IB DP Chemistry B.1 Introduction to biochemistry SL Paper 3

 

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Question 

Insulin was the first protein to be sequenced. It was determined that the end of one chain had the primary structure Phe-Val-Asn-Gln.
Paper chromatography can be used to identify the amino acids in insulin.
a. Draw the structural formula of a dipeptide containing the residues of valine, Val, and asparagine, Asn, using section 33 of the data booklet.
b. Deduce the strongest intermolecular forces that would occur between the following amino acid residues in a protein chain.

c.i. State the name of the process used to break down the insulin protein into its constituent amino acids.
c.ii.Outline how the amino acids may be identified from a paper chromatogram.

▶️Answer/Explanation

Markscheme

a.

correct structures of Val AND Asn
correct amide link
[2 marks]
b. Phenylalanine and valine:
London/dispersion/instantaneous induced dipole-induced dipole forces OR
permanent dipole-induced dipole «interactions»
Glutamine and asparagine:
hydrogen bonds
Do not accept dipole-dipole interactions.
[2 marks]
c.i. hydrolysis
[1 mark]

c.ii.compare $\mathrm{R}_{\mathrm{f}}$ with known amino acids
OR
compare distance moved with known amino acids
Accept “from $R_f$ “.
[1 mark]

 
 

Question 

Lipids provide energy and are an important part of a balanced diet.
a. Identify the type of chemical reaction that occurs between fatty acids and glycerol to form lipids and the by-product of the reaction.

b. Arachidonic acid is a polyunsaturated omega-6 fatty acid found in peanut oil.
Determine the number of carbon-carbon double bonds present if the iodine number for the compound is 334. (Arachidonic acid $M_{\mathrm{r}}=304.5$ )
c. Deduce the structure of the lipid formed by the reaction between lauric acid and glycerol (propane-1,2,3-triol) using section 34 of the data booklet.
d. Outline one impact food labelling has had on the consumption of foods containing different types of lipids.
e. Determine, to the correct number of significant figures, the energy produced by the respiration of $29.9 \mathrm{~g}_{\text {of }} \mathrm{C}_5 \mathrm{H}_{10} \mathrm{O}_5$.
$$
\Delta H_c\left(\mathrm{C}_5 \mathrm{H}_{10} \mathrm{O}_5\right)=205.9 \mathrm{~kJ} \mathrm{~mol}^{-1}
$$
f. Explain why lipids provide more energy than carbohydrates and proteins.

▶️Answer/Explanation

Markscheme

a. Type of reaction:
condensation
OR
esterification/triesterification
OR
nucleophilic substitution/nucleophilic displacement/ $\mathrm{S}_{\mathrm{N}} 2$
By-product:
water $/ \mathrm{H}_2 \mathrm{O}$
Do not accept just “substitution/displacement”.
[2 marks]

b. ALTERNATIVE 1
$$
\begin{aligned}
& \text { ” } \frac{334}{253.8}=\text { 1.32 AND « } \frac{100}{304.5}=\text { D } 0.328 \\
& « \frac{1.32}{0.328} \approx 4 \\
&
\end{aligned}
$$
ALTERNATIVE 2
$$
\begin{aligned}
& \text { «334 } \times \frac{304.5}{100} \approx 1017 \\
& \text { « } \frac{1017}{253.8} \approx 4 \\
&
\end{aligned}
$$
Award [2] for correct final answer.
[2 marks]

c.

glycerol backbone
ester formula AND linkage
Accept a skeletal structure.
Penalize missing hydrogens or incorrect bond connectivities once only in Option B.
Accept condensed formula for ester.
[2 marks]
d. has affected consumption of trans-fats/cis-fats/saturated fats/unsaturated fats/hydrogenated/artificially altered fats
OR
reduce/eliminate trans-fats/increase in cis-fats
OR
reduce/eliminate saturated fats
OR
increase unsaturated fats
Do not accept “decrease in fat” alone.
Accept “lipid” for “fats”.
[1 mark]

e. $« \frac{29.9 \mathrm{~g}}{150.15 \mathrm{~g} \mathrm{~mol}^{-1}}=\geqslant 0.199$ «mol»
$« 0.199 \mathrm{~mol} \times 205.9 \mathrm{~kJ} \mathrm{~mol}^{-1}=» 41.0 « \mathrm{~kJ} »$
Ignore significant figures in $M 1$.
Award [2] for correct final answer.
Award [1 max] for incorrect significant figures in final answer.
[2 marks]
f. ratio of oxygen to carbon in lipids lower
OR
lipids less oxidized
OR
lipids more reduced
more energy per mass/g released when lipids are oxidized
Accept “raverage» oxidation number of carbon in linoleic acid is lower” for M1.
[2 marks]

 

 
 

Question 

Dietary recommendations are made by scientists.
a. The formation of proteins from amino acids is an example of an anabolic reaction in the human body. State the source of energy for such a synthetic reaction.
b. Suggest why it is advisable for those living in northerly or southerly latitudes (that is away from the equator) to take vitamin D supplements during the winter.
c. Explain how a xenobiotic is biomagnified.

▶️Answer/Explanation

Markscheme
a. catabolism «of food/nutrients»
OR
«cellular» respiration
Accept “ATP” but not “burning of food/nutrients”.
b. not enough sunlight/UV light «for synthesis of vitamin D in the skin»

c. cannot be metabolized/broken down
OR
not biodegradable
OR
accumulates in lipid/fat tissues
increased concentration as one species feeds on another «in the food chain» $\checkmark$

 
 

Question 

,Starch is a natural polymer of glucose.
a. Draw the structure of the repeating unit of starch and state the type of linkage formed between these units.
Type of linkage:
b. Formulate the equation for the complete hydrolysis of a starch molecule, $\left(\mathrm{C}_6 \mathrm{H}_{10} \mathrm{O}_5\right)_n$.
c. Calculate the energy released, in $\mathrm{kJ} \mathrm{g}^{-1}$, when $3.49 \mathrm{~g}$ of starch are completely combusted in a calorimeter, increasing the temperature of $975 \mathrm{~g}$ of water from $21.0^{\circ} \mathrm{C}$ to $36.0^{\circ} \mathrm{C}$. Use section 1 of the data booklet.
d. Explain how the inclusion of starch in plastics makes them biodegradable.
▶️Answer/Explanation

a.
continuation bonds $A N D$-O- attached to just one end $A N D$ both $\mathrm{H}$-atoms on end carbons must be on the same side [ $\boldsymbol{C}$ ]
Note: Square brackets not required.
Ignore ” $n$ ” if given.
Mark may be awarded if a polymer is shown but with the repeating unit clearly identified.
Type of linkage:
glycosidic [ $\sim]$
Note: Accept “ether”.
b. $\left(\mathrm{C}_6 \mathrm{H}_{10} \mathrm{O}_5\right)_n(\mathrm{~s})+n \mathrm{H}_2 \mathrm{O}(\mathrm{l}) \rightarrow n \mathrm{C}_6 \mathrm{H}_{12} \mathrm{O}_6$ (aq) $[\checkmark]$
Note: Accept ” $(n-1) \mathrm{H}_2 \mathrm{O}$ “.
Do not award mark if ” $n$ ” not included.
c. $q=« m c \Delta T=975 \mathrm{~g} \times 4.18 \mathrm{~J} \mathrm{~g}^{-1} \mathrm{~K}^{-1} \times 15.0 \mathrm{~K}=» 61100$ «J $/ 61.1$ «J»] [ «heat per gram $=\frac{61.1 \mathrm{~kJ}}{3.49 \mathrm{~g}}=» 17.5$ «kJ g${ }^{-1} »[\boldsymbol{U}]$
Note: Award [2] for correct final answer.
d. Any two of:
carbohydrate grains swell/break plastic into smaller pieces $[\boldsymbol{W}$
inclusion of carbohydrate makes the plastic more hydrophilic/water soluble $[\boldsymbol{V}]$
carbohydrates are broken down/hydrolysed/digested by bacteria/micro-organisms $[\boldsymbol{\sim}]$
plastic becomes more accessible to bacteria as holes/channels are created in it $[\boldsymbol{\sim}]$
«presence of» carbohydrate weakens intermolecular/London/dispersion forces between polymer chains in the plastic [ $\boldsymbol{\sim}$ ]
Note: Accept “starch” for “carbohydrate” throughout. Do not accept carbohydrates are broken down/hydrolyzed.

Question 

Phosphatidylcholine is an example of a phospholipid found in lecithin.
Phosphatidylcholine may be formed from propane-1,2,3-triol, two lauric acid molecules, phosphoric acid and the choline cation.

\text { a(i)Deduce the structural formula of phosphatidylcholine. }

a(ii)dentify the type of reaction in (a).
b. Lecithin is a major component of cell membranes. Describe the structure of a cell membrane.
c. Predict, giving a reason, the relative energy density of a carbohydrate and a lipid of similar molar mass.
d. Lecithin aids the body’s absorption of vitamin E.

Suggest why vitamin $\mathrm{E}$ is fat-soluble.
e. Phospholipids are also found in lipoprotein structures.
Describe two effects of increased levels of low-density lipoprotein (LDL) on health.

▶️Answer/Explanation

Markscheme

a(i).

phosphodiester correctly drawn [ $\boldsymbol{\sim}]$
both ester groups correctly drawn $[\sim]$
Note: Accept protonated phosphate.
Accept phosphodiester in centre position.
a(ii)ondensation [ $\boldsymbol{V}]$
Note: Accept “esterification”.
Accept “nucleophilic substitution/ $S_N$ “.
b. phospholipid bilayer/double layer
OR
two layers of phospholipids [ $\boldsymbol{V}]$
polar/hydrophilic heads facing aqueous environment $A N D$ non-polar/hydrophobic tails facing away from aqueous environment [ $\boldsymbol{D}$ ]
Note: Award [2] for a suitably labelled diagram.
Award [1 max] for a correct but unlabelled diagram.
Accept “polar/hydrophilic heads on outside AND non-polar/hydrophobic tails on inside for M2.
c. carbohydrates less energy dense AND carbohydrates higher ratio of oxygen to carbon/more oxidized/less reduced [ $\boldsymbol{]}$ ]

d. long non-polar/hydrocarbon chain «and only one hydroxyl group»
OR
forms London/dispersion/van der Waals/vdW interactions with fat [ $\boldsymbol{J}]$
Note: Accept “alcohol/hydroxy/OH” for “hydroxyl” but not “hydroxide”.
e. atherosclerosis/cholesterol deposition «in artery walls» [ $\boldsymbol{V}]$
increases risk of heart attack/stroke/cardiovascular disease/CHD [ $\mathcal{V}]$
Note: Accept “arteries become blocked/walls become thicker”, “increases blood pressure”, or “blood clots”.
Do not accept “high cholesterol”.

 
 

Question 

\text { Lactose is a disaccharide formed by the condensation reaction of the monosaccharides galactose and glucose. }

a. Describe what is meant by a condensation reaction.
b. Draw the structure of galactose on the skeleton provided.

c. Explain how the inclusion of carbohydrates in plastics makes them biodegradable.

▶️Answer/Explanation

Markscheme
a. «reaction in which» two reactants/molecules/functional groups bond/react «to form a larger molecule/single main product» small/tiny molecule
OR
$\mathrm{H}_2 \mathrm{O}$ formed
Accept formula or name of a specified small molecule other than water such as ammonia, ethanoic/acetic acid, ethanol, hydrogen sulfide etc. for $M 2$.
Do not accept just “molecule formed”.
Award [1 max] for an example giving an equation of a condensation reaction such as the formation of a disaccharide.

b.

Accept “alpha” or “beta” form of galactose.
c. Any two of:
makes the plastic more hydrophilic/water soluble
carbohydrates are broken down/hydrolysed by bacteria/microorganisms
makes plastic more accessible to bacteria as holes/channels are created
OR
plastic of lower density is more permeable/susceptible to water/oxygen/heat/pressure
weakens intermolecular/London/dispersion/instantaneous induced dipole-induced dipole forces «between polymer chains in the plastic»
Accept “van der Waals/vdW” for “London” forces.
[Max 2 Marks]

 
 

Question

Most foods are complex mixtures and many components of them are nutrients.

Identify the types of nutrients A, B and C.

A     M12/4/CHEMI/SP3/ENG/TZ1/F1.b_1

B     M12/4/CHEMI/SP3/ENG/TZ1/F1.b_2

C     M12/4/CHEMI/SP3/ENG/TZ1/F1.b_3

[3]
b.

State the names of two types of nutrient other than those shown in part (b).

[2]
c.
▶️Answer/Explanation

Markscheme

A: protein / polypeptide/tripeptide;

B: carbohydrate / sugar / monosaccharide / glucose;

C: lipid / triglyceride / vegetable oil / fat;

b.

vitamins;

minerals;

water;

c.

Examiners report

This question was generally well answered by many candidates. Though most had a general idea of the difference between a food and a nutrient, many did not appreciate the distinction between an “unhealthy” food and one that isn’t a nutrient.

b.

This question was generally well answered by many candidates. Though most had a general idea of the difference between a food and a nutrient, many did not appreciate the distinction between an “unhealthy” food and one that isn’t a nutrient.

c.

Question

Glucose, C6H12O6, is a monosaccharide that our body can use as a source of energy.

Deduce the equation for the cellular respiration of glucose.

[1]
a.

Calculate the energy, in kJ, produced from 15.0g of glucose if its enthalpy of combustion is −2803kJmol−1.

[2]
b.

Glucose is the basic building block of starch which can be used to make bioplastics. Outline two advantages and two disadvantages of biodegradable plastics.

Two advantages:

Two disadvantages:

[4]
c.

Bioplastics are broken down by enzyme catalysed reactions. Sketch a graph illustrating how the rate of this reaction varies with pH.

[1]
d.
▶️Answer/Explanation

Markscheme

C6H12O6 (aq) + 6O2 (aq) → 6CO2 (aq) + 6H2O (l)

Accept equations for anaerobic respiration, such as C6H12O6 (aq) → 2C3H6O3 (aq)
Ignore ATP if added as a product.

 

a.

\(n\left( {{{\rm{C}}_{\rm{6}}}{{\rm{H}}_{{\rm{12}}}}{{\rm{O}}_{\rm{6}}}} \right)\left\langle { = \frac{{15.0}}{{180.18}}} \right\rangle  = 0.0833 \ll {\rm{mol}} \gg \)

«energy=0.0833×2803=»233«kJ»

Award [2] for correct final answer.
Accept -233«kJ».

b.

Two advantages:   
renewable resource

broken down/digested by bacteria or other organisms within a relatively short time/quickly
reduce «volume of» plastic waste/landfill

reduce use of petrochemicals
OR
reduce use of fossil fuels as hydrocarbon source

degrade into non-toxic products

Any two advantages for [2 max].
M2: reference must be made to time. Do not accept “biodegradable” (since stated in question).
Ignore any mention of cost.

Two disadvantages:
require use of land «for crop production»

increased use of fertilizers/pesticides «leading to pollution»
OR
eutrophication

might break down before end of use
release of methane/CH4/greenhouse gas «during degradation»

Any two disadvantages for [2 max].
Ignore any mention of cost.

c.

typical curve as shown in example above

Accept any curve with a single maximum (not just bell-shaped).
Ignore features such as pH values on a pH scale or a pH value at maximum (if given).
Do not penalize if curve does not touch the x-axis.

d.

Question

Carbohydrates are energy-rich molecules which can be synthesized in some plant cells from inorganic compounds.

State the raw materials and source of energy used in the process described above.

[1]
a.

The structures of two molecules, X and Y, are shown below.

(i) Justify why both these molecules are carbohydrates.

(ii) Distinguish between these molecules in terms of their functional groups.

[2]
b.

Amylose is an unbranched polysaccharide composed of repeating units of glucose.

(i) Draw the structure of the repeating unit of amylose. Use section 34 of the data booklet.

(ii) Amylose is a major component of starch. Corn starch can be used to make replacements for plastics derived from oil, especially for packaging. Discuss one potential advantage and one disadvantage of this use of starch.

[3]
c.
▶️Answer/Explanation

Markscheme

CO2 AND H2O AND sun

Accept names.
Accept “sunlight/light/photons” instead of “sun”.

a.

i

both have formula Cx(H2O)y
OR
both contain several OH/hydroxyl «groups» AND a C=O/carbonyl «group»

Accept “both have the formula CnH2nOn /empirical formula CH2O” but do not accept “both have same molecular formula/have formula C3H6O3”.

Accept “aldehyde or ketone” for “carbonyl”.

ii

Accept “alkyl” for “R”.
Accept “X: aldose/aldehyde AND Y: ketose/ketone”.
Accept “CO” for “C=O”.

b.

i

continuation bonds AND open O on either but not both ends

Brackets are not necessary for the mark.
Do not accept β-isomer.
Mark may be awarded if a polymer is shown but with the repeating unit clearly identified.
3-D representation is not required.

ii

Advantage:
Any one of:

biodegradable / break down naturally/by bacteria

Do not accept just “decompose easily”.

compostable

does not contribute to land-fill

renewable/sustainable resource

starch grains swell AND help break up plastic

lower greenhouse gas emissions

uses less fossil fuels than traditional plastics

less energy needed for production

Disadvantage:
Any one of:

land use «affects biodiversity/loss of habitat»

growing corn for plastics instead of food

«starch» breakdown can increase acidity of soil/compost

«starch» breakdown can produce methane «especially when buried»

sensitive to moisture/bacteria/acidic foods

«bioplastics sometimes» degrade quickly/before end of use

cannot be reused

poor mechanical strength

eutrophication

increased use of fertilizers/pesticides/phosphorus/nitrogen «has negative environmental effects»

Ignore any reference to cost.
Accept “prone to site explosions/fires” or “low heat resistance” for disadvantage.

Only award [1 max] if the same example is used for the advantage and disadvantage.

c.

Question

Sugars exist in both straight chain and ring forms.

Biodegradable plastics produced from starch present one solution to the environmental problem created by the use of large quantities of plastics.

Deduce the straight chain structure of ribose from its ring structure drawn in section 34 of the data booklet.

[1]
a.i.

Using the partial structure given, complete the structural formula of the molecule formed from the condensation of two cyclic \(\alpha \)-glucose molecules.

M17/4/CHEMI/SP3/ENG/TZ1/12.a.ii

[1]
a.ii.

Constructing models that allow visualizations of the stereochemistry of carbohydrates is essential to understand their structural roles in cells.

Describe how Haworth projections help focus on the position of attached groups.

[1]
b.

State one advantage of starch based polymers besides being biodegradable.

[1]
c.i.

Biodegradable boxes made from polylactic acid, PLA, disintegrate when exposed to water.

State the formula of the product formed when water reacts with PLA.

[1]
c.ii.
▶️Answer/Explanation

Markscheme

All OH groups must be on the same side.

Accept structures with chiral carbon atoms shown as C or C* instead of crosses.

[1 mark]

a.i.

M17/4/CHEMI/SP3/ENG/TZ1/12.a.ii/M

Accept –O– in a straight line provided both H’s are above the plane.

[1 mark]

a.ii.

«allow» 3-D perspective of structures «of cyclic monosaccharide molecules»
OR
«show» cis/same side arrangement of «attached» groups
OR
«show» trans/opposite side arrangement of «attached» groups
OR
«make» carbon and hydrogen implicit

[1 mark]

b.

abundant/renewable/allows use of «local» vegetation
OR
less use of fossil fuel/oil based plastics
OR
air permeable/better breathing of products
OR
«can be» mixed/blended with synthetic polymers

Do not accept answers related to biodegradable examples.

Ignore any reference to cost.

Accept “carbon neutral/do not contribute to global warming”.

Accept “require less energy to produce”.

Accept “do not produce toxic products”.

[1 mark]

c.i.

HO–CH(CH3)–COOH/CH3CH(OH)COOH

Do not accept C3H6O3.

Do not accept OH–CH(CH3)–COOH.

[1 mark]

c.ii.

Question

Peptidase enzyme in the digestive system hydrolyses peptide bonds.

A tripeptide Ala-Asp-Lys was hydrolysed and electrophoresis of the mixture of the amino acids was carried out at a pH of 6.0. Refer to section 33 of the data booklet.

Identify the type of metabolic process that occurs in the hydrolysis of the peptide during digestion.

[1]
a.

Identify the name of the amino acid that does not move under the influence of the applied voltage.

[1]
b.i.

Deduce, giving a reason, which amino acid will develop closest to the negative electrode.

[2]
b.ii.

The breakdown of a dipeptide in the presence of peptidase was investigated between 18 °C and 43 °C. The results are shown below.

Comment on the rate of reaction at temperature X in terms of the enzyme’s active site.

[1]
c.

The solubility of a vitamin depends on its structure.

Identify the vitamin given in section 35 of the data booklet that is the most soluble in water.

[1]
d.

Pollution from heavy metal ions has become a health concern.

Outline how the presence of heavy metal ions decreases the action of enzymes.

[1]
e.

Outline how lead ions could be removed from an individual suffering from lead poisoning.

[1]
f.
▶️Answer/Explanation

Markscheme

catabolism/catabolic

[1 mark]

a.

alanine

Do not accept ala.

[1 mark]

b.i.

Lys/lysine

pH «buffer» < pI «Lys»
OR
buffer more acidic than Lys «at isoelectric point»
OR
«Lys» exists as 

OR

«Lys» charged positively/has +1/1+ «overall» charge «and moves to negative electrode»

Do not apply ECF from M1.

Accept converse argument.

Do not accept just “has H3N+ group” for M2 (as H3N+ is also present in zwitterion).

Do not penalize if COOH is given in the structure of lysine at pH 6 instead of COO.

[2 marks]

b.ii.

highest frequency of successful collisions between active site and substrate
OR
highest frequency of collisions between active site and substrate with sufficient energy/\(E \geqslant {E_{\text{a}}}\) AND correct orientation/conformation
OR
optimal shape/conformation of the active site «that matches the substrate»
OR
best ability of the active site to bind «to the substrate»

Accept “number of collisions per unit time” for “frequency”.

Do not accept “all active sites are occupied”.

[1 mark]

c.

ascorbic acid/vitamin C

[1 mark]

d.

react/bind/chelate with enzyme
OR
disrupt ionic salt bridges
OR
affect shape of tertiary/quaternary structures
OR
precipitate enzymes
OR
break/disrupt disulfide bridges/bonds

Do not accept “changes shape of active site” by itself.

[1 mark]

e.

«use of» host-guest chemistry
OR
chelation «therapy»

Accept specific medication/chelating agent such as EDTA, CaNa2 EDTA, succimer, D-penicillamine, dimercaprol.

[1 mark]

f.

Question

A chemical reaction occurs when a phospholipid is heated with excess sodium hydroxide.

Glycerol is one product of the reaction. Identify the two other organic products.

[2]
a.

Identify the type of reaction which occurs.

[1]
b.
▶️Answer/Explanation

Markscheme

C17H31COONa 

[(CH3)3NCH2CH2OH]OH

Accept “NaC17H31COO”.

Accept “(CH3)3N+CH2CH2OH OR [(CH3)3NCH2CH2OH]+” if positive charge is shown.

Accept suitable names (eg, sodium linoleate, choline hydroxide etc.) OR correct molecular formulas.

[2 marks]

a.

hydrolysis

Accept “nucleophilic substitution/displacement / SN/SN2 /saponification”.

Do not accept “acid hydrolysis”.

[1 mark]

b.

Question

Lactose is a disaccharide formed by the condensation reaction of the monosaccharides galactose and glucose.

Describe what is meant by a condensation reaction.

[2]
a.

Draw the structure of galactose on the skeleton provided.

[1]
b.

Explain how the inclusion of carbohydrates in plastics makes them biodegradable.

[2]
c.
▶️Answer/Explanation

Markscheme

«reaction in which» two reactants/molecules/functional groups bond/react «to form a larger molecule/single main product»

small/tiny molecule

OR

H2O formed

Accept formula or name of a specified small molecule other than water such as ammonia, ethanoic/acetic acid,
ethanol, hydrogen sulfide etc. for M2.

Do not accept just “molecule formed”.

Award [1 max] for an example giving an equation of a condensation reaction such as the formation of a disaccharide.

a.

Accept “alpha” or “beta” form of galactose.

b.

Any two of:

makes the plastic more hydrophilic/water soluble

carbohydrates are broken down/hydrolysed by bacteria/microorganisms

makes plastic more accessible to bacteria as holes/channels are created

OR

plastic of lower density is more permeable/susceptible to water/oxygen/heat/pressure

weakens intermolecular/London/dispersion/instantaneous induced dipole-induced dipole forces «between polymer chains in the plastic»

Accept “van der Waals/vdW” for “London” forces.

[Max 2 Marks]

c.

Question

Insulin was the first protein to be sequenced. It was determined that the end of one chain had the primary structure Phe–Val–Asn–Gln.

Paper chromatography can be used to identify the amino acids in insulin.

Draw the structural formula of a dipeptide containing the residues of valine, Val, and asparagine, Asn, using section 33 of the data booklet.

[2]
a.

Deduce the strongest intermolecular forces that would occur between the following amino acid residues in a protein chain.

[2]
b.

State the name of the process used to break down the insulin protein into its constituent amino acids.

[1]
c.i.

Outline how the amino acids may be identified from a paper chromatogram.

[1]
c.ii.
▶️Answer/Explanation

Markscheme

M18/4/CHEMI/SP3/ENG/TZ1/06.a/M

correct structures of Val AND Asn

correct amide link

[2 marks]

a.

Phenylalanine and valine:

London/dispersion/instantaneous induced dipole-induced dipole forces

OR

permanent dipole-induced dipole «interactions»

Glutamine and asparagine:

hydrogen bonds

Do not accept dipole-dipole interactions.

[2 marks]

b.

hydrolysis

[1 mark]

c.i.

compare Rf with known amino acids

OR

compare distance moved with known amino acids

Accept “from Rf”.

[1 mark]

c.ii.

Question

Lipids provide energy and are an important part of a balanced diet.

Identify the type of chemical reaction that occurs between fatty acids and glycerol to form lipids and the by-product of the reaction.

[2]
a.

Arachidonic acid is a polyunsaturated omega-6 fatty acid found in peanut oil.

Determine the number of carbon–carbon double bonds present if the iodine number for the compound is 334. (Arachidonic acid Mr = 304.5)

[2]
b.

Deduce the structure of the lipid formed by the reaction between lauric acid and glycerol (propane-1,2,3-triol) using section 34 of the data booklet.

[2]
c.

Outline one impact food labelling has had on the consumption of foods containing different types of lipids.

[1]
d.

Determine, to the correct number of significant figures, the energy produced by the respiration of 29.9 g of C5H10O5.

ΔH(C5H10O5) = 205.9 kJ mol−1

[2]
e.

Explain why lipids provide more energy than carbohydrates and proteins.

[2]
f.
▶️Answer/Explanation

Markscheme

Type of reaction:

condensation

OR

esterification/triesterification

OR

nucleophilic substitution/nucleophilic displacement/SN2

By-product:

water/H2O

Do not accept just “substitution/displacement”.

[2 marks]

a.

ALTERNATIVE 1

«\(\frac{{334}}{{253.8}}\) =» 1.32 AND «\(\frac{{100}}{{304.5}}\) =» 0.328

«\(\frac{{1.32}}{{0.328}}\) ≈» 4

ALTERNATIVE 2

«334 × \(\frac{{304.5}}{{100}}\) ≈» 1017

«\(\frac{{1017}}{{253.8}}\) ≈» 4

Award [2] for correct final answer.

[2 marks]

b.

M18/4/CHEMI/SP3/ENG/TZ2/06.c/M

glycerol backbone

ester formula AND linkage

Accept a skeletal structure.

Penalize missing hydrogens or incorrect bond connectivities once only in Option B.

Accept condensed formula for ester.

[2 marks]

c.

has affected consumption of trans-fats/cis-fats/saturated fats/unsaturated fats/hydrogenated/artificially altered fats

OR

reduce/eliminate trans-fats/increase in cis-fats

OR

reduce/eliminate saturated fats

OR

increase unsaturated fats

Do not accept “decrease in fat” alone.

Accept “lipid” for “fats”.

[1 mark]

d.

«\(\frac{{29.9{\text{ g}}}}{{150.15{\text{ g mo}}{{\text{l}}^{ – 1}}}}\) =» 0.199 «mol»

«0.199 mol × 205.9 kJ mol–1 =» 41.0 «kJ»

Ignore significant figures in M1.

Award [2] for correct final answer.

Award [1 max] for incorrect significant figures in final answer.

[2 marks]

e.

ratio of oxygen to carbon in lipids lower

OR

lipids less oxidized

OR

lipids more reduced

more energy per mass/g released when lipids are oxidized

Accept “«average» oxidation number of carbon in linoleic acid is lower” for M1.

[2 marks]

f.
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