Biochem Module 5

• Be able to explain why a specialised protein is needed to transport oxygen from the lungs to the tissues

  
  

  No other amino acid side-chains form a coordinate bond to the oxygen and hold it in place whilst it is being transported in the bloodstream and release it at its final destination, tissues. So, hemaglobin, a red blood cell protein carries the oxygen and is specialised enough to coordinate to oxygen and hold it tightly whilst it is being transported but then release it when it gets to tissues.
• Explain the different functions of myoglobin and hemoglobin

  Hemoglobin:

  • Function: Transport oxygen in the blood.
  • Location: Red blood cells.
  • Structure: Four polypeptide chains, binds up to four oxygen molecules.
  • Oxygen Affinity: Modulated by pH and CO2 levels (Bohr effect), cooperative binding.

  Myoglobin:

  • Function: Store and release oxygen in muscle cells.
  • Location: Muscle tissue.
  • Structure: Single polypeptide chain, binds one oxygen molecule.
  • Oxygen Affinity: Higher affinity for oxygen, releases oxygen under low oxygen conditions, no cooperative binding.
• Be able to explain the role of erythrocytes in oxygen transport

  Erythrocytes (red blood cells) are essential for oxygen transport due to their high hemoglobin content and unique structural features. They pick up oxygen in the lungs, transport it through the bloodstream, and release it to tissues where it is needed. They also play a key role in returning CO2, a waste product, from the tissues to the lungs for exhalation. This dual function of carrying oxygen and assisting in CO2 transport ensures efficient respiratory gas exchange and maintains the body’s metabolic needs
• Define the terms oxyhemoglobin and deoxyhemoglobin

  
  

  Oxyhemoglobin is when hemoglobin has oxygen at its binding site. Deoxyhemoglobin is when hemoglobin does not have oxygen bound at its binding site
• Explain what circumstances blood is red or blue in colour

  
  

  Oxyhemoglobin is bright red, while deoxyhemoglobin is purple/blue.
• Be able to describe how oxygen binding to hemoglobin can be measured

  
  

  Using the different colours of deoxy and oxy-hemoglobin we can measure the UV/visible spectrum of blood. As more oxygen binds to hemoglobin the visible spectrum moves from the blue spectrum to the red spectrum.
• Be able to explain the role of the globins in oxygen binding and transport

  Hemoglobin:

  • Role: Transport oxygen from the lungs to the tissues and return CO2 from the tissues to the lungs.
  • Structure: Tetramer with four subunits, each containing a heme group.
  • Function: Binds oxygen in the lungs and releases it in tissues, regulated by cooperative binding and the Bohr effect.

  Myoglobin:

  • Role: Store and release oxygen in muscle cells.
  • Structure: Monomer with a single heme group.
  • Function: Binds oxygen tightly, releases it during periods of high demand to ensure a steady supply of oxygen in muscles.
• Be able to describe where myoglobin is found in sea and terrestrial mammals.

  Terrestrial Mammals:

  • Location: Found in skeletal muscles and the heart.
  • Function: Supports muscle activity and endurance by providing a steady oxygen supply during exertion.

  Sea Mammals:

  • Location: Found in high concentrations in skeletal muscles.
  • Function: Enables prolonged dives by storing large amounts of oxygen and supporting muscle function underwater
• Explain the similarities and differences in the 3D structures of myoglobin and hemoglobin

  Both have domain structure and have a heme porphyrin group that binds in a hydrophobic pocket which is where the iron binds

  
  

  HB = Quaternary structure because Hb has 4 polypeptide chains that interact with each other

  
  

  MB = Tertiary structure because Mb has 1 polypeptide chain
• Where do homotropic effectors bind to hemoglobin?

  
  

  • Location:
  • Homotropic effectors, such as oxygen, bind directly to the active binding sites of the protein.
  • In hemoglobin, the active binding sites are the heme groups within each subunit.
  • Specific Binding Site:
  • Oxygen molecules bind to the iron ions (Fe²⁺) at the center of the heme groups
• Explain the differences in binding features of CO and O2 to hemoglobin

  • Affinity:
  • CO has higher affinity than O2.
  • Specificity:
  • CO binds mainly to heme iron.
  • O2 interacts with heme iron and globin chains.
  • Effects:
  • CO forms carboxyhemoglobin, impairing oxygen transport.
  • O2 facilitates oxygen delivery to tissues.
  • Consequences:
  • CO poisoning causes tissue hypoxia.
  • O2 binding ensures cellular oxygen supply.
• Explain the effect of homo and heterotropic effectors on the conformation of hemoglobin

  
  

  • Homotropic:
  • Directly binds to active sites.
  • Stabilizes the R state, enhancing further binding.
  • Heterotropic:
  • Binds to allosteric sites.
  • Alters conformation, affecting oxygen affinity and release.
• explain the effect of BPG on the binding curve and P50 of hemoglobin

  • Binding Curve:
  • BPG shifts the hemoglobin oxygen binding curve to the right.
  • This decreases hemoglobin's affinity for oxygen, promoting oxygen release to tissues.
  • P50:
  • P50, the partial pressure of oxygen at which hemoglobin is 50% saturated, increases with higher BPG concentration.
  • Higher P50 indicates decreased oxygen affinity, facilitating oxygen release in tissues.
• describe where and how BPG binds to hemoglobin

  • Location: BPG binds within a pocket in the central cavity of hemoglobin.
  • Mechanism: BPG interacts with positively charged amino acids in the beta globin chains.
  • Role: Stabilizes the T state, reducing oxygen affinity, and promoting oxygen release in tissues.
• explain what biochemical changes occur to assist with respiration at high altitude

  • Increased Erythropoiesis:
  • Stimulated by hypoxia, leading to more red blood cells.
  • Enhanced Ventilation:
  • Increased breathing rate compensates for low oxygen levels.
  • Elevation of BPG:
  • Helps release oxygen from hemoglobin.
  • Improved Oxygen Extraction:
  • Tissues may increase capillary density for better oxygen uptake.
• describe the differences in fetal hemoglobin that decrease its anity for BPG and what outcome this has.

  • Composition:
  • HbF: Two alpha and two gamma globin chains (α2γ2).
  • HbA: Two alpha and two beta globin chains (α2β2).
  • BPG Affinity:
  • HbF has gamma (γ) chains with reduced affinity for BPG compared to beta (β) chains in HbA.
  • Outcome:
  • Higher oxygen affinity in HbF due to reduced BPG binding.
  • Facilitates efficient oxygen transfer across the placenta from mother to fetus.
• Explain the effect of CO2 on the binding curve and P50 of hemoglobin

  • Effect on Binding Curve:
  • Increased CO2 concentration shifts the hemoglobin oxygen binding curve to the right.
  • This shift decreases hemoglobin's affinity for oxygen, promoting oxygen release to tissues.
  • Effect on P50:
  • P50, the partial pressure of oxygen at which hemoglobin is 50% saturated, decreases with higher CO2 concentration.
  • Lower P50 indicates decreased oxygen affinity, facilitating oxygen release in tissues with high CO2 levels.
• describe where and how CO2 binds to hemoglobin and how it is transported back to the lungs

  • Binding Site: CO2 binds to amino terminal groups of globin chains.
  • Formation of Carbaminohemoglobin: CO2 combines with globin chains to form carbaminohemoglobin.
  • Transport: Carbaminohemoglobin is carried in the bloodstream to the lungs.
  • Release: In the lungs, CO2 dissociates from hemoglobin and is exhaled during respiration.
• explain the effect of H+ on the binding curve and P50 of hemoglobin

  
  

  • Effect on Binding Curve:
  • Increased H+ concentration (decreased pH) shifts the hemoglobin oxygen binding curve to the right.
  • This shift decreases hemoglobin's affinity for oxygen, promoting oxygen release to tissues.
  • Effect on P50:
  • P50, the partial pressure of oxygen at which hemoglobin is 50% saturated, increases with higher H+ concentration.
  • Higher P50 indicates decreased oxygen affinity, facilitating oxygen release in tissues with low pH.
• Be able to explain what the BOHR effect is and how it affects the structure of hemoglobin

  A key mechanism by which hemoglobin adjusts its oxygen-binding affinity based on the local environment's pH and CO2 concentration. This ensures efficient oxygen delivery and CO2 transport, adapting to the varying needs of different tissues and maintaining homeostasis
• describe the structure of sickle cell hemoglobin and pinpoint the amino acid substitutions from normal hemoglobin and the mutated form

  • Amino Acid Substitution:
  • Glutamic acid (Glu) at position 6 of the beta-globin chain is replaced by valine (Val).
  • Effect:
  • Substitution leads to polymerization of HbS molecules into insoluble fibers.
  • Alters shape of red blood cells, causing them to become rigid and sickle-shaped.
  • Consequences:
  • Reduced blood flow, tissue damage, and symptoms of sickle cell disease.
  • Comparison:
  • Normal Hemoglobin (HbA) has glutamic acid (Glu) at position 6.
• describe the conditions under which the fibre formation occurs and why, and the state of hemoglobinFiber Formation and Hemoglobin State:

  
  

  • Conditions:
  • Fiber formation in hemoglobin occurs under low pH and high deoxyhemoglobin concentration.
  • Reasons:
  • Low pH destabilizes hemoglobin's T state, promoting fiber formation.
  • Deoxyhemoglobin's reduced solubility leads to its precipitation and fiber formation.
  • State of Hemoglobin:
  • Deoxyhemoglobin tends to aggregate and form fibers under specific conditions.
  • Fiber formation alters red blood cell shape, seen in conditions like sickle cell disease
• Roles of proteins in biological systems

  • Structural support (e.g., collagen)
  • Storage (e.g., ferritin)
  • Transport (e.g., hemoglobin)
  • Defense (e.g., antibodies)
  • Movement (e.g., actin and myosin)
  • Regulation (e.g., insulin)
  • Enzymatic activity (catalyzing reactions)
• Hemoglobin


  • Composed of four polypeptide chains, each containing a heme group with Fe2+
  • Has an iron ion with an octahedral geometry surrounded by six ligands
  • Can exist in oxygenated (oxyhemoglobin) and deoxygenated (deoxyhemoglobin) forms
• As oxygen binds to hemoglobin


  The visible spectrum shifts from blue (deoxyhemoglobin) to red (oxyhemoglobin), reflecting the change in the iron ion's oxidation state
• Positive cooperativity in hemoglobin


  The binding of one oxygen molecule increases the affinity for subsequent oxygen molecules, leading to conformational changes that enhance oxygen binding
• Allosteric behavior in hemoglobin

  • Ability to switch between tense (T) and relaxed (R) states based on oxygen availability
  • T-state has low oxygen affinity, while the R-state has high oxygen affinity
• Alpha-helical proteins mb and nb

  • Both have a heme group containing Fe2+
  • Consist of a single polypeptide chain with a 3D structure
  • Have a high nitrogen content
• Heme group in hemoglobin

  • Binds to oxygen molecules, allowing for the transport of oxygen in the bloodstream
  • Essential for the reversible binding and release of oxygen
• Positive cooperativity in hemoglobin

  Enhances its ability to bind and release oxygen efficiently, ensuring optimal oxygen transport and delivery to tissues
• Conformational changes in hemoglobin

  Increase its affinity for oxygen, leading to a higher saturation of oxygen molecules at high oxygen concentrations
• Oxyhemoglobin


  Bright red and carries oxygen
• Deoxyhemoglobin


  • Blue and lacks oxygen
  • The color change reflects the different oxidation states of the iron ion in the heme group
• Oxygen binding to hemoglobin


  Oxygen binds to the Fe2+ in the heme group, causing a conformational change in the hemoglobin molecule
• 2,3-BPG


  Binds to the central cavity of hemoglobin, shifting the oxygen-binding curve to the right
• CO2 binding to hemoglobin

  Lowers pH and decreases oxygen affinity
• Allosteric effectors in the context of hemoglobin

  Molecules that bind to sites other than the heme group, influencing hemoglobin's oxygen-binding affinity
• Oxygen binding to hemoglobin

  The Fe2+ in the heme group moves into the plane of the heme, causing a series of conformational changes
• 2,3-BPG binding to hemoglobin

  Shifts the oxygen-hemoglobin dissociation curve to the right, promoting the release of oxygen from hemoglobin
• Oxygen binding to hemoglobin


  Breaks ionic interactions at the alpha and beta subunit termini