Unit 11 - Muscle Contraction and Conversion of Muscle into Meat Flashcards
What are the steps to a muscle contraction?
- action potential
- release of calcium from sarcoplasmic reticulum
- change in the conformation of thing filaments
- slide of thick and thin filaments
What are the four steps to a muscular contraction?
- action potential starts in the neuromuscular junction (synaptic connection between the terminal end of a motor nerve and a muscle, the action potential travels through the sarcolemma and is also transmitted through its invaginations (t-tubules)
- action potential causes a release of calcium from the sarcoplasmic reticulum into the sarcoplasm
increase levels of calcium in the sarcoplasm causes the filaments to slide - at the relaxed stage: tropomyosin blocks myosin binding sites on actin subunits
increased levels of calcium - released from sarcoplasmic reticulum
ca binds to troponin and changes the conformation of troponin
this pushed tropomyosin off and exposes the myosin binding sites - myosin heads will rotate and bend
actin filament will be pulled along using ATP in the process
What are the three types of muscle fibres?
Type I fibres - slow twitch, oxidative fibres
- slow contraction speed
- ability to utilize oxygen for production of energy
Type II fibres - fast twitch, short contraction time
- Type II beta - primarily on anaerobic (glycolytic) metabolism to produce energy
- Type II alpha - uses both oxidative and glycolytic metabolism to produce energy
What types of fibres do muscles usually contain?
all three types
the relative distribution of fibre types varies among specific muscles
What muscle fibres make the muscle more red in colour and why?
muscles with a greater proportion of slow twitch fibres are typically more red in colour, they have a higher content of myoglobin (oxygen-binding protein in muscle)
how far does each muscle fibre type make it to in respiration processes (metabolism)?
Type I fibres - all the way to ETC
Type II beta - only until pyruvate production
Type II alpha - all the way to ETC
Which is more efficient, glycolytic or oxidative?
oxidative - produces a lot more ATP because it goes through ETC whereas glycolytic do not
What are some characteristics of type I muscle fibres?
slow contraction speed
aerobic metabolism
highest content of myoglobin
low concentration of glycogen
red colour
What are some characteristics of type II beta muscle fibres?
fast contraction speed
anaerobic metabolism
least amount of myoglobin
high amount of glycogen
white colour
What are some characteristics of type II alpha muscle fibres?
fast contraction speed
anaerobic and aerobic metabolism
intermediate amount of myoglobin
intermediate amount of glycogen
intermediate pink colour
What are the three steps to the conversion of muscle to meat?
- starts when the animal is harvested
- onset of rigor mortis (stiffness of death)
- completion of rigor mortis
What happens in the first step of the conversion of muscle into meat?
as the animal succumbs to exsanguination and resulting anoxia (total depletion of oxygen) the skeletal muscle continues to synthesize and utilize ATP in a futile attempt to sustain cellular homeostasis
once oxygen is depleted from the muscle - glycogen present in the muscle is anaerobically metabolized for the sole purpose of ATP production - nothing goes in or out of the muscle
the carcass is still contracting the tissues are still alive - the higher the glycogen stores, more lactate produced after slaughter
What is the second step to the conversion of muscle to meat?
anaerobic metabolism is less efficient in generating ATP than aerobic metabolism. the ATP hydrolysis exceeds its generation and triggers the onset of rigor mortis (final contraction)
with less ATP available, the thick and thin filaments detachment is compromised
What is the third step to the conversion of muscle to meat?
as postmortem metabolism proceeds, the muscle gradually loses the ability to generate ATP. In the absence of ATP, myosin binds irreversibly to actin, leading to the completion of rigor mortis
the completion of rigor mortis occurs at 1-12hr
Why must ATP be generated constantly in the muscle?
the energy capacity of muscle tissue must maintain ATP homeostasis over a wide range of cellular challenges and circumstances. There is a limited capacity of the muscle to store ATP so it must be generated constantly
What are the two methods of ATP energy production in the muscle?
phosphagen system
glycogenolysis (breakdown of glycogen) + glycolysis
What is the phosphagen system?
form of anaerobic metabolism. It uses phosphocreatine (PCr) to generate ATP
- immediate energy source that rapidly buffers ATP levels during high energy demands
Is the phosphagen system the main system for ATP synthesis in the muscle?
no, phosphocreatine is limited in the muscle, because the muscle cannot store too much
it is used when glycogen isn’t available
What is the general reaction for phosphagen system?
phosphocreatine gives its phosphate to ADP to make it ATP
CK (creatine kinase) enzyme catalyzes the transfer of an inorganic phosphate to ADP
CK
creatine kinase
What are the steps to the phosphagen system?
- PCr is limited and drops its amount quickly
- increase levels of ADP
- activates AK (adenylate kinase) to buffer the ATP levels (converts 2 ADP into one ATP)
- AMP is irreversibly deaminated by the enzyme adenosine monophosphate deaminase into IMP
which shifts the equilibrium of the AK reaction in the direction of ATP formation
After death what is the primary source of ATP metabolism?
the capacity of the phosphagen system to maintain postmortem ATP homeostasis is limited
the catabolism of muscle glycogen through glycogenolysis (glycogen degradation) and glycolysis becomes the dominant pathway for ATP production
What is the reaction for glycogenolysis?
glycogen + Pi -> (glycogen phosphorylase) glycogen + glucose 1 phosphate
G1P -> (phosphoglucomutase) G6P
What occurs after glycogenolysis?
G6P obtained directly enters the glycolytic pathway (glycolysis)
