Study Guides (248,451)
Canada (121,559)
Biology (475)
Quiz

Lecture Material for Test 5.docx

11 Pages
66 Views
Unlock Document

Department
Biology
Course
BIOLOGY 2F03
Professor
Lovaye Kajiura
Semester
Fall

Description
Lecture Material for Test 5 November 10, 2010 Chapter 7 Slide 1 -myoglobin in our muscle to facilitate diffusion of oxygen into muscles -first found in sperm whale as an oxygen storing molecules -monomer, single polypeptide chain, 8 alpha helices, globular -heme molecule is site where iron II (ferrous) is located -ferric iron insoluble, ferrous iron is reduced form -smaller than hemoglobin thus was solved first -hemoglobin and myoglobin are homologous -hemoglobin is a tetramer -more complex to solve, took more time to solve -soak crystals with mercury -can change intensity of amplitude -structure is not compromised by heavy atom -change in amplitude allowed calculation of phase -phase and amplitude together allowed solving of electron density which then can be used to solve structure Structure of sperm whale myoglobin -8 alphahelical chains -Kendel created his own nomenclature for chain and atom identification -still used today for myolgobin -modified for other structures -heme group bound to helice c and F in myglobin The heme group -tetra pyrrole – creates pii electron system which absorbs electromagnetic energy -gives myoglobin its colour -binds iron -histidine residue that is important for ligating heme group -ferrous II can be converted to ferrous III in presence of oxygen -blood turns brown with oxidated to ferrous III -groups in close association to place tetra pyrrole ring in right plane -onces oxygen ligated to 6 position, oxygen hydrogen bonded to another side chain of histidine -positions the iron so it can bind optimally to oxygen -fraction of myoglobin that is oxygenated: fractional saturation -when it at ½ = useful constant: related to eq’m constant -concentration of oxygen refers to partial pressure -p50 – molecule is half saturated = K -rectangular parabola -binds in 1:1 ratio since it’s a monomer Hemoglobin structure -alpha and beta structures are homologous to each other -conformational change when iron binds First experimental evidence of an allosteric change in protein Oxygen Binding Curve of Hemoglobin -sigmoidal curve -uptake is cooperative November 15, 2010 Structure of sperm whale myoglobin -solved by John Kendrew -8 alpha helical segments -soluble globular protein -tetrapyrolle group where oxygen binds (to iron) -myoglobin in whale stores oxygen for diving -in humans, used for transporting oxygen from blood to peripheral tissues (skip a few slides) Oxygen –binding curve of myoglobin -1:1 ratio -as partial pressure increases, saturation increases -at p50 : partial pressure of o2 when saturated at 50% Hemoglobin structure a)deoxyhemoglobin -hemo 10 times less affinity of myoglobin -when one oxygen binds, the rest of are induced to bind -result of having similar/same parts in a protein -tetramer affords it a mechanism to sense the oxygen concentration and change the affinity for the remaining unit: cooperative process: binding to one that induces conformational change that is communicated from one subunit to another subunit -get sigmoidal relationship b) hemoglobin -a little diff than deoxygenated -grey arrows show slight twisting First experimental evidence of an allosteric change in a protein -known that crystals of hemoglobin had a diff structure -crystallographers had to solve the structure twice from crystals since deoxy and oxy were diff -crystals formed in soln -created anaerobic environment: deoxy -pump nitrogen into soln -fig 7-6 -shows subtle change in beta and alpha subunits Oxygen-binding curve for hemoglobin -myoglobin has rectangular hyperbola saturation curve (1 oxygen per myoglobin -monomer so can’t change another myoglobin -sharper: has higher affinity -dotted curve: if hemoglobin binding wasn’t cooperative -hill eqn -theoretical binding -can get much or saturation at p50 where physiology is needed -as hemo moves through circulation, gives out oxygen -myo needs a a lower pressure to become saturated since it is exposed to much lower concentrations of oxygen -fractional saturation at 50% gives p50 Mathematical relationship -Hill eqn -n = number of subunits -assumes that it binds simultaneously though that is not really happening -use it to determine the degree of cooperative binding -hem 2.8 to 3 -if n = 4 = infinite binding Fig 7.8 -adjust the value of n until it fits the experimental data -btw o.1 and 0.9 = straight line relationship -slope of hill plot where saturation = half to give coefficient -hemo has around n of 3 -value is less than 4 since cooperativity is not infinite -but since it is greater than 1 , cooperativity if quite high -oxygen binds with a 100 times greater affinity -eq’m constant (p50) is lower when affinity is higher -small K = high affinity T state and R state -this is not unique to hembolobin -T = tense -R = relax -deoxy seemed to be more tight -oxygenated tend to more relaxed Movement of the heme and the F helix -there is a diff -when oxygen binds , satisfies electronic requiremtns of iron -as covalent bond forms betw oxygen and Fe -Fe binds less tightly to heme group -doesn’t have the same requirements -thus relaxes -causes porphoirin ring to lose distortion -moves to a a planar state Which causese heme group to be dragged down -to accommodate small change, helix shifts -altered by less than 1 A -helix tilts , larger change at ends of helix Changes at the alpha-beta subunits interfaces -aa at interface btw the alpha and beta subunit to shift into a diff conformations -5 A shift -quanternary change -network of H bonding -series of ion pairing that occurs at the termini -alpha is positively charged -ion pairings manifested in deoxyhemoblobin -when it binds to oxygen, these interactions are torn apart -local environment of ionizable groups usually has a pH that can alter the pKa of the groups -as ion pairing that occur at termini are altered, pKa increases, has higher affinity for proton The Bohr Effect -when protein in lungs, partial pressure of oxygen is such that the protein picks up oxygen from the lungs -exercise – deplete amt of oxygen needed by muscle -muscle uses glycolysis, not citric acid cycle -lactic acid accumulates and pH starts to drop -when pH drops, the affinity of oxygen for hemoglobin starts to drop as well -hemoglobin when reaches peripheral tissues releases a greater amt of oxygen than before Figure 7.13 -carbon dioxide becomes soluble (Reacts with water to form bicarbonate and a proton) -rxn occur spontaneously but doesn’t occur fast enough -red blood cells also carry carbonic anhydrase that catalyses this rxn and makes it occur -one of the highest enzymatic rxns known -eq’m can be drawn toward bicarbonate direction by removing proton -hemoglobin can mop up proton due to increased pKa of conformational change -when it binds oxygen, pKa drops, proton released which drives the next rxn -bicarboante converted back to carbon dioxide and carbon dioxide is released The effects of BPG and CO2 on hemoglobin’s o2 dissociation curve -purified hemoglobin has higher affinity for oxygen than in blood -compound called BPG present in red blood cells that binds to hemoglobin -cuases conformation of T state to be stablilized -shifts p50 -also need CO2 which can rxn with amino terminus BPG -metabolite proceed in RBC that accumulates to 4 millimolar -binds to hole in tetramer -deoxy (T state) has big hole that narrows when oxygen binds -that site is structure to bind BPG -the negative charges on BPG are satisfied by positive on alpha and beta aa -that hole is only big enough to accomodate BPG in T state -BPG keeps hemoglobin in conformation in t state -beta subunit in fetus has a paralog -zeta subunit: his replaced by serine -positive charge replaced by neutral aa -reduced BPG affinity -fetal hemoglobin has higher affinity for oxygen than maternal hemoglobin -oxygen transfers to baby -high altitude training/adaptation -RBC increase (takes long time – about a week) -body can change BPG quite rapidly -BPG doubles – T state favoured -releases larger fraction of oxygen -degree of saturation does not improve but the release changes The symmetry model of allosterism -induced fit model – when protein bind to enzyme, conformational change -more like hand-glove model than lock-key model -allosteric control model (allo – another, steri - site or structure) -binding of ligand at one site causes a conformation change at another site -can only explain positive cooperativity (infinite cooperativety) The sequential model of allosterism -systematic – where one subunit binds, induces conformational change -may have higher of lower affinity -more general model where can explain both negative and positive cooperativity -these two models are general principles in multisubunit enzymes that involved in regulatory processes Table 7-1 -mutants can change p50 or degree of coopertivity -list of diff mutations Sickle cell anemia -provides a degree of resistance to malaria -that is why mutation is fixed in popn (African) -valine cause interaction btw hemoglobin molecules -an aggregate of hemoglobin Structure of a deoxyhemoglobin S fibre -glu to val causes a change in physical properties of molecule -causes it to aggregate -red blood cells have bi concave structure needed to travel through capillaries -sickle cells get clogged in capillaries and cuts of blood flow, eventually lethal Figure 7.20 Hydroxyurea -reduces sickling process, reduced blockage in capillaries and relieves symptoms -hydroxyurea induces expression of fetal hemoglobin -changes T to R eqm slightly -aggregation only occurs in T form (deoxygenated form) -increases oxygenated form – reduces aggregation Fig 7.21 -heterozygotes have -spleen removes old red cells in blood -cells that are infect with parasite of malaria -pH of envionrment drops -shif
More Less

Related notes for BIOLOGY 2F03

Log In


OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit