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B2.10a Modelling protein formation Using models can help us understand more about some processes. The assembly line in a car factory can be used as a model to describe how proteins are put together. When making a car, you start with a design of a complete car that is then broken down into its component parts. A plan is made of the order in which the parts must be put together to create a whole car. The plan is used to construct the assembly line, where the component parts are added one at a time until each car is complete. To make the whole process simpler and faster, the cars move along the assembly line as they are being built and the component parts are fitted at the same point on the line each time. This means that robots specially designed to handle particular components don't have to move. 1 Draw a flowchart to explain how a car is put together on an assembly line. 2 Draw a flowchart to explain how a protein is put together in a cell. 3 Match the main stages of building a car to the main stages in building a protein and explain your choices: e.g. the DNA in building a protein is like the … in building a car because … 4 Explain the advantages of using a model to explain a complex process such as protein manufacture. 5 a Describe any parts of the car assembly model that don't match protein manufacture well. b Is this a problem for understanding protein manufacture? Explain your answer. © Pearson Education 2011. Edexcel GCSE Additional Science Activity Pack This document may have been altered from the original. B2.10b Building proteins Higher You are going to build an amino acid chain starting from the DNA code. Remember that in complementary base pairing, A (adenine) pairs with T (thymine), and C (cytosine) pairs with G (guanine). Also remember that in RNA the base T is replaced by U (uracil). Here is a sequence of bases from the coding strand of some DNA. This sequence codes for a sequence of amino acids that begins with the amino acid Met (short for methionine). TACCTGCGCCTTCATAGC 1 Copy the sequence. Then write down the sequence of bases in the mRNA strand that will form during transcription. The mRNA strand moves out of the nucleus into the cytoplasm and joins to a ribosome. The ribosome reads the base sequence in triplets (codons). 2 Use brackets to mark the triplets on your mRNA strand. In the cytoplasm there are many different kinds of tRNA. Each kind of tRNA has a different triplet of bases and the triplet controls which amino acid is attached to the tRNA, as shown in the diagram. Some of the different tRNAs found in cytoplasm attached to their amino acids. Only the tRNA with the complementary triplet of bases will attach to a triplet on the mRNA strand on the ribosome. Enzymes separate the amino acid from the tRNA and attach it to the growing amino acid chain. 3 Match the correct tRNAs from the diagram to the triplets on your mRNA strand. Write down the sequence of amino acids in the chain that is formed. 4 Check your amino acid sequence with another student. If the sequences aren't the same, compare each of your answers to find where the error occurred. © Pearson Education 2011. Edexcel GCSE Additional Science Activity Pack This document may have been altered from the original. B2.10c Making a protein Jon and Felice were trying to make a model to explain how DNA controls the sequence of amino acids in which proteins are made. They had some coloured popper beads in red, green, white, yellow, blue and orange. They decided to use the first letter of each colour as the code for that colour of bead. Jon wrote a code for a protein using these letters: G R R B W G Y B R W O Y. 1 In this model of how proteins are made: a what do the coloured popper beads represent b what do the letters represent c what does the code that Jon wrote represent? Jon gave Felice his letter code. Felice used the code to make a string of popper beads that matched the order of the code. 2 Which colour was used most often in the string? 3 What does the string of popper beads represent? 4 What in DNA controls the order of amino acids when a protein is made? When Jon and Felice wrote up their investigation they wrote: Each of our letters is like the small groups of bases in DNA that code for different amino acids. 5 Complete their write-up to explain how this model helps to show how DNA controls which proteins are made. © Pearson Education 2011. Edexcel GCSE Additional Science Activity Pack This document may have been altered from the original. B2.10d Codes for proteins Higher Name Class Date You do not need to remember the details on this sheet for your exam but you could be asked to apply your knowledge to unfamiliar situations. The table shows how ribosomes decode the triplets of bases (codons) on an mRNA strand to make proteins. Each triplet is the code for one particular amino acid. The shortened names of the amino acids are shown in italics next to the triplet code. Second position U U First position CUG A G 1 AUC AUA AUG GUU GUC GUA GUG Phe Phe Leu Leu Leu Leu Leu Leu Ile Ile Ile Met Val Val Val Val UCU UCC UCA UCG CCU CCC CCA CCG ACU ACC ACA ACG GCU GCC GCA GCG A Ser Ser Ser Ser Pro Pro Pro Pro Thr Thr Thr Thr Ala Ala Ala Ala UAU UAC UAA UAG CAU CAA CAG AAC AAA AAG GAU GAC GAA GAG G Tyr Tyr STOP STOP His His Gln Gln Asn Asn Lys Lys Asp Asp Glu Glu UGU UGC UGA UGG CGU CGA CGG Cys Cys STOP Trp Arg Arg Arg Arg Ser Ser Arg Arg Gly Gly Gly Gly The table is not complete. Use the rules shown in the table to fill in the missing letters. 2 Use the table to find: a how many different codons code for the amino acid serine (Ser) b how many different codons there are in total, which code for an amino acid c how many different amino acids there are. 3 The start of a DNA template strand of a gene looks like this: TAC CGG TCG TGT AGG TGG TGG TAG 4 U C A G U C A G U C A G U C A G Third position C UUU UUC UUA UUG CUU CUC C a The complementary DNA strand to the template strand is called the coding strand. Write out the first 24 bases of the coding strand for this gene. b Write out the first 24 bases of the mRNA strand for this gene. (Remember that, instead of T in DNA, the base is U in RNA.) c Use the table to write out the first eight amino acids that this gene codes for. What would be the coding strand of the gene that codes for the protein below? There is more than one answer. Give just one solution. Met-Phe-Lys-Trp-Asp. Extra challenge 5 When scientists were trying to work out how many bases coded for one amino acid, they considered codes that used one base per amino acid and then two bases per amino acid. Explain why three bases was the smallest number that could possibly code for one amino acid. © Pearson Education 2011. Edexcel GCSE Additional Science Activity Pack This document may have been altered from the original.