PART I: MULTIPLE CHOICE (60 points; two points per question)
Circle the letter next to the single correct answer.
1. The periplasmic space of E. coli contains:
a) binding proteins for certain sugars
b) beta-lactamase
c) membrane derived oligosaccharides
d) all of the above
e) none of the above
2. A heterotroph uses organic molecules as:
a) carbon source
b) source of reducing power
c) source of energy
d) all of the above
e) none of the above
3. An organotroph uses organic molecules as:
a) carbon source
b) source of reducing power
c) source of energy
d) all of the above
e) none of the above
4. Which of the following is used as a source of reducing power for biosynthesis?
a) NADH
b) proton motive force
c) ATP
d) NADPH
e) malonyl-CoA
5. Transient catabolite repression is due to:
a) excretion of cyclic AMP into the medium
b) degradation of cyclic AMP receptor protein
c) phosphorylation of enzyme III of the phosphotransferase system
d) inhibition of adenylate cyclase
6. The proton motive force in bacteria can be used to
a) make ATP
b) drive the transport of certain sugars
c) energize the flagella
d) all of a, b and c
e) none of the above is correct
7. Inducer exclusion is the result of:
a) excretion of cyclic AMP by the phosphotransferase system
b) inhibition of transport proteins by enzyme III
c) repression of adenylate cyclase by glucose
d) blocking of porins by glucose-6-phosphate
8. During carbon source regulation the phosphorylated form of enzyme III of the phosphotransferase system:
a) inhibits adenylate cyclase
b) activates adenylate cyclase
c) inhibits lactose transport protein
d) activates lactose transport protein
9. During the transport of maltose:
a) the LamB porin carries maltose across the periplasmic space
b) synthesis of OmpF porin is decreased
c) ATP is used as an energy source
d) TonB protein supplies energy
10. During the metabolism of sugar alcohols:
a) they are oxidized to sugar acids
b) they are reduced to give sugars
c) their phosphate derivatives are reduced to fructose-6P
d) their phosphate derivatives are split to give two glycerol-3P
11. When E. coli is growing at low osmotic pressure it makes more:
a) proline in the cytoplasm
b) putrescine in the periplasmic space
c) membrane derived oligosaccharides in the cytoplasm
d) both (a) and (b) are true
e) none of the above is correct
12. When E. coli is shifted to high osmotic pressure:
a) proline is excreted and glycine betaine is taken up
b) glycine betaine is synthesised from glycine
c) trehalose is made from glucose
d) all of (a), (b) and (c) are true
13. Transport of potassium into E. coli:
a) is controlled by a two component regulatory system
b) is induced at low osmotic pressure
c) is prevented by membrane derived oligosaccharides
d) is due to binding of potassium by putrescine
14. Choline:
a) is found as the main osmotic solute in insects
b) can be converted to glycine betaine
c) is found in the lipids of E. coli only during stationary phase
d) is transferred from lipids to membrane derived oligosaccharides
15. When E. coli is shifted to high osmotic pressure:
a) EnvZ protein binds to DNA
b) synthesis of OmpR protein is increased
c) phosphorylation of MicF increases
d) synthesis of OmpC protein is increased
16. The porin proteins of E. coli
a) are found in the cytoplasmic membrane
b) are energized by the proton motive force
c) form phosphorylated intermediates
d) exlude molecules greater than about 700 in molecular weight
e) have four subunits
17. Cross-linking of two peptidoglycan chains requires:
a) outer membrane lipoprotein
b) cleavage of the signal sequence
c) breaking of the D-Ala-D-Ala linkage
d) bactoprenol carrier lipid
e) none of the above
18. Bacitracin inhibits cell wall synthesis at a step involving:
a) bactoprenol carrier lipid
b) UDP-N-acetyl-glucosamine
c) D-alanine
d) diaminopimelic acid
e) phosphatidyl glycerol
19. The lipoprotein of the gram-negative cell envelope is:
a) covalently linked to the peptidoglycan
b) the receptor for the sex-pilus
c) covalently attached to the lipid A
d) found in the outer layer of the outer membrane
e) none of the above is true
20. Lipopolysaccharide is found
a) only in the inner half of the outer membrane
b) only in the inner half of the inner membrane
c) in both halves of the outer membrane
d) only in gram-positive bacteria
e) none of the above is true
21. Efficient iron uptake by bacteria needs siderophores in order to:
a) reduce Fe3+ to Fe2+
b) incorporate the iron into heme
c) solubilize Fe3+
d) siderophores are only needed by pathogens
e) all of the above
22. Which of the following is used as the activated precursor for synthesis of phospholipids in bacteria?
a) CDP-diglyceride
b) UDP-glycerol
c) fatty acyl-CoA
d) UDP-ethanolamine
23. Clavulanic acid:
a) produces giant spherical cells when given in sublethal doses
b) is an inhibitor of beta-lactamases
c) is a hydrophilic penicillin designed to cross the outer membrane better
d) inhibits penicillin binding proteins
24. The fluidity of the cytoplasmic membrane is regulated by changing the:
a) amount of heat generated by respiration
b) proportion of unsaturated fatty acids
c) proportion of cyclopropane fatty acids
d) amount of cardiolipin
25. Abequose and rhamnose are found in:
a) the glycan chains of peptidoglycan
b) the core region of lipopolysaccharide
c) in some O-antigens
d) in membrane derived oligosaccharides
26. The elongation step of fatty acid synthesis uses:
a) malonyl-ACP
b) acetyl-ACP
c) acetyl-CoA
d) mevalonyl-CoA
e) malonyl-CoA
27. The signal sequence
a) has a negative charge at the end
b) consists of mostly hydrophobic amino acids
c) is about fifty amino acids long
d) is cleaved off by the transpeptidase
28. During protein export, chaperonins act to:
a) guide the signal sequence to the membrane
b) guide proteins to the outer membrane
c) supply energy
d) prevent premature folding
29. The TonB protein:
a) provides energy for iron transport
b) removes the signal sequence from exported proteins
c) protects cells against colicins
d) is a siderophore
30. Penicillin binding proteins
a) bind penicillins in order to protect bacteria
b) open the bond between bactoprenol phosphate and muramic acid
c) are involved in peptidoglycan cross-linking
d) are found in the outer membrane of E. coli
e) none of the above is true
PART II: ESSAY QUESTIONS (40 points; 20 points per question)
Choose any TWO questions. Answer by notes and diagrams where appropriate. Remember that one diagram is worth a thousand words.
31. Explain how the phosphotransferase system controls the level of cyclic AMP and blocks inducer transport. How is the lactose operon switched off in the presence of glucose and on in its absence?
32. Explain how the following types of transport system operate and how they get their energy: a) facilitated diffusion b) proton symport c) iron uptake using a siderophore
33. What are the characteristics of a signal sequence? Describe how a newly synthesized periplasmic protein, such as b-lactamase is transported to its correct location in the cell. At what stage is ATP used and at what stage is the proton motive force used?
34. What three phospholipids are found in the cell membrane of E. coli? Starting with glycerol phosphate and fatty acids outline the pathway by which E. coli synthesizes phospholipids. How does E. coli change its phospholipid composition as it enters stationary phase?
35. Explain how a generalized two component regulatory system works. Describe the way in which the OmpF and OmpC porins are controlled by OmpR, EnvZ and MicF in response to changes in the osmotic pressure of the culture medium.
36. Starting with the UDP-disaccharide/pentapeptide precursor for making the peptidoglycan on the inside of the cytoplasmic membrane explain the following:
a) how the precursor gets across the cytoplasmic membrane
b) the effect of bacitracin
c) how the precursors are assembled and crosslinked in place
d) how crosslinking of peptidoglycan is affected by penicillin
PART I: MULTIPLE CHOICE (60 points; two points per question)
Circle the letter next to the single correct answer.
1. The periplasmic space of E. coli contains:
a) bactoprenol carrier lipid
b) lipopolysaccharide
c) membrane derived oligosaccharides
d) all of the above
e) none of the above
2. An organotroph uses organic molecules as:
a) carbon source
b) source of reducing power
c) source of energy
d) all of the above
e) none of the above
3. An autotroph uses organic molecules as:
a) carbon source
b) source of reducing power
c) source of energy
d) all of the above
e) none of the above
4. Which of the following is used as a source of reducing power for biosynthesis?
a) NADH
b) proton motive force
c) ATP
d) NADPH
e) malonyl-CoA
5. Transient catabolite repression is due to:
a) degradation of cyclic AMP receptor protein
b) degradation of cyclic AMP
c) inhibition of adenylate cyclase
d) excretion of cyclic AMP into the medium
e) activation of adenylate cyclase
6. The proton motive force in bacteria can be used to
a) make ATP
b) energize protein secretion
c) energize the flagella
d) (a) and (b)
e) (b) and (c)
f) all of (a), (b) and (c)
7. Inducer exclusion is the result of:
a) inhibition of adenylate cyclase by CRP protein
b) inhibition of transport proteins by enzyme III
c) inhibition of adenylate cyclase by glucose-6-phosphate
d) blocking of porins by enzyme III
8. During carbon source regulation the phosphorylated form of enzyme III of the phosphotransferase system:
a) inhibits adenylate cyclase
b) activates adenylate cyclase
c) inhibits degradation of cyclic AMP
d) activates degradation of cyclic AMP
9. During the transport of lactose:
a) the proton motive force is used as an energy source
b) ATP is used as an energy source
c) phosphoenolpyruvate supplies energy
d) both ATP and the proton motive force are used as energy sources at different stages of uptake
10. By weight, cells contain more of:
a) DNA
b) ribosomal RNA
c) messenger RNA
d) transfer RNA
11. When E. coli is growing at low osmotic pressure it makes more:
a) putrescine in the cytoplasm
b) trehalose in the periplasmic space
c) membrane derived oligosaccharides in the cytoplasm
d) both (a) and (b) are true
e) all of (a), (b) and (c) are correct
12. The porin proteins of E. coli
a) are found in the cytoplasmic membrane
b) are energized by the proton motive force
c) form phosphorylated intermediates
d) exclude molecules greater than about 7000 in molecular weight
e) have three subunits
13. Cross-linking of two peptidoglycan chains requires:
a) outer membrane lipoprotein
b) energy provided by TonB protein
c) breaking of the D-Ala-D-Ala linkage
d) bactoprenol carrier lipid
e) none of the above
14. Glycolysis results in the net production, per original hexose of:
a) 2ATP + 2NADH
b) 4ATP + 2NADH
c) 2ATP + NADH
d) 4ATP + NADH
15. Phosphofructokinase:
a) converts fructose to fructose-1-P
b) converts fructose to fructose-6-P
c) converts fructose-6-P to fructose diphosphate
d) converts fructose-1-P to fructose-6-P
16. The OmpA protein of the gram-negative cell envelope is:
a) covalently linked to the peptidoglycan
b) a special porin for anionic nutrients
c) the receptor for the sex-pilus
d) covalently attached to lipopolysaccharide
e) found only in the inner layer of the outer membrane
17. Lipopolysaccharide is found
a) only in the inner half of the outer membrane
b) only in the inner half of the inner membrane
c) only in the outer half of the inner membrane
d) only in the outer half of the outer membrane
e) in both halves of the outer membrane
18. Which of the following is used as the activated precursor for synthesis of phospholipids in bacteria?
a) CDP-diglyceride
b) UDP-glycerol
c) ADP-glycerol
d) UDP-diglyceride
e) CDP-triglyceride
19. The type of enzyme which moves a phosphate group from one position to another on the same molecule is a:
a) racemase
b) epimerase
c) kinase
d) mutase
e) phosphorylase
20. When the temperature changes, bacteria regulate the fluidity of the cytoplasmic membrane by changing:
a) the amount of heat generated by respiration
b) the proportion of unsaturated fatty acids
c) the proportion of cyclopropane fatty acids
d) the ratio of phosphatidyl glycerol to cardiolipin
21. Glucosamine is found in:
a) the peptide cross-links of peptidoglycan
b) the O-antigen of lipopolysaccharide
c) the lipid A component of lipopolysaccharide
d) membrane derived oligosaccharides
e) all of the above
22. The elongation step of fatty acid synthesis uses:
a) malonyl-ACP
b) acetyl-ACP
c) acetyl-CoA
d) mevalonyl-CoA
e) malonyl-CoA
23. The TonB protein:
a) provides energy for iron transport
b) removes the signal sequence from exported proteins
c) senses the osmotic pressure in the culture medium
d) recognizes and binds to siderophores
24. Choline:
a) is found in the phospholipids of animals
b) is found attached to lipid A
c) is found in bacterial lipids only during stationary phase
d) is transferred from lipids to membrane derived oligosaccharides
25. The signal sequence
a) has a positive charge at the end
b) consists of mostly hydrophilic amino acids
c) is found only in outer membrane proteins
d) is cleaved off by the transpeptidase
26. During protein export chaperonins act to:
a) insert the signal sequence into the membrane
b) guide proteins to the outer membrane
c) remove the signal sequence
d) prevent premature folding
27. A typical two component regulatory system
a) has a sensor protein which phosphorylates the operator
b) has a regulator protein which phosphorylates itself
c) has a regulator protein which phosphorylates the operator
d) has a sensor protein which phosphorylates the regulator
28. When E. coli is shifted to high osmotic pressure:
a) EnvZ protein binds to DNA
b) synthesis of OmpR protein is increased
c) phosphorylation of MicF increases
d) synthesis of OmpF protein is decreased
29. Efficient iron uptake by bacteria needs siderophores in order to:
a) reduce Fe3+ to Fe2+
b) incorporate the iron into heme
c) solubilize Fe2+
d) siderophores are only needed by pathogens
e) none of the above is correct
30. Penicillin binding proteins
a) bind penicillins in order to protect bacteria
b) break the bond between bactoprenol phosphate and N-acetyl glucosamine
c) break the bond between N-acetyl glucosamine and N-acetyl muramic acid
d) are covalently attached to the peptidoglycan
e) none of the above is true
PART II: SHORT ANSWER QUESTIONS (10 points per question)
31. Choose any one of the 3 following molecules and draw a fully labelled diagram of its structure. Although you are not expected to memorize every atom, you should know the component parts, how they are linked together, and their names.
a) A single subunit of peptidoglycan (i.e. what is attached to the
lipid carrier just before export across the membrane)
b) A molecule of phospholipid
c) A siderophore - choose one of the two classes and illustrate how
the siderophore binds the iron
31. Choose any 5 of the following inhibitors and explain briefly its effect: D-cycloserine; bacitracin; phosphonomycin; clavulanic acid; methyl-glucose (or deoxy-glucose); fluoride; caffeine; arsenate; albomycin; penicillin.
PART III: ESSAY QUESTION (20 points per question)
Choose any ONE questions. Answer by notes and diagrams where appropriate. Remember that one diagram is worth a thousand words.
33. Draw diagrams to compare the transport of maltose and lactose into a cell of E. coli. Explain what sources of energy are used.
34. Describe how a newly synthesized outer membrane protein, such as a porin is transported to its correct location in the cell. At what stage is ATP used and at what stage is the proton motive force used?
35. Outline the structure of a typical lipopolysacharide molecule. Where in the cell envelope is it located? What is a rough mutant? How are two lipopolysacharide molecules held together? What is endotoxin and why is it toxic?
36. Explain how E. coli adapts itself to growing in medium of high osmotic pressure. Include an explanation of what compatible solutes are and give an example of a compatible solute which E. coli does synthesize and one it cannot synthesize completely but can take up if present in the medium.
37. Explain how glucose-6-phosphate is converted to pyruvate. Where are ATP and NADH produced? What are the two main controlling steps and how are they regulated?
PART I: MULTIPLE CHOICE (68 points; two points per question)
Circle the letter next to the single correct answer.
1. Cephalosporins differ from penicillins as follows:
a) cephalosporins do not possess a sulfur atom
b) cephalosporins have two side chains
c) cephalosporins have two five membered rings fused together
d) cephalosporins are resistant to beta-lactamases
e) cephalosporins have an extra sulfur atom
2. Clavulanic acid is a beta-lactam derivative which:
a) is resistant to beta-lactamases
b) at sublethal concentrations gives giant spherical cells
c) penetrates the outer membrane of gram-negative bacteria effectively
d) inhibits beta-lactamases
e) has its sulfur atom as part of a six membered ring
3. A chemotroph uses organic molecules as:
a) carbon source
b) source of reducing power
c) source of energy
d) all of the above
e) none of the above
4. Which of the following is used as a source of reducing power for biosynthesis?
a) NADH
b) proton motive force
c) acetyl-CoA
d) NADPH
e) malonyl-CoA
5. Transient catabolite repression is due to:
a) binding of cyclic GMP to CRP protein
b) degradation of cyclic AMP
c) inhibition of adenylate cyclase
d) excretion of cyclic AMP into the medium
e) activation of adenylate cyclase
6. The proton motive force in bacteria can be used to
a) energize peptidoglycan synthesis
b) energize protein secretion
c) energize flagellar motion
d) (a) and (b)
e) (b) and (c)
7. Inducer exclusion is the result of:
a) inhibition of transport proteins by enzyme III
b) inhibition of adenylate cyclase by CRP protein
c) inhibition of adenylate cyclase by HPr protein
d) blocking of porins by enzyme III
e) binding of enzyme III to the CRP protein
8. During the transport of maltose:
a) the proton motive force is used as an energy source
b) ATP is used as an energy source
c) phosphoenolpyruvate supplies energy
d) both ATP and the proton motive force are used as energy sources but at different stages of uptake
9. By weight, cells contain more of:
a) transfer RNA
b) ribosomal RNA
c) messenger RNA
d) peptidoglycan
e) lipopolysaccharide
10. When E. coli is growing at low osmotic pressure it makes more:
a) putrescine in the cytoplasm
b) trehalose in the periplasmic space
c) membrane derived oligosaccharides in the cytoplasm
d) putrescine in the periplasmic space
e) trehalose in the cytoplasm
11. The TonB protein of E. coli
a) binds siderophores
b) is found in the outer membrane
c) forms phosphorylated intermediates
d) monitors the osmotic pressure of the medium
e) uses energy from the proton motive force
12. The metabolism of maltose is more efficient than lactose because:
a) the proton motive force is used to transport lactose
b) sodium is used instead of protons to transport maltose
c) maltose is split by a phosphorylase
d) the galactose released by splitting lactose yields less energy than glucose
13. Which of the following is used as the activated precursor for synthesis of phospholipids in bacteria?
a) CDP-diglyceride
b) UDP-glycerol
c) ADP-ethanolamine
d) GDP-diglyceride
e) CDP-choline
14. Membrane derived oligosaccharides consist of:
a) glucosamine chains with short fatty acids attached
b) galactose chains with phosphoglycerol side chains
c) glucose chains with phosphoglycerol side chains
d) glucose residues attached to bactoprenol carrier lipid
e) glucosamine chains with attached ethanolamine groups
15. Approximately what percentage of the dry weight of a gram-negative bacterial cell is due to the cell envelope?
a) 2
b) 4
c) 10
d) 15
e) 20
16. The PhoE protein of the gram-negative cell envelope is:
a) covalently linked to the peptidoglycan
b) a special porin for anionic nutrients
c) the receptor for bacteriophage lambda
d) covalently attached to lipopolysaccharide
e) found only in the outer layer of the outer membrane
17. The OmpA protein of the gram-negative cell envelope is:
a) covalently linked to the peptidoglycan
b) a special porin for oligosaccharides
c) the receptor for the sex-pilus
d) involved in providing energy for iron transport
e) found only in the inner layer of the outer membrane
18. The enzyme beta-lactamase attacks penicillin derivatives as follows:
a) it breaks open the C-N bond in the four membered ring
b) it removes the side chain from the penicillin nucleus
c) it removes the sulfur from the five membered ring
d) it splits the four membered ring off from the rest of the penicillin nucleus
e) none of these is the correct mechanism
19. Unsaturated fatty acids are made by E. coli by:
a) using NADPH and oxygen after the chain has reached its final length
b) using NADPH and oxygen when the precursor is 10 carbons long
c) introducing a trans double bond when the precursor is 6 carbons long
d) introducing a cis double bond when the precursor is 10 carbons long
e) adding a short isoprenoid unit with a double bond to a growing chain
20. When fatty acids are transported into E. coli they are first found as:
a) fatty acyl-ACP
b) fatty acyl-AMP
c) fatty acyl-CoA
d) UDP-fatty acid
e) CDP-fatty acid
21. Choline:
a) is converted to ethanolamine when E. coli grows at low osmotic pressure
b) carries both a positive and a negative charge
c) is found in bacterial lipids during stationary phase
d) is transferred from phospholipids to membrane derived oligosaccharides when E. coli grows at low osmotic pressure
e) is converted to betaine when E. coli grows at high osmotic pressure
22. The function of capsular polysaccharides is to:
a) store surplus carbohydrate
b) anchor bacterial cells to the intestinal lining
c) protect against dehydration
d) keep the periplasmic space inflated at low osmotic pressure
e) keep out molecules of greater than 1,000 molecular weight
23. The fatty acid chains of the cell envelope lipoprotein are found
a) only in the inner half of the outer membrane
b) in the periplasmic space
c) only in the outer half of the inner membrane
d) only in the outer half of the outer membrane
e) covalently attached to the peptidoglycan
24. The signal sequence
a) has a negative charge at the very end
b) consists of mostly hydrophilic amino acids
c) is recognized by the SecB protein
d) is cleaved off by the leader peptidase
e) is found at the carboxyl end of proteins to be exported
25. During protein export chaperonins act to:
a) insert the signal sequence into the membrane
b) guide proteins to the outer membrane
c) carry proteins across the periplasmic space
d) prevent premature folding of exported proteins
e) provide energy for protein export by using the PMF directly
26. When E. coli is shifted to high osmotic pressure the primary response is that:
a) EnvZ protein binds to DNA
b) potassium transport increases
c) trehalose synthesis increases
d) cyclic AMP is excreted
e) proline is replaced by putrescine
27. A typical two component regulatory system
a) has a sensor protein which phosphorylates the operator
b) has a regulator protein which phosphorylates itself
c) has a regulator protein which phosphorylates the operator
d) has a sensor protein which phosphorylates the regulator
e) has a regulator protein which phosphorylates the repressor
28. During carbon source regulation the phosphorylated form of enzyme III of the phosphotransferase system:
a) inhibits adenylate cyclase
b) activates adenylate cyclase
c) inhibits degradation of cyclic AMP
d) activates degradation of cyclic AMP
e) induces synthesis of CRP protein
29. When the temperature changes, bacteria regulate the fluidity of the cytoplasmic membrane by changing:
a) the proportion of unsaturated fatty acids
b) the proportion of hydroxylated fatty acids
c) the ratio of phosphatidyl glycerol to phosphatidyl choline
d) the proportion of cyclopropane fatty acids
e) the ratio of phosphatidyl glycerol to phosphatidyl ethanolamine
30. Efficient iron uptake by bacteria needs siderophores in order to:
a) reduce Fe3+ to Fe2+
b) incorporate the iron into cytochromes
c) solubilize iron in the absence of oxygen
d) siderophores are only needed by pathogens
e) solubilize ferric iron
31. Selenium and nickel are trace metals which are needed:
a) by many bacteria when growing anaerobically
b) by all living cells under all conditions
c) only by gram-negative bacteria
d) only by eukaryotes
e) none of the above is true
32. Ferrichrome:
a) is made by E. coli to bind iron and is stolen by fungi
b) is made by fungi to kill E. coli which steals iron
c) is made by fungi to bind iron and is stolen by E. coli
d) is made by E. coli to kill competing fungi which steal iron
33. If the galactose of the outer core is lost from the lipopolysaccharide of E. coli as a result of mutation the bacteria become:
a) resistant to some bacteriophage but sensitive to others
b) resistant to all bacteriophage which use lipopolysaccharide as receptor
c) unable to survive
d) unable to use siderophores for iron transport
34. Phosphofructokinase is an important regulatory control point because:
a) it uses ATP to activate sugars
b) most sugar derivatives are metabolized via to fructose-6-phosphate
c) fructose is a better carbon source than all sugars except glucose
d) it synthesizes ATP
e) it binds protein III of the phosphotransferase system
PART II: SHORT ANSWER QUESTION (12 points)
35. Choose any 4 of the following molecules and explain briefly which larger molecule of the cell envelope they form part of, and where in it they are located. If you prefer you may show the position with diagrams. (For molecules with several possible locations, just give one correct location.)
D-alanine; dideoxy-sugars; eight carbon sugars; ethanolamine; diaminopimelic acid; hydroxy-myristic acid; cis-vaccenic acid; N-acetyl glucosamine; glucosamine (without the N-acetyl group).
PART III: ESSAY QUESTION (20 points)
Choose any ONE question. Answer by notes and draw diagrams where appropriate. Remember that one diagram is worth a thousand words.
36. Describe how the following inhibitors affect the synthesis and assembly of the peptidoglycan: penicillin; bacitracin; phosphonomycin; D-cycloserine. What features of a penicillin derivative help it cross the outer membrane of gram-negative bacteria? What features protect against beta-lactamases?
37. Explain how a typical two component regulatory system works. How are two component regulatory systems involved in the adaptation of E. coli to medium of high osmotic pressure?
38. Draw diagrams to compare the transport into E. coli of two sugars, one which uses ATP as an energy source and the other which uses the proton motive force.
39. What are the characteristics of a signal sequence? What is a chaperonin? Describe how a newly synthesized periplasmic protein, such as beta-lactamase is transported to its correct location in the cell. At what stage is ATP used and at what stage is the proton motive force used?
40. Explain how the glucose transport system of E. coli controls the level of cyclic AMP and how it blocks the transport of the inducers for other sugar degradation systems. How is the lactose operon switched off in the presence of glucose and on in its absence?