Metabolism: the cellular factory

Question 1

Describe metabolism

Answer 1

• allows components of the cell to be biosynthesised from simple precursors harvested from the environment
• the machinery that builds the cell

Question 2

To build a cell, metabolism must do four things:

Answer 2

• harvest energy from the environment
• transduce it into a usable form
• harvest electrons from the environment
• use energy and electrons

Question 3

How is energy and electrons used in metabolism?

Answer 3

• convert simple carbon (and N, P, S-containing) molecules into more complex molecules that constitute monomer units of major cellular macromolecules
• join monomers together to make lipids for the cell membrane, carbohydrate polymers for the cell wall, polypeptides for proteins and nucleic acids for RNA and DNA

Question 4

Formation of polysaccharides

Answer 4

requires energy

Question 5

Describe starch

Answer 5

carbohydrate storage in plants

Question 6

Describe starch formation

Answer 6

needs 2 ATP for addition of each glucose unit

Question 7

Describe cell wall formation

Answer 7

• glycogen -> glucose-1-phosphate by glycogen phosphorylase
  -> UDP-glucose by UDP-glucose pyrophosphorylase (UTP -> P-P)
  -> UDP via cellulose synthase
• gluten chains
• assembly and crystallisation into cellulose microfibrils

Question 8

Synthesis of monomers needs

Answer 8

electrons

Question 9

Describe glucose formation

Answer 9

6CO2 + 24H+ + 24e- -> C6H12O6 + 6H20

Question 10

Describe palmitic acid formation

Answer 10

16CO2 + 92H+ + 92e- -> C15H31COOH + 30H20

Question 11

Describe glycine formation

Answer 11

2CO2 + NO3- + 15H+ + 14e- -> CH2NH2COOH + 5H20

Question 12

Where do autotrophs get their electrons?

Answer 12

photosynthetic H2O splitting

Question 13

Where do eterotrophs source their electrons

Answer 13

organic molecules such as glucose

Question 14

Describe heterotrophic NADPH

Answer 14

generated via the pentose phosphate pathway

Question 15

Describe biosynthesis of glutamate

Answer 15

• NO3- -> NO2- via nitrate reductase (NADPH -> NADP+)
  -> NH4 via nitrite reductase (NAD(P)H -> NAD(P)+)
• NH4+ + 2-oxoglutrate -> glutamate via glutamate dehydrogenase (NADPH -> NADP+)

Question 16

Describe the biosynthesis of other amino acids from glutamate

Answer 16

• transamination reactions
• pyruvic acid + glutamate -> alanine + 2-oxoglutarate
• oxaloacetate to aspartate via transaminase (glutamate -> alpha-ketoglutarate)
  -> asparagine via asparagine synthesise (glutamine -> glutamate; ATP -> AMP + PPi)

Question 17

Describe transamination

Answer 17

transfer of amine group

Question 18

Describe the biosynthesis of other amino acids

Answer 18

• carbon skeletons for amino acids are drawn from TCA cycle
• glycolysis and the pentose phosphate pathway

Question 19

Describe the logic of glycolysis (from the perspective of ATP synthesis)

Answer 19

• formation of a doubly- phosphorylated hexose (c=6) sugar
• generating a doubly-phosphorylated triose sugar
• substrate-level phosphorylation: transfer of phosphoryl group from triose sugar to ADP