growth and physiology 2

Question 1

how pH salinity and temp extremes affect microbial growth on graph

Answer 1

1. Increased lag
2. Decreased slope
3. Shorter plateau
4. More rapid decline
5. Less cells produced

Question 2

PH - measure of acidity

Answer 2

Microbes have an optimum pH with decreased growth above and below that pH

Question 3

Salinity - Concentration of salt – NaCl

6 points

Answer 3

1. Effect on amount of free water – water activity (Aw)
2. More solute dissolved and interacting with water the lower the Aw
3. Normally Aw lower inside cell than outside so water flows inwards by osmosis
4. If high salt concentration outside cell osmosis reversed
5. Cells accumulate small molecules (compatible solutes) with no effect on cell metabolism. Counteracts water moving in.
6. If salt concentration too high cells lose water, shrink, dehydrate - plasmolysis

Question 4

temperature

Answer 4

1. All have a minimum, optimum and maximum temperature for growth

Question 5

what are the 4 main groups depending on their cardinal temperatures

Answer 5

1. Psychrophiles 0-25 C
2. Mesophiles 15-45 C
3. Thermohiles 45-70 C
4. Hyperthermophiles (extreme thermophiles) 70-110 C

Question 6

Sterilisation - kill organisms and spores

Dry heat 1

Answer 6

heating in an oven at between 160-180 C for 2-4 hours.

Used for glassware, equipment but seldom for media or food.

Question 7

Sterilisation - kill organisms and spores

Dry heat 2

Answer 7

heating in a bunsen flame.

Used for microbiological loops, etc.

Question 8

Sterilisation - kill organisms and spores

moist heat

Answer 8

autoclaving using pressurised steam. At a pressure of 101 kPa

temperature of steam is 121 C.

Used for media and equipment, and food that is canned.

Can affect nutritional value, texture and taste.

Question 9

Pasteurisation – not sterile

Answer 9

Temperatures below 100C.

Aim is to kill pathogens and reduce number of other organisms.

Does not destroy spores. Used for products damaged by heat.

Question 10

Bacteria

cell membrane

Answer 10

Ester-linked fatty acids, protein

Question 11

Bacteria

cell wall

Answer 11

Murein (peptidoglycan), lipopolysaccharide

Question 12

archaea

cell membrane

Answer 12

Ether-linked isoprenoids, protein

Question 13

archaea

cell wall

Answer 13

Protein, glycoprotein, pseudomurein, wall-less

Question 14

Eukarya

cell membrane

Answer 14

Ester-linked fatty acids, protein, sterols

Question 15

Eukarya

cell wall

Answer 15

Various, no peptidoglycan

Question 16

5 features of Cell membranes

Answer 16

1. Boundary of cell
2. Separate internal aqueous, polar environment from external (usually) aqueous, polar environment
3. Consist of lipid which is non-polar so acts as a barrier
4. The membrane lipids have associated polar regions
5. Arrange in sandwich so polar regions to interior and exterior of cell with non-polar region between

Question 17

6 features of Cell membrane lipids

Fatty acids ester-linked to glycerol

Answer 17

1. Two fatty acids with non-polar hydrocarbon chains
2. Fatty acids are not branched
3. One highly polar group including phosphate
4. Called phospholipids or phosphoacylglycerols
5. Arrange in a bilayer
6. Found in Bacteria and Eukarya

Question 18

4 features of archaea cell membrane

Isoprenoid chains ether-linked to glycerol

Answer 18

1. Two non-polar branched isoprenoid chains
2. One polar group
3. Arrange in a bilayer if a diether
4. Cross whole membrane if tetraether

Question 19

importance of cell wall

5 points

Answer 19

1. Cell walls provide rigid structure to prevent prokaryotic cells bursting
2. Higher concentration of solutes inside cell than outside
3. Osmosis causes water to move into cell
4. Causes cell to swell
5. Would burst in absence of cell wall

Question 20

Peptidoglycan or murein
(Peptide chains linking polysaccharide)

[not sure if necessary to learn. leave]

5 points

Answer 20

1. Tetra-peptide – 4 amino acids: L-alanine,D-glutamic acid, L-lysine or diaminopimelic acid (DAPA), D-alanine
2. D-amino acids - not in proteins. DAPA only in some prokaryotic cell walls
3. Penta-glycine peptide cross links between the tetra-peptide
4. Polysaccharide – long polysaccharides with repeating two units [N-acetyl muramic acid (NAM) and N-acetyl glucosamine (NAG)]
5. Murein – muramic acid and protein

Question 21

Teichoic acids [not sure if necessary to learn. leave]

6 points

Answer 21

1. Derivatives of polyalcohols - glycerol (3 x –OH) and polyribotol (5 x –OH)
2. Terminal –OH link to phosphate groups which ionise to give -ve charges
3. Sugars or alanine may attach to non-terminal –OH groups
4. May chain
5. Teichoic acids link to the NAM in peptidoglycan
6. Also link to lipid in membrane – lipoteichoic acids

Question 22

Outer membrane (found in some bacteria) looks like standard lipid bilayer but…

6 points

Answer 22

1. Inner half contains a lipoprotein which links to peptidoglycan (called LPP) and phospholipids
2. Outer half contains lipopolysaccharides (LPS)
3. LPS composed of Lipid A and long polysaccharide chains extending to the outside of the cell
4. Lipid A has 4 fatty acid chains linked to a glucosamine-phosphate complex
5. Polysaccharide links to one of the glucosamines
6. Important antigenic properties and may be toxic

Question 23

Gram-positive and Gram-negative cell walls

2 points

Answer 23

1. Bacteria can be divided into two groups on the basis of a stain called the Gram stain
2. Difference depends on structure of cell wall

Question 24

gram-positive cell walls

Answer 24

thick layer of peptidoglycan with teichoic acids and some surface proteins

Question 25

gram negative cell walls

2 points

Answer 25

1. thin layer of peptidoglycan with outer membrane containing lipopolysaccharide.
2. Porin transport protein in outer membrane.

Question 26

categorising
Direct observation
3 points

Answer 26

1. Information about shape and
   size of cells
2. Information about their staining characteristics
   Gram +ve or Gram -ve
3. Information about shape, size, colour of colonies on agar plates

Question 27

categorising
biochemical analysis
3 points

Answer 27

1. chemical analysis of the organisms themselves:

Archaeal cell membranes contain lipids which are ether-linked whereas bacteria have ester-linked lipids

Some bacteria have an outer membrane containing lipopolysaccharides while some do not

2. biochemical analysis of metabolic products:

Some bacteria produce lactic acid from glucose, yeasts produce ethanol from glucose

Some micro-organisms can release oxygen from hydrogen peroxide

3. Carry out range of specific tests to obtain biochemical characteristics

Question 28

categorising

How organisms are classified

Answer 28

1. Phenotypic classification depends on the similarity of the observable characteristics of organisms
   e. g. colony size, shape, colour; motility; rod or coccus; Gram-positive or Gram-negative; spores; biochemical parameters.

Question 29

categorising
Molecular analysis
4 points

Answer 29

1. Development of molecular biology techniques allows detailed information about genotypes (genetic characteristics)
2. Sequencing of nucleic acids showed specific similarities and differences between taxonomic groups (Phyla)
3. Used 16S ribosomal RNA to help understand evolutionary development
4. Some reclassification of organisms as a result of molecular analysis