Muscle function, energy supply Flashcards
(42 cards)
What is the main source of energy for the musculoskeletal system and general info about energy for the muscles?
Glucose
1) Each cell has 1 billion ATP molecules that last for less than one minute
2) 60-70% of the energy in the human body is degraded to heat, the remainder is for the mechanical work and cellular activities
What is the main energy source for the cardiac muscle?
Fatty acids
What is the main source of energy?
Carbohydrates and the most important form of energy is ATP
Can we store ATP?
No, because ATP are regulators as they will affect the activation and inhibition of the pathway
How does our body avoid ATP accumulation?
- ATP has 3 phosphates and the 3rd phosphate is the phosphate that has the highest amount of energy so, in this case, the enzyme creatine phosphate will take that phosphate and add it to creatine-forming creatine phosphate (as a storage form) and ADP
- Once we need that ATP we convert the Creatine phosphate back to creatine adding the phosphate to ADP
Where is creatine phosphate mostly found?
in the muscles
Where does gluconeogenesis occur in the body?
In the liver
What are the different energy sources available for the muscles?
1) From glucose (aerobic & anaerobic)
2) From TCA cycle
3) From muscle glycogen
4) From gluconeogenesis, protein & fat
5) From creatine phosphate
What is the importance of glucose?
1) Yields a great amount of energy upon oxidation
2) It can be efficiently stored in a polymeric form
3) Many organisms and tissues can meet their energy needs on glucose only
4) Some tissues like the brain use only glucose for their energy needs
5) It is a precursor to synthesize the skeleton of many different structures (like the non-essential amino acids)
What is the importance of glycolysis?
- Sequence of enzyme-catalyzed reactions where glucose is converted into pyruvate, which can be further oxidized aerobically in addition to that it can be used as a precursor in biosynthesis
- Glycolysis is divided into 5 investment stages where 2 ATPs are used and 5 payoff stages where 4 ATPs and 2NADH are produced
- It requires no oxygen
- 10-step reaction that occurs in the cytoplasm
- The end products are two pyruvates that depend on the availability of oxygen in the cell, if O2 was available then we would get the 6CO2 if not there would be a different fate
How can we gain energy from glycolysis?
1) Substrate level phosphorylation (“Cash” ATP): usually uses kinases, in a reaction that converts a high-energy molecule to a low-energy one via transferring a phosphoryl group
2) Oxidative phosphorylation, Electron carriers that can be converted into ATP (“Coupons” NADH/FADH2): they are electron carriers that are converted into energy via the ETC using oxidative phosphorylation, this is the main source of energy production
What are the regulatory steps in glycolysis?
1) Reaction number 1: Converting glucose into glucose-6-phosphate, using ATP converting it into ADP, via the enzyme hexokinase
2) Reaction number 3: Converting Fructose-6-phosphate into fructose-1,6-bisphosphate via the enzyme phospho-fructokinase-1, using ATP converting it into ADP
3) Reaction number 10: converting phosphoenolpyruvate into two pyruvates, via the enzyme pyruvate kinase, producing 2 ATP’s from 2 ADPs
- all of their enzymes are kinases
- The only kinase that reacts reversibly in glycolysis is phosphoglycerate kinase
Which reactions in glycolysis produce energy?
1) Reaction number 6 (oxidation-reduction rxn): converting glyceraldehyde-3-phosphate into 1,3-bisphosphoglycerate via the enzyme glyceraldehyde-3-phosphate dehydrogenase using 2 phosphates and 2NAD producing 2 NADH + 2H
2) Reaction 7: converting 1,3-bisphosphoglycertae into 3-phosphoglycerate via the enzyme phosphoglycerate kinase (the only reversible kinase) converting 2ADP into 2ATP
3) Reaction number 10: converting phosphoenolpyruvate into two pyruvates, via the enzyme pyruvate kinase, producing 2 ATP’s from 2 ADPs
What is the commitment step in glycolysis?
Reaction number 3 converting fructose-1-phosphate into fructose-1,6-bisphosphate using phospho-fructokinase-1 converting an ATP into ADP
What is the importance of the first reaction in glycolysis?
1) It adds a phosphate onto glucose making it unable to leave the cell
2) decreases the concentration of glucose favoring its entry into the cell
3) this reaction also G6P will not always continue towards glycolysis but it will be used in different pathways depending on the cell’s need
Summarize the energy production in glycolysis
1) Things we used: 2ATP & 2NAD+
2) Things we made: 2 pyruvates, 4 ATP, 2 NADH (must be reoxidized for glycolysis to continue)
- Glycolysis is heavily regulated (ensures proper use of nutrients, and the production of ATP only when needed)
How is glycolysis inhibited and activated?
- Glycolysis requires glucose and NAD+ to start
1) Inhibited by high levels of ATP
2) Activated by high levels of AMP
What is the fate of pyruvate?
- Depends on the availability of oxygen
1) If O2 is available, Pyruvate is oxidized to Acetyl-CoA which enters the Krebs cycle
2) If O2 is not available pyruvate is reduced to lactic acid via the enzyme lactate dehydrogenase (this is the final product in anaerobic glycolysis in eukaryotic cells, or ethanol in different organisms) and this solves the NAD+ problem as more NADH is produced and there is little to no NAD+ available
- The body produces lactate relying on the fact that O2 will eventually enter the body (the body will utilize the lactate by transforming it into pyruvate and then into glucose) this occurs in the liver as the lactate travels to it via the blood “Cori Cycle”
What happens in our body when we exercise vigorously?
1) NADH production exceeds the oxidative capacity of the respiratory chain, increasing the NADH/NAD+ ratio and favoring the reduction of pyruvate to lactate
2) Lactate will then accumulate in the muscles causing a drop in the pH, resulting in muscle cramps
3) Most of this lactate will then diffuse into the bloodstream where it can be used by the liver to make glucose
What is meant by lactic acidosis?
Elevated concentrations of lactate in the plasma, occur when there is a collapse in the circulatory system, like Myocardial infarction, pulmonary embolism, and uncontrolled hemorrhage
Describe the Cori cycle
It is the reverse of glycolysis as the lactate reaches the liver it is converted back to glucose utilizing 6 ATP’s for the muscle to use that glucose and produce 2 ATP’s (futile cycle)
What happens if we do not have enough glucose for glycolysis?
1) Cori cycle
2) Glycogen breakdown (glycogenolysis)
How do we produce energy from the breakdown of glycogen?
- Glycogen is the storage form of glucose
- Glycogen is made up of two bonds (a-1,4) between the glucose molecules and (a-1,6) the branching bond
- Glycogen phosphate (contains pyridoxal phosphate PLP as a prosthetic group “vitamin B6 derivative”) leaving us with some (a1,6 branches) and glucose-1-phosphate, which is converted to glucose-6-phosphate by phosphoglucomutase
- a1,6 bond will be broken down by debranching enzyme which has two activities (transferase (which moves some of the glucose in the branch to the main chain “only 3 glucose residues” from a 4-limit branch) and 1,6 glucosidase)
What happens to the pyruvate when there is oxygen?
Cellular respiration takes place, pyruvate is converted to Acetyl-CoA (an important step that is not part of glycolysis nor the Krebs cycle)
