TMC 11 Flashcards
What is the difference between type I, type IIa, type IIb, type lid/x muscle fibres?
Type I - oxidative metabolism, slow twitch, mitochondria rich, fatigue resistant, endurance and posture
Type IIa - oxidative metabolism, fast twitch. fatigue rapidly, strength and speed
Type IIb - glycolytic metabolism, fast twitch. fatigue rapidly, strength and speed
Type lid/x - glycolytic metabolism, fast twitch. fatigue rapidly, strength and speed
What stains are used to differentiate between muscle fibres?
haematoxylin and eosin
What is the difference between oxidative metabolism and glycolytic metabolism?
Glycolytic metabolism:
anaerobic
In cytoplasm
Rapid
2 ATP per glucose
~2 min of tetanic contraction sustained
Lactic acid
Glycogen
Oxidative metabolism:
Aerobic
Mitochondria
36 ATPs
Relatively slow
~40 mins to several hours of tetanic contraction
What are the properties of fast glycolytic muscle fibers?
Generates maximum forces for short periods of time
Less blood, mitochondria, myoglobin
Low fat, high glycogen
Relies on glycogen and anaerobic glycolysis
Short duration, high intensity contractions
Enlargement of muscle fibres through production of new microfilaments
What are the properties of slow oxidative muscle fibers?
Extended, aerobic work
Well perfused in blood, high mitochondria, myoglobin
Sustains low intensity contractions for long periods
Muscle fibres can acquire greater oxidative capacity
What is the function of MEF2 transcription factor?
Turns on several muscle specific genes
Includes myoglobin, myosin heavy chain, slow troponin I etc.
Explain how the MEF2 transcription factor is converted from inactive to active form
Controlled by HDAC4 and HDAC5
These bind to MEF2 in the nucleus and repress its activity
HDAC kinase is activate din response to calcium which phosphorylates HDAC4 and HDAC5
Phosphorylated HDAC4 and HDAC5 translocate out of nucleus
This phosphorylation masks the part of the protein required for entry into the nucleus and unmasks a part of the protein required for export from the nucleus
What kind of activity stimulates activation MEF2?
Exercise
10Hz electrical stimulation
Stimulation of nerve linked to muscle
Explain the relationship between exercise and MEF2.
Activates HDAC kinase which phosphorylates HDAC4/5 which translocates HDAC out of nucleus allowing MEF2 to activate
What is the role of HDAC kinase and how is this enzyme activated?
Phosphorylates HDAC4/5 which translocates HDAC out of nucleus allowing MEF2 to activate
What is the effect of phosphorylation on HDAC4 and HDAC5?
translocates out of nucleus allowing MEF2 to activate
What are calcium transients?
The changes in Ca++ concentration over time
Explain how the activity of the NFAT transcription factor is controlled.
NFAT is found phosphorylated in the cytosol.
Activated calcineurin which is activated by activated calmodulin (Ca++ binded to it) , dephosphorylates NFAT
NFAT then translocates into nucleus and attaches itself to a promoter
Here it turns on muscle specific genes
What is the difference between the properties of NFAT when phosphorylated and dephosphorylated?
Phosphorylated - is absent from nucleus causing a cessation of Ca++ waves
Dephosphorylated - in nucleus, turns on specific muscle genes which causes Ca++ waves
What is ubiquitin?
76 amino acid protein
When attached to a protein, the tagged protein is targeted for degradation by the proteasome
