3rd year revision

Question 1

What type of transport/translocation is rare in bacteria?

Answer 1

Facilitated diffusion (except glycerol)

Question 2

What is primary translocation?

Answer 2

Where translocation is linked to a biochemical reaction. E.g. group translocation, enzyme-linked solute translocation

Question 3

What is secondary translocation?

Answer 3

Where translocation is linked to metabolism indirectly via an ion gradient, e.g. uniport, symport, antiport

Question 4

What is group translocation?

Answer 4

A type of primary translocation. Chemical modification occurs concurrently with translocation, e.g. PTS

Question 5

What is enzyme-linked solute translocation?

Answer 5

A type of primary translocation. Substrate is not modified but translocation is the result of biochemical reaction

Question 6

What type of group translocation is found only in bacteria?

Answer 6

The PEP-dependent carbohydrate phosphotransferase system (PTS)

Question 7

What carbohydrates are often translocated in the PTS?

Answer 7

Hexoses, hexitols, disaccharides

Question 8

What is PEP?

Answer 8

Phosphoenolpyruvate; the source of energy in the PTS

Question 9

How is the PTS energy-efficient?

Answer 9

The substrate is phosphorylated as it enters the cell, so the combined transport and modification is energy-efficient

Question 10

What type of bacteria often utilise the PTS?

Answer 10

Obligate and facultative anaerobes because it is an energy-efficient process

Question 11

Draw basic diagram of PTS

Answer 11

DO IT

Question 12

What are the properties of Enzyme I and HPr?

Answer 12

Are soluble, cytoplasmic proteins’ general PTS proteins; are required for all phosphotransferases in the cell

Question 13

What are the properties of the Enzyme II complex and its domains?

Answer 13

Is sugar specific, consists of several domains, may be parts of a single polypeptide chain or separate proteins
IIA domain: contains the first phosphorylation site
IIB domain: contains the second phosphorylation site
IIC domain: membrane-associated, involved in translocation of substrate, no phosphorylation
(IID domain: present in some systems, translocation)

Question 14

What else is the PTS centrally involved in?

Answer 14

Metabolic regulation and as an environmental sensor

Question 15

Is the lac operon positive or negatively controlled, and what does this mean?

Answer 15

Negatively controlled, so involves a repressor.

Question 16

What is the basis of a negatively controlled operon?

Answer 16

In the absence of an inducer, repressor prevents expression of structural genes
In the presence of an inducer, repressor cannot bind to operator so gene expression occurs

Question 17

What is the inducer in the lac operon?

Answer 17

In nature, the inducer is allolactose (not lactose), formed via a minor reaction by ß-galactosidase
In lab, IPTG, induces enzyme synthesis but is not metabolised by the system (shows induction and metabolism are independent processes)

Question 18

Draw structure of lac operon

Answer 18

DO IT

Question 19

What are the properties of each component of the lac operon?

Answer 19

lacI codes for repressor, has its own promoter
lacZ codes for ß-galactosidase; hydrolysis of lactose –> glucose + galactose
lacY codes for lactose permease; a transmembrane protein which helps lactose get into the cell
lacA codes for galactoside trans-acetylase which transfers an acetyl group from CoA to hydroxyl group of galactosides, is not used for lactose metabolism but is physiologically important for maintaining viability of cell

Question 20

What is required for formation of allolactose?

Answer 20

Basal level of both lactose permease (LacY) and ß-galactosidase (LacZ)

Question 21

What is diauxic growth?

Answer 21

Where the bacterium uses the “best” carbon source first, e.g. E.coli growing on a medium containing glucose and lactose will utilise glucose first

Question 22

What is catabolite repression?

Answer 22

The repression of catabololic enzyme synthesis by a “good” (readily utilised) carbon source, therefore, conserves energy by ensuring that enzymes for utilisation of the non-preferred carbon source aren’t synthesis unnecessarily

Question 23

When glucose is present in high concentration, what is the cAMP concentration like?

Answer 23

Low

Question 24

What happens to cAMP as glucose concentration decreases?

Answer 24

cAMP concentration increases correspondingly

Question 25

What can high levels of cAMP do?

Answer 25

Activate lac operon

Question 26

How is cAMP synthesised?

Answer 26

From ATP by adenylate cyclase

Question 27

What was observed in adenylate cyclase mutants?

Answer 27

Cannot make cAMP so cAMP conc low

Mutants unable to use lactose, maltose, xylose (repressed carbon source)

Question 28

Other mutants were unable to use repressed carbon sources to support growth but had normal cAMP levels. What discovery did this observation lead to?

Answer 28

Identification of cAMP receptor protein (CRP/CAP), a regulatory protein dependent on cAMP

Question 29

What does the cAMP/CRP complex do?

Answer 29

Activates transcription of catabolite response operons (positive control)`

Question 30

What is the PEP-dependent PTS?

Answer 30

A type of group-translocation used by prokaryotes to transport and phosphorylate various carbohydrates, particularly hexoses, hexitols, and disaccharides