Biochem chapter 7

The difference between the concerted and sequential models of oxygen binding to hemoglobin is

whether the transition between T and R states is an "all‑or‑nothing" event or an intermediate state exists with a mixture of R and T states in the same molecule.

Which five statements about hemoglobin and myoglobin structure are true?

-Both hemoglobin and myoglobin contain a prosthetic group called heme, which contains a central iron atom -Each iron atom can form six coordination bonds. One of these bonds is formed between iron and oxygen -By itself, heme is not a good oxygen carrier. It must be part of a larger protein to prevent oxidation in the iron atom -Hemoglobin is a heterotetramer, wheras myoglobin is a monomer -Heme is compose of an organic protoporphyrin component and metal atom

Hemoglobin is a protein in red blood cells that binds to oxygen. Which physiological changes that naturally occur in the body reduce hemoglobin's affinity for oxygen?

-Decrease in pH -accumulation of carbon dioxide

Myoglobin

-Exponential lookin ass (hyperbolic) -Has a higher affinity to oxygen

In addition to transporting oxygen from the lungs to the tissues, hemoglobin also plays a minor role in transporting carbon dioxide from the tissues to the lungs. How is this accomplished?

Carbon dioxide reacts with the amino termini of globin chains to form carbamate.

The illustration shows several oxygen‑dissociation curves. Assume that curve 3 corresponds to hemoglobin with physiological concentrations of CO2CO2 and 2,3-bisphosphoglycerate (2,3-BPG) at pH 7.

Curve 1: a loss of quaternary structure Curve 2: decrease in CO2 and an increase in pH Curve 3: no perturbation Curve 4: an increase in 2,3-BPG

Which statement that best explains the role of BPG in O2O2 transport from mother to fetus?

HbA-bound O2 will tend to move to HbF because HbF has a lower affinity for BPG , allosteric inhibitor of O2 binding

BPG binds tighter to ___ which ____ its affinity for O2

HbA; lowers

Which hemoglobin has a higher affinity for O2O2 at the tissue pO2pO2 of around 4 kPa?

HbF

The binding of oxygen to myoglobin and hemoglobin has what effect on the heme iron?

It causes the iron to move closer to the approximate plane of the porphyrin ring.

How does training at high altitudes benefit athletes?

The body acclimatizes to the lower oxygen concentration found at high altitudes by producing more red blood cells, making oxygen uptake and transport more efficient upon return to lower altitude

Identify the best description of the cause of altitude sickness.

an organism's inability to absorb and transport enough oxygen throughout the body at higher altitudes

Rapidly metabolizing tissues generate protons and carbon dioxide in high concentrations. The result is that the the oxygen‑binding curve of hemoglobin (Y versus pO2)

shifts to the right, which reflects less saturation of hemoglobin at higher pO2 levels.

T state

stabalized by increased ion pairing at the alps 1 beta 2 and alpha 2 beta 1 interfaces; iron ion produces from heme towards his F8; tense state of hemoglobin

In fetal hemoglobin (HbF), the two β subunits are replaced with two γ subunits. The result is that HbF has a higher affinity for oxygen than the mother's adult hemoglobin (HbA).

the decreased affinity of 2,3‑BPG to the γ subunits of HbF.

What drives the loading of oxygen onto hemoglobin molecules in the lungs?

the high partial pressure of oxygen pressure of oxygen in the lungs

Hemoglobin S (HbS), which is an abnormal form of hemoglobin responsible for sickle‑cell anemia, is the result of a mutation in the gene for the β subunit.

a negatively charged amino acid R group to a positively charged amino acid R group.

Which amino acids would be expected to produce a similar sickling effect if substituted for Val at position 6?

alanine, leucine

Neither Hemoglobin or Myoglobin

-O2 binds irreversibly to this molecule -Carbon monoxide binds at an allosteric site, lowering oxygen binding affinity

Hemoglobin

-S shaped curve -As oxygen binds to this molecule the shape of the molecule changes, enhancing further oxygen binding -the binding pattern for this molecule is considered cooperative

Select all the statements that correctly describe the cooperative binding of oxygen to hemoglobin.

-The hemoglobin- oxygen binding curve is sigmoidal -Hemoglobin consists of four heme-bound subunits

Complete the sentences about heme. Some terms will not be used.

-The prosthetic group of hemoglobin and myoglobin is heme -The organic ring component of heme is porphyrin. -Under normal conditions, the central atom of heme is Fe2+ -In deoxyhemoglobin, the central iron atom is displaced 0.4 Å out of the plane of the porphyrin ring system. -The central atom has six bonds: four to nitrogen atoms in the porphyrin, one to a histidine residue, and one to oxygen.

Based on the oxygen‑binding graph (Graph A), at what partial pressure of oxygen (𝑝O2)(pO2) is lamprey hemoglobin half‑saturated?

10 torr

Which of the following statements best describes how 2,3‑bisphosphoglycerate (2,3‑BPG) reduces hemoglobin's affinity for oxygen?

2,3‑BPG binds to positively charged Lys and His residues in the center of the hemoglobin tetramer, which stabilizes the T state.

For each of the six scenarios, determine whether the hemoglobin binding curve would shift left or shift right.

Left: The adult hemoglobin is replaced by an infant's fetal hemoglobin; hemoglobin is isolated from red blood cells and stripped of 2,3-BPG; tetrameric hemoglobin is dissociated into its subunits Right: The blood pH drops from 7.4 to 7.2; the CO2 concentration in the blood increases; the concentration of 2,3-BPG increases during acclimation to high altitude

How does HbS aggregation occur in sickle‑cell anemia? Place the steps in the correct order. Note that deoxyhemoglobin is in the T state; oxyhemoglobin is in the R state.

No aggregation to Sickled red blood cell: O2 decreases, R state Hb shifts to T state Hb, Val interacts with the pocket of a beta chain on another HbS, Additional T state HbS interact with the growing aggregate to form an insoluble fiber

Each chain of hemoglobin can be viewed as existing in one of two states: the R (relaxed, high‑affinity) state and the T (tense, low‑affinity) state.What is the relationship of the R and T states to oxygen binding?

Oxygen binding converts hemoglobin from the T state to the R state.

Identify the best description of a heme group.

one of four iron-containing parts of hemoglobin that bind to oxygen molecules

What drives the diffusion of oxygen?

partial pressure of oxygen

Choose two amino acids that would be reasonable candidates for the pocket-Val 66 interaction.

phenylalanine, leucine

R state

relaxed state of hemoglobin; narrowed pocked between beta subunits; iron ion assumes a planar conformation