3 - Prokaryotic structure and function Flashcards
Why is a higher S/V ratio important
Allows for more efficient uptake and diffusion of nutrients, facilitating rapid growth
Shapes of prokaryotes
- Spherical (Cocci)
- Rod shaped (Bacilli)
- Spiral/Helical
- Pleomorphic (Variable)
- comma-shaped
- filamentous
- square
- stalked
(Rods and cocci most common)
How does size affect the S/V ratio
A rod shaped bacteria has a higher S/V ratio than a spherical shaped bacteria of the same volume. Some bacteria can be very large and maintain high S/V ratio due to convoluted membranes
What are the different arrangements of prokaryotes
- Singular
- Diplococcus (Pair of Cells)
- Chains (Streptococcus)
- Tetrads / Regular Packets (4 or 8 cell packets)
- Clusters (Staphylococcus)
Binary fission (Bacterial Growth)
When on bacterial cell undergoes repeated rounds of division on a solid surface. Results in colony composed of identical cells
What is the chemical composition of bacteria
- 70% water
- 30% dry weight (protein (15), DNA (1) , RNA (6), polysaccharides (2), lipids (2), small molecules (4))
Components of bacterial cell
- Nucleoid
- Plasmids
- Cytoplasm
- Inclusion bodies
- Internal membranes
- Plasma (cytoplasmic) membrane
- Cell wall
What is a nucleoid
Irregularly shaped region in cytoplasm that contains double stranded DNA. Not a nucleus, no membrane surrounding it.
Length of bacterial chromosomes
Varies widely, Up to 700x longer than cell. Complexed to nucleoid-associated proteins (NAPs) that enable supercoiling.
Plasmids
- Free in the cytoplasm
- Usually circular (single or multiple copies)
- Small supercoiled dsDNA (2-200 kb)
- Replicate independently of the bacterial host chromosome
- Carry genes which are not essential to the bacterial host but may be useful in certain environments
Examples of plasmids
- F-plasmid of E. coli mediates gene transfer from cell to cell
- R plasmids encode resistance
- Virulence plasmids carry virulence genes (increase virulence of host)
- Plasmids may carry metabolism genes
Cytoplasm
The material bounded by the plasma membrane. 70% water
What are 70S ribosomes composed of
- Proteins and rRNA
- Two protein subunits (30S and 50S)
Protoplast
The plasma (cell) membrane and everything within
Cytosol
The liquid component of cytoplasm.
Contains plasmids, inclusions and 70S ribosomes float in cytosol.
Cytoskeleton
Role in cell division, localisation of proteins to certain sites, help determine cell shape, possibly chromosome and plasmid segregation to daughter cells
What are inclusion bodies
Common in all cells, formed by aggregation of organic or inorganic substances. Used for storage of C or energy
Name 5 organic inclusion bodies
- PHB granules
- Glycogen
- Carboxysomes
- Gas vacuole
- Cyanophycin
PHB Granules
- Carbon and energy reserve
- Found in many bacteria
Glycogen
- Carbon and energy reserve
- Found in many bacteria
Carboxysomes
- Carbon dioxide fixation
- Found in autotrophic bacteria
- Example of microcompartment (large polyhedron made of protein)
Gas vacuole
- Function: Flotation, gas can enter but not water
- Found in aquatic bacteria
- Aggregates of small, hollow cylindrical protein structures called gas vesicles
Cyanophycin
- Function: Nitrogen reserve
- Only found in Cyanobacteria
Name 3 inorganic inclusion bodies
- Sulphur granules
- Volutin granules
- Magnetosome
Sulphur granules
- Function: Reserve of electrons for metabolism
- Found in bacteria that use H2S as electron donor, and accumulate the resulting S
Volutin granules
- Function: Phosphate and energy reserve
- Found in many bacteria
- Stain helps identify species - characteristic
Magnetosome
- Intracellular chains of magnetite particles, bound by a membrane
- Function: Allow swimming to optimum depth, allow bacteria to move toward iron rich settlements
- Found in magnetotactic aquatic bacteria
- Each particle is a tiny magnet, allows orientation of cell in Earth’s magnetic field
What are the two internal membranes that can be found in bacteria
Thylakoid and plasma membranes
Thylakoid membrane (Internal Membrane)
Function is photosynthesis, found in photosynthetic bacteria. Lined with particles containing pigments
what is the composition of the plasma membrane
- Amphipathic (polar and nonpolar ends) phospholipids organised as a bilayer
-Proteins within bilayer - Fluid-mosaic model: proteins float in bilayer
Function of the plasma membrane
- Selectively permeable membrane barrier that determines transport of molecules into and out of the cell
- Nutrient and waste transport
- Prevents loss of essential components - while allowing movement of other molecules
- Location of many metabolic processes
Composition of the cell wall
Composed of peptidoglycan, different for gram positive and gram negative
Function of cell wall
- Maintains cell shape
- Provides protection from osmotic shock and anti bacterial agents
- Contains components contributing to pathogenicity
What bacteria contain a cell wall
all bacteria except Mycoplasma
Gram positive cell wall
Stains purple. Has a thick later of peptidoglycan which contains teichoic acids and are sensitive to cell wall targeting antibiotics and lysozyme.
And an inner membrane
Gram negative cell wall
Stains pink. Has a thin layer of peptidoglycan and does not contain teichoic acids. Has an outer and inner membrane this sandwiches the peptidoglycan layer and is resistant to penicillin and lysozyme
Periplasm
Region between the outer membrane and the plasma membrane in gram negative cell walls
What is the gram stain and what is used
Differentiates gram positive and negative bacteria. Crystal violet –> Grams iodine –> alcohol –> Safranin
Why do gram positive stain purple
Thick meshlike cell wall retains the purple crystal violet stain
Why do gram negative stain pink
Thinner cell wall that doesn’t retain the crystal violet. These are then counterstained pink by safranin
Explain the 4 steps in gram staining
- Crystal violet: Dye is taken up equally by all cells
- Grams Iodine: Is a mordant which enhances the binding of dye to cell walls
- Alcohol: Gram negative cell walls are thin and cannot retain the dye (become colourless. +’ve stay purple)
- Safranin: Counterstain, only unstained gram negative cells can take up the dye. Crystal violet in gram positives repel the counterstain
What are the steps of binary fission
chromosome duplication, cell elongation, division septum, division
Osmotic shock
A mammalian cell in high conc. H20 will burst
Compare the size, shape and arrangement of prokaryotic cells with that of eukaryotes
What are the main structural features of a bacterial cell?
Describe the structure and function of: nucleoid, plasmid, cytoplasm, cytoskeleton, organic
inclusion bodies, inorganic inclusion bodies, internal membranes, plasma membrane, cell
wall/peptidoglycan
What is binary fission
What is the purpose of Gram staining and how does it work?
List the differences between the cell envelope of Gram positive and Gram negative bacteria
