Molecular Cell Biology & Disease Flashcards
(41 cards)
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
Increased activity of CFTR
* 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
Increased activity of CFTR
* cAMP leads to phosphorylation of CFTR, opening Cl- channel
* Thus, molecules that raise cAMP regulate CFTR
18
CFTR mutations protect us from diarrhoea?
19
CTFR mutations – a potential lifesaver?
* 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
Dystrophin
provides mechanical stability to muscle
cell surface membrane
Links contractile motor proteins to
plasma membrane (sarcolemma)
21
Dystrophin
Consequences of loss:
* Increased susceptibility to muscle damage
and necrosis
* Excessive inflammatory response
* Impaired regeneration after damage
22
Dystrophin
Imbalance between damage and repair → loss of muscle fibres
and increased fibrosis → decreased functional capacity & death
23
24
Duchenne V Becker MDs
25
Duchenne V Becker MDs
26
Can we fix it?
* 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
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31
Summary
* 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
* Reading:
* http://www.cftrscience.com
* http://www.nobelprize.org/
