DNA and the Production of Proteins Course Notes. Cell Biology. Sub-Topic 1.3 DNA and the Production of Proteins

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1 Cell Biology Sub-Topic 1.3 DNA and the Production of Proteins On completion of this subtopic I will be able to state that: Chromosomes contain genetic information that gives rise to an organism s characteristics. This genetic information is the instructions for building proteins which are essential for life. Chromosomes are made from a chemical called deoxyribonucleic acid (DNA). DNA is a double stranded helix. Each strand of DNA is made up of subunits which have DNA bases as part of their structure. The two DNA strands are held together by complementary base pairs. The four bases found in DNA are called Adenine (A), Thymine (T), Cytosine (C) and Guanine (G). Adenine is always paired with Thymine and Cytosine is always paired with Guanine. Each section of DNA which codes for a protein is known as a gene. Proteins are built from subunits called amino acids. The sequence of the DNA bases determines the sequence of amino acids in proteins. The sequence of the bases on the DNA therefore determines the function of the proteins they code for. Messenger RNA (mrna) is a single stranded molecule which carries a complementary copy of the genetic code from the DNA, in the nucleus, to a ribosome. The ribosome is the site of protein synthesis. Proteins are assembled from amino acids at the ribosome. Duncanrig Secondary School 2017 page 1 of 7

2 Chromosomes and DNA Chromosomes are thread like structures found in the nucleus. They contain genetic information that gives rise to an organism s characteristics. This genetic information carries the instructions for building proteins which are essential for life. Chromosomes are made from a chemical called DNA (deoxyribonucleic acid). gene 1 gene 2 chromosome DNA Each section of DNA which codes for a protein is known as a gene. Structure of DNA Rosalind Franklin, James Watson, Francis Crick and Maurice Wilkins discovered the structure of DNA in April DNA is a double stranded molecule. The strands are coiled together like a twisted ladder or spiral staircase in a structure known as double helix. Each strand is made up of different subunits which can contain 4 different bases. The strands are linked together by the bases. The bases make up the rungs of the ladder. There are four types of base: Adenine (A), Thymine (T) Cytosine (C) and Guanine (G). Duncanrig Secondary School 2017 page 2 of 7

3 The bases can only connect to a specific base partner. adenine pairs with thymine (A T) cytosine pairs with guanine (C G) Base pairing is said to be complementary and always follows the same rules. The arrangement of the bases is very important as this determines what the organism will be and all the genetic characteristics it will have. A DNA Molecule T Colour thymine yellow Colour adenine purple A Colour guanine pink G Colour cytosine green C Write the appropriate letter in each shape on the DNA molecule. DNA molecule bases Using the complementary base pair rule, add the missing bases to the DNA molecule shown below. Duncanrig Secondary School 2017 page 3 of 7

4 Circle the correct answer to the following questions: 1. Chromosomes are found in the a. nucleus b. cytoplasm c. chloroplast d. vacuole 2. A section of chromosome which carries a piece of genetic information which codes for a protein is called a a. ribosome b. gene c. base d. nucleus 3. Which diagram best shows the range of base types found in DNA? a. b. c. d. Proteins Cells need to make proteins. Using the class resources make a list of some types of proteins and their functions. Duncanrig Secondary School 2017 page 4 of 7

5 Protein Synthesis Proteins are made up of many subunits called amino acids linked together in long chains. Each protein has its own sequence of amino acids. The sequence of amino acids determines the structure and function of the protein. The genetic information in the DNA carries the instructions to make proteins. The sequence of the bases on the DNA encodes information for the sequence of amino acids in proteins. A group of three bases is the code for one amino acid. Sequence of bases on part of a chromosome Sequence of amino acids on part of a protein (polypeptide chain) The code for one amino acid is made of 3 bases folded protein Duncanrig Secondary School 2017 page 5 of 7

6 To make proteins a molecule called messenger RNA (mrna) is required. This molecule uses the DNA molecule as a template. Following the complementary base pair rule a single strand of mrna is made along a section of the DNA that corresponds to a gene. Once synthesised, mrna carries the code from the nucleus to the ribosomes where proteins are made. These are found free in the cell or attached to tubular structures in the cytoplasm. At the ribosome the mrna code is translated into an amino acid sequence. Here the ribosome reads the mrna base code. A carrier molecule transports the proper amino acids to the ribosome where they are joined together and built into a polypeptide chain. The polypeptide chain then folds into a particular shape to enable the protein to perform its function. Duncanrig Secondary School 2017 page 6 of 7

7 Answer the following questions: 1. Name the subunits that make up proteins. 2. Use the information below to complete the table to show the differences between DNA and mrna. Each phrase can be used more than once if appropriate. Double stranded molecule Single stranded molecule Found in the nucleus Found in the cytoplasm DNA mrna 3. Explain why the sequence of bases on a DNA molecule is important in the production of proteins. 4. Add a label to the diagram of a plant cell below to show the site of protein synthesis. Duncanrig Secondary School 2017 page 7 of 7