biochem Flashcards
1
Q
major electrolytes in body?
A
Na +and Cl -are the major electrolytes in the ECF
• K + and phosphates (HPO4 2- ) are the major electrolytes in cells
2
Q
when does water move out of the cell?
300 is the plasma level
The loss of cellular water can occur in hyperglycemia because the high concentration of glucose increases the osmolality of the blood. - WATER FOLLOWS
A
When the osmolality of the blood or interstitial fluid is too high, water moves out of the cells.
3
Q
PH of pure water?
A
7 - anything under 7 is acidic
4
Q
Do strong or weak acids disassociate more rapidly
A
strong - and they dissassociate completely
5
Q
Ketone bodies?
A
Organic acids containing carboxylic acid groups (the ketone bodies) are weak acids that dissociate to only a limited extent in water
6
Q
Acidic drugs are best absorbed where?
Drugs are absorbed in there uncharged forms
most drugs are weak acidic or weak bases
A
stomach ASPIRIN (stomach pH = 1-2) - vs basic (intestine) MORPHINE 7.9
7
Q
pH of blood?
A
7.36 and 7.44, and intracellular pH at approximately 7.1
8
Q
how is acid excreted from the body?
A
CO 2in expired air and as ions in the urine, it needs to be buffered in the body fluids.
9
Q
Acid produced everyday?
Body produces a LOT of acid - must be neutralized - or have a problem - pH will go wacky
A
Volatile acid:
Carbon dioxide (CO2 ) – major metabolic acid (22,000mmol/day)
• Nonvolatile acids (40-80 mmol/day)
10
Q
Three types of buffers - first line of defense
A buffer exhibits maximum buffering capacity, when pH=pKa:
A
bicarb, phosphate, protein
A buffer is usually effective at a pH = pKa ±1 ✮
Major buffer systems in the body:
- Bicarbonate-carbonic acid buffer (ECF buffer)
- The most important buffer of the plasma - Proteins (ICF and plasma RBC) - due to histidine residues Hemoglobin (red blood cells) – due to histidine residues
- Phosphate buffer (ICF and urine buffer)
- Ammonia (urine)
11
Q
regulating pH - what does respiratory system reg, vs renal?
A
respiratory - co2,
renal - HCO 3
12
Q
Buffers - how do they change with pH change?
A
As the pH of a buffered solution changes from the pKa to 1 pH unit below the pKa , the ratio of [A- ] to HA changes from 1:1 to 1:10. If more hydrogen ions were added, the pH would fall rapidly because relatively little conjugate base remains.
13
Q
carbonic anhydrase?
This buffer system is more complex than others, because carbonic acid (H2CO3) is formed from dissolved CO 2 which produced in tissues and diffused to plasma).
• The pKa of the bicarbonate buffer is 6.1 (close to the plasma pH of 7.4)
A
CO dissolves in water by Carbonic anhydrase to form the weak acid, carbonic acid (H2 2 CO 3 )
Carbonic anhydrase
Dissociation
CO 2 + H2 O
H2 CO3
HCO3 −
+
H+
14
Q
The bicarbonate: carbonic acid ratio in blood at physiological pH is 20:1 and the pKa value is
6.1, both significantly different from the ‘ideal’.
A
However, two factors contribute in making the bicarbonate: carbonic acid pair effective in blood at physiological pH:
- It is present in high concentrations in blood.
- It is an open system, that can be regulated by two mechanisms: by the excretion of CO 2 via the lungs and by the regulation of the rate of reclamation of HCO 3 − in the r
15
Q
Shift to the right, left?
A
Co2 accumulate - shift equilibrium to right
16
Q
Hemoglobin as a Buffering Agent
Released protons take part in the formation of salt bridges between globin chains of Hb, and lead the change in the conformation of Hb molecule in tissue capillaries.
A
The most important buffer groups of Hb are histidines. Each globin chain contains 9 histidine.
• 95 % of CO 2 which is released from tissues to plasma is diffused into erythrocytes.
17
Q
respiration and ph?
A
when pH falls, respiration increases - washing out the extra CO2
when pH rises - respiration slows, retaining CO2
18
Q
Renal control of acid-base balance
A
The kidneys also play a major role in controlling acidbase homeostasis through their ability to recover filtered HCO 3 − and to generate HCO3 − . It is during HCO 3 − generation that H + ions are excreted.
- Bicarbonate recovery
- By this mechanism HCO3− is not lost.
- Bicarbonate generation
19
Q
phosphate buffer system?
High concentrations of phosphate are prevalent in bone and the intracellular fluid. This is significant in some acidotic states when phosphate can be released from the bones and act as a buffer in the plasma.
A
ECF - and kidneys - but as there isn’t much phosphate in body, not a very good buffer, even though the pK is ideal (6,8)
20
Q
normal PH, PCO2, and HCO3 levels?
A
Normal levels:
– pH: 7.35-7.45 (arterial)
– PCO2 : 35-45 mmHg
– HCO3 - : 22-26 mmol/L
21
Q
Acidaemia - excess H +in the arterial blood, when the resulting pH is less than 7.35
• Alkalaemia - too few H + , with a pH greater than 7.45
A
The causes of these disturbances may be due to:
- Respiratory disorders, with a primary change in PCO2 , due to dysfunction of the respiratory system
- Metabolic (non-respiratory disorders), which initially cause changes in the concentration of HCO3 − , due to metabolic or renal disorders
22
Q
if respiratory problem -
A
renal system compensates, and vice versa
23
Q
Metabolic acidosis - HCO3 is down - pH down
causes:
- Increased production of non-volatile acids:
- Diabetic ketoacidosis (increased ketone body production)
- Lactic acidosis (increased lactate production)
- Chronic renal failure (decreased excretion of sulfate, phosphate)
- Increased loss of HCO 3 - (base):
- Diarrhea (increased loss of HCO 3 - rich intestinal secretions)
- Renal tubular acidosis (failure to secrete H + and reabsorb HCO3 - , aldosterone deficiency or impaired response to aldosterone in the distal tubule)
A
Acute stage: In the acute stage:
– pH is decreased (<7.36)
– PCO 2 is almost normal(<40mmHg)
[HCO3 - ] is decreased (primary abnormality)
24
Q
Metabolic acidosis - compensation?
Until the cause of acidosis is treated, pH does not come back to normal
In the compensated stage, ✮ (clinically more commonly observed) pH is lower than normal (<7.36) - closer to normal pH, when compared to acute stage
PCO 2 is decreased due to compensatory hyperventilation (<35mmHg)
[HCO 3 ] is decreased (primary abnormality)
A
breathing - increased rate of respiration (Kussmaul respiration) → Increased washout of CO2 → ↓↓ PCO2 ✮
If the renal system is functioning, the renal system can also compensate to increase H+ excretion, increase the formation of new HCO3-.
25
metabolic alkalosis - HCO goes up - why?
Causes of metabolic alkalosis:
* Vomiting
* pyloric stenosis resulting in vomiting
* Loss of acidic contents of the stomach, results in relative HCO3- excess.
* Nasogastric suction.
* Excessive consumption of antacids
* Renal loss of H + (Cushing’s disease, bilateral adrenal hyperplasia)
In the acute stage, (clinically, may not be observed)
– pH is increased (greater than 7.44)
– [HCO3 - ] is increased (greater than 25mmol/L) (primary abnormality)
– PCO 2 is almost normal
26
compensation - metabolic alkalosis?
pH is higher than normal (closer to normal pH, when compared to acute stage) ü[HCO 3 - ] is increased (primary abnormality) üPCO 2 is increased (compensatory mechanism)
27
Respiratory acidosis - hypoventilation
CO 2is NOT washed out resulting in elevation of PCO 2(primary abnormality)
In the acute stage:
üpH is decreased (lower than 7.36) üPCO 2 is elevated (primary disturbance) üHCO 3 - is almost normal
Why? Clinical causes:
* Drugs that inhibit the respiratory center (opioids)
* Diseases/ injury of the phrenic nerve (supplies diaphragm)
* Lung diseases like chronic obstructive pulmonary disease, fibrosis of the lung, respiratory distress syndrome in premature infants
* Obstruction to the respiratory tract – due to foreign body in trachea
increased arterial PCO 2(hypercapnia), which decreases the [HCO3 − ] / PCO 2 ratio. The underlying problem is due to CO2 retention, as a result of hypoventilation.
28
compensation - respiratory acidosis
pH is lower than normal (<7.36) - closer to normal pH, when compared to acute stage
PCO2 : Elevated (as the primary defect is still not corrected – respiratory system is still not functioning optimally)
[HCO3 - ]: Elevated (due to renal compensation)
During compensation, the renal system comes to the rescue
* Kidneys excrete more H+ , and generate more HCO3 - , and thus the [HCO3 - ] levels increase
* The excretion of phosphate and ammonia in urine increase
29
Respiratory alkalosis
increase in rate of respiration → increased washout of CO 2 → ↓↓PCO 2 (primary disturbance)
Causes of hyperventilation
* Anxiety
* Fever
* Hysteria
* Hypoxia (high altitude) stimulates the respiratory center and increases the rate of respiration. When a person stays for a long time at the high altitude, the compensatory mechanisms are active and [HCO3 - ] levels fall
• Mechanical ventilation
✮
In the acute stage:
– pH is increased (<7.44)
– PCO 2 is ↓↓ (<35mmHg)
– [HCO3 - ] is almost normal
30
compensation respiratory alkalosis
In the compensated phase ✮ :
– pH is higher than normal - closer to normal pH, when compared to acute stage
– PCO2 : Decreased (as the primary defect is still not corrected – respiratory system is still hyperventilating)
– [HCO3 - ]:Decreased(due to renal compensation)
renal system tries to bring the pH back towards normal
• The kidneys do NOT secrete H + into urine
31
saME - MEtabolic
REverse - REspiratory
Look only at pH and CO2
if pH is UP and co2 is UP - - metabolic alkalosis
if pH is UP and co2 is DN - respiratory alkalosis
if pH is DOWN and co2 is DOWN - - MET Acidosis
if PH is Down and co2 is UP - Respiratory Acidosis
32
Glycine -
smallest (great for tight helixes, turns
no assymetric carbon atom
33
peptide bonds
produces molecule of water -
carboxyl group of one amino acid and the amino group of the incoming amino acid combine and release a molecule of water.-
links two consecutive alpha-amino acids from C1 (carbon number one) of one alpha-amino acid and N2 (nitrogen number two) of another along a peptide or protein chain
34
What do introns and exons do?
Introns and exons are nucleotide sequences within a gene. Introns are removed by RNA splicing as RNA matures, meaning that they are not expressed in the final messenger RNA (mRNA) product, while exons go on to be covalently bonded to one another in order to create mature mRNA.
35
polycistronic v monocistronic
prokaryotes - mRNA carries more than one gene
monocistronic - eukaryotes - carries message for only one gene
36
types of RNA
3 main classes:
Ribosomal RNA – rRNA
Messenger RNA – mRNA
Transfer RNA – tRNA
```
Other:
Small nuclear RNAs – snRNAs
MicroRNAs – miRNAs
Small interfering RNAs – shRNAs, siRNAs
Heterogeneous nuclear RNA – hnRNA
```
Ribozymes - RNAs with catalytic activity. Ribozymes function during protein synthesis, in RNA processing reactions, and in the regulation of gene expression.
37
when is mRNA formed?
after processing of heterogeneous nuclear RNA
hnRNA (heterogenous nucleus RNA)
25% make it through
38
tRNA
clover leaf like structure. The structure is stabilized by hydrogen bonding
carry amino acids to ribosomes and recognizes the genetic code (codon) sequence on an mRNA
39
tRNA acceptor arm at 3' - at the OH end -
the 5' end has the phosphate
CCA can carry amino acids
40
T arm, D arm, variable arm
. T-arm
contains the TΨC (riboThymidine, pseudouridine, cyTidine) sequence necessary for tRNA-ribosome binding. T arm Tethers tRNA molecule to ribosome.
4. D-arm
contains Dihydrouridine residues necessary for tRNA recognition by the correct aminoacyl-tRNA synthetase. D-arm Detects the tRNA by aminoacyl-tRNA synthetase
5. Extra arm or Variable arm
41
Small nuclear RNA - splicing
snRNAs - in nucleus,
splicing nhRNA to create mature mRNA
U1, U2, U5, and U4/U6 particles
snurps are bound to the snRNAs
42
Small Nucleolar RNAs
process rRNA
often resulting in the methylation and pseudouridylation of specific nucleosides in nucleolus.
43
MicroRNAs and siRNAs (Small Interfering RNAs) were first defined by their participation in RNA interference (RNAi)
After being transcribed miRNA undergoes processing in the nucleus to form a double-stranded precursor that is then exported into the cytoplasm. There, the precursor is cleaved into a short RNA helix by a ribonuclease protein called dicer. The individual strands are then separated and incorporated into RNA-induced silencing complex (RISC). This multiprotein complex uses its associated miRNA as a template to bind to complementary sequences found on target mRNAs. An exact match generally results in mRNA degradation, but a partial match also causes translational repression by preventing ribosome and transcription factor binding
may have evolved as a defense mechanism against double-stranded RNA viruses.
are small, conserved, noncoding RNA molecules that posttranscriptionally regulate gene expression by targeting the 3′untranslated region ✮ of specific mRNAs for degradation or translational repression.
Abnormal expression of miRNAs contributes to certain malignancies (eg. by silencing an mRNA from a tumor suppressor gene). For example, the species miR-155 is enriched in B cells derived from Burkitt's lymphoma, and its sequence also correlates with a known chromosomal translocation
44
Folding proteins
what are actin and myosin made of?
Proteins
Muscles are composed of two major protein filaments: a thick filament composed of the protein myosin and a thin filament composed of the protein actin. Muscle contraction occurs when these filaments slide over one another in a series of repetitive events.
45
Translation
is not the synthesis of single amino acids, but adding of existing amino acids to growing polypeptide chain (peptide bonds)
46
how are amino acids made?
Amino acids used for translation can be:
Synthesized in our body by from other molecules (non essential AA)
Digested with foods (essential AA)
47
suffering from lack of protein? calories?
Kwashiorkor (Protein malnutrition)
| Marasmus (Total calorie malnutrition)
48
Pyridoxal-P (B6-P)
transports AA into tissue
49
what else moves or stimulates AAs to travel??
Hormones
Insulin, growth hormone and testosterone favour the uptake of amino acids by tissues (anabolic hormones).
Estradiol stimulates selectively their uptake by uterus.
Epinephrine and glucocorticoids: Stimulate the uptake of amino acids by the Liver.
50
Cystinuria COLA - transporter defective
Genetic -
the amino acid cystine builds up and forms stones instead of going back into the bloodstream.
One transporter is responsible for active transport of Cysteine, Ornithine, Lysine, and Arginine (COLA) and is responsible for the reabsorption of these amino acids by the kidney, and absorption by intestine
In the inherited disease cystinuria, this transporter is defective and all 4 amino acids occur in urine, intestinal absorption is also impaired
Common 1:7000
kidney stones and block the urinary tract – stones can damage kidneys and nearby organs – death possible – oral hydration is important
Cysteine molecules are not filtered by the kidney can be oxidized in urine to form cystine
These form hexagonal white crystals, which grow into pink or yellow stones
51
Hartnup
Pellagra symptoms - (may not be niacin deficiency alone!)
sunlight, fever, drugs and stress and preceded by poor nutrition
Autosomal recessive disease affecting the SLC6A19 gene – defective absorption of neutral amino acids, incl., tryptophan (a precursor of serotonin, melatonin and niacin)
The majority of patients are clinically normal despite the defect in the uptake of several essential amino acids
Infant form – photosensitivity, intermittent ataxia and tremor
Later, dermatitis, dementia and diarrhea (Pellagra-like dermatosis) – provoked by sunlight, fever, drugs and stress and preceded by poor nutrition
Attacks diminish with age
52
Melatonin – from Tryptophan
circadian rhythms and puberty
53
Chaperones
Chaperonins are cylindrical protein complexes that contain chambers in which newly synthesized polypeptides can fold without interference from other macromolecules in the cell
function in many cell compartments, including the endoplasmic reticulum
Not all proteins are able to fold themselves
Chaperones promote the correct folding
Chaperones also help unfolded or misfolded proteins achieve their proper three-dimensional conformation
stabilize unfolded proteins, unfold them for translocation across membranes or for degradation, and/ or to assist in their correct folding and assembly.
54
what does heat do to folding?
Exposure of cells to heat shock or other forms of physiological stress elevates the level of misfolded proteins.
55
HSP 60, 70, 90, 100?
60 barrel
Hsp 60 system - barrel shape
Required for correct folding of cellular proteins that do not fold spontaneously
Refolding a protein after it has crossed a cellular membrane
Hsp 70 system - ATPase - stabilization of extended chains, membrane translocation, regulation of the heat shock response
90 very important
Hsp 90 - binding and stabilization/regulation of steroid receptors, protein kinases, Buffer for genetic variation
Hsp100 - thermotolerance, proteolysis, resolubilization of aggregates
56
Four levels of folding - what level do all proteins reach?
2 - helix or sheet - energetically stable structure - some (like collagen) have different shape
HYDROGEN BONDS
An individual protein may contain both types of secondary structures. Some proteins, like collagen, contain neither but have their own more characteristic secondary structures.
57
3, 4 levels of folding?
3 - shape of the protein as a whole (globular, fibrous)
heat or urea disrupt tertiary structure to denature proteins, causing loss of function.
4, interactions among subunits. Hemoglobin
Tertiary—positioning of the secondary structures in relation to each other to generate higher-order three-dimensional shapes (the domains of the IgG molecule are examples). Tertiary structure also includes the shape of the protein as a whole (globular, fibrous). Tertiary structures are stabilized by weak bonds (hydrogen, hydrophobic, ionic) and, in some proteins, strong, covalent disulfide bonds. Agents such as heat or urea disrupt tertiary structure to denature proteins, causing loss of function.
Quaternary—in proteins such as hemoglobin that have multiple subunits, quaternary structure describes the interactions among subunits.
58
Primary structure
two types of bond
peptide (peptidyl transferase)
disulfide
polypeptide backbone - includes disulfide bonds
```
Primary structure ultimately determines:
Higher levels of structure✮
Protein Function✮
Amino acid sequence is specific
Coded by gene✮
```
59
what controls peptide bonds?
peptidyl transferase
Amide linkage between the carboxyl group of one amino acid and the -amino group of another
Formation is controlled by enzyme peptidyl transferase (large ribosomal subunit)
60
disulfide bonds
(Inter chain and intrachain) – a covalent linkage between 2 cysteine residues to form a cystine
61
large ribosomal subunit?
(peptidyl transferase)
I think this is what she was always drawing - what about the smaller one?
62
peptide bond?
carboxyl group of one molecule reacts with the amino group of the other molecule, releasing a molecule of water (H2O).
Uncharged but polar - can participate in Hydrogen bonding
Shows Electronic resonance
Has a partial double bond character
No freedom of rotation
Rigid and planar - All 6 of the atoms O, C, N, H are coplanar
Generally a trans bond -Because of the steric interference of the R-groups when in the cis position
63
naming peptides?
N terminal LEFT
Free amino end of the peptide chain (N-terminal) is written to the left
Free carboxyl end of the peptide chain (C-terminal) is written to the right
All amino acid sequences are read from the N- to the C-terminal end of the peptide
64
Sickle cell anemia problem?
A genetic mutation leading to one incorrect amino acid substitution in a protein comprising thousands of amino acids can result in that protein having a different shape and little or even no biological activity✮
Eg. sickle cell disease ✮
65
Marfan's - ADominant
15, Fibrillin - stabilizes elastin
defective connective tissue
mutations in the FBN1 gene on chromosome 15 for the highly α-helical fibrillary protein fibrillin, which is a major component of microfibrils found in the extracellular matrix.
Fibrillin – is a glycoprotein that forms a sheath around elastin.
Patients have defective connective tissue, particularly in the ligaments and aorta.
Marfan’s – Auto DOMINANT – Lincoln was Famously Dominant! – our 15th President (not really!)
Fibrillin is effected (not elastin) –Fibrillin stabilizes elastin
Chromosome 15
66
Fibrillin
– is a glycoprotein that forms a sheath around elastin.
67
clinical manifestation of Marfan?
Clinical manifestation:
excessively long extremities and fingers (Arachnodactyly)
Pectus carinatum (more specific) or pectus excavatum;
hypermobile joints
predisposition to dissecting aortic aneurysms and valvular disease:
cystic medial necrosis of aorta
aortic incompetence and dissecting aortic aneurysms
mitral valve prolapse LOUD heart murmurs
dislocation of the lens (typically upward and outward and temporally)
NO mental retardation (similar diseases do)
68
proteases
Enzymes that hydrolyze peptide bonds
69
2dary structure
The two regular secondary structures:
a-helix
b-sheet pleated
Collagen exception
linking the carbonyl and amide groups of the peptide bonds by means of hydrogen bonds (H-bonds) HYDROGEN bonds in 2dary structures ONLY
Folding of polypeptide chain along a single axis
70
Alpha Helix
right handed, most stable
Each peptide bond forms 2 H-bonds:
One to the peptide bond of the 4th residue above
One to the peptide bond of the 4th residue below
common secondary structural element of:
globular proteins
membrane-spanning domains
DNA-binding proteins
Right-handed
A rigid, rod-like structure
The lowest energy and most stable conformation for a polypeptide chain
Forms spontaneously
Peptide bond planes are parallel to the axis of the helix
Stability arises from the formation of the maximum possible number of H-bonds
R groups extend outward
71
Alpha helix
GLYCINE -
(To make tight helix- glycine or SMALL AA used – allows it to be wound properly)
or form tight turns
H-bonds are formed between:
Each carbonyl oxygen atom of a peptide bond and the hydrogen attached to the amide nitrogen of the peptide bond 3.6 amino acid residues further along the polypeptide chain
Each peptide bond forms 2 H-bonds:
One to the peptide bond of the 4th residue above
One to the peptide bond of the 4th residue below
Destabilized by the presence of proline “IMINO ACID” ✮
A helix breaker – may see helix – break - helix (break by proline)
Its ring structure exerts geometric constraint
The nitrogen in the peptide linkage does not contain the H atom required to form H-bonds
72
Breaker of helix bonds?
proline “IMINO ACID” ✮
A helix breaker – may see helix – break - helix (break by proline)
Its ring structure exerts geometric constraint
The nitrogen in the peptide linkage does not contain the H atom required to form H-bonds
73
Beta pleated sheet
Composed of 2 or more peptide chains or segments of polypeptide chains that are arranged either parallel or anti-parallel to each other
Stability arises from the formation of the H-bonds
(To make tight helix- glycine or SMALL AA used – allows it to be wound properly)
Two separate chains – or long chain – makes a U turn
Antiparallel strands are often the same polypeptide chain folded back on itself, with simple hairpin turns or long runs of polypeptide chain connecting the strands.
74
Beta pleated sheet ✮ At turns
– glycine and proline
75
a-Helices and b-pleated sheets are patterns of regular structure
bends, loops, and turns are irregular secondary structures that do not have a repeating element of hydrogen bond formation.
They are characterized by an abrupt change of direction and are often found on the protein surface.
76
Proline and glycine
likely used at turns – proline breaks the helix, glycine allows the tight turn
77
Beta bends
. Beta bend (reverse turn, beta turn) ✮
For example, b-turns are short regions that usually involve four successive amino acid residues.
They often connect strands of antiparallel b-sheets
Make a tight 180°turn
Allow the polypeptide chain to abruptly reverse its direction
Help to form a compact, globular shape
Surface of proteins-Charged residues
Generally composed of :
Glycine – has the smallest R group
Proline – causes a kink in the polypeptide chain
78
PRION disease
folding problem -
mad cow
Creutzfeldt Jacob
not known what causes - the abnormal three-dimensional structure is suspected of conferring infectious properties, collapsing nearby protein molecules into the same shape
misfolded proteins with the ability to transmit their misfolded shape onto normal variants of the same protein
They characterize several fatal and transmissible neurodegenerative diseases in humans and many other animals
Prion variants of the normal prion protein (PrPc), whose specific function is uncertain, are hypothesized as the cause of transmissible spongiform encephalopathies (TSEs), including scrapie in sheep, chronic wasting disease (CWD) in deer, bovine spongiform encephalopathy (BSE) in cattle (commonly known as "mad cow disease") and Creutzfeldt–Jakob disease (CJD) in humans.
79
Normal Prion proteins
regulated cell death, communication between neurons, sleep patterns, long-term memory, stem cell renewal, immunity
Normal Prion proteins (PrPc)
May be involved to the regulated cell death, communication between neurons, sleep patterns, long-term memory, stem cell renewal, immunity
found throughout the body
mainly alpha-helical structure (three ⍺-helices and two β –sheets)
binds copper (II) ions with high affinity
sensitive to proteolysis
80
Prion disease
Beta sheets - higher proportion
Resistant to standard sterilizing procedures
survive in soil for many years
form plaques
Mutated (PrPsc, PrPr): something wrong with hydrogen bonds
triggers the production of more pathologic variants in a conformational chain reaction
protease-resistant
Aggregations of these abnormal isoforms form highly structured amyloid fibers, which accumulate to form plaques
Resistant to standard sterilizing procedures
survive in soil for many years
81
types of prion disease
Prion variants of the normal prion protein (PrPc), whose specific function is uncertain, are hypothesized as the cause of transmissible spongiform encephalopathies (TSEs), including scrapie in sheep, chronic wasting disease (CWD) in deer, bovine spongiform encephalopathy (BSE) in cattle (commonly known as "mad cow disease") and Creutzfeldt–Jakob disease (CJD) in humans.
82
Creutzfeldt-Jakob Disease, Classic (CJD):
consumption of beef or beef products
Fatal w/in 2 year
a neurodegenerative disorder
rapidly progressive and always fatal
death usually within 1 year of onset of illness
consumption of beef or beef products containing prion particles(brain)
memory problems, behavioral changes, poor coordination, and visual disturbances, dementia, involuntary movements, blindness, weakness, and coma
83
prion -
kuru - Papua New Guina
Fatal insomnia
very rare, funerary cannibalism
Fore people of Papua New Guinea
body tremors
pathologic bursts of laughter
84
Fatal insomnia
– 100 Years of Solitude Book:
rare disorder that results in trouble sleeping
start out gradually and worsen over time
speech problems, coordination problems, and dementia
death within a few months to a few years
85
Amyloidosis
alzheimers and 17 other described diseases
Beta sheets
Characterized by the formation, accumulation and deposition of highly-organized insoluble fibrillar aggregates amyloid fibrils, consisting of β-pleated sheet- Amyloids
a general term describing diseases caused by accumulation of amyloid
eg. alzheimers and 17 other described diseases
Creates Plaque and tangles
86
Alzheimer's
amyloid precursor protein (APP or bAPP) – extracellular
Amyloid plaques in gray matter:
tau protein - neurofibrillary tangles
most common adult onset neurodegenerative disorders.
Responsible for 100,000 deaths/yr. in the United States
Has a variable clinical picture with onset usually in the sixth to ninth decade of life
etiology is unknown
Caused by:
formation of plaques, made of beta-amyloid (Ab), a protein fragment snipped from a larger protein called amyloid precursor protein (APP or bAPP) – extracellular
Amyloid plaques in gray matter: cerebral extracellular spaces in the brain contain the Ab peptide and other proteins
accumulation of tau protein - neurofibrillary tangles - intracellular
Hyperphosphorylated forms of Tau protein comprise the neurofibrillary tangles that are found within certain neurons (intracellular).
87
beta-amyloid (Ab):
an integral membrane protein
an integral membrane protein
The native biological role of APP:
The most-substantiated role for APP is in synaptic formation and repair
Anterograde neuronal transport (Molecules synthesized in the cell bodies of neurons must be conveyed outward to the distal synapses)
βAPP and all associated secretases are expressed early in development and plays a key role in the endocrinology of reproduction
beta-amyloid (Ab):
Proteolytic cleavage of bAPP results in the generation of an Ab peptide of either 40 or 42 amino acids.
Mediated by the proteases b-secretase and g-secretase
The Ab42 peptide is considered the most neurotoxic.
Cleavage by a third protease - a-secretase - prevents formation of Ab as it digests the protein within the Ab peptide.
88
NB! Smooth muscle relaxation by PSNS is through indirect effect of Ach!!!
Ach -> M receptor in the endothelium -> activation of phospholipase C -> DAG+IP3, Ca++ -> activates NO (nitric oxide) synthase -> synthesis of NO (gas) -> defuses into smooth muscle -> activation of specific signaling cascade
Meaning??
89
Alport syndrome - type IV collagen -
and Goodpastures - autoantibodies
is a disease that damages the tiny blood vessels in your kidneys. It can lead to kidney disease and kidney failure. It can also cause hearing loss and problems within the eyes. Alport syndrome causes damage to your kidneys by attacking the glomeruli.
90
tropocollagen
is (biochemistry) a component of fibres of collagen in which three polypeptide chains are coiled around each other.
91
what creates different types of collagen?
Combination of ɑ-chains forms different collagen types
92
Alpha helix of collagen
primary structure
glycine - main
proline - structural support
Lysine - binds carbs - hydroxylysine
93
secondary structure -
winds 3 together - superhelix - H bonds
winding of three alpha helixes
left-handed polypeptide helices, that are twisted around each other, forming a rope-like right-handed superhelix structure
Stabilized by H-bonds between individual polypeptide chains ✮
Helices with approximately 3 residues per turn
94
inside fibroblast
procollagen - nuclear, RER, golgi
Vitamin C
95
outside fibroblast -
Secretion to extracellular space and cleavage
pro to tropocollagen
crosslinking fibrils and fibers - COPPER
96
preprocollagen?
beginning of transcription
N-terminal signal sequence (5` end, starts from the first methionine) → ribosome binding to the RER
3. Signal sequence directs growing polypeptide chain into the cisternae of the rough ER
4. The hydrophobic signal sequence is removed by signal peptidase in the rER to form pro-α chains.
97
when is vitamin C needed?
Requires molecular oxygen and Vitamin C✮
Vitamin C deficiency - Scurvy
Catalyzed by prolyl hydroxylase and lysyl hydroxylase
Post-translational hydroxylation of specific proline and lysine in RER
Post-translational hydroxylation of specific proline and lysine in RER, formation of hydroxylysine and hydroxyproline.
98
when is procollagen formed?
propeptides windinto triple helix -
can now go to GOLGI
The resulting molecule has pro- peptide extensions on both ends, still preventing spontaneous assembly into collagen fibrils
In the ER some of the pro-a-chains have extra amino acids at N and C terminus (propeptides)
These propepdide regions of 3 pro-a-chains are involved to assembly into procollagen ✮– triple helix formation - can now be transferred to the Golgi
Carboxy-terminal globular domains fold and disulfide bonds are formed
Winding of the triple helix occurs from the carboxyl towards the amino terminus
The resulting molecule has pro- peptide extensions on both ends, still preventing spontaneous assembly into collagen fibrils
Problems forming triple helix - Osteogenesis Imperfecta
99
problems forming triple helix?
osteogenesis imperfecta
100
What happens in golgi?
Modification of oligosaccharide continues in the Golgi.
| Completed soluble procollagen is released from the cell via secretory vesicles - exocytosis
101
where does cleavage of N- and C- procollagen peptidases remove the terminal propeptides - proteolytic processing occur?
outside cell
tropocollagen - now no extra parts, but still needs to join fibrils to become a fiber - crosslinking
no propeptides,
102
problems with cleavage?
Ehler's Danlos (also can result if problems with crosslinking
103
fibrils to become a fiber - crosslinking
lysyl oxidase - NEEDS COPPER - Cu2+
lysyl oxidase
104
Problems with cross-linking - Ehlers-Danlos syndrome, Menkes disease
Fibrils aggregate and cross-link to form collagen fibers.
