Molecular Cell Biology & Disease Flashcards
1
Q
Learning Outcomes
A
- Outline some of the major causes of molecular diseases.
- Describe the molecular causes of several example diseases
- Autophagy
- Recycling of cellular proteins, etc.
- Cystic fibrosis (and cholera)
- a mutation of a transport protein (channelopathy) and in cholera
transport itself not the problem, but control of the channel is, due to
disruption of second messenger cascade (in this case cAMP). - Muscular Dystrophies
- Mechanotransduction of motor proteins to the cytoskeleton /
membrane
2
Q
Causes of disease
A
- Genetic mutations due to heredity / radiation / chemical
- Infectious agents (animals, fungi, bacteria, viruses, prions)
- Chemical agents (drugs, industry, heavy metals)
- Direct trauma
- And these can affect…
- Structural molecules of cells
- Enzymes & Biochemical Pathways Cell Signalling/Regulation
- Cell Membrane Transport
- Many of the above and more …….
3
Q
Problems…
A
- Structural molecular problems
- Genetic etc.
- Prions (mad cow’s disease / KJS in humans / Parkinson’s)
- Chemical denaturation (industrial exposure)
- Overstimulation (e.g. temporary hearing loss & receptor protein
change)
4
Q
Problems…
A
- Cell membrane transport problems
- Channelopathies (e.g. congenital deafness, cystic fibrosis, heart
diseases) - Problems with regulation of membrane transport (e.g. diarrhoea,
cholera)
4
Q
A
the 2016 Nobel Prize in Physiology
or Medicine
Yoshinori Ohsumi
“for his discoveries of mechanisms
for autophagy”
5
Q
Problems…
A
- Cell signalling problems
- Neurochemical release & reuptake (e.g. mental illness/drug
intoxication) - Intracellular second messenger problems (e.g. cholera)
- Hormonal Imbalance (secretion, reception – e.g. gigantism,
dwarfism) - Other problems with pathways for cell signals & reception (e.g.
cancer)
5
Q
Problems…
A
- Enzyme function problems
- Turning enzymes on via regulatory pathways
- Turning enzymes off via regulatory pathways
- Blocking enzymatic pathways
- Absence of enzymes
5
Q
Autophagy – “self eating”
A
- Autophagosomes are transient membranous orgnls
- They form, then engulf cellular contents, such as damaged proteins
and organelles. - Fuses with the lysosome, where the contents are degraded into
smaller constituents.
6
Q
Autophagy – “self eating”
A
- Lysosomes contain enzymes for digestion of cellular
contents.
7
Q
Autophagy – “self eating”
A
- Clears old/damaged proteins
and provides the cell with
nutrients and building blocks
for renewal.
8
Q
A
- Microautophagy:
- Lysosome itself engulfs small components of the cytoplasm by inward
invagination of the lysosomal membrane.
8
Q
A groundbreaking experiment!
A
- Ohsumi used yeast cells where vacuoles are lysosomes
- If he could disrupt the degradation process in the vacuole while the
process of autophagy was active, then autophagosomes should
accumulate within the vacuole - Cultured mutated yeast lacking vacuolar degradation enzymes and
simultaneously stimulated autophagy (starvation) - Ohsumi then studied thousands of yeast mutants and identified 15
genes that are essential for autophagy
8
Q
A
- Macroautophagy (dominant):
- An isolation membrane (phagophore) sequesters a small portion of the
cytoplasm, including soluble materials and organelles, - Now called an autophagosome → fuses with the lysosome (autolysosome)
- Degrades materials contained within it.
9
Q
Mechanisms of Autophagy
A
- 3 classes: macroautophagy, microautophagy, and chaperonemediated autophagy.
9
Q
A
- Chaperone-mediated autophagy.
- Proteins directly translocate across the lysosomal membrane during
chaperone-mediated autophagy. The chaperone protein Hsc70 (heat shock
cognate 70) recognize proteins, Lamp-2A acts as a receptor on the lysosome,
and unfolded proteins are delivered into the lysosomal lumen through a
translocation complex.
10
Q
A
11
Q
A
12
Q
2007
A
- Mario Capecchi, Martin Evans, Oliver Smithies
- CFTR-/- homozygotes display defective chloride transport in epithelia
of airways and intestines, failure to thrive, meconium ileus, and
pathological alterations of gastrointestinal glands. - First to create a model of a human disease by gene targeting in mice.
13
Q
Cystic fibrosis → CFTR gene
A
- Malfunction in the exocrine system
(saliva, sweat, tears, and mucus) - Develop an excessively thick mucus
within the lungs and GIT - Impairs digestive and respiratory
function, leading to irreversible
damage (lung failure). - Cause? A defect in a Cl-membrane
transport protein (CFTR gene)
13
Q
CFTR mutation affect function or production
A
- Class I
- Defective CFTR protein synthesis
- Class II
- Defective post-translational processing &
trafficking - Class III
- Defective gating
- Class IV
- Defective conductance
- Class VI
- Reduced protein stability
- Class V
- Reduced synthesis (splicing defect →
nonsense mediated decay
14
Q
Loss of CFTR function manifests cystic fibrosis
pathophysiology
A
15
Q
CFTR gating
A
- Opening
- cAMP activates PKA, phosporylates R-domain, allows Cl- to pass out
down its concentration gradient - Closing
- Protein phosphatases (PPases) remove phosphates from R-domain,
channel closes
15
Q
A
16
Q
CFTR gating
A
17
Q
Increased activity of CFTR
A
- Secretatogogues
- raise cAMP level in gut cells
- Copious Clsecretion leads to copious water secretion, 10-
20 L/day, death from dehydration likely - Na+
/glucose co-transporter not affected so oral
rehydration with sugar and salt solution life-saving
17
Q
Increased activity of CFTR
A
- cAMP leads to phosphorylation of CFTR, opening Cl- channel
- Thus, molecules that raise cAMP regulate CFTR
18
Q
CFTR mutations protect us from diarrhoea?
A
19
Q
CTFR mutations – a potential lifesaver?
A
- Dehydration by enterotoxin-induced secretory diarrhoea is
the single largest cause of death in the Developing World - Suggested that those with one CF allele may have advantage
with cholera: they are less susceptible to enterotoxininduced diarrhoea - Maximal secretion rates lower for CF sufferers & so
dehydration slower than normal with cholera - Study showed Salmonella typhi enter GIT cells via CFTR.
CFTR mutants internalise fewer bacteria!
20
Q
Dystrophin
A
provides mechanical stability to muscle
cell surface membrane
Links contractile motor proteins to
plasma membrane (sarcolemma)
21
Q
Dystrophin
A
Consequences of loss:
* Increased susceptibility to muscle damage
and necrosis
* Excessive inflammatory response
* Impaired regeneration after damage
22
Q
Dystrophin
A
Imbalance between damage and repair → loss of muscle fibres
and increased fibrosis → decreased functional capacity & death
23
Q
A
24
Q
Duchenne V Becker MDs
A
25
Q
Duchenne V Becker MDs
A
26
Q
Can we fix it?
A
- Yes, we can! (sort of, some times, and not entirely… )
- Skip the mutated exon? Short protein, but functional (like Becker MD)
- Exon-skipping designer oligonucleotide drugs – Eteplirsen
- Quite literally, this - CTCCAACATCAAGGAAGATGGCATTTCTAG
27
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A
28
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A
29
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A
30
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A
31
Q
Summary
A
- Outline some of the major causes of molecular diseases.
- Describe the molecular causes of several example diseases
- Autophagy
- Protein recycling that is essential to cellular function
- Cystic fibrosis (and cholera)
- a mutation of a transport protein (channelopathy) and in cholera transport
itself not the problem, but control of the channel is, due to disruption of
second messenger cascade (in this case cAMP). - Muscular Dystrophies
- Mechanotransduction of motor proteins to the cytoskeleton/membrane
32
Q
- Reading:
A
- http://www.cftrscience.com
- http://www.nobelprize.org/
