4 3 1 Structure and Function of DNA

4. 3. 1 Structure and Function of DNA BUTTONS Clicking here will allow you hear information on the Clicking some information. back asome page. move to theto next Clicking here will reveal antoanswer. Clickingherewillreveal bring you this page. topic. Clicking here again will stop the sound. TOPICS Jump to … … Structure of DNA (3 pages). Jump to … … Function of DNA and the Triplet Code (1 page) Jump to … … Protein Synthesis and Mutations (3 pages). Jump to … … Exercise question (1 page). Jump to … … Examination questions (3 pages).

STRUCTURE OF DNA (1) Click here to hear more information. phosphate Every molecule of DNA in every living organism is made of units made of 3 parts, a phosphate, a sugar and a base. P SUGAR chemical bond P BASE DNA unit SUGAR BASE P SUGAR BASE There are 4 types of bases in DNA. • Adenine (A) • Thymine (T) • Guanine (G) • Cytosine (C) Click here to join units together To connect one unit to the next a chemical bond forms between the sugar of one unit and the phosphate of the next

Click STRUCTURE OF DNA (2) Click to learn more about DNA. • This diagram shows how a large number of units connect to form two chains forming a long chain molecule. The phosphate and sugar molecules make up the backbone of the DNA molecule. • The chains join together as: A joins with T C joins with G Weak hydrogen bonds join all the bases together. DNA unit Sugar- phosphate backbone

Click DNA STRUCTURE (3) Click to hear more about DNA. Sugar phosphate backbone ADENINE THYMINE GUANINE CYTOSINE A T G C Guanine and Cytosine bases Thymine and Adenine bases The two strands twist around each other. Double helix

Click THE FUNCTION OF DNA Click to hear about the function of DNA. HIGHER TIER The order of bases along DNA forms a code for the formation of proteins. The order of the bases along the length of DNA is read every 3 bases. Each set of 3 bases is called a TRIPLET. Below you can see the triplets of bases which code for a protein. A T G A A G G G T T C C A G A C G T A G Each triplet codes for a particular AMINO ACID. Each type of protein has its own sequence of AMINO ACIDS. In the CYTOPLASM the triplet code sequence is used to connect the correct order of amino acids together to produce a protein. amino acids

BUILDING A PROTEIN IN THE CYTOPLASM Click here to hear how to build a protein. This diagram shows another sequence of amino acids ready to form a protein. HIGHER TIER To do this bonds must connect the amino acids together. This is the new protein. THESE ARE SOME EXAMPLES OF DIFFERENT PROTEINS IN THE HUMAN BODY: • Every enzyme e. g. carbohydrase, protease, lipase • Haemoglobin (inside red blood cells) • Keratin (the protein in hair and nails)

HOW TO NAME THE AMINO ACIDS IN A CHAIN? Below is a section of DNA divided into triplets. HIGHER TIER A T G A A G G G T T C C A G A C G T A G methionine lysine glycine serine TASK: proline aspartic acid valine stop 3 rd base in the triplet 1 st base in the triplet Can you name the amino acid which each triplet codes for. TABLE 2 TABLE 1 Click below to TABLE OF AMINO ACID NAMES 2 nd base in the triplet listen to the Asp = aspartic acid Gly = glycine instructions. Lys = Lysine Met = methionine ( code to start every protein) Pro = proline Ser = serine Stop = code to end protein production Val = valine Notice the 4 triplets which can code for the same amino acid – glycine. Find the names of the amino acids before clicking for the answer. Click

DNA MUTATION HIGHER TIER Click here to learn more about DNA mutations. BASES A T G A A G G G T T C C A G A C G T A G methionine lysine glycine serine proline aspartic acid valine stop AMINO ACIDS The amino acid aspartic acid can be coded for by either G A C or G A T This is a MUTATION Changing one base C to T would make NO difference to the sequence of amino acids. The protein formed will be different to the one it should be. This can lead to a new characteristic developing in the organism. BUT if the triplet changed to GAA or GAG, a different amino acid would be placed in the chain.

This is a diagram of a section of DNA. Choose the correct term for each coloured section in order to label the diagram correctly. DNA A PHOSPHATE A CYTOSINE B THYMINE B SUGAR C CYTOSINE C HYDROGEN BOND A SUGAR A HYDROGEN BOND B PHOSPHATE C GUANINE C ADENINE A PHOSPHATE A GUANINE B HYDROGEN BOND C BASE C PHOSPHATE

EXAMINATION QUESTIONS Attempt to answer the examination question before clicking on to see the examiner’s answer. WJEC Biology 2 Summer 2015 Foundation ______ T G C proteins amino acids

WJEC Biology 2 January 2018 - Higher Attempt to answer the examination question before clicking on to see the examiner’s answer. CGC T G G A • • The DNA will code for the wrong amino acid / different amino acid so the protein will be different. (Both parts of the answer are needed for the mark. ) 1: 1

WJEC Biology 2 January 2017 - Higher Attempt to answer the examination question before clicking on see the examiner’s answer. to MITOSIS MEIOSIS In the nucleus. This is because A always bond with T and G always bonds with C. Take care: You must spell these two terms correctly for the mark.