Biochemistry Past Paper 2024 PDF

22 Jawad Alshkirat Noor Aldeen Alfaouri Nafiz Abutarboush 1  Hemoglobin Last lecture we talked about structure-function relationship of proteins, function of hemoglobin and myoglobin, what is heme proteins, the structure of myoglobin an...

22 Jawad Alshkirat Noor Aldeen Alfaouri Nafiz Abutarboush 1  Hemoglobin Last lecture we talked about structure-function relationship of proteins, function of hemoglobin and myoglobin, what is heme proteins, the structure of myoglobin and the function of histidine in it (distal His), function of hydrophobic pocket and oxygen binding curve to myoglobin. To remember that iron can make 6 bonds in ferrous state(Fe2+)..‫ٌعنً تأكد إنك فاهم كل ما فً األعلى ثم أكمل رحلتك‬ How hemoglobin is different from myoglobin?  Less affinity for Oxygen  Hemoglobin has quaternary (multi subunit)so what that’s mean?? What's the benefit of hemoglobin consisting of four subunits? Why it isn’t like myoglobin, one polypeptide chain making the same function? ‫معلومه قبل الجواب‬ Units of hemoglobin‫ زي شكل ال‬myoglobin ‫طبعا الزم نكون عارفٌن انه شكل ال‬ Structure-function relationship ‫ٌعنً بكون فً تقارب باألشكال النهم الثنٌن نفس الوظٌفة‬. Affinity for O2 ‫حتى انهم اقرب إلى ان ٌكونوا متطابقٌن لوال بعض االختالفات البسٌطه لتحدٌد‬ The answer: to decrease the affinity of hemoglobin relative to myoglobin so the oxygen can transport to myoglobin, because if the subunits doesn’t bind to each other their affinity will be like the myoglobin so the transport of O2 become difficult (down we will explain why this happen). Hemoglobin is tetrameric hemeprotein (four protein chains known as globin with each bound to heme) In adults, the four globin proteins are of two different types known as α and β so a hemoglobin protein is an α2β2 globin protein 2 -The α and β chains contain multiple α helices where α contains 7 α- helices and β contains 8 α-helices (similar to myoglobin). Upon the way how proteins perform their function we classify them to 1. Simple proteins: simple behavior/functionresult (can consist of one or more subunit) 2. Cooperative proteins : cooperative behavior between the subunit, (so that’s mean the cooperative proteins must consist of more than one subunit). There are two models explain how cooperative proteins perform their function:  Sequential model : the ligand bind to subunit will make the binding of ligand for next subunit easier.  Concerted model : all of the subunit will bind to ligand at the same time. (Ligand here is oxygen since we study hemoglobin) The hemoglobin apply these two models sequential and concerted ‫الصور مش للحفظ بس لتوضٌح ال‬ models 3 The saturation curve of hemoglobin binding to O2 has a sigmoidal shape. ▪ at 100 mm Hg, hemoglobin is 95-98% saturated (oxyhemoglobin). ▪ as the oxygen pressure falls, oxygen is released to the cells. Any cooperative behavior has this sigmoidal shape. Sigmoid shape‫الزم نعرف هاي الخصائص عن ال‬ ‫ و بعدها بصٌر العكس لعند ما‬y axis ‫ عشان ٌعطٌنً شوٌه من‬x axis ‫انه اول اشً الزم اعطً كتٌر من‬ ً‫ (وهذا فعلٌا الً بصٌر ف‬. plateau ً‫ بصٌر ف‬saturation ‫نوصل انه كل البروتٌن صار مشبع‬ )sequential model ‫الهٌموغلوبٌن و تحدٌدا بفسر كٌف انه بصٌر االرتباط بصٌراسهل بنا ًء على‬  P50 is the partial pressure of oxygen (O₂) at which 50% of the hemoglobin (or any other protein with similar oxygen-binding properties) is saturated with oxygen ▪ In contrast to a low P50 for myoglobin, the P50 of hemoglobin is approximately 26 mm Hg P50 myoglobin2 mmHg P50 is a feature of protein PO2 tissue20 mmHg So it is constant When the pressure become less than P50 the protein start to release the O2. and when the pressure is more than P50 the protein starts to store oxygen (more saturation). 4 As a result the oxygen transport from: hemoglobintissuemyoglobin. ‫ عشان هٌك الهٌموغلوبٌن‬P50‫ رح ٌكون فً البداٌه بالرئه و بالتالً اكٌد الضغط فٌها اعلى من ال‬O2‫ال‬ ً‫ الهٌموغلوبٌن ٌعن‬P50 ‫ االنسجه اقل من‬P50‫راح ٌفلل و بعدها بروح على االنسجه و بطبٌعه الحال‬ ‫ االنسجه‬P50 ‫ اقل من‬P50 ‫ الى النسٌج و من ثم الى المٌوغلوبٌن عشان‬O2‫الضغط اقل و بالتالً بنتقل ال‬ )‫(اختصار ٌعنً من الضغط األعلى الى األقل‬. ▪ Hemoglobin must bind oxygen efficiently and become saturated at the high oxygen pressure found in lungs (approximately 100 mm Hg). ▪ Then, it releases oxygen and become unsaturated in tissues where the oxygen pressure is low (about 20 mm Hg). As we said above that hemoglobin consist of four subunits (2alpha,2Beta) everyone has heme group that can bind to one oxygen so the hemoglobin can bind to four oxygens. Now we will know how the subunits in hemoglobin attach to each other ▪ The chains interact with each other via hydrophobic interactions. So the alpha and beta make a dimer by ▪ Therefore, hydrophobic amino acids are not only present in the interior of the protein chains, but also on the surface. 5  ▪ Electrostatic interactions (salt bridges) and hydrogen bonds also exist between the two different chains So the dimer and dimer attach by Because these bond between the dimers the relation can be change means the affinity can be changed. ‫ بغٌر قدره البروتٌن كله على االرتباط بالمركبات و هذا‬dimers ‫ٌعنً اي اشً بأثر على الروابط بٌن ال‬.‫اشً رح نشوفه لقدام كمان‬ Hemoglobin is allosteric ▪ Hemoglobin is an allosteric protein (from Greek "allos" = "other", and "stereos" = "shape"). – An allosteric protein: a protein where binding of a molecule (ligand) to one part of the protein affects binding of a similar or a different ligand to another part of the protein. ▪ Hemoglobin exists in two forms, T-state and R-state ▪ The T-state is also known as the "taut" or "tight" state and it has a low- binding affinity to oxygen. ▪ The R-state is known as the "relaxed" state and it has 500 times higher affinity to oxygen than as the T conformation. ▪ Binding of O2 causes conformational changes in hemoglobin, converting it from the low affinity T-state to the high affinity R- state. Any cooperative protein is consider as allosteric Why this change happen (with respect of hemoglobin)? ▪ when heme is free of oxygen, it has a domed structure and iron is outside the plane of the heme group. ▪ when oxygen binds to an iron atom, heme adopts a planar structure and the iron moves into the plane of the heme pulling proximal histidine (F8) along with it. ▪ this movement triggers changes in tertiary structure of individual hemoglobin subunits 6  ▪ Breakage of the electrostatic bonds at the other oxygenfree hemoglobin chains. ▪ in myoglobin, movement of the helix does not affect the function of the protein. ‫ بصٌر فً تغٌر بسٌط فً شكله من منحنً الى خطً تقرٌبا‬heme‫ مع ال‬O2 ‫ عندما ترتبط ذره‬:‫للتوضٌح‬ ‫ و ال‬Fe‫ بداٌه من عند ال‬amino acids‫ لكن هذا التغٌر بصٌر بٌن كل ال‬angstrom Å)0.3-0.4) ‫ ٌعنً التغٌر القلٌل جدا ٌؤدي الى تحوٌل البروتٌن‬dimers‫ الى انه ٌصٌر تغٌر بالشكل بٌن ال‬distal his TR ‫من‬ ▪ Conformational changes lead to cooperativity among binding sites. ▪ Binding of the first O2 breaks some salt bridges with the other chains increasing the affinity of the binding of a second molecule. ▪ Binding of the second O2 molecule breaks more salt bridges increasing the affinity towards binding of a third O2 even more, and so on. ▪ Binding is cooperative. It is a protective mechanism ▪ A sudden drop in pulmonary capillary oxygen tension does not affect hemoglobin saturation. 7 –High altitudes The protective mechanism because its behavior. The same thing, at the first there’s must be a high ppO2 for a low saturation so when it 100% saturation, if PPO2 decrease for any reason this will be difficult to effect the%saturation. )‫(ٌعنً صعب ٌتعبأ فً البداٌه و صعب ٌقفد لما ٌكون مشبع‬ )sigmoidal ‫)ما ننسى كمان انه هاي الخاصٌه من خصائص ال‬ Physiology & biochemistry Very important PH can effect the hemoglobin PH in tissue less than the lungs since all cell in our body produce CO2,so this acidity effect on the shape of hemoglobin convert it from R state to T state.Therefore, its affinity decrease mean easier release of O2 than accept. This is pohr effect(effect of acidity on hemoglobin). Also CO2 itself go and attach to N-terminal of the subunits to form what's called (carbamate), this carbamate convert hemoglobin to T state. The carbon dioxide molecules form a carbamate with the four terminal- amine groups of the four protein chains in the deoxy form of the molecule.‫ لها تأثٌر مزدوج‬CO2 ‫مهم جدا جدا نعرف أنه ال‬ The CO2 has a double effect the first is by PH and the acidity and the second is by itself making carbamate. 8.‫وكالهما مهمٌن جدا لعمل الهٌموغلوبٌن بكفاءة‬ Another thing about hemoglobin, in the core of it we can see there is a space because all the subunit meet together by their positively charged amino acid mainly(His/Lys), in this place the bisphosphoglycerate (BPG) bind and convert hemoglobin to T state In fetus hemoglobin consist of 2 alpha and 2 gama subunits in gama there’s no ( His) so that decrase the binding of BPG with it mean the fetal hemoglobin has more affinity to O2 than mother hemoglobin. This very important for transport O2 from mother to the fetus (cycle of life) ‫ٌعنً ارتباط كتٌر مهم للشخص نفسه عشان ٌحصل النسٌج على االكسجٌن و كمان لألجنه لكً ٌحصلوا على االكسجٌن‬. ‫من امهاتهم‬ ‫ ما ٌكون متكسر النه بتكسر بسرعه النه‬BPG ‫ عشان‬fresh ‫كمان بعملٌات نقل الدم ٌفضل انه ٌكون الدم المنقول للمرٌض‬. ‫ و ما رح ٌطلع االكسجٌن الً بداخله‬R state ‫اذا كان متكسر هٌك رح ٌكون الهٌموغلوبٌن ب‬ BPG is a product from glycolysis pathway ‫تمت كتابة هذا الشٌت عن روح والدة زمٌلنا عمرو رائد من دفعة تٌجان‬ ‫دعواتكم لها بالرحمة والمغفرة‬ Thank you 9