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MICR2208 > 3 - Prokaryotic structure and function > Flashcards

3 - Prokaryotic structure and function Flashcards

1
Q

Why is a higher S/V ratio important

A

Allows for more efficient uptake and diffusion of nutrients, facilitating rapid growth

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2
Q

Shapes of prokaryotes

A
  • Spherical (Cocci)
  • Rod shaped (Bacilli)
  • Spiral/Helical
  • Pleomorphic (Variable)
  • comma-shaped
  • filamentous
  • square
  • stalked
    (Rods and cocci most common)
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3
Q

How does size affect the S/V ratio

A

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

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4
Q

What are the different arrangements of prokaryotes

A
  • Singular
  • Diplococcus (Pair of Cells)
  • Chains (Streptococcus)
  • Tetrads / Regular Packets (4 or 8 cell packets)
  • Clusters (Staphylococcus)
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5
Q

Binary fission (Bacterial Growth)

A

When on bacterial cell undergoes repeated rounds of division on a solid surface. Results in colony composed of identical cells

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6
Q

What is the chemical composition of bacteria

A
  • 70% water
  • 30% dry weight (protein (15), DNA (1) , RNA (6), polysaccharides (2), lipids (2), small molecules (4))
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7
Q

Components of bacterial cell

A
  • Nucleoid
  • Plasmids
  • Cytoplasm
  • Inclusion bodies
  • Internal membranes
  • Plasma (cytoplasmic) membrane
  • Cell wall
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8
Q

What is a nucleoid

A

Irregularly shaped region in cytoplasm that contains double stranded DNA. Not a nucleus, no membrane surrounding it.

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9
Q

Length of bacterial chromosomes

A

Varies widely, Up to 700x longer than cell. Complexed to nucleoid-associated proteins (NAPs) that enable supercoiling.

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10
Q

Plasmids

A
  • 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
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11
Q

Examples of plasmids

A
  • 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
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12
Q

Cytoplasm

A

The material bounded by the plasma membrane. 70% water

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13
Q

What are 70S ribosomes composed of

A
  • Proteins and rRNA
  • Two protein subunits (30S and 50S)
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14
Q

Protoplast

A

The plasma (cell) membrane and everything within

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15
Q

Cytosol

A

The liquid component of cytoplasm.
Contains plasmids, inclusions and 70S ribosomes float in cytosol.

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16
Q

Cytoskeleton

A

Role in cell division, localisation of proteins to certain sites, help determine cell shape, possibly chromosome and plasmid segregation to daughter cells

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17
Q

What are inclusion bodies

A

Common in all cells, formed by aggregation of organic or inorganic substances. Used for storage of C or energy

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18
Q

Name 5 organic inclusion bodies

A
  • PHB granules
  • Glycogen
  • Carboxysomes
  • Gas vacuole
  • Cyanophycin
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19
Q

PHB Granules

A
  • Carbon and energy reserve
  • Found in many bacteria
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20
Q

Glycogen

A
  • Carbon and energy reserve
  • Found in many bacteria
21
Q

Carboxysomes

A
  • Carbon dioxide fixation
  • Found in autotrophic bacteria
  • Example of microcompartment (large polyhedron made of protein)
22
Q

Gas vacuole

A
  • Function: Flotation, gas can enter but not water
  • Found in aquatic bacteria
  • Aggregates of small, hollow cylindrical protein structures called gas vesicles
23
Q

Cyanophycin

A
  • Function: Nitrogen reserve
  • Only found in Cyanobacteria
24
Q

Name 3 inorganic inclusion bodies

A
  • Sulphur granules
  • Volutin granules
  • Magnetosome
25
Q

Sulphur granules

A
  • Function: Reserve of electrons for metabolism
  • Found in bacteria that use H2S as electron donor, and accumulate the resulting S
26
Q

Volutin granules

A
  • Function: Phosphate and energy reserve
  • Found in many bacteria
  • Stain helps identify species - characteristic
27
Q

Magnetosome

A
  • 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
28
Q

What are the two internal membranes that can be found in bacteria

A

Thylakoid and plasma membranes

29
Q

Thylakoid membrane (Internal Membrane)

A

Function is photosynthesis, found in photosynthetic bacteria. Lined with particles containing pigments

30
Q

what is the composition of the plasma membrane

A
  • Amphipathic (polar and nonpolar ends) phospholipids organised as a bilayer
    -Proteins within bilayer
  • Fluid-mosaic model: proteins float in bilayer
31
Q

Function of the plasma membrane

A
  • 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
32
Q

Composition of the cell wall

A

Composed of peptidoglycan, different for gram positive and gram negative

33
Q

Function of cell wall

A
  • Maintains cell shape
  • Provides protection from osmotic shock and anti bacterial agents
  • Contains components contributing to pathogenicity
34
Q

What bacteria contain a cell wall

A

all bacteria except Mycoplasma

35
Q

Gram positive cell wall

A

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

36
Q

Gram negative cell wall

A

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

37
Q

Periplasm

A

Region between the outer membrane and the plasma membrane in gram negative cell walls

38
Q

What is the gram stain and what is used

A

Differentiates gram positive and negative bacteria. Crystal violet –> Grams iodine –> alcohol –> Safranin

39
Q

Why do gram positive stain purple

A

Thick meshlike cell wall retains the purple crystal violet stain

40
Q

Why do gram negative stain pink

A

Thinner cell wall that doesn’t retain the crystal violet. These are then counterstained pink by safranin

41
Q

Explain the 4 steps in gram staining

A
  1. Crystal violet: Dye is taken up equally by all cells
  2. Grams Iodine: Is a mordant which enhances the binding of dye to cell walls
  3. Alcohol: Gram negative cell walls are thin and cannot retain the dye (become colourless. +’ve stay purple)
  4. Safranin: Counterstain, only unstained gram negative cells can take up the dye. Crystal violet in gram positives repel the counterstain
42
Q

What are the steps of binary fission

A

chromosome duplication, cell elongation, division septum, division

43
Q

Osmotic shock

A

A mammalian cell in high conc. H20 will burst

44
Q

Compare the size, shape and arrangement of prokaryotic cells with that of eukaryotes

A
45
Q

What are the main structural features of a bacterial cell?

A
46
Q

Describe the structure and function of: nucleoid, plasmid, cytoplasm, cytoskeleton, organic
inclusion bodies, inorganic inclusion bodies, internal membranes, plasma membrane, cell
wall/peptidoglycan

A
47
Q

What is binary fission

A
48
Q

What is the purpose of Gram staining and how does it work?

A
49
Q

List the differences between the cell envelope of Gram positive and Gram negative bacteria

A

MICR2208 (26 decks)

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