Bacterial Cell Walls & Prokaryotic & Eukaryotic Cells

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Felix Villarreal Biology 2420 ACC

cell wall

the outer most layer
of the cell. In many cases it comes in direct contact with the environment.

Functions of Cell Wall

1. Provide structure and shape and protect cell from osmotic forces
2. Assist some cells in attaching to other cells or in eluding antimicrobial drugs
3. Not present in animal cells, so can target cell wall of bacteria with antibiotics

Bacterial Cell Wall Composition Classification

1. Gram positive
2. Gram Negative

Peptidoglycan

composed of sugars, NAG, and NAM; cell wall composition of most cells

Peptidoglycan Structure

Chains of NAG and NAM attached to other chains by tetrapeptide crossbridges
a. covalent bond connections
b. short chains of amino acids

Characteristics of Gram Positive Cell Walls

1. Relatively thick layer of peptidoglycan
2. Contain unique polyalcohols called teichoic acids (Some covalently linked to lipids, forming lipoteichoic acids that anchor peptidoglycan to cell membrane)
3. Retain crystal violet dye in Gram staining procedure; so appear purple

1. n-acetyl muramic acid (NAM)
2. n-acetyl glucoasmine (NAG)

The gram positive cell wall is referred to as a peptidoglycan layer and is composed of alternating subunits of two carbohydrates: ____ and ______.

Characteristics of Gram-negative cell walls

1. Have only a thin layer of peptidoglycan
2. Bilayer membrane outside the peptidoglycan contains phospholipids, proteins, and lipopolysaccharide (LPS)
3. May be impediment to the treatment of disease
4. Appear pink following Gram staining

Gram Negative Cell Wall Layers

1. outer membrane
2.

outer membrane

composed of lipopolysaccarhides (LPS).

peptidoglycan layer

composed of sugars, NAG, and NAM; cell wall composition of most cells

Archaeal Cell Walls

1. Do not have peptidoglycan
2. Contains variety of specialized
polysaccharides and proteins
3. Gram-positive archaea stain purple
5. Gram-negative archaea stain pink

Characteristics of Prokaryotes

1. Don't have membrane surrounding their DNA
2. lack a nucleus
3. Lack various internal structures bound with phospholipid membranes
4. Are small, ~1.0 µm in diameter
5. Have a simple structure
6. Composed of bacteria and archaea

Characteristics of Eukaryotes

1. Have membrane surrounding their DNA
2. Have a nucleus
3. Have internal membrane-bound organelles
4. Are larger, 10-100 µm in diameter
5. Have more complex structure
6. Composed of algae, protozoa, fungi, animals, and plants

Cell Membrane Protien Function

act as recognition proteins, enzymes, receptors, carriers, or channels

Types of Cell Membrane Proteins

1. Integral proteins
2. Peripheral proteins
3. Glycoproteins

Functions of Phosolipid Bilayer

1. Regulates nutrient and water intake
2. Regulates waste removal
3. Site of prokaryotic respiration
4. Site of prokaryotic flagella attachment
5. Involved in the distribution of genetic material
during binary fission

Phosolipid Bilayer

Thin pliable lipid and protein envelope
that defines a cell.

Funtions of Prokaryotic Cytoplasmic Membranes

1. Energy storage
2. Harvest light energy in photosynthetic PK's
3. Selectively permeable
4. Naturally impermeable to most substances
5.Proteins allow substances to cross membrane
6. Maintain concentration and electrical gradient

Prokaryotic Glycocalyces

1. Gelatinous, sticky substance surrounding the outside of the cell
2. Composed of polysaccharides, polypeptides, or both

External Structures of Prokaryotic Cells

1. Glycocalyces
2. Flagella
3. Axial Filaments
4. Pili (Fimbriae)

Types of Glycocalyces

1. Capsule
2. Slime Layer

Capsule

glycocalyces external structure of prokaryotic cells that is firmly attached to the cell surface and is composed of polysaccharides or polypeptides

Slime Layer

glycocalyces external structure of prokaryotic cells that is water soluble, loosely attached and consists of polysaccharide fibers that extend form the bacterial surface.

Functions of Slime Layer

1. Protection from drying out
2. Sticky layer that allows prokaryotes to attach
to surfaces
3. Associated with biofilms

Functions of Capsule

1. Protects cells from drying out
2. Protection from phagocytosis and from being
recognized and destroyed by host
3. Osmotic barrier
4. Reservoir for nutrients
5. Virulence factor

Prokaryotic Flagella

1. Structures of locomotion
2. Originate in the plasma membrane
3. In bacteria rotate like a propellar
4. Many different arrangements

Prokaryotic Flagella Structure

1. Composed of filament, hook, and basal body
2. Flagellin protein (filament) deposited in a helix at the lengthening tip.
3. Base of filament inserts into hook
4. Basal body anchors filament and hook to cell wall by a rod and a series of either two or four rings of integral proteins
5. Filament capable of rotating 360º

Arrangments of Prokaryotic Flagella

1. Monotrichous - One arm
2. Lophotrichous - multiple arms on one end
3. Amphitrichous - one arm on each end
4. Peritrichous - multiple arms all over body

Prokaryotic Axial filament (endoflagella)

external structure of prokaryotic cells that originate in the cell membrane and transverses the length of the cell in the periplasmic space. Their shaped is formed by the rotation movement created to move the cell and they are responsible for spirochete morphology.

Function of Prokaryotic Flagella

1 Rotation propels bacterium through environment
2. Rotation reversible, can be clockwise or counterclockwise
3. Bacteria move in response to stimuli (taxis)
a. Runs
b.Tumbles

Prokaryotic Fimbriae and Pili

external structures of prokaryotic cells that are rod-like proteinaceous extensions

Prokaryotic Fimbriae

external structures of prokaryotic cells that are sticky, bristlelike projections. These hollow tubes protrude from some bacteria and are composed of protein. As many as hundreds per cell.

Functions of Prokaryotic Fimbriae

1. Used by bacteria to adhere to one another, to hosts, and to substances in environment
2. Serve an important function in biofilms
Virulence factor

Prokaryotic Pili (Conjugation Pili)

Tubules composed of pilin that mediate the transfer of DNA from one cell to another (conjugation). Only or two per cell.

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.

Types of Bacterial Inclusion Bodies

1. poly-Beta-hydroxybutyric acid
2. glycogen 7. ribosomes
3. polyphosphate granules (metachromatic granules)
4. Sulfur granules 8. nucleoid material
5. mesosome 9. plasmid
6. gas vacuoles 10. endospores

poly-Beta-hydroxybutyric acid

stores lipids for use in plasma membrane

glycogen

stores starch like polymer of sugar for energy production

Polyphosphate granules (metachromatic granules)

storage for phosphates for plasma membrane and the formation of ATP from ADP.

Sulfur granules

stores sulfur which is necessary for the metabolic reactions in biosynthesis.

Mesosomes

invagination of the plasma membrane that increases the surface area of the plasma membrane and serves as a site for the attachment and distribution of genetic material during binary fission.

binary fission

cell division of prokaryotic cells.

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.

ribosomes

responsible for the synthesis of proteins.

nucleoid material

the genetic material of bacteria, which usually is balled up in the cell. During binary fission it unravels within the cell in order to be copied and distributed to the daughter cells.

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. They may be transferred from one bacterial cell to another by the F-pili.

Endospores

survival mechanism of certain genera of bacteria such as Clostridium and Bacillus whose function is to protect the bacterial chromosome.

Characteristics of Endospores

1. Composed of a complex of dipicolinc acid and calcium.
2. Very resistant to heat, desiccation, freezing, and other physical properties such as pesticides, antibiotics, dyes, and acids.
3. remain dormant for many years until the environment becomes suitable to sustain the life of the bacteria

Eukaryotic Cell Walls

Fungi, algae, plants, and some protozoa have cell walls but no glycocalyx that are composed of various polysaccharides.

Composition of Plant cell walls

cellulose

Composition of Fungal cell walls

cellulose, chitin, and/or glucomannan

Composition of Algal cell walls

cellulose, proteins, agar, carrageenan, silicates, algin, calcium carbonate, or a combination of these.

Eukaryotic Plasma Membrane

1. Consist of a lipid bilayer and associated proteins.
2. Contains high levels of sterols such as cholesterol.
3. No respiratory enzymes

eukaryotic glycocalyces

1. Never as organized as prokaryotic capsules
2. Help anchor animal cells to each other
3. Strengthen cell surface
4. Provide protection against dehydration
5. Function in cell-to-cell recognition and communication

eukaryotic flagella

external appendage of eukaryotic cells that moves like a whip. Does not rotate, but undulates rhythmically.

eukaryotic cilia

external appendage of eukaryotic cells found peritrichously to the cell. They move in an undulating manner and motility much more rapid than with flagella.

nucleoplasm

Semi-liquid portion of nucleus in eukaryotic cells that contains chromatin.

chromatin

masses of DNA associated with histones

nucleoli

structure present in nucleoplasm where RNA is synthesized

Endoplasmic reticulum

Netlike arrangement of flattened, hollow tubules continuous with nuclear envelope that functions as a transport system. Site where lipids and proteins are produced. Two forms.

Types of

Smooth endoplasmic reticulum (SER)
Rough endoplasmic reticulum (RER)

Smooth endoplasmic reticulum (SER)

plays role in lipid synthesis

Rough endoplasmic reticulum (RER)

ribosomes attached to its outer surface; transports proteins produced by ribosomes

Golgi body

Composed of flattened hollow sacs surrounded by phospholipid bilayer
1. Receives, processes, and packages large molecules for export from cell
2. Packages molecules in secretory vesicles that fuse with cytoplasmic membrane

vacuoles and vesicles

1. Store and transfer chemicals within cells
2. May store nutrients in cell

Lysosomes

contain catabolic enzymes

Peroxisomes

contain enzymes that degrade poisonous wastes

Mitochondria

membranous organelle of eukaryotic cells that has two membranes composed of phospholipid bilayer and respiratory enzymes. It produces most of cell's ATP.
Interior matrix contains 70S ribosomes and circular molecule of DNA

Chloroplasts

membranous organelle of photosynthetic eukaryotic cells that harvest light. They have two phospholipid bilayer membranes and DNA and 70S ribosomes

Endosymbiotic Theory

Eukaryotes formed from union of small aerobic prokaryotes with larger anaerobic prokaryotes

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