9- Metabolism 2 - fate in pyruvate

Question 1

where is NAD+ derived from?

Answer 1

niacin, a vitamin
- there’s only limited amounts of NAD+ present in a cell

Question 2

how is NAD+ regenerated and why does it need to be?

Answer 2

in glycolysis: NAD+ reduced to NADH & H+

NADH must be re-oxidised to let glycolysis continue

NAD+ is regenerated through oxidative metabolism of pyruvate

Question 3

what is general function of NADH?

Answer 3

to deliver electrons (to respiratory chain)

Question 4

where does the citric acid cycle occur?

Answer 4

in mitochondria

Question 5

what are cristae?

Answer 5

the folds of the inner membrane of mitochondria

Question 6

what is mitochondrial matrix space?

Answer 6

space between the folds of inner membrane

Question 7

where are the enzymes for the TCA cycle?

Answer 7

in matrix of mitochondria

Question 8

what does the inner membrane of mitochondria contain?

Answer 8

proteins for electron transport chain, ATP synthase and transport proteins

Question 9

how does pyruvate enter mitochondrial matrix?

Answer 9

pyruvate transporter: H+/pyruvate symporter by facilitated diffusion

(very large H+ gradient from cytosol to matrix - pH gradient)

Question 10

how does ATP, ADP & inorganic phosphate (Pi) move in/out of mitochondria?

Answer 10

through a similar process as pyruvate - voltage gradient drives ADP, ATP exchange and PH gradient drives phosphate import

Question 11

how does pyruvate make acetyl CoA?

Answer 11

• The pyruvate dehydrogenase complex (PDC) catalyses the oxidative decarboxylation of pyruvate to acetyl-CoA

Question 12

what is PDC?

Answer 12

• pyruvate dehydrogenase complex (PDC) consists of 3 enzymes
• is allosterically regulated by phosphorylation
• it catalyses pyruvate -> acetyl CoA
• PDC activity determines glucose oxidation in well oxygenated tissues

Question 13

is pyruvate →acetyl CoA reversible or irreversible reaction?

Answer 13

irreversible (Acetyl-CoA cannot be converted back to pyruvate)

Question 14

how many reactions in total are in TCA cycle?

Answer 14

8 reactions - all homeostatic = always return to same starting part if precursor available

Question 15

what are the process of TCA cycle? (describe the pathway of all the carbons)

Answer 15

• 2 carbon unit (from acetyl CoA) condenses to 4 carbon unit resulting in 6 carbon unit (citrate)
• 6 carbon unit decarboxylated twice = yields 2 CO2 and 2 NADH
• this makes 4 carbon unit = yield NADH, FADH2, GTP

another 2 carbon unit from acetyl CoA then joins to 4 carbon unit and cycles again

Question 16

does TCA cycle generate energy?

Answer 16

it makes reducing equivalents - it generates 1 GTP per turn and that can be turned to ATP so tiny energy yield but insignificant

Question 17

what catalyses the first starting reaction of acetyl CoA to CoA-SH (coenzyme A) ?

Answer 17

citrate synthase

Question 18

what is the only enzyme of TCA cycle not located in mitochondrial matrix?

Answer 18

succinate dehydrogenase - it’s integrated in the inner mitochondrial membrane

Question 19

what does succinate dehydrogenase catalyse?

Answer 19

succinate + FAD -> fumarate + FADH2

Question 20

what happens to electrons in each turn of TCA cycle?

Answer 20

in each turn:
3 pairs of electrons + NAD+ →NADH + H+

transfer of 1 pair of electrons to reduce FAD →FADH2

Question 21

what is GTP formed from?

Answer 21

GDP + Pi by substrate level phosphorylation

Question 22

how many carbons are uptaken and how many released in 1 TCA cycle? and in what form?

Answer 22

uptake of 2 carbon atoms in form of acetyl-CoA and release of 2 carbon atoms in form of CO2

Question 23

what is an example of stage 2 metabolic disorder?

Answer 23

PDC deficiency = PDCD

pyruvate hydrogenase (PDH) is enzyme of pyruvate dehydrogenase complex

• gene located on X chromosome so survivable for females but not males

Question 24

how many NADH produced overall per 1 glucose molecule?

Answer 24

10
(2 from glucose - pyruvate and then 3 in TCA cycle x 2 = 10)

Question 25

how many H+ produced overall per 1 glucose molecule?

Answer 25

10

Question 26

how many FADH2 produced overall per 1 glucose molecule?

Answer 26

2 (1 produced per turn and 2 turns for glucose due to splitting in glycolysis)

Question 27

how many CO2 produced overall per 1 glucose molecule?

Answer 27

6

(1 in pyruvate →acetyl CoA and 2 in TCA cycle) X 2, as 2 3-carbon molecules

Question 28

what does high ATP, NADH and acetyl CoA mean?

Answer 28

plenty of energy

Question 29

what does high ADP and NADH+ mean?

Answer 29

lack of energy

Question 30

what does high succinyl-CoA and acetyl CoA mean?

Answer 30

plenty of precursor molecules for biosynthetic reactions

Question 31

how is pyruvate converted to acetyl CoA?

Answer 31

enzyme pyruvate dehydrogenase takes CO2 from pyruvate and then adds what is left od pyruvate with co enzyme A (CoA-SH) to make acetyl CoA

• in the same process 2 electrons + NAD+ to make NADH

Question 32

what is the first step of TCA cycle?

Answer 32

citrate synthase catalyses - acetyl CoA added to oxaloacetae (4C) and releases CoA-SH to make citrate (6C)

Question 33

what step of TCA cycle is FADH2 produced?

Answer 33

succinate dehydrogenase catalysing succinate to fumurate with FAD -> FADH2

Question 34

what are the 3 steps of the TCA cycle that NADH is produced?

Answer 34

• isocitrate (6C) converted to alpha-ketoglutarate, catalysed by isocitrate dehydrogenase - also converts NAD+ -> NADH and also makes CO2 (
• alpha ketoglutarate to succinyl-CoA (makes NAD+ to NADH and CO2), catalysed by alpha ketoglutarate dehydrogenase
• final step: malate to oxaloacetate, catalysed by malate dehydrogenase (NAD+ -> NADH)

Question 35

what step produces GTP?

Answer 35

succinyl CoA -> succinate, catalysed by succinate thiokinase, phosphate + GDP -> GTP and also CoA-SH