BMSC210 CH3.3 Flashcards
What are the distinguishing characteristics of prokaryotic cells?
Small, simple, lack a nucleus or membrane-bound organelles
What are the internal and external structures of prokaryotic cells?
Cell wall, plasma membrane, cytoplasm, ribosomes; pili, flagella, capsule
How do prokaryotic cells differ from eukaryotic cells?
Prokaryotic cells lack a nucleus or membrane-bound organelles
What is cytoplasm?
gel-like substance composed of water and dissolved chemicals
What is a plasma membrane?
membrane that surrounds the cytoplasm
What are chromosomes?
genetic blueprints of the cell
What are ribosomes?
organelles for protein production
What are the two largest categories of cells?
Prokaryotic cells and eukaryotic cells
What is the main difference between prokaryotic cells and eukaryotic cells?
Presence or absence of nucleus and nuclear membrane
Which domains do prokaryotic microorganisms belong to?
Archaea and Bacteria
Which domain do eukaryotic organisms belong to?
Eukarya
How does the size of eukaryotic cells compare to prokaryotic cells?
Eukaryotic cells are larger
Do prokaryotic cells have membrane-bound organelles?
No, generally lacking
What are the structures typically associated with prokaryotic cells?
cell membrane, chromosomal DNA, ribosomes, cell wall
What is the role of the cell wall?
Protects the cell from changes in osmotic pressure
Which types of organisms have a cell wall?
Most prokaryotes and some eukaryotes
What is osmotic pressure?
Differences in solute concentration on opposing sides of a semipermeable membrane
What can pass through a semipermeable membrane?
Water
What can’t pass through a semipermeable membrane?
Solute molecules
What is osmosis?
Diffusion of water
Which way does water diffuse in osmosis?
From low concentration to high concentration
What happens to the concentrations on both sides in osmosis?
They become equal
What is the name for extreme osmotic pressure on a cell?
Osmotic shock
How is the external environment of a cell described?
Isotonic, hypertonic, or hypotonic
What is an isotonic medium?
Solute concentrations are approximately equal inside and outside the cell.
What happens in a hypertonic medium?
Solute concentration outside the cell exceeds that inside the cell. Water moves out of the cell.
What happens in a hypotonic medium?
Solute concentration inside the cell exceeds that outside the cell. Water moves into the cell.
What can happen to a cell in a hypotonic medium?
The cell can swell and potentially burst.
What is tonicity?
The ability of a cell to withstand changes in osmotic pressure
Why are cells with a cell wall better able to withstand changes in osmotic pressure?
They can maintain their shape
What advantages do cell walls provide prokaryotic cells?
Cell walls provide shape, structural support, and protection against osmotic stress.
What is the nucleoid in prokaryotic cells?
The nucleoid is the region within prokaryotic cells where the circular, haploid chromosome is located.
Where is prokaryotic DNA and DNA-associated proteins concentrated?
Nucleoid region
Which domains of life possess ribosomes?
All three domains - bacteria, archaea, and eukarya
What are ribosomes made of?
Proteins and ribosomal RNA (rRNA)
What is the size of prokaryotic ribosomes?
70S
What is the size of eukaryotic cytoplasmic ribosomes?
80S
What does ‘S’ stand for in 70S and 80S?
Svedberg unit
What is the difference between bacterial and archaeal ribosomes?
Different proteins and rRNA molecules
How are archaeal ribosomes similar to eukaryotic ribosomes?
More similar than bacterial ribosomes
What are the sizes of prokaryotic ribosomes?
30S (small subunit) and 50S (large subunit)
What are inclusions?
Cytoplasmic structures that store excess nutrients
What is the function of magnetosomes in magnetotactic bacteria?
Align along a magnetic field
What are endospores?
Structures that protect the bacterial genome in a dormant state
What are the characteristics of vegetative cells compared to endospores?
Vegetative cells are sensitive to extreme temperatures and radiation, gram-positive, have normal water content and enzymatic activity, and are capable of active growth and metabolism. Endospores are resistant to extreme temperatures and radiation, do not absorb Gram stain, are dehydrated with no metabolic activity, and are dormant with no growth or metabolic activity.
What is the process by which vegetative cells transform into endospores?
Sporulation
What is the first step in the process of sporulation?
Formation of a septum
During sporulation, what does the septum do?
Divides cell asymmetrically
What is a forespore during sporulaton?
Copy of cell’s chromosomes
What forms around the cortex during sporulation?
Protein spore coat
What happens to the DNA of the mother cell during sporulation?
Disintegrates
What is the final stage in the maturation of an endospore?
Formation of an outermost exosporium.
When is the endospore released during sporulation?
Upon disintegration of the mother cell.
How are the endospores visualized in staining?
Malachite Green spore stain
How long can endospores persist in a dormant state?
Up to thousands of years
What happens to endospores when living conditions improve?
They undergo germination
What happens to the cell after germination?
It becomes metabolically active again
What are some clinically significant endospore-forming gram-positive bacteria?
B. anthracis, C. tetani, C. difficile, C. perfringens, C. botulinum
What is the function of an endospore?
Survival under unfavorable conditions
What is the function of a cell wall in prokaryotic cells?
Provides structural support.
What is meant by selective permeability?
Allows some molecules to enter or leave the cell while restricting others.
What is the plasma membrane structure of most bacterial and eukaryotic cell types?
Bilayer composed mainly of phospholipids and proteins
What type of linkages are found in the phospholipids of the plasma membrane of most bacterial and eukaryotic cells?
Ester linkages
What is the structure of the bacterial plasma membrane?
Phospholipid bilayer with embedded proteins
How do archaeal plasma membranes differ from bacterial and eukaryotic plasma membranes?
Formed with ether linkages instead of ester linkages
What is the difference between archaeal phospholipids and those of bacterial and eukaryotic cells?
Archaeal phospholipids have branched chains
What are some functions of proteins in prokaryotic plasma membranes?
Cell-to-cell communication, sensing environmental conditions, pathogenesis (in bacteria)
What is the function of glycoprotein and glycolipid complexes?
Allowing the cell to interact with the external environment
Where do glycoproteins and glycolipids extend from?
The surface of the cell
What is one of the most important functions of the plasma membrane?
Control transport of molecules into and out of the cell
What are membrane transport mechanisms responsible for?
Transporting molecules across the plasma membrane
What is the purpose of maintaining internal conditions within a certain range?
Maintain homeostasis
What is the process by which molecules move from a higher concentration to a lower concentration?
Simple diffusion
What is simple diffusion also known as?
Passive transport
What molecules can cross the membrane bilayer directly by simple diffusion?
Carbon dioxide
What type of molecules need the help of carriers or channels in the membrane?
Charged molecules and large molecules
What is the process called when molecules are ferried across the membrane?
Facilitated diffusion
What are aquaporins?
Family of membrane proteins
What do aquaporins provide channels for?
Facilitated diffusion of water
What is the process called when cells move molecules against concentration gradients?
Active transport
What is a major difference between passive and active transport?
Active transport requires energy
What are the three general types of active transport in bacteria and archaea?
Coupled Transport, ATP-binding cassette transporters, Group Translocation
What is the driving ion in symport and antiport in bacteria and archaea?
Proton
In symport, does the driving ion move in the same direction as the substrate for transport?
Yes
What is antiport?
Driving ion and substrate move in opposite directions
What are ATP-binding cassette transporters?
Protein superfamily that transports substrates using ATP energy
What does ABC stand for in ABC-transporters?
ATP-binding cassette
What type of energy do ATP-binding cassette transporters use?
Energy of ATP hydrolysis
What are the three components of an ABC transporter?
1) Membrane-spanning carrier proteins, 2) ATP binding peripheral proteins, 3) Substrate-binding protein
Where is the substrate-binding protein located in Gram-negative bacteria?
Periplasm
Where is the substrate-binding protein located in Gram-positive bacteria?
Outside of cell membrane
What types of molecules do ABC transporters import?
Ions, amino acids, peptides, sugars, hydrophilic molecules
What do exporters in gram-negative bacteria transport?
Lipids and some polysaccharides
What is the PTS system?
Transfer of phosphate from PEP to sugar carriers.
What is the role of the membrane component of the PTS system?
Phosphorylates the sugar as it enters the cell.
What are some prokaryotic cells that have membrane structures for photosynthesis?
Cyanobacteria and photosynthetic bacteria
What is the major component of bacterial cell walls?
Peptidoglycan
What is the structural composition of peptidoglycan?
Long chains of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)
What gives peptidoglycan its two-dimensional tensile strength?
Formation of peptide bridges
Why are antibiotic drugs designed to interfere with peptidoglycan synthesis?
To weaken the cell wall and make bacterial cells more susceptible to osmotic pressure
How do certain cells of the human immune system recognize bacterial pathogens?
By detecting peptidoglycan on the surface of a bacterial cell
What enzymes do these cells use to destroy the bacterial cell?
Lysozyme
What are the two common types of cell wall structures that the Gram staining protocol differentiates?
Gram-positive and Gram-negative
What is the external layer found in bacteria of the family Mycobacteriaceae?
Waxy mycolic acids
Why are bacteria with mycolic acid layer referred to as acid-fast?
Acid-fast stains are needed to penetrate the mycolic acid layer for microscopy
What are the two common cell wall structural types in bacteria?
Gram-positive and Gram-negative.
How would you describe the structure of Gram-positive cell walls?
Gram-positive cell walls have a thick layer of peptidoglycan with embedded teichoic acid.
What are the three layers of Gram-negative cell walls?
Inner membrane, peptidoglycan layer, outer membrane
How are acid-fast cells stained?
Red by carbolfuschin
What is the second lipid bilayer called in Ingram-negative cells?
Outer membrane
Where is lipid A located in a gram-negative bacterial cell?
Embedded in the outer membrane
What are the components of the outer membrane of a gram-negative bacterial cell?
Lipopolysaccharide (LPS)
How does the cell wall structure of archaea differ from bacteria?
Archaeal cell walls do not contain peptidoglycan; instead, they contain pseudopeptidoglycan or glycoproteins/polysaccharides.
What is pseudopeptidoglycan (pseudomurein)?
A polymer similar to peptidoglycan found in archaeal cell walls.
What are glycocalyces?
Sugar coats exterior to the cell wall
What are the two important types of glycocalyces?
Capsules and slime layers
Where is a capsular polysaccharide layer located?
Outside of the cell wall
How is a slime layer different from a capsular polysaccharide layer?
A slime layer is loosely attached and easily washed off
What is the function of glycocalyces?
Allow cells to adhere to surfaces
What is the significance of biofilms?
Provide protection to microbes
How do biofilms protect cells?
Prevent desiccation and hinder immune responses
What are capsules?
Organized layer of polysaccharides
What is the role of a capsule in a microbe’s pathogenicity?
Capsule makes it difficult for phagocytic cells to engulf and kill the microorganism.
Which bacterium is known for producing a capsule that aids in its pathogenicity?
Streptococcus pneumoniae
Why is staining capsules for microscopy challenging?
Capsules are difficult to stain; negative staining techniques are used.
How can capsules be used?
To help identify specific pathogenic strains.
What is an S-layer composed of?
A mixture of structural proteins and glycoproteins.
What are filamentous appendages in bacterial cells?
Protein appendages that extend outward and allow interaction with the environment
What are the filamentous appendages that can attach to other surfaces, transfer DNA, or provide movement?
Fimbriae, pili, and flagella.
What do fimbriae commonly refer to?
Short bristle-like proteins projecting from the cell surface by the hundreds.
What is the function of fimbriae?
Enable cell attachment to surfaces and other cells.
Why is adherence to host cells important for pathogenic bacteria?
Colonization, infectivity, and virulence.
What are pili?
Longer protein appendages aiding in attachment to surfaces.
What is the function of the F pilus or sex pilus?
Important in DNA transfer between bacterial cells.
What are two protein appendages that bacteria may produce?
Fimbriae and pili
What is the function of flagella?
To move cells in aqueous environments
What are bacterial flagella composed of?
Flagellin protein subunits
What is the function of bacterial flagella?
Spin in solution like propellers
Where is the motor for the flagellum located?
Basal body embedded in the plasma membrane
What connects the basal body to the filament of the flagellum?
Hook region
Do gram-positive and gram-negative bacteria have the same basal body configuration?
No, they have different configurations due to differences in cell wall structure
What is the arrangement of flagella in a bacterium with a singular flagellum?
Monotrichous
What is the arrangement of flagella in a bacterium with a flagellum or tufts of flagella at each end?
Amphitrichous
What is the name for flagella that cover the entire surface of a bacterial cell?
Peritrichous flagella.
What are the main components of a bacterial flagellum?
Basal body, hook, and filament
Can flagellated bacteria have different arrangements of their flagella?
Yes
What are four common flagella arrangements of bacteria?
Monotrichous, amphitrichous, lophotrichous, peritrichous
What are some environmental signals that bacteria respond to?
Light, magnetic fields, chemical gradients
What is chemotaxis?
Movement in response to a chemical gradient
How are flagella arranged in peritrichous bacteria?
All bundled together in a streamlined way
What is the overall effect of runs and tumbles when an attractant exists?
Movement towards higher concentration
What is the name of the pattern where movement is more random when no chemical gradient exists?
Biased random walk
How do bacteria achieve directional movement?
By changing the rotation of their flagella
What happens to flagellar rotation in the absence of a chemical gradient?
Cycles between counterclockwise (run) and clockwise (tumble) with no overall directional movement.
