Midterm 2 Flashcards
Understand Concept and content for the second midterm
_____ and _____ are dependant on the relationship between cell proliferation (process that results in an increase in the number of cells), differentiation and death
Tissue turnover, homeostasis
In cell proliferation, extracellular signals such as _____ and _____, play an essential role
growth factors, hormones
Penetrate the cell membrane and bind to specific receptors that directly effect genomic regulatory mechanisms
Steroids (e.g. testosterone, estrogen, cortisol)
Act on membrane receptors to activate kinases as a result of inability to pass cell membrane
Polypeptide growth factors (e.g. IGF-I, IF-2)
True or False: Growth factors both enable the cell to enter the cell cycle and are required to inhibit the cell from dying, to some extent.
True
The phases of the cell cycle are…
G0, G1, S, G2, and M
cdks and cdk Inhibitors refer to…
Cyclin-Dependant Kinases and Cyclin-Dependant Kinase Inhibitors
When a cell is not in the cell cycle and receives the appropriate growth stimulation it leaves _____ phase.
G0
Regulates progress in the cell cycle
cyclins and cdks
What must be present to activate a cdk?
Cyclins
Cyclin-cdk complexes phosphorylate _____ to stimulate expression of important cell cycle genes
proteins
True or False: cdk inhibitors regulate the amount of proteins that a ribosome can translate
False… cdk inhibitors regulate the activity of cyclin-cdk complexes alongside tumor surpressors
p53 is a…
tumour suppressor gene
Promote cell cycle
Growth factors, cyclins, oncogenes and cdks
Halt cell cycle
Tumour suppressor genes and cdk inhibitors
Cyclin and cdk associated with G1
Cyclin D and cdk 4/6
Cyclin and cdk associated with transitioning from G1 to S phase
Cyclin E and cdk 2
Cyclin and cdk associated with transitioning from S to G2 phase
Cyclin A and cdk 2
Cyclin and cdk associated with transitioning from G2 to M phase
Cyclin B and cdk 1
Finite number of cellular divisions possible, regardless of expression levels of protein and factors that promote proliferation
Hayflick Limit
The Hayflick Limit is a result of the replication of DNA for the chromosomes of the sister cells resulting from the cell division. Why does the DNA strand shorten every time a cell divides?
DNA polymerase cannot add nucleotides to the new 5’ end
Internal mechanism to deal with DNA strand shortening during cell proliferation
Telomeres
Telomeres consist of approximately 1,000 to 1,700 _____ and a _____ overhang from the 3’ end
base pairs, single strand
A reverse transcriptase that is responsible for adding base pairs to the telomere
Telomerase (Telomere terminal transferase)
A chromosome telomere shortens by _____ base pairs every replication
50
True or False: Telomeric length is equivalent throughout an organism, but varies between species
False… Telomeric length varies between cell types and from one chromosome to another (e.g. faster replicating cells like leukocytes > slower replicating cells like skin fibroblasts)
Is telomerase activity greater or lesser in adult cells
Lesser or even absent
An indicator of cellular senescence and aging is…
The halt of cell proliferation
Rank in order of a greatest telomere length maintenance during cell division to least telomere length maintenance during cell division:
Normal Cells
Germ Cells
Stem Cells
Germ Cells > Stem Cells > Normal Cells
Can skeletal muscle fibers proliferate?
No, it is terminally differentiated or post-mitotic tissue
Addition of _____ allows for repair and adaptation of muscle fibers.
nuclei
Adult mammalian skeletal muscle is very stable; no more than _____ of the _____ are replaced on a weekly basis.
1-2%, myonuclei
The two types of cells that provide a sufficient source of new myonuclei for muscle regeneration
Satellite cells and myogenic stem cells
Undifferentiated mononuclear cells first identified by Alexander Mauro in 1961 (from a frog)
Muscle satellite cells
Satellite cells are termed “satellite” due to their _____ position in relation to the fiber.
peripheral
Satellite cells are located between which two membranes?
The plasma membrane (proximal) and the basement membrane (distal)
Do satellite cells or myonuclei have both decreased organelle content and a smaller nuclear size?
Satellite cells
Pax7
A marker for satellite cells as it can only be found on satellite cells. It is required for satellite cell development.
Molecular markers for identifying quiescent, activated and proliferating satellite cells
MNF, Pax7, c-Met, M-cadherin, NCAM, VCAM-1
Molecular markers for identifying activated and proliferating satellite cells
Desmin, myf5, MyoD
At _____ days after the primary muscle fiber has been formed, satellite cells are present in limb muscle
18
The percentage of satellite cells in all muscle falls rapidly following _____
birth
The number of satellite cells is much greater in _____ fibers than _____ fibers
slow, fast
Why might satellite cells be more abundant in slow fibers than fast fibers?
Because slow fibers are used to greater extent and receive a greater amount of “wear and tear” and thus need more myonuclei to repair the fiber. And with greater levels of myofibers there needs to be greater satellite cell levels to replace the nuclei
Satellite cells are quiescent until activated in response to _____, _____ and _____
disease, damage, excercise
When injury or damage occurs, satellite cells are activated, enter the _____ _____ and _____
cell cycle, proliferate
Muscle precursor cells must do what before fusing to the myofiber?
Terminally differentiate
When can new myofibers form as a result of two satellite cells fusing together?
During severe disease states such as muscular dystrophy
Transplantation of one myofiber containing 7 satellite cells can give rise to _____ new myofibers
> 100
The quality of being able to divide many times is to have a high _____ _____
proliferative potential
What are the two types of cellular division that satellite cells can undergo?
Planar division and apical-basal division
Division on a horizontal plain that results in one cell maintaining contact with the basal lamina and the other losing contact
Apical-basal division
Typically generates two identical daughter cells (symmetric division)
Planar division
Division on a vertical plain that results in both cells maintaining contact with the basal lamina and the sarcolemma
Planar division
Typically generates one cell committed to becoming a myotube and another cell with proliferative potential (asymmetric division)
Apical-basal division
True or False: The majority of satellite cells that divide will differentiate and form myotubes or incorporate into existing fibers
True
Is the regenerative capacity of satellite cells limited?
Yes
Growth factors that stimulate muscle regeneration and satellite cell expansion can be produced by _____, _____ and _____ sources
autocrine, paracrine, endocrine
_____ cells typically become activated _____ hours after tissue damage
Satellite, 6
Satellite cells’ main growth factors
IGF-I & IGF-II, HGF (hepatocyte growth factor), FGF (fibroblast growth factor) and LIF (leukemia inhibitory factor)
Other factors that play a role in satellite cell activation
NO, testosterone, IL-6 (interleukin-6), PDGF (platelet-derived growth factor), and EDGF (endothelial-derived growth factor)
What are some things that can be modulated by satellite cell growth factors?
Activation, chemotaxis, proliferation and differentiation
When quiescent, do satellite cells express markers associated with myogenic potential and terminal differentiation?
No, they do not express markers such as MyoD, Myogenin, Myf5, Desmin or MHC.
Once activated, satellite cells express varying amounts of these factors at different stages of development and then are _____ altered
morphologically
What molecules are upregulated during activation of satellite cells to help with cell migration and attachment?
Adhesion molecules
Increased activity of cyclin-cdk complexes in satellite cells allows for the early regulation of _____. Then a decrease in _____ results in an increase in _____.
MyoD, MyoD, Myf5
Foxo1 is activated, which activated p21 (a cdk inhibitor). p21 inhibits cyclin E-cdk 2 preventing progression through G1
Low growth factor levels. Cell remains quiescent and does not express MyoD or Myf5
MAPK (mitogen activated protein kinase) is activated, which inhibits Foxo1. p21 is not activated and IGF-I upregulates MyoD and Myf5.
In response to growth factors. Cell enters cell cycle and proliferates.
What are the three factors that characterize differentiation in satellite cells?
A downregulation of Pax7, exiting the cell cycle, and terminal differentiation
Satellite cell differentiation occurs primarily due to:
A change in growth factor levels and type, and changes in intracellular factors that regulate proliferation and differentiation
True or False: Proliferating satellite cells express high levels of p21
False… p21 is an inhibitor of cyclin E-cdk 2 and prevents the cell from progressing through G1 phase
An inhibition of _____ and an upregulation of _____, _____ and _____ promotes differentiation
p21, MyoD, myogenin, MRF4
Various other growth factors bind receptors and increase PI3K (phosphatidylinositol) levels. PI3K upregulates MyoD, myogenin and MRF4. PI3K also activates p21.
Proliferation and cell cycle are halted and differentiation results.
Another name for GDF-8 (growth and differentiation factor-8)
Myostatin
What is myostatin and TGF-B’s role in proliferation and differentiation of satellite cells?
To inhibit satellite cell proliferation and differentiation by upregulation of cdk inhibitors (e.g. p21) and inhibition of MyoD
Activin Type IIB Receptor
The receptor associated with myostatin
At approximately 7-10 days, differentiated satellite cells mature and become incorporated into the existing _____
myocyte
Terminally differentiated myocytes express _____, _____, _____, and _____ _____
myogenin, desmin, MHC, creatine kinase
Which type of muscle shows a significant decrease in satellite cells when aging?
Type II fibers
Older satellite cells express less _____ and _____ to the same differentiation stimulus as younger cells
FOX01, p27 (a cdk inhibitor)
Older satellite cells also form fewer and smaller _____ as well as a decrease in their ability to _____
myotubes, fuse
True or False: Individuals with muscular dystrophy undergo more skeletal muscle regeneration by age 4-5 than a healthy individual of age 60
True
In muscular dystrophy overall muscle loss over time results from _____ of satellite cells
exhaustion
How could satellite cells and muscle derived stem cells be used in a therapeutic application?
The cells could be isolated by surface markers then cultured. After this cells could be exposed to appropriate conditions to promote their myogenic potential, and then transplanted.
FACS analysis
Fluorescent Activated Cell Sorter analysis
In FACS, a _____ charge is generated on the cell by the beam if it fluoresces and a _____ charge is generated if it does not
negative, positive
What issue may present when trying to use growth factors to stimulate satellite cell activation, growth, and differentiation?
Cardiac muscle may also respond
Use of a myostatin _____ or _____ may also be used to promote satellite cell activation and proliferation as well as muscle growth
blockade, knockdown
What important roles do mitochondria have?
ATP production, signalling in apoptosis (programmed cell death), regulate cellular oxidative stress, encode for some of their own proteins using their own mtDNA
True or False: Mitochondrial numbers vary greatly depending on cell type
True
Give two examples of mitochondria being located near areas of high energy demands
Mitochondria near myofibrils, and mitochondria near nucleus of rapidly dividing cell species
Basic structure of mitochondria
Outer membrane, inner membrane, space between the two membranes (intermembrane space) and a space within the inner membrane (matrix)
mtDNA (Mitochondrial DNA) was first discovered in _____
1963
The _____ of the mitochondria contains a small genome of approximately _____ base pairs
16,500
mtDNA is a double-stranded _____ molecule similar to bacteria
circular
mtDNA is very compact with only one non-coding region. Less than _____ of the genome is non-coding
6%
Unlike most nuclear genes which have _____ copies, mtDNA have _____ copies of genes
2, multiple
Is mtDNA maternal or paternal?
Maternal
Human cells can contain thousands of copies of ______ with _____ copies found per mitochondria
mtDNA, 2-10
True or False: Terminally differentiated cells can increase mtDNA and mitochondrial content
True, through a process known as mitochondrial biogenesis
mtDNA contains 13 genes needed to synthesize 13 essential _____ subunits of the _____ _____ system
polypeptide, oxidative phosphorylation
mtDNA also contains sequences for 22 _____ genes and 2 _____ genes
tRNA, rRNA
The 13 proteins encoded by mtDNA are composed of:
7 subunits for NADH dehydrogenase, 1 subunit for cytochrome c reductase, 3 subunits for cytochrome c oxidase, and 2 subunits of ATP synthase
NADH dehydrogenase (_____), cytochrome c reductase (_____), cytochrome c oxidase (_____) and ATP synthase (_____)
complex I, complex III, complex IV, complex V
True or False: Complex II is encoded by the mtDNA exclusively
False… Complex II is encoded by nDNA exclusively
The mutation rate of mtDNA is due to 4 factors:
1) no protective histone cover, 2) mtDNA repair is less efficient, 3) mtDNA has very few non-coding regions, 4) close proximity to ETC resulting in it being highly susceptible to oxidative stress
The presence of more than one type of organellar genome
Heteroplasmy
_____ can occur within or between tissues depending on how the mtDNA segregates (_____)
Heteroplasmy, replicative segregation
Percentage of _____ mtDNA to _____ mtDNA determines how serious the disease is
mutant, wild-type *ratio can range from 100:0 to 1:99
The threshold level for symptoms is usually around _____ mutation expression
70%
mtDNA mutations are most common in _____ tissues, such as the _____, the _____ and skeletal muscle because the cells cannot divide further
post-mitotic, brain, heart
What can mtDNA mutation result in?
Exercise intolerance, deafness, diabetes, or infant death
Which fiber type has the greater amount of mitochondrial content?
Slow fibers
Mitochondrial content can be increased through _____ activity and disease
contractile
Mitochondrial content can be decreased through _____ and _____
inactivity, disease
What are the two distinct types of mitochondria in muscle?
Subsarcolemma mitochondria or SS (directly below the sarcolemma) and intermyofibrillar mitochondria or IMF (interspersed between the myofibrils)
Percentage of mitochondria in skeletal muscle that are IMF? SS?
IMF = 75%, SS = 25%
Why is there a greater number of IMF mitochondria?
Because there are higher energy needs at the myofibrils than at the sarcolemma.
_____ mitochondria have a higher rate of respiration (greater rate of ATP production) and greater concentration of ATP at rest
IMF
Three properties that are differ in IMF and SS mitochondria are:
1) membrane composition, rate of ROS (reactive oxygen species) production, 3) susceptibility to apoptotic signalling
Which of the following is false? a) mitochondria originated from 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)
List 4 things that stimulate mitochondrial biogenesis
1) exercise, cold/fasting, nitric oxide, energy deprivation (exercise)
How does exercise stimulate mitochondrial biogenesis?
During exercise cytosolic calcium increases, stimulates CaMKIV, activates CREB, activates PCG-1alpha which upregulates transcription factors involved in mitochondrial biogenesis
How does cold/fasting stimulate mitochondrial biogenesis?
Activates cAMP, activates PKA, activates CREB, activates PCG-1alpha which upregulates transcription factors involved in mitochondrial biogenesis
How does NO (nitric oxide) stimulate mitochondrial biogenesis?
Activates cGMP, activates PCG-1alpha which upregulates transcription factors involved in mitochondrial biogenesis
How does energy deprivation from exercise stimulate mitochondrial biogenesis?
ATP becomes depleted and ADP levels rise, activates AMPK (to reduce ADP levels), activates PCG-1alpha which upregulates transcription factors involved in mitochondrial biogenesis
What is the main molecule that upregulates transcription factors involved in mitochondrial biogenesis and promotes fiber type switching from Type II to Type I?
PCG-1alpha
The fibers in a Tg mouse, a mouse that is overexpressing _____, become more oxidative by increasing _____, TN I (slow) and cytochrome c _____
PCG-1alpha, myoglobin, oxidase
Why are mtDNA mutations and mitochondria myopathies most frequently diagnosed in skeletal muscle?
1) high energy demands so clinical manifestations are easily noticed, 2) post-mitotic tissue so mutations can accumulate over time, 3) muscle biopsies are a frequent procedure (especially over neural biopsies)
The oxidative phosphorylation system is composed of _____ proteins. _____ are derived from mtDNA and _____ are from nDNA
90, 13, 77
True or False: Both nDNA and mtDNA mutations can disrupt oxidative phosphorylation and other important mitochondrial functions
True
Generally symptom severity is dependant on the _____ requirements of the _____ in a mitochondrial myopathy
energy, tissue
What would the muscle biopsy of a patient with mtDNA single deletion look like if the muscle was stained for SDH and COX?
There would be excessive SDH staining (enzyme from TCA cycle encoded by nDNA), but no staining of cytochrome c oxidase (composed of 3 subunits derived from mtDNA)
Why would you stain for both SDH and COX if suspicious of a mitochondrial myopathy?
Because about 1,500 mitochondrial proteins are nuclear encoded and thus you need the stain to determine whether the mutation lies within the mtDNA or the nDNA
Mitochondrial proteins that are encoded in nDNA are synthesized in what area of the cell?
The cytosol as an unfolded precursor protein
2 major chaperone proteins found in the cytosol that function to bring unfolded proteins to the mitochondria are _____ and _____
Hsp70 (heat shock protein 70), MSF (Mitochondrial Import Stimulation Factor)
What are TOM and TIM?
Translocases of the Outer Membrane (from cytosol to intermembrane space) and Translocases of the Inner Membrane (from intermembrane space to matrix)
What is the function of a translocase?
To allow for the passage of precursor proteins across a membrane
What is uncoupled respiration?
When protons leak across the inner membrane without generating ATP. Identical to normal metabolic respiration except the protons pass through UCPs (uncoupling proteins) instead of ATP synthase
Where are UCPs most prominent?
The liver and skeletal muscle
The uncoupling process can increase the metabolic rate by _____
35-45%
What are some characteristics of mice who overexpress UCP?
Increased metabolic rate and oxygen consumption. Reduced resting fat stores and increased resistance to obesity following a high fat diet
In order for _____ to be metabolized it must first enter the cell through one of several transporters (i.e. FAT/CD36)
fat
In order to be oxidized by the mitochondria, fatty acids must be _____, forming _____ _____
activated, fatty acyl-CoA
Fatty acid + ATP + CoA results in…
Fatty acyl-CoA + AMP + PPi
Where can you find the enzyme responsible for activating fatty acid? What is it called?
In the outer membrane of the mitochondria. It is called acyl-CoA synthetase.
What 4 mitochondrial proteins facilitate the transport of fatty acyl-CoA across the inner membrane?
1) carnitine, 2) carnitine palmitoyl transferase I, 3) carnitine palmitoyl transferase II, 4) carnitine acylcarnitine translocase
_____ replaces CoA in order for the fatty acid to be able enter the matrix of the mitochondria by help of CPTI
Carnitine
Responsible for translocating fatty acyl-carnitine across the inner membrane into the matrix
Carnitine acylcarnitine translocase
Once in the matrix CPTII replaces _____ for _____
carnitine, CoA
True or False: Once in the matrix fatty acyl-CoA is consumed in Beta-oxidation
True
What are VDAC, and where can they be found?
Voltage Dependant Anion Channels. They can be found in the outer membrane.
What are ANT, and where can they be found?
Adenine Nucleotide Translocators. They can be found in the inner membrane.
ANT and VDAC are both known to participate in what role?
Apoptosis
Oxidative phosphorylation capacity (i.e. the ability to produce _____) decreases in skeletal muscle with aging
ATP
What three things decrease in skeletal muscle with age?
mtDNA copies, mitochondria and ATP production (i.e. oxidative phosphorylation capacity)
