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Kin 3Z03 Neuromuscular Plasticity > Cell Review > Flashcards

Cell Review Flashcards

1
Q

nucleus
how many are in motoneurons
how many in muscle fiber

A
  • contains genetic info for proteins which carry out cell functions
    motoneuron has 1 in the cell body
    muscle fibers have more than one (multinucleated)
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2
Q

where is the other 1% of DNA that’s not in the nucleus found?

A

in mitochondria - it codes for 14 proteins

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3
Q

central dogma of gene expression

A
  • DNA has coding and noncoding sequences (exons and introns)

exons code for proteins

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4
Q

codon

A

3 nucleotide sequences of RNA that code for AA

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5
Q

stages of gene expression

A
  1. transcription - RNA made from DNA
  2. RNA processing - splicing of pre-mRNA to mature mRNA
  3. transport of mRNA to cytosol from nucleus
  4. translation - mRNA into AA chain
  5. post-translational modifications - affect protein behaviour
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6
Q

sites of gene expression regulation

A
  1. transcriptional control - turned up or down
  2. processing control - regulated @ nucleus
  3. transport/export control
  4. mRNA stability control - how quickly mRNA is degraded (the longer it’s there, the greater chance it has of being translated)
  5. translational control - turned on or off
  6. post-translational control with post-translational modifications
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7
Q

promoter

A

a sequence of DNA critical for controlling transcription

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8
Q

transcription start site

A
  • everything downstream is the coding region

- everything upstream is part of basal transcription machinery

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9
Q

TATA box

A
  • the promoting region of the gene where the TATA binding protein (TBP) and transcription initiation complex bind on to
  • found immediately upstream of transcription start site
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10
Q

DNA response/control elements

A

DNA sequences found before the TATA box

  • 6-12 nucleotides long
  • bind with proteins called transcription factors (facilitate transcription and are specific to a particular DNA sequence)
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11
Q

mRNA processing

A
  • promoter region removed from pre-mRNA
  • 5’ cap added to block promoter
  • 3’ poly A tail added
  • splicing - removal of introns by spliceosome
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12
Q

2 untranslated regions remain in mature mRNA
what are they?
why do they remain there?

A

5’ untranslated region and 3’ untranslated region

- are there to ensure mRNA gets translated (targets proper region of cytosol and keeps mRNA stable until then)

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13
Q

types of substitution mutations

A

one nucleotide in, one out

  • nonsense
  • conservative missense
  • nonconservative missense
  • sense
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14
Q

nonsense mutation

A

results in premature stop codon

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15
Q

conservative missense mutation

A

results in a different AA being coded for that has similar properties as the original AA

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16
Q

nonconservative missense mutation

A

results in a different AA being coded for that has different properties that the original AA
- causes a different charge or conformation of the protein

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17
Q

sense mutation

A

a different codon results in the same AA that was originally coded for
- the lowest risk mutation

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18
Q

frameshift mutation

A
  • result of insertions, deletions and inversions (sometimes)
  • changes reading frame of a gene so changes codon sequence of everything downstream
  • everything upstream is unaffected
  • resultant protein is often degraded or useless
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19
Q

examples of inheritance

A

autosomal dominant
autosomal recessive
x-linked recessive, carrier mother
mitochondrial

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20
Q

autosomal dominant inheritance
% chance of offspring presenting clinically
example

A

one parent has a single copy of the mutated gene

  • chance of offspring presenting clinically with the affected copy is 50%
    ex. myotonic dystrophy
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21
Q

autosomal recessive inheritance
% chance of offspring presenting clinically
example

A

2 copes of the affected gene are required for offspring to have the gene so both parents would have to be carriers

  • 25% chance of offspring presenting clinically with the disease
    ex. SMA
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22
Q

x-linked recessive inheritance, carrier mother

% chance of offspring and results

A

mutated gene is on the x chromosome. none of the other 22 autosomes are affected

  • mother is almost always the carrier
  • 50% chance of female offspring being a carrier
  • 50% chance of male offspring having the disorder
    ex. DMD
23
Q

mitochondrial inheritance

% chance of offspring presenting clinically

A

passed from the mother always bc all mitochondrial DNA comes from the mother

  • all children to a certain extent will present clinically with mito disorder
  • if father has mito disease, there’s no chance of offspring having the disease bc his mito DNA does not get passed onto them
24
Q

monogenic

A

a single gene results in a single disorder

ex. most mitochondrial diseases are monogenic

25
Q

extrafusal muscle fibers

A
  • innervated by alpha motoneurons

- generate force to move the skeleton

26
Q

intrafusal muscle fibers

A
  • innervated by gamma motoneurons

- modulate sensitivity of muscle spindles to stretch

27
Q

input resistance of slow oxidative MNs

A
  • SO MNs have higher input resistance therefore require less synaptic activation to initiate APs
  • will reach threshold first, based on the size principle
28
Q

upper motorneurons (UMNs) and lower motoneurons (LMNs) and their origins

A

UMNs originate in motor cortex and synapse with LMNs or alpha MNs in the brainstem or ventral horn of SC
- LMN synapse with skeletal muscle

29
Q

components of a motor unit

A

includes the alpha MN and the muscle fibers it innervates

30
Q

alpha motoneuron pool

A

represents all alpha MNs that innervate one muscle

31
Q

motor nucleus

A

all of the cell bodies of motoneurons in a motor pool

32
Q

alpha motoneuron subtypes

A

slow twitch (S)
fast-twitch fatigue resistant (FR)
fast-twitch fatiguable (FF)

33
Q

what muscle fibres do slow twitch (S) MNs innervate

A

type 1 slow oxidative fibers

34
Q

what muscle fibres do fast-twitch fatigue resistant (FR) MNs innervate

A

type 2a FOG fibers

35
Q

what muscle fibres do fast-twitch fatiguable (FF) MNs innervate

A

type 2b, 2x, 2d FG fibers

36
Q

how are characteristics of alpha MNs related to the muscle fibers they innervate?

A

they are similar morphologically

37
Q

immunofluorescence technique

A
  • following muscle biopsy muscle sample is frozen, sliced into cross sections
  • antibodies are used to identify the specificity of a molecule (they’re protein specific)
  • goal is to identify different fiber types in a sample when the antibodies fluoresce under microscope
38
Q

histochemical staining technique

A
  • uses enzymes to identify proteins (instead of antibodies)
  • looks at enzyme activity to determine probable fibre types in a muscle sample
  • isn’t as specific as immunofluorescence
39
Q

criteria to identify alpha MNs

A
  1. location - cell bodies found in ventral lateral horn of SC
  2. size of cell bodies - greater than or equal to 25um (they’re pretty big)
    - if both these criteria are met, then the cell must be an alpha motoneuron
40
Q

what technique can be used to identify muscle fiber and spinal MU type?

A

immunohistochemistry/immunofluorescence

41
Q

NeuN

A

a hormonal nuclei protein that identifies all neurons

42
Q

DAPI

A

identifies ALL nuclei of neurons and other types of cells

43
Q

CHAT

A

choline acetyltransferase

  • important for ACh synthesis
  • identifies all alpha MNs in the ventral horn
44
Q

using neuronal tracers

A
  • technique only done on animals to identify which MU work with what muscles
  • dye injected into muscle of interest and it moves up the NMJ, to the MN cell body (somata) via axonal transport
  • SC cross sections of motor nuclei region are found and only MNs that target muscle will stain positive for the dye
  • it’s good to inject different coloured tracers into different limbs when looking at multiple muscles because there’s a lot of overlap in motor columns in SC
45
Q

does muscle fiber type influence MN phenotype or is it the other way around?

A

both can happen

46
Q

SV2A

A

synaptic vesicle protein 2A

  • is found in axon terminals and is important for synaptic vesicle release
  • is found in most type 1 fibers and about half of type 2A fibers (not in type 2) so it’s a good marker of more oxidative fibers
47
Q

if we change phenotype of a muscle, does MN type also change?
how do we know?

A

yes

- viral DNA transduction test

48
Q

viral DNA transduction

what is it?

A
  • used in a study to induce muscle phenotype change
  • an innocuous virus is injected into the muscle that has been modified to carry a specific gene sequence
  • virus hijacks gene machinery and adds a gene for a protein called PGC-1α
49
Q

PGC-1α

A

a transcription co-activator
- works and cooperates w transcription factors to cause transcription
- mice that overexpress this gene develop more slow twitch oxidative fibres
therefore! this protein has the ability to change muscle phenotype independently from exercises
- ie this protein increases SV2A levels in αMNs

50
Q

viral DNA transduction technique

results of this experiment?

A
  • a small green fluorescent protein (GFP) is associated with PGC-1α virus so that wherever the virus is taken up, will fluoresce green
  • we saw that PGC-1α was effective in creating type 1 fibers
  • to see if more type 1 MNs were present, we tested for SV2A in NMJ - it was there
    results: if we have phenotype change to more type 1 fibers, we want to see more SV2A which would indicate a change to more type 1 MUs
51
Q

h

A

h

52
Q

h

A

h

53
Q

h

A

h

Kin 3Z03 Neuromuscular Plasticity (5 decks)

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