MCS Flashcards
What is conformation?
Unique 3D shape of a protein
- Conformation depends on amino acid sequence
FUNCTIONS: (7)
1) Enzymatic catalyst
2) Systematic movement ( muscles)
3) Transport and storage of small molecules and ions.
4) Mechanical System ( skin and bones)
5) Immune system ( Anti bodies)
6) Communication:
- Hormones: Some hormones are proteins
-cellular receptors and neurotransmitters are proteins
7) Growth and Differentiation( Controlling gene expression):
- Repressor proteins supress DNA sequences
- Transcription and Translation.
All amino acids are optically active, except which one?
Glycine
What is an Imino acid?
An amino acid with a secondary amino group..
What is an example of an imino acid?
Proline.
What configuration is required for amino acids to be optically active?
L configuration.
What is D- configuration?
Bacteria and Invertebrates.
What does amphoeteric mean?
BOTH acidic and basic properties.
- amphoteric properties, depend on how easily side chains dissociate.
What is a “left handed isomer” classified as?
L isomer
What is a “right handed isomer” classified as?
D isomer.
isoelectric point:
Point at which overall charge of protein is ZERO
Are proteins branched or unbranched
Proteins are unbranched polymers.
What is a “residue” ?
Amino acid in a poly peptide chain.
Poly peptides are formed by what type of reaction?
Condensation.
When is an amino acid protanated/deprotanated?
If ph is higher than pka, then it is deprotonated.
If ph is lower than pka, then it is protonated.
Globular:
tight folding poly peptide chains.
SOLUBLE
Fibrous:
Straight poly peptide chains forming fibres or sheets
INSOLUBLE.
STRUCTURE? Covalent, back bone
and amino acid sequence:
Primary Structure
STRUCTURE? Bonds between other neighbouring residues
Secondary strucure
Bonds involved in the Secondary structure
Hydrogen bonding
Ultimately, forming alpha helix or beta pleated sheets
Hydrogen bonding (HELICAL):
If the h-bonds form between peptide bonds in the SAME CHAIN.
Hydrogen bonding( EXTENDED structures):
If h-bonds form between peptide bonds in different chains.
Alpha helix brief description:
Rod like structures with peptide bonds coiled tightly inside.
- side chains face outwards
- coils turn in a clockwise direction.
- There are 3.6 residues, per turn of helix.
Beta- pleated sheets
c-c bonds are tetrahedral
chains lay side by side
- chains may run in the “same directions” ( Parallel beta sheets)
What does “pleated” mean?
C-C bonds are tetrahedral, and can’t be in straight lines.
What’s the anti-parallel Beta strucutre:
E.g. when chains run in opposite directions to each other.
For example, in a globular protein.
How would an anti parallel beta structure be likely to form?
When an EXTENDED structure folds back on itself.
STRUCTURE? Spatial arrangement of residues:
Tertiary Strucuture.
Hydrophillic chains are
OUTSIDE
Hydrophobic chains are
INSIDE
What is the electrical state of a monoamino?
Electrically neutral
what does folding indicate?
State of greatest stability.
Conformation: At points of instability:
At points of instability, FLEXIBILTY in the chain allows water to gain maximum energy.
- Which helps form the strucuture.
STRUCTURE? Arrangement of polypeptide chains in a multi-chain protein:
Quaternary strucutre.
What is Denaturation?
Disruption of weak types of interactions:
such as:
- h-bonds
-vdw
-ionic links
- Hydrophobic/hydrophilic interactions
Advantage of “disruption” :
Helps to maintain the 3D shape of a protein
Disadvantage of Disruption
Causes a decrease in biological activity.
What does “LABILE” mean?
Means a protein is EASILY DISRUPTED
What external factors could cause disruption?
- extreme temperature/ pH
- High salt concentrations
- Organic solvents.
Where is collagen found in the body?
Skin, cartilage, tendons, blood vessels, bones and teeth
How many strands in collagen and how long is each strand roughly?
Fibrous protein
3 strands
each strand is roughly 1000 residues long.
Repeating motif of collagen?
GLY-PRO-PRO
I
OH
What is2 things are special about collagen?
1) LOCKING EFFECT
2) SUPER HELIX FORMATION
Locking effect:
- Due to stability of PRO-PRO
I
OH - And due to H-bonding between residues.
Super helix formation:
Due to amino acid occupying every 3rd residue.
Is a globular soluble/insoluble
SOLUBLE
Is a fibrous protein soluble/insoluble
INSOLUBLE
Protein folding disease:
Ultiamately causes anemia.
A single mutation changes a glutamic acid in B-globulin chain, into a valine.
- Causing protein to change conformation
- which causes hydrophobic part to become EXPOSED
which causes polymerisation
Which causes genetic mutation in homozygous individuals.
What does GENETIC MUTATION from protein folding disease cause?
Reduces ELASTICITY in red blood cells
Causing Sickle cell anemia.
5 ways to treat sickle cell anaemia?
1) Sickle cell pain: Hydroxycarbamide
2) Sickle cell crisis: paracetamol/ibuprofen
- A warm towel on affected body part
3) Prevent infections: Daily dose of antibiotics. (e.g. penicillin)
4)If SEVERE: blood transfusions, folic acid, hydroxycarbamide
5) Sickle cell care: Stem cell/bone marrow transplant
Advantage of Hydroxycarbamide as a treatment?
Increases levels of haemoglobin.
Disadvantage of hydroxycarbamide as a treatment of sickle cell anaemia?
Could decrease levels of white blood cells and platelets
What is a disadvantage of stem cell/ bone marrow transplant as a treatment:
Transplanted cells could attack host cells.
Strongest to weakest bonds:
From strongest->weakest
Covalent
Ionic
Hydrophobic/hydrophilic interactions
H-bonds
Van der Waals.
Calculating buffer range of an amino acid:
Calculating buffering range of an amino acid:
pH= pka +- 1
pH calculations
pH = pka + log (HCO3-)/ (H2CO3)
Ka= (H+)(A-)/(HA)
Pka= -log ka
Ka= 10^-pka
Pneumonic to remember amino acids:
Phenyloanine - aromatic non-polar
R
Valine
Trytophan - aromatic non polar
Isoleucine
Methionine
Thernonine- aliphatic hydroxyl
Histidine- polar
Arginine- polar
Leucine- polar
Lysine- polar
What is an enzyme?
proteins that act as biological catalysts
What is a cofactor
organic molecules.
Where are enzymes found?
mitochondria
lysosome
Endoplasmic reticulum
What are coenzymes?
Small cofactors
prosthtic group is a …..
Tightly bound coenzyme
Cosubstrate is a…
loosely bound coenzyme.
What is glycolysis
Pyruvate -> glucose
What is gluconeogenesis
Opposite of glycolysis
Glucose -> pyruvate
What enzyme breaks down long fatty acid into “acetate” ?
Beta-ox
whereas acetate-> long fatty acid chain
is catalysed by the enzyme “FAS”
4 ways how enzymes catalyse reactions:
1) provide reactive surfaces and a suitable environment
2) Brings reactions together and allows transition state to be reached.
3) Weakening bonds in reactants
4) Reduces energy required to reach “transition state”
What is transition state?
State where the substrate is no longer a substrate, but not a product either.
Enzymes vs Inorganic catalysts: (4)
1) Enzymes are chemically similar, whereas inorganic catalysts are chemically diverse
2) Enzymes are LABILE, whereas I.O are stable to heat
3) Enzymes are specific whereas I.O are non-specific
4) Enzymes are inhibited in a specific way, whereas I.O tends to not be inhibited.
Things in common between Enzymes and Inorganic catalysts:
BOTH unchanged at the end of a reaction
BOTH don’t affect final equilibrium.
( But allow equilibrium to be reached faster)
Enzyme specificity (In DECREASING order);
1) ABSOLUTE
2) STEREOCHEMICAL: PREFERS “D” OVER “L”
3) Group/function
4) LOW: gluthathione- s transferse: can catalyse a large number of substrates.
Denaturation of an enzyme=
Loss of biological activity
DEFINTION
What is a “unit of enzyme activity” ?
The amount of enzyme causing transformation of 1 micro mol of substrate per minute at 25 degrees celcius.
DEFINITION
What is “specific activity” ?
Number of units of enzyme activity per mg of enzyme protein.
DEFINITION
What is KATAL (KAT)
Amount of enzyme activity that transforms one mol of substate per second.
For “reaction velocity” , [ S] graphs:
Increasing [E] will increase reaction velocity, as long as there is enough substrate molecules to bind to it.
For reaction velocity, [E] graphs:
Increasing substrate concentration will increase rate at which products formed up to a max value (Vmax).
Vmax graph:
At Vmax active sites are full, so graph plateaus.
Turnover number of an enzyme equation:
Vmax = K2 [ E ] T
What is “Kcat”
Kinetic constant
DEFINITION
Turnover number of enzyme
Number of substrate molecules converted to products, when enzyme’s active site is occupied with substrate.
Catalytic efficiency equation:
See notes
When [ S ] is less than Km: (4)
1) [E] is roughly same as [ET]
- [ET] is just the total enzyme concentration
2) Velocity of catalysis depends on Kcat/Km, [S] and [ET] values.
3) Kcat/Km is rate constant for S and E and can be used as a measure of catalytic efficiency.
4) You can use Kcat/Km values to determine an enzymes preference for different substrates.
What does it mean if a reaction is at Vmax?
Enzymes cant work any faster
Active sites are full
Units: Conc/time
DEFINITION
Km:
[S] at which reaction velocity is at half maximal.
units: Molar (M)
Siginificance of Km
Using mathematical proof
We find that Km = [S]
How can Km be applied to “affinity” ?
Km is a measure of affinity of an enzyme for its substrate.
What does a lower km mean for “affinity” ?
Lower km means
GREATER AFFINITY
What does inverting michaelis-Menten equation do graphically?
Turns hyperbolic curve into a straight line equation.
- kinetic parameters can be accurately estimated.
What type of graph is lineweaver bunk plot?
Straight line graph
What are the 2 types of enzyme inhibition:
Competitive and non-competitive inhibition
Competitive inhibition:
- Bind to the active site through intermolecular bonds
- Reversible reactions
- Increase in substrate concentration lowers the chance of competitive inhibitor binding.
- DON’T alter Vmax.
Non competitive inhibitor:
- Bind to allosteric site: can inhibit reaction without affecting strength of substrate bonding.
- Km unchanged
- Non competitive inhibitors decrease Vmax.
-Reversible/irreversible
- Non competitive inhibition disrupts active sites.
Allosteric enzymes:
Modulation
I
Inhibition
I
Activation
I
Co-operating
DEFINITION:
Homotropic Allostery:
Binding of identical molecules in a co-operative manner.
DEFINTION:
Heterotrophic Allostery:
Co-operative binding of some other substances as well as the substrate.
What does Allosteric activator do?
Increases activity
What does Allosteric inhibitor do?
Decreases activity.
What is Kcat and K2.
They are the same thing.
The kinetic constant K2 is Kcat
What are the rate laws for competitive and non competitive inhibitors?
Look at rate laws on notes.
- competitive inhibitor only binds to E
- non competitive inhibitor only binds to ES
What is Ki?
How potent an inhibitor is.
- concentration required to produce half maximum inhibition
Catabolism:
Breaking down of large complex molecules, into smaller simpler ones.
tricarboxylic acid pathway=
Kreb cycle.
cori cycle:
Cycle involving glucose lactate and alanine.
What is the normal level of plasma NH3
0.5mg/L
Urea cycle:
- only in the liver
- MAIN PURPOSE: DETOXIFICATION
Irreversible - maintain ratio of urea: ammonia ( 500:1)
What does fumarate break down into:
Fumarate
malate
oxaloacetate ( NH2 transferred to oxaloacetate makes Asparate)
Asparate (Asparate combines with Acetyl CoA to create citrate)
Citrate
Pyruvate -> glucose
What are the basic metabolites?
1)Acetate
2) Acetone
3) urea
4) pyruvate
Glycolysis process:
glucose
fructose1,6-bisphosphate
2x3 carbon compounds ( oxidised to pyruvate) and ATP is produced
pyruvate
Enzymes involved in Glycolysis: (the 3 kinases)
1) Hexokinase - catalyses the phosphorylation of glucose
2) Phosphofructokinase- catalysed fructose 6 phosphate to fructose 1,6 bisphosphate using ATP
3) Pyruvate kinase
What is the function of hexokinase:
- Catalyses transfer of phosphate from ADP to Oh group on the 6th carbon to form glucose 6 phosphate.
What is the function of phophofructokinase?
Catalyses phosphorylation of fructose 6 phosphate to produce fructose 1,6 phosphate.
What is the function Pyruvate Kinase?
Catalyses transfer of phosphate group from phosphoenolpyruvate (PEP) to ADP to produce pyruvate.
Regulation of glycolysis pathway:
1) Hexokinase inhibited by glucose 6-phophate.
2) Phosphofructokinase: Inhibited by ATP, lowers affinity for fructose 6 phosphate
3) Pyruvate kinase: L- type found in the liver
M- type found in the muscle and brain
What does fructose 1,6 bisphosphate do?
Activates both pyruvate kinase isozymes (L and M type)
What does ATP do (regarding pyruvate kinase)?
Inhibiting both forms (L- type and M type)
- to slow down glycolysis
How is alanine involved with pyruvate kinase?
Alanine allosterically inhibits it.
What is Beriberi?
A neurologic and cardiovascular caused by deficiency of thiamine.
Beriberi:
prosthetic group: Thiamine pyrophosphate
for the enzyme pyruvate dehydrogenase, alpha ketoglutarate dehydrogenase
- transketolase.
What does low transketolase activity indicate:
Beriberi of red blood cells.
What are the end products of KREBS:
CO2 and NADH
High energy electrons from NADH passed onto ETC.
KREBS carbon input and output:
2 carbons IN from acetyl CoA
2 carbons OUT as they leave as CO2
Regulation of Krebs cycle
Main regulators are Allosteric enzymes.
What are the allosteric enzymes that regulate the krebs cycle?
1) Isocitrate dehydrogenase
2) alpha- ketoglutarate dehydrogenasee
Isocitrate dehydrogenase (krebs)
Simulated by ADP, enhances the enzymes affinity for substrates
What inhibits isocitrate dehydrogenase?
1) NADH, by displacing NAD+
2) ATP
Alpha-ketoglutarate dehydrogenase
What is it inhibited by?
Succinyl Co A ( it’s catalytic products)
NADH ( it’s catalytic products)
ATP
What are the different proton pumps in ETC (3)
1) NADH-Q
2) Q-cytochrome C oxidase
3) Cytochrome C oxidase
Q:ubiquinone
Pump 1:
Reduced form “Q”
carries electrons from pump 1 to pump 2.
Pump 2:
Ubiquinone carries electrons from FADH2 to pump 2
What does succinate Q reductase do?
transfers electrons from FADH2 to ubiquinone.
Pump 3:
Cytochrome C allows electrons to pump 2 to pump 3.
What does pump 3 do?
Catalyses reduction of oxygen.
Proton Pumping: ETC
1) As electrons pass through the ETC, they fall into lower energy states
2) Energy is used to protons from matrix to the intermembrane space
3) A gradient of H+ ions is generated.
ADP + Pi -> ATP
What is the electron acceptor?
Oxygen.
ATP synthase consists of…
2 sub units (f0 and f1)
f0:
forms a channel which protons can cross the lipid bilayer
f1:
Gathers free energy derived from proton movement down chemical gradient.
How is ETC regulated?
Regulated by ADP levels
- unless ADP- > ATP, electrons don’t usually flow through the ETC
Way of remembering afferent and efferent.
Afferent
Efferent
Arrives
Exits
Afferent neurones:
Signal travels from peripheral tissue to CNS
Efferent neurones:
Signal travels from CNS to peripheral tissue
what does “amitotic” mean
Not able to divide
What is the input region of the neurone?
Dendrites
What is the conducting component of the neurone?
Soma
What is the output region of the neurone?
Axon.
What is the cell body and what is special about it?
The cell body is the biosynthetic CENTRE OF THE NEURONE
- cell body does not contain centrioles.
What’s a good attribute of dendrites?
They provide a large surface area.
DENDRITES:
- receive the signal inputs which gets converted into “charge of membrane voltage” (Vm).
CELL BODY:
The cell body= Large nucleus with a nucleolus.
- surrounded by granular cytoplasm
- mitochondria throughout
- microtubules throughout
which are important for intracellular transport and maintaining cell shape.
Function of the cell body:
Producing proteins and neurotransmitters.
- And transfers “changes in Vm” to axon hillock.
AXON HILLOCK:
First part of the OUTPUT pathway
- generates action potential if enough stimulation is received from the cell body.
- Expresses the ion channels that are needed for action potential.
AXON:
Each neurone has 1 axon arriving from the axon hillock.
- Different axons vary in diameter
^ which affects conduction - Axons allow “axoplasmic transport” to nerve terminals.
What are axon branches known as?
Axon collaterals.
What is the charge of a membrane at rest on the OUTSIDE and INSIDE?
OUTSIDE= positive charge
INSIDE= Negative charge
Depolarisation:
When positive and negative swap themselves, after an action potential has flown down an axon.
Repolarisation:
After a nerve has carried out is action, it can be recharged.
- Nerve can carry out its function again.
What does “amphipathic” mean?
Readily forms bilayers.
- hydrophillic substnaces cant readily diffuse in/out.
What does “amphipathic” mean?
Readily forms bilayers.
- hydrophilic substances cant readily diffuse in/out.
What is the Membrane Potential for MOST cell types?
-50mV
What is the Membrane Potential for “resting skeletal muscles” ?
-90mV
What is the membrane potential for neurones?
(-65 to -70 mV)
What is the Na+/K+ ATPase pump?
For active transport powered by ATP
Do most animal cells have higher intracellular concentration of “K+ or Na+ ions “
K+
- higher concentration of K+, causes an ionic gradient to be generated.
What fraction of a resting cell’s ATP is used to power the Na+/K= ATPase pump?
1/3
What are the 3 functions of the pump?
1) Control cell volume
2) Allows nerves and muscle cells to get electrically excitable.
3) Drives the active transport of sugars and amino acids.
- BONUS: helps to polarise membranes
For NA+/K+ ATPase pump, INSIDE is the cell losing +ve charge or gaining +ve charge?
LOSING +VE CHARGE.
this is because 3Na+ ions are outputted, and 2 K+ ions are inputted.
For NA+/K+ ATPase pump, OUTSIDE is the cell losing +ve charge or gaining +ve charge?
OUTSIDE OF THE CELL, GAINS +VE CHARGE
What is an ion channel?
Proteins that span across membrane and form selective pores.
- This increases the PERMEABILITY, allowing transfer of ions down their electrochemical gradient.
What are the 2 ways ion channels can be operated?
1) Ligand operated (ionotropic)
2) Voltage operated
Sodium ion channel:
- Has 4 repeating units
”+” helix contains many lysine and arginine residues.
- membrane depolarisation shifts the position of the helices, OPENING THE CHANNEL.
How is the sodium channel caused to be open?
Depolarisation causes positions of helix to shift
opening the channel.
What are the general steps of the normal nerve function? ( different types of polarisation etc)
1) Na+ channels open, depolarising the membrane, allowing an action potential to be fired
2) K+ channels open repolarising the membrane
- Na+/K+ ATPase pumps ensure ions are in the right place.
What do “volatage operated sodium channels” do?
They control nerve conduction.
What are “anaesthetics” and how do they work?
They interfere with the inhibition of nerve conduction,
by diffusing into axons and stopping Na+ channels.
What can A LOT of anesthetics cause?
Nerve blockage
as an action potential can not be fired.
Types of drugs that block channels:
- Anaesthetics
-Antiepileptics (phenytoin) - Antidysrhythmic (disopyramide)
- Tetrodotoxin
- Saxitoxin
- Conotoxins
Types of drugs that block inactivation:
- Batrachotoxin
- Scorpion toxins
- DDT
- Pyrethroids
Where does an action potential start?
At the axon hillock
- Action potentials tend to flow in ONE DIRECTION ( down the axon).
If prior to depolarisation the Vm was -65mV, what would it be after depolarisation.
+60mV
Action potential propagation:
Small diameter axons and Large diameter axons
Small diameter axon=
High resistance
and slow conduction speeds
Large diameter axons=
Low resistance
and faster conduction speeds.
What is myelin sheath made up of
And what is the function
- Made up of Schwann cells
- Rapid fire of action potentials
How does a few ion channels affect myelin sheath?
Ensures that myelin is a good electrical insulator.
Oligodendrocytes:
Myelinating cells of CNS
- They insulate multiple axons
Are dendrites myelinated or unmyelinated?
Dendrites will always be UNmyelinated.
What is saltatory conduction, and what is the benefit of it?
Salatatory conduction is when action potentials JUMP FROM NODE TO NODE (nodes of ranvier)
What is saltatory conduction, and what is the benefit of it?
Saltatory conduction is when action potentials JUMP FROM NODE TO NODE (nodes of ranvier)
Axon Classification:
A= myelinated axon
alpha, beta, mew, delta = Diameter of axon
C= UNmyelinated neurone
What are synapses and what do they do?
Synapses are gaps between neurones.
Synapses are involved in cell signalling and communication.