Haemoglobin transports oxygen around the body of many ...

Haemoglobin transports oxygen around the body of many animals.

(a) Haemoglobin is a protein with a quaternary structure.

Explain the meaning of quaternary structure.

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(b) When fully saturated, each molecule of haemoglobin is bound to four molecules of oxygen.

The graph shows the percentage saturation of haemoglobin with oxygen at different partialpressures.

Give the formula for calculating the percentage saturation of haemoglobin with oxygen.

Percentage saturation ofhaemoglobin with oxygen

=

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(c) The first molecule of oxygen to bind causes a change in the shape of the haemoglobinmolecule.

This change of shape makes it easier for other oxygen molecules to bind to thehaemoglobin molecule.

Explain how the graph provides evidence for this.

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(d) Suggest one advantage of this change in the affinity of haemoglobin for oxygen.

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(e) Tests on the man whose blood was used to construct the graph gave the following data.

• Concentration of haemoglobin in blood = 150 g dm −3.• Volume of oxygen carried by fully saturated haemoglobin = 1.35 cm 3 g−1.• Resting heart rate = 60 beats minute −1.• Volume of blood pumped out of left ventricle each beat = 60 cm 3.

Use these data and information from the graph to calculate the volume of oxygen releasedto the man’s tissues per minute whilst he was at rest.

Show your working.

Answer =______________cm3 minute−1

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(Total 8 marks)

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Haemoglobin is a protein. It is made of two alpha polypeptides and two beta polypeptides. Eachalpha polypeptide has 141 amino acids and each beta polypeptide has 146 amino acids.

(a) What term is used to describe the structure of a protein made of two or more polypeptides?

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(b) Calculate the minimum number of DNA bases needed to code for the number of aminoacids in one alpha polypeptide.

Answer = ____________________

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(c) Describe the role of haemoglobin in supplying oxygen to the tissues of the body.

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Anaemia is a condition in which there is a decrease in the concentration of haemoglobin in blood.In some people with anaemia, substances are produced which change the oxygen dissociationcurve of haemoglobin.

The graph shows the effect of these substances on the oxygen dissociation curve ofhaemoglobin.

(d) (i) Use information in the graph to find the difference in the percentage saturation ofhaemoglobin with oxygen between a healthy person and a person with anaemia at apartial pressure of oxygen of 4 kPa.

Answer = ____________________

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(ii) Explain the advantage to a person with anaemia of the change shown in the oxygendissociation curve.

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(Total 8 marks)

The diagram shows a molecule of haemoglobin.

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(a) What is the evidence from the diagram that haemoglobin has a quaternary structure?

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(b) (i) A gene codes for the α-polypeptide chain. There are 423 bases in this gene that codefor amino acids. How many amino acids are there in the α-polypeptide chain?

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(ii) The total number of bases in the DNA of the α-polypeptide gene is more than 423.

Give two reasons why there are more than 423 bases.

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2. ____________________________________________________________

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(c) The haemoglobin in one organism may have a different chemical structure from thehaemoglobin in another organism. Describe how.

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(d) The graph shows oxygen dissociation curves for horse haemoglobin and for llamahaemoglobin. Horses are adapted to live at sea level and llamas are adapted to live in highmountains.

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Use the graph to explain why llamas are better adapted to live in high mountains thanhorses.

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(Total 8 marks)

(a) A fish uses its gills to absorb oxygen from water. Explain how the gills of a fish are adaptedfor efficient gas exchange.

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Mackerel live in the surface waters of the sea. Toadfish live on the seabed in deep water.

(b) The concentration of oxygen is higher in the surface waters than it is in water close to theseabed. Suggest why.

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(c) The graph shows oxygen dissociation curves for toadfish haemoglobin and for mackerelhaemoglobin.

Explain how the shape of the curve for toadfish haemoglobin is related to where thetoadfish is normally found.

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(d) Scientists analysed the sequence of amino acids in one polypeptide chain in thehaemoglobin of four different species of ape. The only difference they found affected theamino acids at three positions in the polypeptide chain. Their results are shown in the table.The letters are abbreviations for particular amino acids.

Species Position 87 Position 104 Position 125

Chimpanzee T R P

Bonobo T R P

Gorilla T K P

Orang utan K R Q

What information do the data in the table suggest about the relationships between thechimpanzee, the bonobo and the gorilla? Explain your answer.

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(Total 12 marks)

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The diagram shows part of the metabolic pathway involved in the clotting of blood in response toan injury.

Haemophilia is a condition in which blood fails to clot. This is usually because of a mutant alleleof the gene for Factor VIII.

(a) Explain how mutation could lead to faulty Factor VIII.

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(b) Use information in the diagram to explain how faulty Factor VIII causes haemophilia.

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(c) A boy had haemophilia caused by faulty Factor IX. When his blood was mixed with bloodfrom a haemophiliac with faulty Factor VIII, the mixture clotted. Suggest an explanation forclotting of the mixture.

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(2)

(Total 6 marks)

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Mark schemes

(a) (Molecule contains) more than one polypeptide (chain).

Accept: has four polypeptides1

1.

(b)

1

(c) 1. At low partial pressure of oxygen, little increase in saturation as oxygen increases;

2. (then) rapid rise as it gets easier for oxygen to bind.

Accept use of appropriate numbers from graph2

(d) Ensures rapid / more intake of oxygen in lungs / release of oxygen in tissues.1

(e) Volume of blood leaving heart = (0.6 × 0.6) dm3 minute−1 = 3.6 dm3 minute-1

Mass of haemoglobin in this volume of blood = (3.6 × 150) g = 540g

Volume of oxygen at 100% saturation of this haemoglobin = (540 × 1.35) = 729 cm3

The graph shows 60% of this volume of oxygen has been released to the tissues, so finalanswer is (729 × 0.6) = 437.4 cm3 minute −1

3

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(a) Quaternary (structure);

Accept phonetic spelling eg quarternary/quarternery /4°

Award no mark for quaternary as part of a list1

(b) 423;1

(c) 1. Oxyhaemoglobin formed/ haemoglobin is loaded/uptakes/associates/binds with oxygen in area of higher ppO2 /in gas exchange surface/lungs/gills;

Reference to “react with” = max 1

Accept: reversible interaction with oxygen

Ignore: haemoglobin is carried / contained in red blood cells2. (oxygen) unloaded/dissociates from/released (in area of lower

ppO2 / in capillaries/to cells/tissues);2

(d) (i) 56(%);

Accept responses in the range 54-58(%)1

(ii) 1. (Anaemia curve shifted to right) haemoglobin has loweraffinity for oxygen / binds less tightly;

Assume reference is to haemoglobin of anaemia unless stated2. releases more oxygen / oxygen is released quicker / oxygen

dissociates/ unloads more readily to muscles/tissues/cells;3. (For) respiration;

Accept: even with a lower haemoglobin concentration / meetdemand for ATP/energy;

3[8]

2.

(a) More that one polypeptide / chain;

Ignore references to haem / other groups1

(b) (i) 141;1

3.

(ii) 1. Stop / start sequences;

2. Non coding DNA (in the gene) / introns / multiple repeats / junk DNA;

Do not credit “some bases repeated”

3 Two chains / a non-coding strand / complementary base pairs;

4. Addition of base by mutation;2 max

(c) Different primary structure / amino acids / different number of polypeptide chains;

Question is about haemoglobin so do not credit differences in DNA1

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(d) 1. Low partial pressure of oxygen in lungs;

2. (Llama) haemoglobin able to load more oxygen / (llama)haemoglobin saturated (at low / particular partial pressure of oxygen);

3. Higher affinity for oxygen;

The terms used in the graph (or near approximations) should beused in this answer.

Ignore references to unloading

The answer must relate to llamas3

[8]

(a) 1. Large surface area provided by lamellae / filaments increases diffusion / makesdiffusion efficient;;

Q Candidates are required to refer to lamellae or filaments. Do notpenalise for confusion between two

2. Thin epithelium / distance between water and blood;

3. Water and blood flow in opposite directions / countercurrent;

4. (Point 4) maintains concentration gradient (along gill) / equilibrium not reached /as water always next to blood with lower concentration of oxygen;

5. Circulation replaces blood saturated with oxygen;

6. Ventilation replaces water (as oxygen removed);6

4.

(b) Mixing of air and water (at surface);

Air has higher concentration of oxygen than water;

Diffusion into water;

Plants / seaweeds near surface / in light;

Produce oxygen by photosynthesis;2 max

(c) Not much oxygen near sea bed;

Toadfish haemoglobin (nearly) saturated / loads readily at / has higher affinity foroxygen at low partial pressure (of oxygen);

2

(d) The chimpanzee and the bonobo are more closely related (than to the gorilla);

They have identical amino acids / one of the amino acids is different in the gorilla;2

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(a) mutation changes the amino acid sequence / primary structure of Factor VIII protein;changes the tertiary structure / 3D shape;

2

5.

(b) (mutant) Factor VIII protein is non-functional / does not work with Factor IX;so no conversion of Factor X to active form and pathway blocked;

2

(c) boy’s blood contains (active) Factor VIII;Factor VIII haemophiliac’s blood contains (active) Factor IX;the mixture has both Factors and so the pathway cancomplete / blood clots;

2 max

[6]

of 15Loxford School

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