Amino Acids, Protein and DNA - Science Skool!22... · 5 (a) (i) A section of a protein is formed...
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Amino Acids, Protein and DNA
Transcript of Amino Acids, Protein and DNA - Science Skool!22... · 5 (a) (i) A section of a protein is formed...
Amino Acids, Protein
and DNA
WMP/Jun10/CHEM4
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6 (a) Consider the tripeptide shown below that is formed from three amino acids, K, L and M.
6 (a) (i) Name the process by which the tripeptide is split into three amino acids.
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6 (a) (ii) Give the IUPAC name for the amino acid K.
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6 (a) (iii) Draw the structure of the zwitterion of amino acid L.
(1 mark)
6 (a) (iv) Draw the structure of the species formed by amino acid M at low pH.
(1 mark)
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CH2N
H
CH3
CO CNH
H
CH(CH3)2
CO CNH
H
from K from L from M
(CH2)4NH2
COOH
(16)
WMP/Jun10/CHEM4
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6 (b) Consider the amino acid serine.
6 (b) (i) Draw the structure of the product formed when serine reacts with an excess of CH3Br
(1 mark)
6 (b) (ii) Draw the structure of the dipeptide formed by two molecules of serine.
(1 mark)
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CH2N
CH2OH
H
COOH
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6 The three amino acids shown below were obtained by hydrolysis of a protein.
6 (a) (i) Draw the zwitterion of alanine.
(1 mark)
6 (a) (ii) Draw the species formed when valine is dissolved in an alkaline solution.
(1 mark)
6 (a) (iii) Draw the species formed by lysine at low pH.
(1 mark)
WMP/Jan10/CHEM4
COOHH2N C
CH3
alanine
H
COOHH2N C
CH(CH3)2
valine
H
COOHH2N C
CH2(CH2)3NH2
lysine
H
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6 (b) Draw the two dipeptides formed by the reaction of alanine with valine.
(2 marks)
6 (c) Name a suitable method by which the mixture of amino acids formed by hydrolysis ofthe protein can be separated.
.............................................................................................................................................(1 mark)
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WMP/Jan10/CHEM4
6
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6 The complex cisplatin acts as an anticancer drug by changing the properties of DNA when itreacts with guanine, a component of DNA.
When cisplatin is absorbed into the human body, it undergoes a ligand substitution reactionand one chloride ligand is replaced by a water molecule forming a complex ion Q.
6 (a) Write an equation for this substitution reaction to form the complex ion Q.
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6 (b) The complex ion Q can bond to guanine in two different ways.
6 (b) (i) The first way involves a hydrogen atom, from one of the ammonia ligands on Q,bonding to an atom in a guanine molecule. State the type of bond formed toguanine and identify an atom in guanine that could form a bond to this hydrogenatom.
Type of bond .............................................................................................................
Atom in guanine .......................................................................................................(2 marks)
6 (b) (ii) The second way involves a ligand substitution reaction in which an atom in aguanine molecule bonds to platinum by displacing the water molecule from Q.State the type of bond formed between guanine and platinum when a watermolecule is displaced and identify an atom in guanine that could bond toplatinum in this way.
Type of bond .............................................................................................................
Atom in guanine .......................................................................................................(2 marks)
WMP/Jan10/CHEM5
Pt
Cl
Cl
NH3
NH3
O
N
N
connects toDNA chain
guaninecisplatin
N N
H
H
H
N
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6 (c) State and explain one risk associated with the use of cisplatin as an anticancer drug.
Risk ....................................................................................................................................
Explanation ........................................................................................................................(2 marks)
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WMP/Jan10/CHEM5
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WMP/Jan12/CHEM4
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7 The amino acids aspartic acid and phenylalanine react together to form a dipeptide.This dipeptide can be converted into a methyl ester called aspartame.
Aspartame has a sweet taste and is used in soft drinks and in sugar-free foods forpeople with diabetes.
Hydrolysis of aspartame forms methanol initially. After a longer time the peptide linkbreaks to form the free amino acids. Neither of these amino acids tastes sweet.
7 (a) Apart from the release of methanol, suggest why aspartame is not used to sweetenfoods that are to be cooked.
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7 (b) Give the IUPAC name of aspartic acid.
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7 (c) Draw the organic species formed by aspartic acid at high pH.
(1 mark)
C COOHH2N
H
CH2
COOH
phenylalanine aspartameaspartic acid
COOHH2N
CH2
C
H
CN
CH2
C
HH
CCH2N
CH2
COOH
H OO
O CH3
WMP/Jan12/CHEM4
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7 (d) Draw the zwitterion of phenylalanine.
(1 mark)
7 (e) Phenylalanine exists as a pair of stereoisomers.
7 (e) (i) State the meaning of the term stereoisomers.
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7 (e) (ii) Explain how a pair of stereoisomers can be distinguished.
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WMP/Jun13/CHEM4
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6 Alanine and aspartic acid are naturally occurring amino acids.
6 (a) Draw the structure of the zwitterion formed by alanine.
(1 mark)
6 (b) Draw the structure of the compound formed when alanine reacts with methanol in thepresence of a small amount of concentrated sulfuric acid.
(1 mark)
6 (c) Draw the structure of the species formed by aspartic acid at high pH.
(1 mark)
6 (d) Draw the structure of a dipeptide formed by two aspartic acid molecules.
(1 mark)
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NH2
H3C C COOH
alanine aspartic acid
H
NH2
H C COOH
CH2COOH
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7 (a) The structures and common names of two amino acids are shown.
7 (a) (i) Draw the structure of the zwitterion of proline.[1 mark]
7 (a) (ii) Draw the structure of the tripeptide formed when a proline molecule bonds to twoalanine molecules, one on each side.
[2 marks]
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(14)WMP/Jun15/CHEM4
H
H2N C COOH
CH3
alanine
H
COOH
proline
N
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5 Proteins contain sequences of amino acids joined by peptide links.Amino acid chains (polypeptides) are attracted to each other by hydrogen bonding.
5 (a) (i) A section of a protein is formed from one molecule of each of the amino acids glycine(H2NCH2COOH) and alanine (H2NCH(CH3)COOH).
Add bonds and atoms to the diagram to complete a structural formula for this section ofthe protein.
[2 marks]
5 (a) (ii) Draw a diagram to show how an amino acid chain can form a hydrogen bond withanother amino acid chain.Your diagram need only show the relevant atoms from one amino acid in each chain.
[1 mark]
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(14)WMP/Jun16/CHEM4
CC
NC
CN
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5 (b) Leucine, serine and glutamic acid are naturally-occurring amino acids.
5 (b) (i) Give the IUPAC name of leucine.[1 mark]
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5 (b) (ii) Draw the structure of the zwitterion of serine.[1 mark]
5 (b) (iii) Draw the structure of the ester formed by two molecules of serine.[1 mark]
5 (b) (iv) Draw the structure of the species formed by glutamic acid at low pH.[1 mark]
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(15)WMP/Jun16/CHEM4
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HOCH2 COOH HOOC(CH2)2COOH(CH3)2CHCH2
H
C
NH2
leucine serine glutamic acid
H
C
NH2
COOH
H
C
NH2
