Unit 11 - Muscle Contraction and Conversion of Muscle into Meat

Question 1

What are the steps to a muscle contraction?

Answer 1

1. action potential
2. release of calcium from sarcoplasmic reticulum
3. change in the conformation of thing filaments
4. slide of thick and thin filaments

Question 2

What are the four steps to a muscular contraction?

Answer 2

1. 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)
2. 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
3. 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
4. myosin heads will rotate and bend
   actin filament will be pulled along using ATP in the process

Question 3

What are the three types of muscle fibres?

Answer 3

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

Question 4

What types of fibres do muscles usually contain?

Answer 4

all three types
the relative distribution of fibre types varies among specific muscles

Question 4

What muscle fibres make the muscle more red in colour and why?

Answer 4

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)

Question 5

how far does each muscle fibre type make it to in respiration processes (metabolism)?

Answer 5

Type I fibres - all the way to ETC
Type II beta - only until pyruvate production
Type II alpha - all the way to ETC

Question 6

Which is more efficient, glycolytic or oxidative?

Answer 6

oxidative - produces a lot more ATP because it goes through ETC whereas glycolytic do not

Question 6

What are some characteristics of type I muscle fibres?

Answer 6

slow contraction speed
aerobic metabolism
highest content of myoglobin
low concentration of glycogen
red colour

Question 7

What are some characteristics of type II beta muscle fibres?

Answer 7

fast contraction speed
anaerobic metabolism
least amount of myoglobin
high amount of glycogen
white colour

Question 8

What are some characteristics of type II alpha muscle fibres?

Answer 8

fast contraction speed
anaerobic and aerobic metabolism
intermediate amount of myoglobin
intermediate amount of glycogen
intermediate pink colour

Question 9

What are the three steps to the conversion of muscle to meat?

Answer 9

1. starts when the animal is harvested
2. onset of rigor mortis (stiffness of death)
3. completion of rigor mortis

Question 10

What happens in the first step of the conversion of muscle into meat?

Answer 10

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

Question 11

What is the second step to the conversion of muscle to meat?

Answer 11

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

Question 12

What is the third step to the conversion of muscle to meat?

Answer 12

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

Question 13

Why must ATP be generated constantly in the muscle?

Answer 13

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

Question 14

What are the two methods of ATP energy production in the muscle?

Answer 14

phosphagen system
glycogenolysis (breakdown of glycogen) + glycolysis

Question 15

What is the phosphagen system?

Answer 15

form of anaerobic metabolism. It uses phosphocreatine (PCr) to generate ATP
- immediate energy source that rapidly buffers ATP levels during high energy demands

Question 16

Is the phosphagen system the main system for ATP synthesis in the muscle?

Answer 16

no, phosphocreatine is limited in the muscle, because the muscle cannot store too much
it is used when glycogen isn’t available

Question 17

What is the general reaction for phosphagen system?

Answer 17

phosphocreatine gives its phosphate to ADP to make it ATP
CK (creatine kinase) enzyme catalyzes the transfer of an inorganic phosphate to ADP

Question 18

CK

Answer 18

creatine kinase

Question 19

What are the steps to the phosphagen system?

Answer 19

1. PCr is limited and drops its amount quickly
2. increase levels of ADP
3. activates AK (adenylate kinase) to buffer the ATP levels (converts 2 ADP into one ATP)
4. 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

Question 20

After death what is the primary source of ATP metabolism?

Answer 20

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

Question 21

What is the reaction for glycogenolysis?

Answer 21

glycogen + Pi -> (glycogen phosphorylase) glycogen + glucose 1 phosphate

G1P -> (phosphoglucomutase) G6P

Question 22

What occurs after glycogenolysis?

Answer 22

G6P obtained directly enters the glycolytic pathway (glycolysis)

Question 23

What occurs in glycolysis?

Answer 23

each siz carbon glucose moiety of glycogen is mobilized into two three carbon pyruvate molecules

Question 24

What occurs after glycolysis if its anaerobic conditions?

Answer 24

pyruvate is reduced to lactate by the enzyme lactate dehydrogenase (LDH)

Question 25

Why is lactate produced after glycolysis?

Answer 25

to regenerate NAD+ that is required to allow glycolysis to continue under anaerobic conditions

Question 26

What is the reaction for pyruvate to lactate?

Answer 26

pyruvate + NADH + H+ -> (LDH) Lactate + NAD+

Question 27

does lactate accumulate in the muscle?

Answer 27

yes

Question 28

What is responsible for pH drop during the conversion of muscle into meat?

Answer 28

although lactate accumulates in the muscle, lactate is not responsible
LDH reaction functions as a buffer by consuming one H+ from the system for every pyruvate molecule converted to lactate
what ACTUALLY causes it is the hydrolysis of ATP generated through postmortem glycolysis (90%) the other 10% is from H+ from ATP hydrolysis before death

Question 29

Why is lactate used as an indicator of postmortem metabolism?

Answer 29

because both H+ and lactate accumulate in the muscle
therefore if lactate increases, so does H+ and therefore a way of measuring acidity

Question 30

Talk about graphs measuring glycogen levels in different animals in oxidative vs glycolytic muscles postmortem

Answer 30

oxidative muscle had a higher level of glycogen postmortem compared to glycolytic muscle, therefore if there is more glycogen, glycolysis took place less.
The oxidative muscles terminated glycolysis and glycogenolysis prematurely compared to glycolytic muscle

Question 31

Talk about graphs measuring G6P levels in different animals in oxidative vs glycolytic muscles postmortem

Answer 31

Since G6P is produced by glycolysis, the muscle that has less glycolysis occurring will have less G6P present
the glycolytic muscle has more G6P compared to oxidative muscle because glycolysis is prematurely stopped in oxidative muscle

Question 32

Which will have more glycogen storages, pig or beef?

Answer 32

pig: higher glycogen storages - less efficient
have a higher frequency of glycolytic fibres
beef: lower glycogen stores - more efficient and produce more ATP per glucose molecule
higher frequency of oxidative fibres
high myoglobin content - causes darker colour

Question 33

Talk about graphs measuring lactate levels in different animals in oxidative vs glycolytic muscles postmortem

Answer 33

glycolytic muscles have higher lactate than oxidative muscles
if glycolysis is stopped prematurely in oxidative muscle, a lower level of lactate is observed in comparison to glycolytic muscles

Question 34

Talk about graphs measuring pH levels in different animals in oxidative vs glycolytic muscles postmortem

Answer 34

oxidative muscle have higher pH than glycolytic muscle
differences in pH occurs due to the different energy metabolism in oxidative and glycolytic muscles