3.4. Covalent bonding and coordinate (dative covalent) bonding
A subsection of Chemistry, 9701, through 3. Chemical bonding
Listing 10 of 93 questions
Use Explain briefly what is meant by the word protein. Describe how peptide bonds are formed between amino acids during the formation of a tripeptide. Include diagrams and displayed formulae in your answer. Describe how proteins can be broken down into amino acids in the laboratory without the aid of enzymes. When a small polypeptide S was broken down in this way, three different amino acids were produced according to the following reaction. CH2 S Mr = 165 2 NH2CHCO2H CH3 Mr = 89 2 NH2CHCO2H + Mr = 75 3 NH2CH2CO2H + How many peptide bonds were broken during this reaction? Calculate the Mr of the polypeptide S. Mr =
9701_w08_qp_4
THEORY
2008
Paper 4, Variant 0
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The diagram shows part of one strand of DNA. Draw the complementary strand, labelling the bonds formed to the original strand, and labelling the components of the strand you draw. phosphate sugar T phosphate sugar A phosphate sugar C Briefly describe the roles of each of the following in protein synthesis. tRNA the ribosome Some diseases, such as sickle cell anaemia, are caused by a single mutation in the DNA for a particular gene. This causes the haemoglobin produced to change the shape of red blood cells, reducing their efficiency in carrying oxygen. What is meant by a mutation? Explain why such a mutation could alter the bonding in haemoglobin.
9701_w09_qp_41
THEORY
2009
Paper 4, Variant 1
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DNA is an extremely important chemical in human cells. It has been described as the ‘blueprint of life’. What three types of compound are linked together in DNA? DNA consists of two strands linked together. Draw a block diagram to illustrate this and showing two repeat units in the backbones, labelling the components and showing and labelling the bonds between the strands. DNA is used to encode for the production of a particular protein. Put the following biochemical structures in the correct sequence from the use of DNA as a template to the formation of the protein by writing their names in the relevant box below. tRNA mRNA ribosomes DNA ¨ ¨ ¨ ¨ protein In order to produce proteins, the information stored in the DNA molecules has to be translated to produce an mRNA strand. A sequence of three bases, called a triplet, on the mRNA describes a particular amino acid. These amino acids are then combined together to form proteins. The amino acid specified by each triplet is shown below. U U U U U U U U U U U U U U U U C C C C C C C C C C C C C C C C A A A A A A A A A A A A A A A A G G G G G G G G G G G G G G G G U U U U C C C C A A A A G G G G G U A C Val Arg Ser Lys Asn Thr IIe Arg Gln His Pro Leu Leu Phe Ser Tyr Cys Trp Stop Stop Stop Met Start Ala Asp Glu Gly 5’ 3’ 3’ 3’ 3’ The sequence of three bases in a triplet is read from the middle outwards e.g. UGG specifies Trp. There are four different bases present in mRNA. How many different triplets are possible using these four bases. What peptide fragment would the following sequence code for when read from left to right? (Use 3-letter abbreviations for amino acids.) 5’ – A U G A G C C G A C U U G A C G U G – 3’ ………………………………………………………………………………… What would be the effect of changing the 11th base from U to C?
9701_w10_qp_43
THEORY
2010
Paper 4, Variant 3
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Proteins are complex molecules made up from long chains that are folded to give a three-dimensional structure. Study the table which describes aspects of bonding in proteins. For each description of a bonding type, indicate whether it contributes to the primary, secondary or tertiary structure of a protein. bonding type structure involved disulfi de bonds between parts of the chain hydrogen bonds in a β-pleated sheet ionic bonds between parts of the chain peptide links between amino acids Explain, with the use of diagrams as appropriate, the difference between competitive and non-competitive inhibition of enzymes. The diagram shows one strand of DNA. Draw a matching strand showing clearly, with labels, the bonds holding the two strands together. Name the bases in your strand, indicating clearly which base bonds to each base in the strand shown. phosphate T phosphate phosphate G sugar sugar names of bases
9701_w12_qp_41
THEORY
2012
Paper 4, Variant 1
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Proteins are complex molecules made up from long chains that are folded to give a three-dimensional structure. Study the table which describes aspects of bonding in proteins. For each description of a bonding type, indicate whether it contributes to the primary, secondary or tertiary structure of a protein. bonding type structure involved disulfi de bonds between parts of the chain hydrogen bonds in a β-pleated sheet ionic bonds between parts of the chain peptide links between amino acids Explain, with the use of diagrams as appropriate, the difference between competitive and non-competitive inhibition of enzymes. The diagram shows one strand of DNA. Draw a matching strand showing clearly, with labels, the bonds holding the two strands together. Name the bases in your strand, indicating clearly which base bonds to each base in the strand shown. phosphate T phosphate phosphate G sugar sugar names of bases
9701_w12_qp_42
THEORY
2012
Paper 4, Variant 2
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The proteins in the human body are complex polymers made up of around 20 different amino acids. Alanine is a typical amino acid. N C O OH H H alanine CH3 H C Glycine, H2NCH2CO2H, is the simplest amino acid and differs from each of the other 2-amino acids in a signifi cant way. What is this difference? Protein molecules coil and fold, producing molecules with complex three-dimensional shapes. This is referred to as the secondary and tertiary structures of a protein. State one form of secondary structure and give the type of bonding responsible. structure bonding Give two examples of bonding causing the tertiary structure, and give the amino acid responsible in each case. bonding amino acid bonding amino acid Suggest why globular proteins, such as enzymes, contain relatively small amounts of glycine and alanine when compared to the amounts of some other amino acids. You may wish to refer to their structures given above. DNA consists of a double helix with each strand having a sugar-phosphate ‘backbone’ with one of four bases – adenine (A), cytosine (C), guanine (G) and thymine (T) – attached to the sugar. The two strands of the double helix are held together by hydrogen bonds between pairs of bases. What are the pairs of bases? In protein synthesis, sections of the DNA are copied by mRNA and this, in turn, is read by the ribosome in order to assemble the amino acids for the new protein chain. Each group of three bases codes for one amino acid, with some amino acids having several codes. The codes are summarised below. UUU UUC UUA UUG phe phe leu leu UCU UCC UCA UCG ser ser ser ser UAU UAC UAA UAG tyr tyr stop stop UGU UGC UGA UGG cys cys stop trp CUU CUC CUA CUG leu leu leu leu CCU CCC CCA CCG pro pro pro pro CAU CAC CAA CAG his his gln gln CGU CGC CGA CGG arg arg arg arg AUU AUC AUA AUG ile ile ile met/ start ACU ACC ACA ACG thr thr thr thr AAU AAC AAA AAG asn asn lys lys AGU AGC AGA AGG ser ser arg arg GUU GUC GUA GUG val val val val GCU GCC GCA GCG ala ala ala ala GAU GAC GAA GAG asp asp glu glu GGU GGC GGA GGG gly gly gly gly The coding for all protein chains starts with the AUG, and ends with one of three ‘stop’ codes shown in the table. What amino acid sequence would the following series of bases produce? -AUGGGUAGCCUCGCAUCGUAA- What would be the effect on the amino acid sequence, of a mutation that changed the base at position 10 in the series of bases above from C to G?
9701_w12_qp_43
THEORY
2012
Paper 4, Variant 3
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Protein molecules are formed by the polymerisation of amino acids in the body. The structures of three amino acids are given. OH H2N O OH HO NH2 O OH NH2 O glycine serine valine How many different tripeptides can be made using one molecule of each of the amino acids shown? Draw the tripeptide ser-gly-val, showing the peptide bonds in displayed form. Within the tripeptide, which amino acid provides a hydrophobic side chain? Polypeptide chains can form bonds giving proteins their secondary and tertiary structures. Using the tripeptide in , state two types of bonding that can be formed and the groups in the tripeptide that are involved in this bonding. bond groups bond groups Enzymes are particular types of proteins that catalyse chemical reactions. The effi ciency of enzymes can be reduced by the presence of other molecules known as inhibitors. Explain how both competitive and non-competitive inhibitors prevent enzymes from working effi ciently. competitive inhibitors non-competitive inhibitors The graph shows the rate of an enzyme-catalysed reaction against the substrate concentration in the absence of an inhibitor. rate of reaction concentration of substrate On the same axes, sketch a graph showing the rate of this reaction if a non-competitive inhibitor was present.
9701_w13_qp_41
THEORY
2013
Paper 4, Variant 1
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Protein molecules are formed by the polymerisation of amino acids in the body. The structures of three amino acids are given. OH H2N O OH HO NH2 O OH NH2 O glycine serine valine How many different tripeptides can be made using one molecule of each of the amino acids shown? Draw the tripeptide ser-gly-val, showing the peptide bonds in displayed form. Within the tripeptide, which amino acid provides a hydrophobic side chain? Polypeptide chains can form bonds giving proteins their secondary and tertiary structures. Using the tripeptide in , state two types of bonding that can be formed and the groups in the tripeptide that are involved in this bonding. bond groups bond groups Enzymes are particular types of proteins that catalyse chemical reactions. The effi ciency of enzymes can be reduced by the presence of other molecules known as inhibitors. Explain how both competitive and non-competitive inhibitors prevent enzymes from working effi ciently. competitive inhibitors non-competitive inhibitors The graph shows the rate of an enzyme-catalysed reaction against the substrate concentration in the absence of an inhibitor. rate of reaction concentration of substrate On the same axes, sketch a graph showing the rate of this reaction if a non-competitive inhibitor was present.
9701_w13_qp_42
THEORY
2013
Paper 4, Variant 2
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Questions Discovered
93