Prokaryotic Cells Structural Components And Roles Flashcards
Outline the structure of simple/generalised prokaryotic cell
Nucleoide - singular circular chromosome
Ribosomes - protein synthesis
Plasma membrane - cell regulation
Cell wall - cell integrity
Glycocalyx - extracellular cell protection
Flagella - cell movement in liquid media
Rimbrae/Pili - extracellular attachment
Outline the nuclear envolope for Bacteria, Archaea, and Eukarya
Bacteria: absent
Archaea: absent
Eukarya: Present
Outline membrane bound organelles for Bacteria, Archaea, and Eukarya
Bacteria: Absent
Archaea: Absent
Eukarya: Present
Outline peptidoglycan in cell wall for Bacteria, Archaea, and Eukarya
Bacteria: Present
Archaea: Absent
Eukarya: Absent
Outline chromosomal DNA for Bacteria, Archaea, and Eukarya
Bacteria: singular circular chromosome
Archaea: singular circular chromosome
Eukarya: Multiple linear chromosomes
Outline growth at temperatures above 100 degrees for Bacteria, Archaea, and Eukarya
Bacteria: No
Archaea: Some species
Eukarya: No
Outline the bacterial genome
Typically a single circular chromosome
No nuclear membrane, however chromosomes is restricted to defined region of bacterial cell - nucleoid
Other small circular self replication DNA molecules can be found in cytosol (seperate to main chromosome, known as plasmids)
Outline the difference between the humane and bacteria genome
Human genome very large, contains a lot of “junk”, only small portion codes for functional proteins
Most of bacteria genome is functional, less “junk”
What is the function of the cell wall of bacteria
Rigid macromolecular layer that provides strength to cell
Protects cells from osmotic lysis and confers cell shape
What class of prokaryotes lack cell walls
Mycoplasmas - group of pathogenic bacteria
What is peptidoglycan
A substance that forms a mesh like structure, forming the cell walls of bacteria
Outline the structure of peptidoglycan
Peptidoglycan is a polymer composed of two alternating sugars, NAM and NAG, which are cross linked by short peptides (tetrapeptide side chain). Peptide cross bridge provides additional strength by linking the tetrapeptides of two adjacent peptidoglycan chains together
Outline the gram stain procedure
Crystal violet (purple dye) added to culture - stains cells
Iodine added to culture - fuses stain on cell wall
Alcohol wash added to culture - washes away excess crystal violet from gram negative cells
Safranin applied to culture - stains gram negative a contrasting red/pink
Outline the structure of gram positive bacterial cell wall
Thick external peptidoglycan layer surrounds internal plasma membrane
Thick peptidoglycan cell wall (20 - 80 nm), hence dark stain
Peptidoglycan traps crysta violet, which masks safranin dye
What is responsible for differences in Gram stain reactions
Structural differences between gram positive and gram negative cell walls of bacteria
Outline the structure of gram negative bacteria cell wall
Thin layer of peptidoglycan (5 - 10nm) between an outer plasma membrane, and the inner plasma membrane
Crystal violet easily rinsed away (not retained by thin peptidoglycan), revealing red safranin dye
What is the function of bacterial flagella
To allow bacterial movement in a liquid medium
How does flagella facilitate movement
Long flexible appendage resembling tails
Ptoteinaceous, 10-20 nm in diameter
Number of, and location varies with cell
Act like propeller: rotating them to move through liquid medium
How do bacteria Spence chemical gradients in environment
Too short to sense chemical gradient from head to base/tail
Sense chemical environment in location, move to another location, sense environment of new location and compare with old environment
What is chemotaxis in terms of bacteria
Bacteria move along a concentration gradient towards a chemical attractant (positive) or away from a chemical repellent (negative)
What are Fimbriae
Also called Adherence Pili
Protein structures with adhesive properties that cause bacteria to stick/adhere to surfaces
Not all bacteria possess fimbriae, is an inherited trait
Much shorter and more numberous than flagella (100-1000 per cell, 2-8nm in diameter, 1micrometer in length)
What are pili
Singular large protein structure that facilitates attachment to bacteria
Transfers genetic material from one cell to another
Process called conjugation - form of horizontal gene transfer
What is glycocalyx
A gelatinous polysaccharide and/or polypeptide outer covering. Forms a stick mesh work of fibres
Outline a glycocalyx capsule
Glycocalyx organised into a defined structure attached firmly to a cell wall - capsule
Outline a Glycocalyx slime layer
Glycocalyx disorganised without cell shape, attached loosely to cell wall = slime layer
Outline 2 functions of capsules
Virulence factors - protecting bacteria from phagocytosis and engulfment by immune cells
Prevent cell desiccation
Outline when bacterial endospores are formed
Bacterial endospores are formed during unfavourable growth conditions and germinate under favourable conditions - protect cells from stress
What form of reproduction is used to produce endospores
Asymmetrical reproduction
What are endospores
Highly differentiated cells resistant to heat, harsh chemicals, antibiotics, disinfectants and radiation.
Dormant stage of bacterial life cycle. Can stay dormant for very long time until conditions become favourable
What is transpeptidase
The enzyme that cross links the peptidoglycan chains to form rigid cell walls
