3 - Prokaryotic structure and function

Question 1

Why is a higher S/V ratio important

Answer 1

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

Question 2

Shapes of prokaryotes

Answer 2

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

Question 3

How does size affect the S/V ratio

Answer 3

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

Question 4

What are the different arrangements of prokaryotes

Answer 4

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

Question 5

Binary fission (Bacterial Growth)

Answer 5

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

Question 6

What is the chemical composition of bacteria

Answer 6

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

Question 7

Components of bacterial cell

Answer 7

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

Question 8

What is a nucleoid

Answer 8

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

Question 9

Length of bacterial chromosomes

Answer 9

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

Question 10

Plasmids

Answer 10

• 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

Question 11

Examples of plasmids

Answer 11

• 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

Question 12

Cytoplasm

Answer 12

The material bounded by the plasma membrane. 70% water

Question 13

What are 70S ribosomes composed of

Answer 13

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

Question 14

Protoplast

Answer 14

The plasma (cell) membrane and everything within

Question 15

Cytosol

Answer 15

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

Question 16

Cytoskeleton

Answer 16

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

Question 17

What are inclusion bodies

Answer 17

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

Question 18

Name 5 organic inclusion bodies

Answer 18

• PHB granules
• Glycogen
• Carboxysomes
• Gas vacuole
• Cyanophycin

Question 19

PHB Granules

Answer 19

• Carbon and energy reserve
• Found in many bacteria

Question 20

Glycogen

Answer 20

• Carbon and energy reserve
• Found in many bacteria

Question 21

Carboxysomes

Answer 21

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

Question 22

Gas vacuole

Answer 22

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

Question 23

Cyanophycin

Answer 23

• Function: Nitrogen reserve
• Only found in Cyanobacteria

Question 24

Name 3 inorganic inclusion bodies

Answer 24

• Sulphur granules
• Volutin granules
• Magnetosome

Question 25

Sulphur granules

Answer 25

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

Question 26

Volutin granules

Answer 26

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

Question 27

Magnetosome

Answer 27

- 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

Question 28

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

Answer 28

Thylakoid and plasma membranes

Question 29

Thylakoid membrane (Internal Membrane)

Answer 29

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

Question 30

what is the composition of the plasma membrane

Answer 30

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

Question 31

Function of the plasma membrane

Answer 31

- 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

Question 32

Composition of the cell wall

Answer 32

Composed of peptidoglycan, different for gram positive and gram negative

Question 33

Function of cell wall

Answer 33

- Maintains cell shape - Provides protection from osmotic shock and anti bacterial agents - Contains components contributing to pathogenicity

Question 34

What bacteria contain a cell wall

Answer 34

all bacteria except Mycoplasma

Question 35

Gram positive cell wall

Answer 35

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

Question 36

Gram negative cell wall

Answer 36

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

Question 37

Periplasm

Answer 37

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

Question 38

What is the gram stain and what is used

Answer 38

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

Question 39

Why do gram positive stain purple

Answer 39

Thick meshlike cell wall retains the purple crystal violet stain

Question 40

Why do gram negative stain pink

Answer 40

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

Question 41

Explain the 4 steps in gram staining

Answer 41

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

Question 42

What are the steps of binary fission

Answer 42

chromosome duplication, cell elongation, division septum, division

Question 43

Osmotic shock

Answer 43

A mammalian cell in high conc. H20 will burst

Question 44

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

Question 45

What are the main structural features of a bacterial cell?

Question 46

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

Question 47

What is binary fission

Question 48

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

Question 49

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