Lecture 3- out in the cytosol

Fiber type categorization and performance ability is dependent on

neuromuscular properties

Neuro muscular properties

• electrical properties (neuro)

• mechanical properties (muscualr)

• metabolic properties (muscular)

Slower MUs are recruited before

faster MUs

Faster MUs activate faster than

Slower MUs

Faster MUs cycle

crossbridges faster than slower MUs

Slower MUs have lower anaerobic power but

greater aerobic supply than faster MUs

Conservation of energy

energy cannot be created nor destroyed rather it can only be transferred from one form to another

chemical work

synthesis of cellular molecules (forming ATP)

Mechanical work

muscles contraction (crossbridge power stroke)

Transport work

pump substances against concentration gradient to maintain concentrations (action potentials, Ca+, reuptake to SR)

Metabolism

Describes the sum of cellular processes

Anabolism

• smaller molecules are combined to make larger molecules

  • requires energy in

  • forms or repairs tissues

  • storage of energy as bonds

Catabolism

• larger molecules are broken down to make smaller molecules

  • breaks down food

    • cho

    • fats

    • protein

  • body tissues

    • fat

    • protein

    • bones

powering crossbridge strokes

requires energy ATP

but muscular ATP storage is low (6mmol/kg) and lasts 1-3 seconds

Hydrolysis

the breakdown of ATP into ADP and Pi

• chemical bond is broken through addition of water (released energy needed for crossbridge cycling)

In muscle, ATP is used for

• cross bridge power stroke

• re-sequester calcium to SR (CA2 ATPase)

• restore membrane resting NA and K balance

Limiting factors for metabolic processes

• substrate availability

• enzyme availability

Substrate (fuel) availability

• more substrate results in faster rate (more reactions)

• less substrates results in slower rate (fewer reactions)

enzyme availability

• enzymes lower activation energy needed for a reaction

• more enzymes results in more reactions result in more power

• enzymes bind to substrates

Anaerobic energy sources

• stored ATP

• stored phosphocreatine

• glycolysis

Aerobic Energy sources

• oxidative (aerobic) phosphorylation

  • occurs in mitcohondria

Anaerobic

• doesn’t require oxygen

• occurs in cytosol

Aerobic

• requires oxygen

• occurs in mitochondria

Stored ATP (fuels, timeframe, by products)

ATP, 2s, N/A

Phosphocreatine (fuels, timeframe, by products)

CP, 0-20s, Cr and ATP

Glycolytic (fuels, timeframe, by products)

CHO, 15-120s, latic acid — atp — co2

Aerobic (fuels, timeframe, by products)

CHO — fats — protein, 120s-several hours, ATP — Co2

ATP floats

ATP is floating around freely to be used when needed

Sliding filament theory

1. Crossbridge formation and release of pi

2. Power stroke, ADP is released, myosin undergoes conformational change

3. ATP binds myosin, causing detachment of myosin from actin, cross bridge dissociates

4. ATP hydrolysis occurs, and myosin head cocks

ATP is available

fast, in very limited supply

Phosphocreatine

Phosphocreatine splits PCr+ADP → Creatine Kinase​ → ATP+Creatine

explain phosphocreatine

The enzyme Creatine Kinase hekps transfer a phosphate group (pi) from PCr to ADP which will form ATP again

• ie. donation of bond energy and Pi from PCr to reform ATP from ADP

Bond based energy storage

Energy liberated from hydrolysis of PCr

• rebinds ADP and Pi to form ATP

stored creatine is essentially

• storable, easy to reverse, contains the same amount of energy as ATP bond

Glycolysis

partial breakdown of glucose through series of enzyme-driven fermentation reactions

Glycogenolysis

• partial breakdown of glycogen through series of fermentation reactions

Glycolysis/glycogenolysis requires enzymes

• requires glucose-6-phosphate to begin

  • conversion of glucose costs 1ATP

  • conversion of glycogen costs )atp

Steps to glycolysis

1. glucose is phosphorylated to form glucose-6 phosphate (consumes 1 ATP)

2. Glucose-6 phosphate is rearranged to form fructose 6-phosphate

3. Phosphorylation into fructose bisphosphate (1ATP)

4. Fructose bisphosphate gets turned into two three carbon molecules

5. Dihydroxyacetone phosphate (DHAP) is converted into glyceraldehyde-3-phosphate (G3P), so there are two molecules of G3P available for the next steps.

6. Each G3P is oxidized, and NAD+ is reduced to NADH. An inorganic phosphate is added, forming 1,3-bisphosphoglycerate

7. 1,3-bisphosphoglycerate (1,3BPG) donates a phosphate group to ADP to form ATP and 3-phosphoglycerate (3PG)

8. 3-phosphoglycerate (3PG) is converted into 2-phosphoglycerate (2PG).

9. 2-phosphoglycerate (2PG) loses a water molecule, forming phosphoenolpyruvate (PEP).

10. Phosphoenolpyruvate (PEP) donates a phosphate group to ADP, forming ATP and pyruvate.

end product of gylcolysis

2 molecules of pyruvate

2 molecules of NADH

2 molecules of atp net gain

key steps of glycolysis

• split into 3 C chains and each is converted to pryuvate

Profuction of H plus (step 6)

H binds to NAD and travels to ECT

ATP production through glycolysis

2 ATP per each 3-C chain

Net yield for glucose and glycogen (ATP

glucose: 2 ATP
glycogen 3ATP

glycolysis/glycogen

• glucose needs to get converted to glucose 6 phosphaet (1ATP) but glucogen is good (0 ATP)

limiting factor for glycolysis

phosphofructokinase

What if there’s no where for pryuvate or NADH to go?

they accumulate

• limited NAD prevents glycylosis

• accumulation of pryuvate inhibits glycolysis

how to solve problem of pryuvate and nadh accumulation

conversion of pryuvate to lactate

reaction pyruvate to lactate

conversion of pryuvate to lactate enables

continued glycolysis

in the absence of oxygen we can exercise for

only 2 minutes

• relying on stored ATP, PCr and Glycolysis

energy is required for

• tissue building, membrane transport and muscle action

1 crossbridge =

1 ATP

energy for cellular process is stored as

phosphate bond in ATP

energy for muscle work is provided in

• the cytosol

  • stored ATP

  • glycolytic breakdown (partial) of glucose

  • stored as a bond in PCr

cytosolic metabolism ends with

pyruvate — running out of gas