Midterm 2 Flashcards
Which would likely be more severe:
a) McArdle’s
b) Tauri
McArdle's = phosphorylase deficiency - used for the initial breakdown of glycogen ONLY Tauri = phosphofructokinase deficiency - rate limiting step for BOTH glucose and glycogen
Glycogenoses
abnormal accumulation of glycogen in the muscle
Symptoms of McArdle’s
Phosphorylase deficiency:
- low intensity exercise threshold (high intensity causes muscle fatigue within sec-min after using ATP-PCr stores and blood glucose)
- muscle fatigue without lactate accumulation
- painful muscle contractures (like rigor mortis)
Why would rigor mortis like muscle contractures occur with McArdle’s disease?
ATP is required for myosin to detach from actin. SR-glycogenolytic complex provides ATP for the SERCA pump to pump Ca back into SR, but unable to breakdown glycogen to use it
Why would there be no lactate accumulation seen with muscle fatigue in McArdle’s disease?
high intensity exercise uses glucose as its main fuel source, but since unable to use glycogen it relied on stored ATP, PCr and oxidative phosphorylation. Not using glycolysis means that lactate is not produced
How do paracrystalline inclusions form?
Mitochondrial creatine kinases breakdown ATP into ADP to form phosphocreatine for energy production
Build up of these CK proteins becomes crystallized, removes double membrane and impedes function of mitochondria
What is the cause of fat metabolism disorders?
Dysfunction / deficiency in carnitine or carnitine palmitoyl transferase (CPT) enzymes
Symptoms of fat metabolism disorders
individuals without carnitine or CPT would display:
- muscle weakness
- pain & damage (ATP depletion, acidosis, elevated Ca)
What would a muscle biopsy of an individual with carnitine or CPT enzyme deficiency show?
accumulation of very large fat droplets
muscle changes due to COPD & CHF
- greater atrophy in Type I fibers
- change in fiber type proportion (loss and shift from type I fibers)
- reduced oxidative capacity (decreased mitochondrial content - reduced oxidative enzymes, decreased capillary density and myoglobin)
Why would there be a reduced oxidative capacity in muscle with COPD and CHF?
Aerobic system is impaired so the muscle fibers are less able to undergo oxidative metabolism
What are the muscle changes that come with COPD and CHF
Lower force production
Drop in Type I fibers
Why would ATP depletion result in fatigue and contractures?
Calcium is dis-regulated affecting relaxation and ATP is required to release myosin from actin
Why would a mitochondrial myopathy show an increase in mitochondrial accumulation?
Trying to correct for energy defect = body makes more mitochondria to produce more ATP
A defect in which of the following would likely result in a disorder of fat metabolism?
a) mitochondrial creatine kinase
b) carnitine
c) phosphorylase
d) a and b
e) a, b and c
b) carnitine - as it is specific to fat metabolism
mitochondrial creatine kinase are not specific to fat metabolism
TRUE / FALSE: Mitochondrial myopathies normally affect fat metabolism, whereas glycogenoses effect carbohydrate metabolism?
False
Effects on mitochondria could effect transfer of pyruvate (affecting carbohydrate metabolism) and not on fat metabolism
In what 4 ways can the cell influence proteins to alter signalling?
1 - changes to protein expression
2 - phosphorylation / dephosphorylation (post-translational modifications, oxidizations, glycosylations)
3 - Binding changes
4 - Movement of proteins (localizations)
What regulates cell cycle and proliferation
high amounts of CDK’s and cyclins
What inhibits CDK’s?
P21, P27 and P53 shut down proliferation by acting on CDKs
What is the limited amount of times a cell can undergo cellular division referred to as?
Hayflick Limit
Which of the following cell would likely have the lowest telomerase activity?
a) muscle fiber
b) satellite cell
c) cancer cell
d) stem cell
e) all would be the same
a) muscle fiber
post-mitotic so not undergoing cell division, no maintenance by telomerase
By how many base pairs does the telomere shorten by each replication?
50 base pairs
In adults what percentage of the nuclei in the muscle are satellite cells?
2-5%
In order for a cell to enter the cell cycle, it first requires:
a) increased expression of cyclin-cdk complexes
b) increased expression of cell cycle-specific transcription factors
c) increased levels of second messenger kinases
d) growth factor stimulation
e) all of the above
d) growth factor stimulation
Required to initiate the whole process
Name 2 ways to identify satellite cells:
Staining for Pax7
Location - found between plasma membrane and basement membrane
What would a Pax7 deficiency phenotype show?
smaller overall size, smaller muscles, satellite cells are taped into early on in life to help muscle repair
What fiber type has more satellite cells?
Slow type fibers have more satellite cells
- used more often, more wear and tear and turnover
- more number of overall nuclei
What happens to the satellite cell number as someone ages?
Over time, downward decrease
Satellite cells lost because of damage / death or using them up via proliferation
Planar vs Apical-Basal Division
Planar = division on a vertical plane with cells remaining in contact with the basil lamina and sarcolemma - two identical self cells Apical-Basal = division on a horizontal plane with one cell maintaining contact with the basil lamina - one becoming myotube and one self cell
Why would the cells orientation during division leads to a different cell outcome or phenotype?
Division through horizontal plane - maintaining contact with sarcolemma and basement membrane
Division through vertical plane - maintaining contact with sarcolemma or with basement membrane
• Different signal based on membrane contact
Why would an activated satellite cell have increases in organelle content?
- changes to organelle because of the changes to the cell, will require ATP and cellular signalling for differentiation
- Going from quiescent to active state
Up-regulation of which of the following set of internal cellular factors would help promote satellite cell differentiation?
a) myf5, MyoD, cyclin E
b) p21, Myogenin, MRF4
c) cylcin E, MyoD, Myogenin
d) p21, IGF-1, MAPK
e) all of the above
b) p21, myogenin, MRF4 = promoting differentiation
a) cyclin is involved in proliferation not differentiation
d) IGF - growth factors are external to the cell
How does low growth factor influence the cell
Low growth factor conditions
Foxo1 will turn on p21
P21 will inhibit cdk - inhibiting cyclin complexes to inhibit cell cycle and proliferation
How does high growth factor influence the cell
High growth factor conditions (IGF - released with injury/damage)
Growth factors activate MAPK to inhibit Foxo1 and as a result inhibit P21
Growth factors will also upregulate MyoD and Myf5 (muscle specific transcription factors) + absence of P21 = cyclin complexes to allow cell cycle and proliferation
How would cell differentiation be characterized?
downregulation of Pax7
cell cycle exit
terminal differentiation
downregulation of cyclins and cdks
Cell differentiation
inhibition of cyclin-cdk complexes
upregulation of MyoD, myogenin, MRF4
P21
How is cell differentiation driven in the cell?
Different growth factor signal causes P13K to promote P21
This inhibits cyclin complexes - inhibiting cell cycle and proliferation
P13K also drives factors to increase MyoD, MRF4, myogenin for muscle formation
Why would an activated satellite cell have increases in organelle content?
- changes to organelle because of the changes to the cell, will require ATP and cellular signalling for differentiation
- Going from quiescent to active state
Myostatin
inhibits cell growth and differentiation
inhibits MyoD - formation of muscle
inhbits cdk - cell proliferation
How does myostatin interact in the cell
Myostatin binds to a membrane receptor and activates P21 - inhibiting cdk complex and cell proliferation
Also binds directly to MyoD to inhibit proliferation and differentiation
What is expressed higher in a terminally differentiated myocyte?
myogenin
desmin
MHC
creatine kinase
With aging, which fiber type sees a more dramatic decrease in satellite cells?
Type II - the ones that typically become dysfunction in age
Aging affects on cell proliferation
decreased FOXO1 - less differentiation with same stimulus
unable to undergo as many divisions
thinner MHC
Muscular Dystrophy and satellite cells
MD individuals undergo more skeletal muscle regeneration by the age of 5 than healthy individuals do by 60
Heavily reduced proliferative lifespan of satellite cells
Exhausting of satellite cell pool = net loss of muscle
Muscular Dystrophy and telomere length
Healthy individuals = loss of 13 base pairs/year off telomeres
MD individuals = loss of 164 base pairs/ year off telomere
faster loss because of increate rate of satellite proliferation to repair and build muscle
Inactivity and satellite cells
Inactivity-induced atrophy causes decrease in level of proliferation, more time required for muscle formation to occur
Inactivity causes the activity of the satellite cells to also decrease and decreases ability to form myotubles as well
FACS
fluorescent activated cell sorting
picks out specific cells that have certain characteristics by isolating the ones with the desired antibody markers
Characteristics of satellite cell differentiation
decrease in Pax7
terminal differentiation
inhibition of cyclin-cdks by P21 activated by PI3K
upregulation of MyoD, myogenin and MRF4 by PI3K
Characteristics of satellite cell proliferation
growth factor signal
cyclin-cdk
MyoD and Myf5 - alternating high and low
Role of P21
cdk inhibitor
Activated by FOXO1
keeps cell quiescent
Role of P21
cdk inhibitor
Activated by FOXO1
keeps cell quiescent
Role of growth factors
External cell signals that inhibit P21 (through the inhibition of FOXO1)
Upregulate MyoD and Myf5
Role of myostatin and TGF-beta
upregulation of cdk inhibitors - P21
inhibition of MyoD
turn off muscle growth
What do mature myocytes express?
Myogenin
Desmin
MHC
Creatine kinase
Important Roles of the Mitochondria
role in signalling apoptosis
regulate cellular oxidative stress
encode some of their own proteins through mtDNA
Two external cellular factors (i.e. growth factors) that would inhibit satellite cell differentiation would be?
Myostatin
TGF-beta
During Muscular Dystrophy, a good indicator of the proliferative lifespan (or potential) of satellite cells could be estimated by?
a) number of myonuclei
b) expression of desmin+ cells
c) telomere length
d) myotube formation in culture
e) all of the above
c) telomere length - shows how many proliferations it has gone through
Which of the following cells would you expect to have the highest mtDNA copy number?
a) RBC
b) Slow (Red) skeletal muscle fibers
c) Fast (White) skeletal muscle fibers
d) cardiac muscle cells
e) B and D
d) cardiac muscle cell - continuously in use, relies on oxidative phosphorylation (high amount of mitochondria = high amount of mtDNA copies)
How many base pairs are in the mitochondrial genome?
16569
Shape of mitochondrial DNA
Circular like bacterial DNA, unlike nDNA
Non-coding region in mtDNA vs nDNA
mtDNA = <6% non-coding nDNA = >95% non-coding
Name 4 factors that would contribute to greater damage in mtDNA compared to nDNA:
- no protective histone cover
- mtDNA repair is less efficient
- majority is coding vs non-coding - 95% of nDNA is non-coding so interaction from ROS will most likely not hit coding, but if ROS damages mtDNA very likely to hit a coding area
- close proximity of ROS production at ETC - location = in matrix of mitochondria, where ETC occurs (electrons will create ROS, diseased state increases ROS production = increased chance of damaging the mtDNA)
Which of the following is false?
a) mitochondria originated in bacteria
b) mtDNA has a greater mutation rate than nDNA
c) mtDNA has more protein coding regions than nDNA
d) mtDNA deletions are most common in post-mitotic tissues
e) none of the above
c) mtDNA has more protein coding regions than nDNA - only 13, compared to tens of thousands
Which mitochondrial complex is coded completely nuclear DNA?
Complex II
Term describing mtDNA absent of mutations
homoplasmy
Term describing presence of both mutated and wildtype mtDNA
heteroplasmy
and amounts of wildtype: mutated depend on replicative segregation
The threshold (of mutation rate) for symptoms arising from mtDNA mutations is usually above ____%
70
• cell can still function with mutations present, takes a lot to impair function
• enough normal mtDNA species can support mitochondrial function up to 70% mutated mtDNA
• higher levels need to be achieved before disease states occur
◦ these proteins encode ETC and provide ATP
◦ without these proteins = no ETC = inability to move electrons = impaired ATP production AND production of ROS
What areas of the body do symptoms of mtDNA mutations typically occur and why?
Brain, Heart and Skeletal muscle - posit-mitotic tissues have low replacement which causing persistence of mutations, unable to replace the mutated cells
IMF: SS mitochondria
75% intermyofibrillar mitochondria
25% subsarcolemma mitochondria
What is the master regulator of mitochondrial biogenesis
PGC-1
How does exercise effect PGC-1
Ca release needed for muscle contraction, more frequent muscle contraction with exercise. Calcium signals to the cell that it will need more ATP production
How does energy deprivation effect PGC-1
AMPK is sensitive to changes in ATP:ADP ratio, activating PGC-1. Wants to maintain ATP:ADP homeostasis while using substrate and ATP during exercise
How does fasting affect PGC-1
loss of substrates to make ATP from, switching to fat substrates and using beta oxidation breakdown
How does cold affect PGC-1
ATP production also produces heat, increasing mitochondria = increasing heat production
What is the role of PGC-1?
Effects mitochondrial transcription factors - producing more ETC proteins, replication of mtDNA, producing more mitochondria/ bigger mitochondria
The function of which of the following proteins/complexes could be affected by mutation to mtDNA?
a) NADH dehydrogenase
b) COX
c) SDH
d) a and b
e) a b and c
d) NADH dehydrogenase and COX
Uncoupling Proteins
allow passage of H+ through the inner membrane without the production of ATP
Pathway of fatty acids into mitochondria
Free Fatty Acids (FFA) activated by ATP and CoA becomes Acyl-CoA = passage through outer membrane
CoA is swapped with Carnitine to become Acyl-Carnitine by CAT = passage into matrix
In the matrix CAPTII turns Acyl-Carnitine back into Acyl-CoA to take place in beta oxidation and Kreb Cycle
