Lecture 2/3 Flashcards
What are the primary features of prokaryotes?
-Smaller in size than eukaryotes
-Have 1 chromosome
-No nucleus
-No membrane-bound organelles
-Reproduce by binary fission
What were the first prokaryotic bacteria seen by the naked eye?
Thiomargarita Namibiensis (0.75mm) and was discovered in 1999
What prokaryotic cell was discovered in June of 2022?
Thiamargarita Magnific
__ is where the DNA of bacteria is packaged without being surrounded by a membrane
The nucleoid
The DNA is stabilized in the nucleoid by:
-The neutralization of the negative charge of the DNA by small polyamines and Mg 2+ ions
-Histone-like proteins
Prokaryotic cells are surrounded by complex envelope layers, which function as:
-Protection (from hostile environments such as osmolarity and harsh chemicals and antibiotics)
-Pathogenicity (contributes to the invasiveness of pathogenic bacteria)
What are the 3 layers of the prokaryotic cell envelope?
- The cell membrane- plasma or cytoplasmic membrane
2.The cell wall - Gram + and Gram - - The capsule - encapsulated and encapsulated bacteria
The cell membrane is based on the ___________ and is composed of ____ and ____
fluid mosaic model, phospholipids bilayer, proteins
____ are lipid molecules that play a role in the fluidity of the membrane
Hopanoids
What are the 5 functions of the cell membrane?
- Permeability and transport
- Electron transport and oxidative phosphorylation
- Excretion of hydrolytic exoenzymes and pathogenicity proteins
- Biosynthetic functions
- Chemotactic systems
What are the 4 types of permeability and transport?
GAPS
1. Group translocation = need energy to phosphorylate the molecule during the transport process and then use it in the metabolism. Used to uptake sugars
2. Active transport = need energy and transport proteins (from low to high concentration of solutes)
3. Passive transport = relies on diffusion. Simple diffusion (no energy, no protein) and facilitated diffusion (need channel proteins) ex. transport of O2, CO2, H2O
4. Special transport processes = using specialized molecules such as siderophores to transport ions which is locked up in nature as Fe(OH)3 and insoluble and unavailable for transport
How does electron transport and oxidative phosphorylation in the cell membrane occur?
Analog function to the mitochondria function in eukaryotes.
The cytochrome and other enzymes and components of the respiratory chain, are located in the cell membrane.
How does excretion of hydrolytic exoenzymes and pathogenicity proteins occur in the cell membrane?
6 pathways of protein secretion have been described in bacteria, the type I-VI secretion systems.
Used to secrete hydrolytic enzymes and pathogenicity toxins and other proteins
How do biosynthetic functions work in the cell membrane?
The cell membrane is the site of the enzymes and phospholipid and cell wall biosynthesis.
How does the chemotactic system work in the cell membrane?
The cell membrane has specific receptors that can bind to different kinds of attractants and repellents
Why is the cell wall important?
-Gives the cell shape
- Protects the cell from osmotic lysis
- have components that contribute to the bacteria pathogenicity
-It is the site of action of several antibiotics
What two groups can a bacteria species be divided into based on their cell wall?
Gram-positive and gram-negative
What layer of the cell wall is primarily responsible for the strength of the cell wall
Peptidoglycan layer (murein)
The peptidoglycan layer (murein) is composed of 3 parts:
- A backbone, composed of alternating sugar derivatives NAG and NAM
- A set of identical tetrapeptide side chains attached to NAM. Most have L-alanine, D-glutamate (DAP or L-lysine), and D-alanine
- Peptide cross-links or interbridges
What are the special components of Gram-positive cell walls:
- Teichoic acids - Wall teichoic acids (WTA) and Lipoteichoic acid (LTA)
- Polysaccharides
Teichoic acids:
Teichoic acids are partially responsible for the negative charge of the cell.
The peptidoglycan and teichoic acids together participate in the elasticity, porosity, and tensile strength of the envelope.
Polysaccharides in the cell wall:
in some species, sugars, such as mannose, arabinose, and glucuronic acid exist as subunits of polysaccharide in the cell wall
What are the special components of gram-negative cell walls:
- Outer membrane
- Lipopolysaccharide
- Porin channels
- Lipoprotein
- The periplasmic space
The outer layer of the gram-negative cell wall:
Is a bilayer structure, the outer leaflet contains LPS
It has channel proteins (porins)
Lipopolysaccharide in gram-negative cell wall:
Consists of glycolipids (lipid A) and polysaccharides and it prevents the diffusion of hydrophobic materials (toxic compounds) through the outer membrane.
Polysaccharide part consists of the core + side antigen (O antigen)
O antigen is highly variable (ex in salmonella)
In some bacteria lipid A acts as endotoxin
Porin channels in gram-negative cell wall:
Permit the passive diffusion of low molecular weight hydrophilic compounds, such as sugars, amino acids, and certain ions
Large antibiotic molecules (such as Beta lactams) have very low permeability -> Gram-negative bacteria have resistance to some antibiotics
Lipoprotein in the cell wall:
crosslink the outer membrane and peptidoglycan layers
-to stabilize and anchor the outer membrane layer
-it is the most abundant protein of Gram-negative cells
The periplasmic space in the cell wall:
is the space between the inner and outer membranes and peptidoglycan layers.
- the periplasmic space is approximately 20-40% of the cell volume
-it contains the peptidoglycan layer and a gel-like solution of proteins (binding proteins, hydrolytic enzymes, and detoxifying enzymes)
Some bacteria such as Mycobacteria Tuberculosis have cell walls that contain large amounts of waxes, called :
mycolic acids
Can the acid-fast bacteria cell wall be stained with gram stains?
No
What is the acid-fast bacteria cell wall stained with?
acid-fast stain protocol
Is the permeability of the acid-fast bacteria cell wall higher or lower than for E.Coli
Lower
The low permeability of the acid-fast bacteria cell wall render these bacteria resistant to:
antibiotics, and many harsh chemicals, including detergents, and strong acids
The Mycoplasmas are:
cell wall-lacking bacteria containing no peptidoglycans
Mycoplasmas are resistant to:
cell walls-inhibiting antibiotics (ex penicillins and cephalosporins)
What are 3 enzymes that attack cell walls?
Lysozymes
Autolysis hydrolytic enzymes
Hydrolytic enzymes of higher organisms
-Found in human secretions (tears, saliva, and nasal)
-Break down the peptidoglycan backbone
-The outer membrane of the Gram-negative cell wall prevents access to ___
Lysozymes
-Secreted by the bacteria itself to catalyze the degradation and turnover of peptidoglycan, to participate in cell wall growth and cell separation
-Responsible for dissolution of dead cells
Autolysins hydrolytic enzymes
Such as protozoa and the phagocytic cells of animals that degrade bacterial cell walls and digest whole bacteria
Hydrolytic enzymes of higher organisms
Is an extracellular layer lying outside the cell, composed mainly of polymer of polysaccharides
Capsule
The capsule contributes to the invasiveness of pathogenic bacteria by:
-encapsulated bacteria are protected from phagocytosis
-the glycocalyx plays a role in the adherence of bacteria to the host cells
_______ mutans adhere tightly to the tooth surface by _____
Streptococcus, glycocalyx
What are the 5 cytoplasmic structures in prokaryotic cells?
- Intracytoplasmic membrane systems
- Carboxysomes
- Gas Vesicles
- Inclusion bodies (storage granules)
- Cytoskeleton-like proteins
What cytoplasmic structure in the prokaryotic cell has photosynthetic pigments to preform photosynthesis in phototroph bacteria? Ex: thylakoids, lamellae, or chlorosomes
Intracytoplasmic membrane system
What cytoplasmic structure in prokaryotic cells are protein-covered bodies packed with the enzyme ribulose-bisphosphate carboxylase (Rubisco) for CO2 fixation in autotrophic bacteria?
Carboxysomes
What cytoplasmic structure in the prokaryotic cell is found in aquatic and marine bacteria and used to provide buoyancy and keep the cell high in the water column?
Gas vesicles
What are inclusion bodies used for in the prokaryotic cell?
they are used to store reserve materials in the form of insoluble granules:
-Poly-B-hydroxybutyric acid (PHB) granules-> used to store PHB which is a lipid like compound
-Glycogen granules -> store glycogen
-Volutin granules or metachromatic granules -> used to store inorganic phosphate
-Magnetosomes -> used to store magnetic mineral magnetite (Fe3O4) in certain species of bacteria
What are cytoskeleton-like proteins used for in prokaryotic cells?
They resemble both actin and non-actin cytoskeletal proteins of eukaryotes.
They:
-determine cell shape
-segregation of chromosomes
-regulation of cell division
What are flagella?
Are threadlike appendages composed entirely of proteins and are responsible for bacterial movement.
They are made up of protein subunits called flagellin
What are the 4 different types of flagella?
Monotrichous - single polar flagellum
Amphitrichous - one flagellum at each pole
Lopotrichous- multiple polar flagellum
Peritrichous - flagella distributed over the entire cell
Flagella are highly ___ and some of the immune responses are directed against these proteins
antigenic (H antigens)
____ are small rigid surface appendages on a cell. They inhibit the phagocytic ability of leukocytes and play a role in bacteria motility.
Pili (fimbriae)
Pili are composed of structural protein subunits called ____ and at the tips of pili are __ ____ for attachment properties
pilins, adhesions proteins
What do ordinary pili do?
They play a role in the adherence of the bacteria to the host cells and have antigenic function
Sex pili are responsible for
DNA transfer between the donor cell and the recipient cell during the conjugation process
What are endospores?
Heat-resistant spores that can remain viable for thousands of years.
The process of sporulation is triggered in:
hard conditions such as lack of nutrients and heat
The endospore consists of:
the bacterium’s DNA, ribosomes, and large amounts of calcium dipocolinate which help the endospores maintain dormancy
What are endospores resistant to?
Starvation, high temperature, extreme freezing, UV radiation, desiccation, and chemical disinfectants
What are the two most common spore-forming bacteria?
Gram-positive aerobic genus Bacillus and the anaerobic genus Clostridium
Do eukaryotic cells have a nucleus?
Yes
The nucleus is surrounded by _______
nuclear envelope
The nuclear envelope is composed of:
double lipid-bilayer membranes and has pores and exhibits selective permeability
Eukaryotic cells contain linear ____, which appear as thread-like structures called ____
DNA macromolecules, chromatin
How many subunits do ribosomes have?
2
How are ribosomal subunits synthesized?
By combining rRNA with ribosomal proteins
What type of ribosomes do eukaryotes have?
80S (60S and 40S subunits)
What type of ribosomes do prokaryotes have?
70 (50S and 30 S subunits)
What is important about 16S RNA?
The gene coding of 16S RNA is highly conserved between different species of bacteria and is being used in the bacterial classification and phylogenetic studies)
