Bioenergetics and Muscle Metabolism

ATP Hydrolysis

ATP —> ADP + Pi

• myosin ATPase catalyzes the hydrolysis of ATP

ATP

energy source

• hydrophilic

• compact

• high density

glycogen

carbohydrate used to make ATP

Glycogen is stored in the

liver and skeletal muscle

• specific to the muscle it is stored in

• once glycogen is taken into the muscle it cannot be taken back (one way street!)

glycogen structure

linked as chains

glucose

transport form of carbohydrates

glucose structure

• 6 carbon compound (transport form)

• CHO (carbon, hydrogen, oxygen)

• name reflects structure

fat can only support exercises when doing

50% of max aerobic capacity or lower

50% aerobic max

carbohydrates are required

80% aerobic max

requires adequate muscle glycogen

• glycogen is important for athletic endeavors

fat structure

energy dense (compact)

triglyceride

composed of a glycerol backbone and 3 fatty acids

• cannot support exercise above 50% aerobic max

palmitate

most common fatty acid in mammalians

• 16 carbon compound

*Note:

higher intensity —> more active muscle mass —> more energy —> more ATP

energy systems match

intensity of exercise

minimal ATP is located in the

sarcoplasm

ATP (rates of ATP production)

• 2-3 second duration

• not instantaneous, needs energy from skeletal muscle

• minimal ATP in sarcoplasm: supports short bursts (about 2-3 sets of exercise)

• initial production form

ATP/PCr (rates of ATP production)

• 15-20 second duration

• simplest energy system: single enzyme

• high energy storage

• phosphate: creatine phosphate compound

• supports high intensity

Glycolysis (rates of ATP production)

• 2-3 min duration

• fast glycolysis

• lower intensity, longer duration

*Note: do NOT use term “anaerobic glycolysis” because there is always oxygen present in muscles (will get mad!!)

Oxidative (rates of ATP production)

• hours duration

• slow glycolysis: extended period of time

tradeoff of ATP production rates is

duration

• high rates of ATP for short periods of time

• smaller amounts for longer time (fats)

insulin causes storage of

glycogen and fats (triglyceride)

carbohydrates (left side)

• glycogen is broken down: glucose molecule is broken off chain

• glucose 6 phosphate (G6P) = first glycolysis intermediate

• pyruvate = last glycolysis intermediate

  • 2 path options

    • —> lactate

    • —> mitochondria —> Krebs —> ETC

• hormones help mobilize glycogen

fats (right side)

• triglyceride

• hormone sensitive lipase (HSL)

  • if hormone is activated glycerol will be broken off fatty acids

can use fats/carbs at same time during high intensities!

during exercise insulin

decreases

resting state of glucose (storage form)

glycogen

PcR (figure 2.5)

• Phosphocreatine: phosphate group and creatine

  • stored in sarcoplasm

  • requires single enzyme = creatine kinase: when active splits into creatine and inorganic phosphate

• if there’s no creatine, there’s no phosphate

• inorganic phosphate can be used to make new ATP

• phosphate creatine can be resynthesized quickly after exercise

What replaces PcR post exercise?

aerobic ATP

aerobic ATP % and post exercise time

• 100% = 5 minutes

• 80% = 3 minutes

• 50% = 1 minute

glycolysis can begin with

1. glycogen in skeletal muscle

2. glucose (transport form, in blood)

How much ATP is generated if glycolysis starts with glycogen in skeletal muscle?

3 ATP

How much ATP is generated if glycolysis starts from glucose in blood?

2 ATP

glycogen phosphorylase

in glycolysis breaks bonds and allows G6P to form

• enzyme: breaks glycogen from glucose chain

• muscle: activated by calcium (muscle contraction)

• liver: epinephrine and norepinephrine

hexokinase

in glycolysis causes ATP —> ADP + Pi

• transfers a phosphate from ATP to glucose to form G6P

phosphofructokinase (PFK)

rate limiting enzyme of glycolysis

• activated by: hydrolysis products ADP + Pi

• inhibited by: ATP (not using energy so system is off)

In slow glycolysis pyruvate moves from

sarcoplasm —> mitochondria

In ETC the last step involves

ATP being used as oxygen

Krebs cycle occurs in

mitochondria

For 2 turns of the krebs cycle you get

6 NADH, 2 FADH, 2 ATP

isocitrate dehydrogenase

rate limiting enzyme of krebs cycle

• activated by: ADP +Pi

• inhibited by: ATP

cytochrome oxidase

rate limiting enzyme of ETC

• activated by: ADP +Pi

• inhibited by: ATP

How much total ATP is yielded?

39 ATP starting with glycogen

38 ATP starting with glucose

fat metabolism

difference is # of ATP due to # of carbons

• 8AcoA coming from palmitate (16 carbons)

triglyceride produces

406 ATP

• fat oxidation cannot support more than 50% VO2 max during exercise

• multiple steps, slow process