteria, which usually is balled up in the cell. During binary fission the nucleoid material unravels within the cell in order to be copied and distributed to the daughter cells.
9. Plasmid - small fragments of self-replicating extrachromosomal DNA that codes for the resistance to antibiotics or for the productions of a specific metabolite, i.e. toxins, pigments. These plasmids may be transferred from one bacterial cell to another by the F-pili.
9. Plasmid - small fragments of self-replicating extrachromosomal DNA that codes for the resistance to antibiotics or for the productions of a specific metabolite, i.e. toxins, pigments. These plasmids may be transferred from one bacterial cell to another by the F-pili.
These plasmids may be transferred from one bacterial cell to another by the
F-pili.
10. Endospores - a survival mechanism of certain genera of bacteria such as Clostridium and Bacillus.
The endospores are composed of a complex of dipicolinc acid and calcium and the function of the endospore is to protect the bacterial chromosome.
The endospores are very resistant to heat, desiccation, freezing, and other physical properties such as pesticides, antibiotics, dyes, and acids.
The endospores may remain dormant for many years until the environment becomes suitable to sustain the life of the bacteria.
The endospore will then germinate to form an exact copy of the parent cell that produced it.
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
Three different types of cell walls and their compositions:
Fungal cell walls are composed of cellulose and/or chitin.
Plant cell walls are composed of cellulose.
Algal cell walls are composed of cellulose, silicon, and calcium carbonate.
Consist of a lipid bilayer and associated proteins. The Plasma Membrane of Eukaryotic cells resembles and functions in the same manner as the prokaryotic plasma membrane with the following exceptions;
Contains high levels of sterols such as cholesterol.
No respiratory enzymes are located in the eukaryotic plasma membrane.
Respiration occurs in the mitochondria.
Glycocalyces
Never 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
Flagella
There are several different arrangements of flagella in eucaryotes.
This diagram represents a biflagellated eukaryotic cell.
One of the flagella aids in movement laterally and the other aids in up and down movement.
The eukaryotic flagella move like a whip.
See Flagellar handout.
Flagella Function
Do not rotate, but undulate rhythmically
Cilia Similar to flagella both structurally and functionally but are much shorter and more numerous.
Cilia are found peritrichously to the cell.
Move in an undulating manner and motility by those organisms with cilia is much more rapid than those with flagella.
Membranous Organelles
Nucleus Often largest organelle in cell Contains most of the cell’s
DNA Semi-liquid 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 nuclear envelope – double membrane composed of two phospholipid bilayers
Nuclear envelope contains nuclear pores
Nucleus - double membraned organelle that houses the genetic material of cell.
Nuclear membrane contains numerous pores through which proteins and RNA can move.
Membranous Organelles
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
Endoplasmic reticulum - network of cytoplasmic membranes where lipids and proteins are produced.
Smooth ER - synthesis of lipids
Rough ER - associated with ribosomes and is responsible for the synthesis of proteins.
.
Membranous Organelles
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
Golgi apparatus (dictyosome) is associated with the ER.
It modifies and packages the lipids and proteins manufactured by the ER and places them in vesicles for cellular use.
Membranous Organelles 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
Membranous Organelles Mitochondria
Have two membranes composed of phospholipid bilayer
Produce most of cell’s ATP Interior matrix contains
70S ribosomes and circular molecule of DNA
mitochondria - involved in the production of chemical energy in the form of ATP.
Consist of convoluted inner membrane and outer membrane. Invaginations are called cristae and contain enzymes used to synthesis ATP.
All respiratory enzymes are located in the inner membrane of the mitochondria.
Membranous Organelles Chloroplasts
Light-harvesting structures found in photosynthetic eukaryotes
Have two phospholipid bilayer membranes and DNA
Have 70S ribosomes
Endosymbiotic TheoryEukaryotes formed from union of small aerobic
prokaryotes with larger anaerobic prokaryotessmaller 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
Not universally accepted
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