Catabolic Pathways

Question 1

Muscle Contraction

Answer 1

– Muscle contraction uses ATP
– Actin and myosin interaction
– Filaments sliding across each other
– The faster the contraction, the faster the use of
ATP
– Even at rest, muscle is using ATP
– Maintaining ion gradients
– Sarcoplasmic reticulum and Ca2+

Question 2

Muscle Cell Types

Answer 2

– Type I - “Red”, “Slow”
– Contracts relatively slowly
– Many mitochondria
– Good blood supply
– Type IIb - “White”, Fast”
– Contracts relatively rapidly
– Few mitochondria
– Poor blood supply
– Packed full of contractile filaments

Question 3

Gentle Exercise

Answer 3

We need to elevate the rate of ATP generation
Most readily available fuel is glucose
–-> Glucose transporters move to the cell surface
= This will lower blood glucose!
– And we need to keep that at 5 mM for our
brains!
–> Glucose homeostasis
– Tiny decrease in blood glucose gives big
hormonal responses
–-> Insulin down and glucagon up
–> Stimulation of glycogen breakdown in liver
AND fat breakdown in white adipose tissue

Question 4

significance of increase in ADP

Answer 4

– Through greater availability of ADP
– Increase ATP synthase activity
– Dissipate the proton gradient (our charged battery is being used!)
– Increase electron transport (because now it CAN!)
– Increase availability of H/e - strippers
– Fuel oxidation can increase….
– What fuels are we talking about?

Question 5

Glucose Recycling

Answer 5

Glucose stores (glycogen) are limited
And we cannot convert fatty acids into glucose
== GLUCOSE CONSERVATION AND RECYCLING

– Fatty acids substitute for glucose as a fuel
– Fatty acids prevent glucose from being wastefully oxidised

Question 6

Gentle Exercise

Answer 6

– Initially, glucose is used
– After several minutes fatty acids take over
– Released from White Adipose tissue
– Glucose still gets into the muscles
– But it is only taken as far as lactate
– lactate metabolised in liver for re-synthesis of glucose = Gluconeogenesis

Question 7

Moderate Exercise

Answer 7

– As the pace increases, he rate of fatty acid utilisation increases, but….
– The enzymes that catalyse fatty acid oxidation soon reach their maximum
capacity
Fatty acid oxidation alone cannot maintain ATP production so Inhibition on glucose oxidation is removed = Glucose oxidation occurs!
* Less glucose recycling
* Liver glycogen stores depleted faster

– A mixture of fatty acid oxidation and glucose
oxidation
– The glucose comes from the liver
– Fatty acid oxidation going at full speed already
fatty acid –> CO2
glucose –> CO2

Question 8

Strenuous Exercise

Answer 8

Now limits on speed of oxidation of blood
glucose
– Rate of supply and transport from blood
can’t keep up
– Fatty acids still going as fast as they can!
– So, muscle glycogen now broken down
– ENDOGENOUSLY STORED

fatty acid –> CO2
glucose –> CO2
glycogen –> CO2

Question 9

PDH

Answer 9

(pyruvate dehydrogenase which converts pyruvate to aceytl CoA)
usually PDH is inhibited when there is a high conc of acetly CoA but during exercise and rapidly burning fuel, Acetyl CoA is used faster than made from FA so PDH NOT inhibited by build up of Acetyl CoA

Question 10

Very Strenuous Exercise

Answer 10

– Now rate of ATP production can’t be met by
oxidative phosphorylation alone
– Mitochondrial processes too slow
– Need to top up with extra boost from glycolysis
– Remember glycolysis VERY fast
– Very inefficient
– Now blood lactate levels will rise…
– Glucose must come from muscle glycogen (glycogen also makes pyruvate to produce lactate)
– Transport already at max!
Competitive
Fatty acids –>CO2
Glucose –> CO2
Glycogen –> CO2
Glycogen –> lactate

Question 11

Sprinting

Answer 11

– Uses Type IIb muscles
* Poor blood supply
* Packed full of contractile filaments
* Few mitochondria
* VERY rapid consumption of ATP

– Fuel selection problem
= Use Fatty acids? NO!
* Poor oxygen supply, low mitochondria
= Use Blood Glucose? NO!
* Delay in transporter recruitment, poor fuel supply

Instead : Glycolysis to lactate
–> very fast but creates a problem
– Regeneration of H/e carrier (NAD)
– ATP generation is so inefficient
– Only 2 ATP per glucose (vs >30 if oxidized to CO 2)
– So, LOTS of lactate produced very quickly
– And a very poor blood supply to take it away

Question 12

Creatine

Answer 12

It takes several (many) seconds to get glycogenolysis going
– Creatine Phosphate (CP) is an instant store of ATP but less than five seconds supply (15 mM)
–-> Creatine supplements boost CP levels!

Glycogen –> lactate
Creatine P –> creatine