Pathway enzymes and regulation

Question 1

Hexokinase vs Glucokinase

Answer 1

Both for Glucose –> G6P (GLYCOLYSIS)
Uses one ATP
Glucokinase: Selective for glucose, low Km, low Vmax, inhib by G6P (in all cells)
Hexokinase: Not very selective, hi Km, hi Vmax, inhib by F6P (in liver and B-cells)
LOW Km = HIGH AFFINITY

Question 2

F6P –> F1,6BP

Answer 2

Glycolysis RATE LIMITING STEP
Uses one ATP
Enzyme: PFK1
- ATP, citrate (pushes to glycogen or HMP shunt)
\+ AMP, F2,6BP

Question 3

Phosphoenolpyruvate –> Pyruvate

Answer 3

Glycolysis
gives 2 ATP
Enzyme: Pyruvate Kinase
- Glucagon (shuts it off through PKA)

Question 4

Pyruvate –> Acetyl CoA

Answer 4

Glycolysis --> TCA
gives one NADH and CO2
- Acetyl CoA, NADH
enzyme: pyruvate dehydrogenase
cofactors: thiamine, niacin (defic in thiamine -->Wernicke's aphasia)
- protein kinase
\+ phosphoprotein phosphotase

Question 5

Pyruvate to Lactate gives …

Answer 5

NadH to Nad
So amounts of NadH and Nad drive the direction
enzyme: lactate dehydrogenase

Question 6

TCA cycle produces

Answer 6

CO2 x2
NADH x3
FADH2 x1
GTP x1

Question 7

ETC reg

Answer 7

• DNP uncoupling, oligomycin (shuts off proton flow back in)

Question 8

Pyruvate –> Oxaloacetate

Answer 8

pre-Gluconeogenesis
enzyme: pyruvate carboxylase w/ biotin cofactor
+ ATP, Acetyl CoA
requires ATP from fat oxidation

Question 9

Substrates for Glucose in Gluconeogenesis (and where do they come from)

Answer 9

from RBCs! (at least the lactate is)
Lactate
Amino Acids
Glycerol

Question 10

Oxaloacetate –> Phosophoenolpyruvate

Answer 10

Gluconeogenesis
enzyme: PEPCK (carboxykinase)
+ Glucagon
- insulin

Question 11

F1,6BP –> F-6-P

Answer 11

Gluconeogenesis RATE LIMITING STEP
enzyme: fructose 1,6 bisphosphatase
- fructose 2,6 BP
[- increased glucagon –> activation of PKA –> inactive PFK-2, active FBP-2] not sure about this

Question 12

G-6-P –> glucose

Answer 12

Gluconeogenesis

enzyme: G-6-phosphatase (ONLY IN LIVER AND KIDNEY

Question 13

Glycogen –> G-1-P

Answer 13

Glycogen!!
G --> G1P
enzyme: glycogen phosphorylase
IN LIVER: - glucose, G-6-P, ATP
IN MUSCLE: + Ca, AMP

Question 14

G-1-P –> Glycogen

Answer 14

Glycogen!!
G1P-->UDP Glucose --> Glycogen
enzyme: Glycogen synthase & branching enzyme
\+ insulin, G-6-P
- Glucagon

Question 15

HMP shunt

Answer 15

G-6-P –> 6-P-gluconolactone –> Ribose Sugars (eg ribose 5-phosphate)
enzyme for step 1: G6PD (defic: HEMOYTIC ANEMIA)
NADPH is the e acceptor (provides defense against oxidative stress (–> hemolytic anemia) and used for lipid synth)

Question 16

FFA Synth RLS

Answer 16

Acetyl CoA –> Malonyl CoA
Enzyme: Acetyl CoA Carboxylase
+ insulin (via protein phosphatase)
- glucagon, epi, AMPK (via cAMP dependent protein kinase)

Question 17

TAG to DAG in fasted state

Answer 17

enzyme: HSL (hormone sensitive lipase)
ACTIVATED by kinase (epi etc.)
INACTIVATED by phosphatase (insulin etc. )
OPPOSITE OF NORMAL