Download IB Chemistry Brakke ECA - Topic B TBD09

IB Chemistry
1.
(a)
Brakke
TBD09 – SL Biochemistry Exam
(i)
ECA – Topic B
Name…………………………………………………
Deduce the structure of one of the dipeptides that can be formed when the two amino acids below
react together.
O
O
H2N
CH C
OH
H2N
CH
CH3
CH 3
CH C
OH
CH3
(2)
(ii)
State the name given to this type of reaction and identify the other product of the reaction.
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(2)
(b)
Describe how a mixture of amino acids can be analyzed using electrophoresis.
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(c)
(i)
Explain what is meant by the primary structure of proteins.
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(ii)
Explain, with reference to hydrogen bonding, why the α-helix and β-sheet secondary structures of
proteins are different.
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(4)
(1)
(2)
(Total 11 marks)
2.
Polypeptides and proteins are formed by the condensation reactions of amino acids.
(a)
Give the general structural formula of a 2-amino acid.
(1)
(b)
Give the structural formula of the dipeptide formed by the reaction of alanine and glycine.
State the other substance formed during this reaction.
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(2)
1
IB Chemistry
Brakke
(c)
State two functions of proteins in the body.
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3.
ECA – Topic B
(2)
(Total 5 marks)
When many 2-amino acid molecules react together a protein is formed. These proteins have primary, secondary
and tertiary structures.
(a)
State the type of intermolecular force responsible for maintaining the secondary structure.
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(1)
(b)
Describe two other ways in which the tertiary structure of the protein is maintained.
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(2)
(Total 3 marks)
4.
(a)
The equilibrium, which exist in an aqueous solution of glycine, are shown in the structures below.
+
+
H2N- CH2 – COO
H3N - CH2- COO
H3N - CH2- COOH
A
B
C
State which of the forms A, B or C occurs in the greatest concentration at:
low pH: ...............................
high pH: ..............................
(b)
A mixture of amino acids with different isoelectric points can be separated using electrophoresis.
(i)
Outline the essential features of electrophoresis.
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(2)
(3)
(ii)
Arginine, glutamic acid and glycine undergo electrophoresis at pH 6.0. Using table 20 of the Data
Booklet identify the amino acid that moves towards:
the positive electrode: .....................................................................................
the negative electrode: ....................................................................................
(2)
(Total 7 marks)
5.
(a)
Compare the structural properties of starch and cellulose.
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(4)
(b)
Explain why humans cannot digest cellulose.
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(1)
(Total 5 marks)
2
IB Chemistry
Brakke
6.
(a)
The general formula for saturated fatty acids is CnC2nO2. The molecular formula of linoleic acid is
C18H32O2.
(i)
Determine the number of carbon to carbon double bonds in linoleic acid.
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ECA – Topic B
(1)
(ii)
Iodine number is defined as the number of grams of iodine that adds to 100 g of a fat or oil in an
addition reaction. Determine the iodine number of linoleic acid.
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(2)
(b)
(i)
State one structural similarity between fats and oils.
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(1)
(ii)
Explain, by referring to their structures, why fats are solid at room temperature, but oils are liquid.
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(3)
(Total 7 marks)
7.
(a)
State the name of a disease which results from the deficiency of each of the following vitamins.
vitamin A .................................................................................................................
vitamin B .................................................................................................................
vitamin C .................................................................................................................
(2)
(b)
8.
A person consumes an excess of both vitamin A and C. State, with a reason, which one is more likely to be
stored in the body and which is more likely to be excreted.
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(2)
(Total 4 marks)
The structures of two sex hormones, progesterone and testosterone, are shown in Table 22 of the Data Booklet.
(a)
State the names of two functional groups that are present in both hormones.
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(2)
(b)
Identify which of the two hormones is the female sex hormone and where in the human body it is
produced.
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(2)
3
IB Chemistry
Brakke
(c)
Outline the mode of action of oral contraceptives.
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ECA – Topic B
(3)
(Total 7 marks)
9.
The structures of some hormones are shown in Table 22 of the Data Booklet.
(a)
Identify one hormone with a steroid backbone, state where it is produced and outline its specific role in the
body.
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(2)
(b)
Identify one hormone with a non-steroid backbone, state where it is produced and outline its specific role
in the body.
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(2)
(Total 4 marks)
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