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DNA Unit 7 – Proteins and DNA Structure Self study unit http://topnews.net.nz/content/221657-importance-exercising-increases-it-alters-dna You will be studying this unit by yourselves. University are increasingly using self study to teach whole units. The Access course also does not teach all the units seen on the A level, so there will be areas you need to read up on and make notes. In the work place you will also have to look up topics by yourself. Use the syllabus table and write a set of questions that you will need to ask yourself in order to fulfil the criteria http://topnews.net.nz/content/221657-importance-exercising-increases-it-alters-dna Syllabus you are not sure how toand do replication of DNA. Learning Outcome 3 –If Appreciate theabout structure this, you may find Levelusing 3 the following questioning words useful and material apply them to each statement. 3.1 Recognise that our genetic Level 2 3.1 Accurately describe the structure of DNA, is in the form of chromatin Who, what, where, when, nucleotides, distinguish between during interphase and arranged inwhy, how purines and pyrimidines. chromosomes during cell division. 3.2 Describe DNA as a very large molecule consisting of two strands held together by bases (full names of bases not required for L2 but needed for L3) and twisted into a spiral or helix. 3.3 Explain correctly how in replication the two strands of the DNA molecule unwind and separate, each strand acting as a template for the synthesis of its complementary strand. 3.2 Explain correctly the structure of the DNA molecule, such as, a polynucleotide, antiparallel chains, complimentary base pairs and also the nature of the bonds between the bases in the pairs. 3.3 Explain correctly the semiconservative replication of DNA during interphase. Learning Outcomes Part A – Assessment criteria 3.1 Level 2. Recognise that our genetic material DNA, is in the form of chromatin during interphase & arranged in chromosomes during cell division. By the end of this section you should be able to • • • • WHAT – What is meant by the term DNA? WHAT - Describe what is the purpose/function of DNA. WHERE - Identify the location of DNA in a cell. HOW and WHY - Describe the complex structure of DNA in the form of chromatin in interphase and why this is important • WHY - Explain why DNA is arranged into chromosomes during cell division What is DNA? Where is found? HOW DNA CONTROLS THE CELL’S ACTIVITIES 1. All chemical reactions in cells and therefore, all cell activities, are controlled by enzymes. 2. Enzymes are proteins that catalyse (speed up) reactions. 3. Proteins are strings of amino acids. 4. The shape and order of amino acids in a protein determines what it does. 5. DNA is a code for proteins and therefore controls what proteins are made and when. Learning Outcomes – Part B Assessment criteria 3.2 Level 2 • Describe DNA as a very large molecule consisting of two strands held together by bases (full names of bases not required for L2 but needed for L3) and twisted into a spiral or helix. By the end of this section you should be able to • WHAT - Draw a diagram to show a molecule of DNA • WHAT – Describe the gross structure, to include number of chains, concept of bases and the spiral twist DNA is made up of two strands of nucleotides http://upload.wikimedia.org/wiki pedia/en/b/b8/DNA-structureand-bases.png Learning Outcomes – Part C Assessment criteria 3.1 Level 3 and 3.2 Level 3 • Accurately describe the structure of nucleotides, distinguish between purines and pyrimidines. • Explain correctly the structure of the DNA molecule, such as, a polynucleotide, antiparallel chains, complimentary base pairs and also the nature of the bonds between the bases in the pairs. By the end of this section you should be able to • WHAT – Draw and annotate a detailed diagram to show the structure of a DNA molecule • WHAT – Draw a labelled diagram of a nucleotide • WHAT – Identify the bases as purines or pyrimidines and which are in DNA and which in RNA • WHY – Extension - Appreciate the contributions by Franklin and Watson and Crick in elucidating the structure of DNA • HOW – Explain how the two strands remain together, identifying the base pair combinations • WHY – Describe why the chains are said to run antiparallel to each other, explaining both ‘anti’ and ‘parallel’ A nucleotide A nucleotide has three components A nitrogen-containing base A phosphate group A pentose Sugar Sugar – Nucleotide Sugar – Phosphate base pairs Phosphate backbone backbone Hydrogen bonds Deoxyribonucleic acid DNA Base Base pair Nucleotide http://oak.cats.ohiou.edu/~ballardh/pbio475/Heredity/DNA-double-helix.JPG Nucleic acids Rosalind Franklin (1920- 1958) James Dewey Watson (1928-) Francis Harry Compton Crick (1916-2004) Nobel prize 1962 X-Ray Crystallography - Rosalind Franklin (d1958) It shows that the DNA molecule is double stranded This reflection shows that the molecule is a double spiral, with a twist occurring every 3.4nm which is the equivalent of 10 base pairs http://www.npr.org/programs/atc/features/2002/oct/darklady/dna.jpg There is a set distance (2 nm) between the two strands, evidence that there is always a purine bonded to a pyrimidine ring Questions to test your knowledge so far • What does DNA stand for? • What does RNA stand for? Answer: single human DNA • Where and when are they found in Amolecule, stretched out the cell? a straight line, has a width of about 20 • What is the single unit of DNA Angstrom (about 2 called? nanometers or 0.0000002 cm) and a • Why is it called a double helix? length of approximately 5 cm. • How wide is a DNA molecule? • After how many units does the spiral repeat (i.e. nucleotides are above Answer: About every 10 base pairs one another). Read more: http://wiki.answers.com/Q/What_is_the_ width_of_DNA_molecule#ixzz1sNcJDEsX (can be 11 or 12 as they think there are other forms of DNA shapes only seen in dehydrated forms) (Wikipedia) • The model of DNA proposed by Watson and Crick won them a Nobel prize in 1962. There are many features of their model. – There are five possible bases in polynucleotides. • • • • • Which is the odd one out and why? Which are purines and which are pyrimidines? Which bases are complementary to each other? How do they join together? How are these linked to the width of a DNA double helix? – Extension – How Watson and Crick use the information from the work of Rosalind Franklin to support the model we now accept as the structure of DNA? – What is meant by anti and parallel in the term antiparallel? – What is meant by the designations 3’ and 5’? Learning Outcomes- Part D Assessment criteria 3.3 Levels 2 and 3 • Explain correctly how in replication the two strands of the DNA molecule unwind and separate, each strand acting as a template for the synthesis of its complementary strand. • Explain correctly the semi-conservative replication of DNA during interphase. By the end of this section you should be able to • WHAT – Identify what is meant by semi-conservative replication of DNA • HOW - Identify the steps involved in the replication of DNA • WHY – Explain the advantages of this type of replication (as opposed to conservative replication) • HOW – Evaluate the evidence this process to occur semi-conservatively • WHEN – Describe when in the cell cycle this occurs DNA replicates semiconservatively – from the diagram can you work out what these means? http://www.genelex.com/paternitytesting/images/dna-molecule.jpg The DNA molecule unwinds and unzips Work out the correct order to complete the flowchart The enzyme DNA polymerase joins these nucleotides together to form a complimentary strand. Each strand acts as a template. Free DNA nucleotides come in and line up opposite their complementary base pair. Each new molecule contains half of the original molecule. For this reason the process is called: semi-conservative replication. Two complete DNA molecules are formed. 1. The DNA molecule unwinds and unzips 2. Free DNA nucleotides come in and line up opposite their complementary base pair. 3. The enzyme DNA polymerase joins these nucleotides together to form a complementary strand. Each strand acts as a template. 4. Two complete DNA molecules are formed. Each new molecule contains half of the original molecule. For this reason the process is called: semi-conservative replication. Other possible models of DNA replication http://masterman2013.pbworks.com/w/page/23837643/SD%20DNA%20Replication Meselson and Stahl experiment http://www.biog1105-1106.org/demos/106/unit01/6.dnareplicationmodels.html EXTRA INFORMATION FOR CURIOSITY Forensic uses of DNA http://fig.cox.miami.edu/~cmallery/150/gene/DNA.forensics.jpg