chapter 7: protein function - myoglobin and hemoglobin, muscle contraction, and antibodies

if curve 3 represents oxygen binding to Hb in normal red blood cells, which curve represents oxygen binding to Hb in red blood cells that contain a greater concentration of BPG? a. 1 b. 2 c. 3 d. 4 e. none of the above

d. 4

________ diseases involve the loss of self-tolerance

autoimmune

when the partial pressure of O2 in venous blood is 30 torr, the saturation of myoglobin with O2 is _____ while the saturation of hemoglobin with O2 is _______ a. 0.55, 0.91 b. 0.91, 0.55 c. 2.8 torr, 26 torr d. 0.91, 0.97 e. none of the above

b. 0.91, 0.55

the primary structure of mammalian hemoglobin, an a2B2 tetramer, is approximately _____ identical to myoglobin. a. 2% b. 18% c. 50% d. 78% e. 98%

b. 18%

how many antigen-binding sites are present on an IgG molecule? a. 1 b. 2 c. 3 d. 4 e. 5

b. 2

the affinity of hemoglobin for the 4th oxygen is about 100 times greater than for the ____ oxygen

1st

p50, or oxygen tension, is the oxygen pressure (pO2) at which hemoglobin or myoglobin is 25% saturated with oxygen. A) True B) False

A) True

Rigor mortis, the stiffening of muscles after death, is caused by depletion of cellular ______. in the absence of ______, each _______ head adopts a conformation that does not allow it to release its bound _____ molecule. consequently, thick and thin ______ form a rigid cross-linked array.

ATP ATP; myosin, actin filaments

Elucidation of the structure of hemoglobin was pioneered by the researcher________

Max Perutz

Which of the curves does NOT show cooperative binding? (flip to see graph) a. 1 b. 2 c. 3 d. 4 e. none of the above

a. 1 curve 1 is hyperbolic, which is typically seen with non-cooperative binding

If curve 3 represents the binding of oxygen to normal Hb, which curve represents the binding of oxygen to Hb that has dissociated into separate subunits? a. 1 b. 2 c. 3 d. 4. e. none of the above

a. 1 (nonsigmoidal) when dissociated from one another, the subunits of hemoglobin cannot adopt a low-affinity conformation and so they behave like myoglobin, binding oxygen with a fixed high affinity

Shown below is a general diagram of the oxygen binding site as it occurs hemoglobin and myoglobin. which item in the diagram is incorrectly labeled? A= val E11 B= His F8 C= Phe CD1 D= 02 a. B b. D c. C d. A

a. B

which of the following is not a ligand to the porphyrin ring Fe (II) ion in oxymyoglobin? a. His E7 b. His F8 c. nitrogen atoms in the porphyrin d. oxygen e. all are ligands

a. His E7

Protein X binds reversibly to ligand Y such that X + YXY, and the molar concentrations of X, Y and XY are known. Which of the following represents the dissociation constant (K) for this reaction? a. K= [X][Y]/ [XY] b. K= [XY]/ [X][Y] c. K= [X]+[Y]/ [X+Y] d. K= [XY]/[Y] e. K could not be determined with the information provided

a. K= [X][Y]/ [XY]

What type of allosteric effector is BPG? a. a heteroallosteric effector of hemoglobin b. a heteroallosteric effector of myoglobin c. a homoallosteric effector of hemoglobin d. a homoallosteric effector of myoglobin

a. a heteroallosteric effector of hemoglobin BPG is a heteroallosteric effector because it alters the ability of hemoglobin to bind another ligand, oxygen.

which of the following statements is FALSE? in its interaction with hemoglobin, oxygen is: a. a prosthetic group b. a ligand c. bound at the 6th coordination position of the Fe(ii) ion in the heme d. reversibly bound e. homoallosteric effector

a. a prosthetic group

which of the following amino acids has the most significant role in the molecular mechanisms of hemoglobin's function? a. histidine b. tyrosine c. glycine d. lysine e. glutamine

a. histidine

what are the main bonds or forces that stabilize the dimer formed by two myosin heavy chains? a. hydrophobic interactions b. hydrogen-bonds c. ionic interactions d. disulfide bonds e. isopeptide bonds

a. hydrophobic interactions

while the binding of O2 to myoglobin as a function of pO2 is described by a simple _____ curve, the binding to hemoglobin is described by a more complex _______ curve. a. hyperbolic; sigmoidal b. sigmoidal; hyperbolic c. exponential; hyperbolic d. hyperbolic; concave e. sigmoidal; bell-shaped

a. hyperbolic; sigmoidal

muscle contraction is triggered a. in response to an increase in the cytoplasmic Ca2+ concentration b. in response to a decrease in the cytoplasmic Ca2+ concentration c. in response to an increase in the cytoplasmic cAMP concentration d. in response to a decrease in the cytoplasmic cAMP concentration e. in response to an increase in the cytoplasmic titin concentration

a. in response to an increase in the cytoplasmic Ca2+ concentration

which term best describes the histidine F8 residue in myoglobin and hemoglobin? a. invariant residue b. variable residue c. catalytic residue d. conservatively substituted residue e. homologous residue

a. invariant residue

which of the following best describes the tertiary structure of myoglobin? a. it contains heme, which is slotted into a hydrophobic pocket between a-helix E and a-helix F b. it contains no B-sheet c. it is a heterotetramer d. it contains 8 a-helices e. it contains heme, which is loosely associated via hydrophobic interactions with amino side chains in the heme pocket

a. it contains heme, which is slotted into a hydrophobic pocket between a-helix E and a-helix F

which of the following statements most accurately explains why hemoglobin is able to deliver oxygen to myoglobin in the tissues? a. myoglobin has a hyperbolic oxygen binding curve, whereas hemoglobin has a sigmoidal oxygen binding curve. b. the pH of tissue/ muscle is always higher than that of blood, which aids hemoglobin in giving up its oxygen c. the presence of BPG in the red blood cells shifts the equilibrium towards the R state of hemoglobin d. the iron in the heme group of myoglobin is Fe3+. which has a higher affinity for oxygen

a. myoglobin has a hyperbolic oxygen binding curve, whereas hemoglobin has a sigmoidal oxygen binding curve. the sigmoidal binding curve illustrates hemoglobin's ability to adopt a low affinity state. this enables it to transfer oxygen to myoglobin which always binds oxygen with high affinity

during muscle contraction a. myosin pulls actin filaments toward the M disk b. myosin pushes actin filaments toward the Z disk c. actin pulls myosin toward the Z disk d. actin pushes myosin toward the M disk e. all of the answers above are correct

a. myosin pulls actin filaments toward the M disk

why does the concentration of BPG in red blood cells increase when humans are exposed to high altitudes? a. to allow hemoglobin to release more oxygen at lower partial pressures of oxygen b. to neutralize the increased concentration of hydrogen ions produced when muscle works harder at high altitudes c. to induce the production of more red blood cells d. to allow hemoglobin to bind more oxygen at lower partial pressure of oxygen

a. to allow hemoglobin to release more oxygen at lower partial pressures of oxygen when the partial pressure of oxygen in the lungs is low, the oxygen-saturation of hemoglobin is reduced. this means that there is less total oxygen available for release in the tissues. one way to compensate for this shortfall is to ensure that hemoglobin releases relatively more oxygen in the tissues than usual and this is achieved by increasing the concentration of BPG

the light chain of an IgG molecule is composed of two similar domains made of B-sheets a. true b. false

a. true

A newly-identified protein shows the following behaviour in ligand binding. which of the statements about this protein is false? - sigmoidal curve ( %saturation vs ligand mM) a. when the ligand binds to one subunit, the affinity of the other subunits for the same ligand is reduced b. the protein binds the ligand cooperatively c. the ligand binds reversibly at a specific site on the protein, causing a global change in conformation d. the protein exists in two conformational states which have different affinities for the ligand

a. when the ligand binds to one subunit, the affinity of the other subunits for the same ligand is reduced this statement is false. this curve indicates that the binding of ligand to one subunit INCREASES the affinity of the other subunits for the same ligand

carbon monoxide binds to heme: a. with a higher affinity than oxygen b. resulting in the oxidation of the Fe(II) to Fe (III) c. in a manner that displaces carbon dioxide, causing CO2 poisoning d. from the side opposite oxygen, resulting in a brown colored heme e. with a lower affinity than oxygen

a. with a higher affinity than oxygen

If curve 3 represents the binding of oxygen to Hb in normal red blood cells, which of the curves would represent the binding of oxygen to Hb when a His that interacts with BPG is mutated to a Gly? a. 1 b. 2 c. 3 d. 4 e. none of the above

b. 2 because one of the positively-charged residues involved in BPG binding has been substituted, it is likely that the mutated hemoglobin binds BPG with lower affinity. this means that the R state of hemoglobin is favored relative to the T state, so the oxygen binding curve will shift to the left

which of the following statements about 2,3-bisphosphoglycerate (BPG) binding is FALSE? a. BPG binds to hemoglobin at one site and lower hemoglobin's affinity for oxygen at another site b. BPGA aids oxygen delivery to tissues by increasing the affinity of myoglobin for oxygen c. BPG binds less tightly to fetal hemoglobin than to adult hemoglobin, thereby aiding oxygen transfer to a fetus d. BPG requires a binding site containing multiple positively charged groups

b. BPGA aids oxygen delivery to tissues by increasing the affinity of myoglobin for oxygen

What type of allosteric effector is oxygen? a. a heteroallosteric effector of hemoglobin b. a homoallosteric effector of hemoglobin c. a homoallosteric effector of myoglobin d. a heteroallosteric effector of myoglobin

b. a homoallosteric effector of hemoglobin oxygen causes hemoglobin to switch to the R state, which has a greater affinity for oxygen. this is a homoallosteric effect

which of the following is not a rule of the symmetry model of allosterism? a. an allosteric protein is an oligomer of symmetrically related subunits b. conformational changes occur sequentially as more ligand-binding sites are occupied c. the molecular symmetry of the protein is conserved during the conformational change d. each oligomer can exist in two conformational states, designated R and T; these states are in equilibrium

b. conformational changes occur sequentially as more ligand-binding sites are occupied

Why is the decreased affinity of fetal hemoglobin for BPG advantageous? a. with fewer BPG molecules bound there are more heme residues available for O2 binding b. decreased BPG binding biases that fetal hemoglobin toward the R state c. more free BPG is available to bind to adult hemoglobin, resulting in a shift to the R state d. BPG is available to bind to fetal myoglobin, helping to release O2 in fetal muscle tissue e. none of the above

b. decreased BPG binding biases that fetal hemoglobin toward the R state

oxygen is highly soluble in aqueous solution a. true b. false

b. false

which of the following statements about sickle cell anemia is FALSE? a. in sickle call anemia, hemoglobin molecules aggregate to form long fibers that distort the shape of the red blood cells b. sickle cell anemia is a consequence of a conservative mutation in the B-globin gene c. the mutation in sickle cell anemia replaces a hydrophilic surface residue with a non-polar residue d. sickle cell anemia is a genetic disease

b. sickle cell anemia is a consequence of a conservative mutation in the B-globin gene a mutation that significantly affects the folding or function of a protein cannot be considered conservative

What happens when hemoglobin is converted from the deoxy (T) form to the oxy (R) form? a. the iron in heme is oxidized from Fe2+ to Fe3+ b. the central cavity becomes smaller c. the heme becomes slightly dome-shaped and the iron lies out of the plane of the heme

b. the central cavity becomes smaller

if hemoglobin is in the 'T' state, what is the first component of the peptide chain that moves in response to oxygen binding? a. the Fe2+ ion b. the proximal histidine c. the distal histidine d. the heme group

b. the proximal histidine

Calcium modulates muscle activity through binding to the thin filament protein troponin C. a. false b. true

b. true

myoglobin increases the effective solubility of oxygen in muscle cells. a. false b. true

b. true

how many antigen-binding sites are present on an IgM molecule? a. 2 b. 4 c. 10 d. 16 e. 25

c. 10

IgG is the most common immunoglobulin in the circulatory system and in the extravascular fluid. It is composed of two light chains and two heavy chains. What is the approximate molecular mass of an IgG molecule? a. 23 kDa b. 75 kDa c. 150 kDa d. 360 kDa e. 950 kDa

c. 150 kDa

How does BPG decrease the affinity of hemoglobin for oxygen? a. BPG reacts with oxygen to produce bicarbonate b. BPG blocks the oxygen binding sites directly c. BPG binding to hemoglobin stabilizes the deoxy conformation d. BPG binding to hemoglobin stabilizes the oxy conformation

c. BPG binding to hemoglobin stabilizes the deoxy conformation

why is hemoglobin's affinity for oxygen sensitive to small changes in ph (the Bohr effect): a. the distal histidine becomes charged at lower pH, forcing the oxygen out of its binding pocket b. histidine side chains in the central cavity of hemoglobin are charged at lower pH, decreasing BPG binding c. Histidine side chains in hemoglobin become charged at lower pH forming salt bridges that stabilize the T state d. the affinity of the proximal histidine for the heme Fe2+ ions is pH-dependent

c. Histidine side chains in hemoglobin become charged at lower pH forming salt bridges that stabilize the T state histidine side chains in hemoglobin are more likely to be charged at lower pH and some of those charged side chains can form salt bridges that help to stabilize the T state. other histidine side chains, located in the central cavity, increase the binding affinity for BPG at lower pH. together, these two events confer hemoglobin's sensitivity to changes in pH

which class of antibodies has been implicated in allergic reactions? a. IgA b. IgD c. IgE d. IgG e. IgM

c. IgE

myoglobin's secondary structure is primarily composed of ______ a. parallel B-sheets b. antiparallel B-sheets c. a-helices d. omega- loops e. polyproline helices

c. a-helices

which of the following represents the true promoter of hemoglobin? a. B b. {a}2B2 c. aB d. a

c. aB

how is muscle contraction stimulated by calcium ions? a. calcium ions are released from the sarcoplasmic reticulum and bind to myosin, stimulating ATPase activity b. calcium ions are released from the sarcoplasmic reticulum and bind to tropomyosin, stimulating its ATPase activity c. calcium ions are released from the sarcoplasmic reticulum and bind troponin C, promoting the binding of myosin to actin d. calcium ions are released from the sarcoplasmic reticulum and bind to actin, promoting its binding to myosin

c. calcium ions are released from the sarcoplasmic reticulum and bind troponin C, promoting the binding of myosin to actin

which of the following statements about the structure of myoglobin is FALSE? a. a heme prosthetic group is tightly bound to myoglobin via a coordination bond. b. myoglobin contains a heme prosthetic group that is slotted into a hydrophobic pocket between a-helix E and a- helix F. c. myoglobin contains all three types of secondary structure d. the tertiary structure of myoglobin is a compact, roughly spherical shape

c. myoglobin contains all three types of secondary structure myoglobin contains only 2 types of secondary structure: a-helices and loops. it contains no B-sheet

myoglobin and a single chain of hemoglobin have similar ________ structures. a. primary b. secondary c. tertiary d. quaternary e. none of the above

c. tertiary

what are the two conformations of hemoglobin? a. the R state (the conformation of deoxyhemoglobin) and the T state (the conformation of oxyhemoglobin) b. the T state (the conformation of myoglobin) and the R state (the conformation of deoxyhemoglobin) c. the T state (the conformation of deoxyhgemoglobin) and the R state (the conformation of oxyhemoglobin) d. the T state (the conformation of dideoxyhemoglobin) and the R state (the conformation of deoxyhemoglobin)

c. the T state (the conformation of deoxyhgemoglobin) and the R state (the conformation of oxyhemoglobin)

If a Lys residue that interacts with 2,3-bisphosphoglycerate (BPG) in the central cavity of hemoglobin is changed to a Ser residue, how would this affect hemoglobin behaviour? a. oxygen binding would be less sensitive to pH b. the T state would be more stable c. the T state would be less stable d. oxygen binding would be more sensitive to pH

c. the T state would be less stable the replacement of Lys with Ser would reduce the affinity of hemoglobin for BPG and the T state would be less stable

which of the following statements correctly describes the interaction between an allosteric protein and an allosteric effector? a. the effector activates the protein by causing it to switch from its T (low affinity)n to R (high affinity) form. b. the effector binds non-specifically to one subunit and through induced fit initiates cooperatively between the subunits c. the effector binds reversibly at a specific site on one subunit of the protein, causing a global change in conformation d. the effector binds covalently at a specific site on the protein, causing a global change in shape

c. the effector binds reversibly at a specific site on one subunit of the protein, causing a global change in conformation

the repeating functional unit in a myofibril is called a. the A band b. the I band c. the sarcomere d. the H zone e. the M disk

c. the sarcomere

muscle contraction is directly caused by a. structural changes in actin b. structural changes in myosin c. thick and thin filaments sliding past each other d. structural changes in the Z disk e. none of the above is correct

c. thick and thin filaments sliding past each other

The value of n, the Hill constant (coefficient), for hemoglobin is about ______ as great as the value for myoglobin. a. half b. twice c. three times d. five times e. ten times

c. three times

in sickle-cell anemia, the negatively charged glutamic acid residue is replaced by the neutral amino acid _____ a. tyrosine b. lysine c. valine d. adenosine e. glycine

c. valine

If curve 3 represents the binding of oxygen to Hb at pH 7.4, which curve represents the binding of oxygen to Hb at pH 7.2? a. 1 b. 2 c. 3 d. 4 e. none of the above

d. 4 a change from pH 7.4 to pH 7.2 represents an increase in the concentration of H ions. As the concentration of H+ ions increases, BPG binds to hemoglobin with greater affinity. the T state of hemoglobin is thus favored and its fraction saturation decreases, especially at lower concentration of oxygen. the binding curve will shift to the right relative to its position at pH 7.4

If the gene for myoglobin is "knocked out" in mice, the mice: a. have larger lungs b. respire extremely rapidly c. have dark brown muscle tissue d. appear normal, with lighter colored muscle tissue e. have their growth stunted

d. appear normal, with lighter colored muscle tissue

which of the statements about muscle contraction is NOT true? a. during muscle contraction the sarcomere becomes shorter b. during muscle contraction the I band becomes shorter c. during muscle contraction to the H zone becomes shorter d. during muscle contraction the A band becomes shorter e. during muscle contraction the distance between the Z disk and the M disk becomes shorter

d. during muscle contraction the A band becomes shorter

which of the following statements about sickle cell anemia is INCORRECT? a. sickle-cell anemia is caused from deoxyhemoglobin S forming insoluble filamets b. the mutation causing sickle cell anemia is that hemoglobin S contains Val rather than Glu at the sixth position of each beta chain c. the administration of hydroxyurea is an effective treatment for sickle-cell anemia d. hemoglobin S has a lower affinity for oxygen han normal adult hemoglobin (hemoglobin A) e. individuals who are heterozygous carriers of hemoglobin S in an area where malaria is prevalent are more likely to survive to maturity than individuals who are homozygous for normal hemoglobin

d. hemoglobin S has a lower affinity for oxygen han normal adult hemoglobin (hemoglobin A)

which of the following diseases is not caused by a mutation in hemoglobin? a. hemolytic anemia b. polycythemia c. sickle-cell anemia d. hemophilia

d. hemophilia

Fetal hemoglobin has a higher affinity for oxygen than does adult hemoglobin. which of the following statements correctly outlines the mechanism behind the observation? a. in fetal hemoglobin, the residue Ser143 is mutated to His 143, and so the protein binds BPG with greater affinity. b. in fetal hemoglobin, the residue His 143 is mutated to Ser143, and so the protein binds BPG with greater affinity c. in fetal hemoglobin, the residue Ser143 is mutated to His143, and so the protein binds BPG with lower affinity d. in fetal hemoglobin, the residue His143 is mutated to Ser143, and so the protein binds BPG with lower affinity

d. in fetal hemoglobin, the residue His143 is mutated to Ser143, and so the protein binds BPG with lower affinity the mutation of His143 to Ser143 reduces the number of positively charged groups available to form salt bridges with BPG. this reduces the affinity of hemoglobin for BPG and thus the T (low affinity) state of hemoglobin is less stable

during vigorous exercise, the pH of blood passing through skeletal muscle decreases. how does this decrease affect the behavior of hemoglobin? a. it increases O2 binding to hemoglobin, because it decreases the binding of BPG b. it increases O2 binding to hemoglobin, because it increases the binding of BPG c. it decreases O2 binding to hemoglobin, because it decreases the binding of BPG d. it decreases O2 binding to hemoglobin, because it increases the binding of BPG

d. it decreases O2 binding to hemoglobin, because it increases the binding of BPG as pH decreases, certain histidine side chains become positively charged and hemoglobin binds more BPG. this stabilizes the T state of the protein and decreases O2 binding (%saturation)

the energy needed to drive muscle contraction comes from ATP hydrolysis that is carried out by a. G-actin b. tropomyosin c. myosin tails d. myosin heads e. f-actin

d. myosin heads

which of the following triggers the transition from T state to R state (low to high affinity) in hemoglobin? a. movement of the proximal histidine b. subunit disassociation c. heme binding d. oxygen binding e. oxygen dissociation

d. oxygen binding

Hemerythrin and hemocyanin are: a. human mutant hemoglobins with decreased oxygen affinity. b. hemoglobin variants that are found in animals at high altitude. c. synthetic derivatives of hemoglobin's heme group used in artificial blood substitutes. d. oxygen transport proteins found in invertebrates. e. tetrameric hemoglobin derivatives containing only a-chains (a4 tetramers).

d. oxygen transport proteins found in invertebrates.

Hemoglobin's p50 value is about ______ as great as myoglobin's p50 value. a. one-tenth b. half c. twice d. ten times e. twenty times

d. ten times

the Bohr effect refers to a. the increase in the affinity of Hb for O2 when the O2 concentration goes up b. the decrease in affinity of Hb for O2 when the BPG concentration goes up c. the decrease in affinity of Hb for O2 when the pH goes up d. the decrease in affinity of Hb for O2 when the pH goes down e. the decrease in affinity of Hb for O2 when the BPG concentration goes down

d. the decrease in affinity of Hb for O2 when the pH goes down

The reaction of carbonic anhydrase catalyzes a. the formation of carbamates with the concomitant release of protons b. the hydration of bicarbonate, resulting in the formation of carbonic acid c. the reduction of carbon dioxide with the concomitant consumption of protons d. the hydration of carbon dioxide, forming bicarbonate and protons e. the hydrolysis of carbamates with the concomitant consumption of protons

d. the hydration of carbon dioxide, forming bicarbonate and protons

the Hill plot shows that the fourth oxygen binds to hemoglobin with a _____-fold greater affinity than the first. a. 2 b. 5 c. 10 d. 20 e. 100

e. 100

how many different classes of antibodies are produced by the human immune system? a. 1 b. 2 c. 3 d. 4 e. 5

e. 5

which statement about myosin is NOT true? a. myosin is a heterohexamer b. myosin contains 2 globular heads c. myosin contains six different polypeptides d. myosin aggregates to form thick filaments e. all of the answers above are true of myosin

e. all of the answers above are true of myosin

which statement about antigen-binding sites in antibodies is false? a. an antigen-binding site on an IgG is formed by the amino-terminal ~110 amino acids of a heavy chain b. an antigen-binding site on an IgG is formed by the variable region of a light chain and the variable region of a heavy chain c. the antigen-binding site is composed of two Ig folds d. antigen-binding specificity is determined by the sequences of the hypervariable sequences in both the light chain and the heavy chain e. antigen binding specificity is determined exclusively by the sequences in the carboxyl-terminal ~110 amino acids in the light chain and the heavy chain

e. antigen binding specificity is determined exclusively by the sequences in the carboxyl-terminal ~110 amino acids in the light chain and the heavy chain

Myoglobin's primary physiological role is to facilitate oxygen ________. a. storage b. metabolism c. binding d. reduction e. diffusion

e. diffusion

If curve 3 represents the binding of oxygen to normal Hb, which curve would represent the binding behavior of mutant hemoglobin that binds BPG irreversibly? a. 1 b. 2 c. 3 d. 4 e. none of the above

e. none of the above

which of the following statements about the symmetry model of allosterism is NOT true? a. the protein is an oligomer of symmetrically (or pseudosymmetrically) related subunits b. the oligomer can exist in two conformational states, which are in equilibrium c. the ligand can bind to a subunit in either conformation d. the molecule symmetry of the protein is conserved during the conformational change e. none of the above

e. none of the above

during muscle contraction myosin heads a. walk along thick filaments toward the M disk b. walk along thick filaments toward the Z disk c. walk along thin filaments toward the M disk d. walk along the thin filaments toward the H zone e. walk along the thin filaments toward the Z disk

e. walk along the thin filaments toward the Z disk

the secondary structure of myoglobin consists of ______ a-helices and the connecting loops.

eight

which of the statements below about hemoglobin is INCORRECT: a. it has been dubbed an "honorary enzyme" even though it functions in oxygen transport and does not catalyze a chemical reaction b. the quaternary structure of hemoglobin consists of 4 polypeptide chains c. hemoglobin is part of an oxygen delivery system that is needed for animals that are too large for oxygen to be delivered by simple diffusion d. hemoglobin gives red blood cells their color e. hemoglobin is a tetramer made up of myoglobin-like subunits f. subunit interfaces in hemoglobin are composed of predominantly salt bridges

f. subunit interfaces in hemoglobin are composed of predominantly salt bridges these interfaces are predominantly hydrophobic

in striated muscle, cells undergo mitosis (nuclear division) without cytokinesis (cellular division), giving rise to large myltinuleate cells. Muscle cells would be less effective if cytokinesis occurred with every round of mitosis. each cell of striated muscle is a muscle fiber with numerous ______ positioned end to end. if cytokinesis occurred more frequently, individual muscle cells would be much ________. _________ located in separate small cells would likely _________ and the overall shortening of the muscle would be _____________

sarcomeres; shorter sarcomere; not align optimally; less