DNA Structure LO Describe the structure of DNA

DNA Structure LO: • Describe the structure of DNA using diagrams. • Explain how the bases on the two strands link together. • HT: Describe in simple terms how a protein is synthesised. • HT: Explain the importance of the shape of a protein for enzyme action and function. • HT: Describe what a mutation is and how a mutation could affect the formation of a protein. • HT: Explain that most mutations have little effect but a few have more serious effects on the function of the protein. Keywords: mutation, ribosome, base, complementary, double helix, genetic code, nucleotide, polymer, amino acids, gene mutation. Starter: Describe the structure of DNA. Explain the job of genes.

Genome The genetic information is carried by a chemical called deoxyribonucleic acid (DNA). DNA is a polymer of nucleotides made up of two strands that form a double helix. The DNA is found within structures called chromosomes. A gene is a section of DNA, which carries coding for a particular protein. It contains the instructions for one characteristic of an organism.

Discovery of DNA Throughout the 20 th century, many scientists have tried to study deoxyribonucleic acid (DNA). In the early 1950 s two scientists, Rosalind Franklin and Maurice Wilkins, studied DNA using x-rays. Franklin produced an x-ray photograph that allowed two other researchers, James Watson and Francis Crick to work out the 3 D structure of DNA. The structure of DNA was found to be a double helix. In 1962 Crick and Watson, along with Wilkins, received the Nobel Prize in Physiology or Medicine for their discovery. Rosalind Franklin had died four years earlier and her pivotal contribution wasn't acknowledged until much later. What did Watson and Crick research and find?

DNA video A molecule of DNA has a structure like a ladder that has been twisted. DNA is the molecule that holds the instructions for growth and development in every living thing. Its structure is described as a doublestranded helix held together by complementary base pairs. The basic units of DNA are nucleotides. These nucleotides consist of a deoxyribose sugar, phosphate and base. List the four bases in DNA. There are four different bases in DNA: • adenine (A) • thymine (T) • cytosine (C) • guanine (G).

Nucleotide The basic units of DNA are nucleotides. These nucleotides consist of a deoxyribose sugar, phosphate and base. The DNA molecule is a polymer made up of repeating units called nucleotides. Each base is attached to the sugar molecule of the ‘backbone’ of the DNA. There are four different bases in DNA: • adenine (A) • thymine (T) • cytosine (C) • guanine (G). There are 4 different types of nucleotides as there are 4 different bases. Label the DNA structure diagram.

Polymer- Remember A polymer is a molecule, made from joining together many small molecules called monomers. The word "polymer" can be broken down into "poly" (meaning "many" in Greek) and "mer" (meaning "unit"). Large DNA molecule is made up lots of small nucleotides.

It is the bases of DNA that make up the genetic code. The Human Genome Project revealed that our genome contains approximately 3. 3 billion base pairs. Human genes vary in size from a few hundred bases to more than 2 million. How many different types of nucleotides are there.

Learning Check LO: • Describe the structure of DNA using diagrams. • Explain how the bases on the two strands link together. • HT: Describe in simple terms how a protein is synthesised. • HT: Explain the importance of the shape of a protein for enzyme action and function. • HT: Describe what a mutation is and how a mutation could affect the formation of a protein. • HT: Explain that most mutations have little effect but a few have more serious effects on the function of the protein. Keywords: mutation, ribosome, base, complementary, double helix, genetic code, nucleotide, polymer, amino acids, gene mutation.

Higher Tier Only Genetic Code There are chemical cross-links between the two strands in DNA, formed by pairs of bases. They always pair up in a particular way, called complementary base pairing: Adenine (A) always pairs with Thymine (T) Cytosine (C) always pairs with Guanine (G) Bases always pair up in the same way It is the sequence of base pairs in a gene that provides the code for the cell to build a protein. Describe how the sequence of proteins is determined.

Higher Tier Only A way to remember the base pairs: Cytosine-Guanine Career-Guidance Adeninine-Thymine A-T

Jelly Babies and Liquorice DNA Apparatus: Two long, flexible sweets, such as liquorice ribbons. A few handfuls of soft, highly coloured sweets, such as jelly babies or marshmallows. Cocktail sticks.

Method: 1) Sort the sweets into colours. Keep four of the groups. 2) Pair up the sweets so that one particular colour always goes with another particular colour e. g. red with green and yellow with purple. 3) Stick the pairs onto cocktail sticks. 4) Attach your jelly babys on cocktail stick to the long sweets (liquorice). Carry on doing this until you have something that looks a bit like a ladder. 5) Pick up your ladder and give it a twist. 6) You have made a model of DNA made from sweets! The paired coloured sweets represent the base pairs that contain all the genetic information, while the liquorice is the sugar/phosphate backbone of DNA.

Complete DNA structure cut and paste.

Higher Tier Only

(a) phosphate allow PO 43− 1 do not allow P (b) A / adenine and T / thymine and C / cytosine and G / guanine do not allow U / uracil 1

Learning Check LO: • Describe the structure of DNA using diagrams. • Explain how the bases on the two strands link together. • HT: Describe in simple terms how a protein is synthesised. • HT: Explain the importance of the shape of a protein for enzyme action and function. • HT: Describe what a mutation is and how a mutation could affect the formation of a protein. • HT: Explain that most mutations have little effect but a few have more serious effects on the function of the protein. Keywords: mutation, ribosome, base, complementary, double helix, genetic code, nucleotide, polymer, amino acids, gene mutation.

Proteins We have several hundred thousand proteins in our bodies. Some of these are also found in other organisms. Our hair is the same chemical as feathers, hooves, horns and the shell of a tortoise. Keratin is a hair protein that has a fibrous structure List two types of protein. An antibodies shape corresponds with a matching antigen

Proteins Genes are sections of the DNA. Each gene has the code for creating a specific protein. Proteins are essential chemicals that are involved in nearly every task in the life of the cell. Although proteins are very different in structure, they are all made up of the same 20 types of amino acids. How many types of amino acids are there?

It is the number and combination of these amino acids, and the order in which they’re arranged, that’s important. The sequence of bases in the gene controls which amino acids are created and joined to make a specific new protein (or enzyme) molecule. The four bases (A, C, T and G) work in threes: there is a three-letter code (or triplet) for each amino acid. For example, GGT codes are found in glycine but TCA codes are found in serine, a different amino acid. How many bases do you need to form an amino acid? Protein synthesis animation

Higher Tier Only Protein Synthesis Genes are sections of the DNA. Each gene has the code for creating a specific protein. The sequence of bases in the gene controls which amino acids are created and joined to make a specific new protein (or enzyme) molecule. You do not need to know protein synthesis in detail, but you need to understand how the genetic code works Protein synthesis video

Higher Tier Only Proteins Synthesis Proteins are synthesised on ribosomes (in the cytoplasm), according to a template made up of bases of a gene that have been unzipped from DNA. Carrier molecules bring specific amino acids to add to the growing protein chain in the correct order. Carrier molecule

Learning Check LO: • Describe the structure of DNA using diagrams. • Explain how the bases on the two strands link together. • HT: Describe in simple terms how a protein is synthesised. • HT: Explain the importance of the shape of a protein for enzyme action and function. • HT: Describe what a mutation is and how a mutation could affect the formation of a protein. • HT: Explain that most mutations have little effect but a few have more serious effects on the function of the protein. Keywords: mutation, ribosome, base, complementary, double helix, genetic code, nucleotide, polymer, amino acids, gene mutation.

Higher Tier Only Proteins Synthesis After amino acids are joined together to make proteins, the chain does not stay straight for long. In less than a second, most proteins bend, twist and fold into a particular shape. This is because different amino acids in the chain are attracted to each other, while others repel. What bonds hold the protein structure together? protein Amino acids in the chain are held together by intermolecular forces. This holds the molecule together and crates a unique shape.

Higher Tier Only Proteins Synthesis The sequence of amino acids in a protein is very important. If the sequence was changed, the protein would be a different shape. The complex shape is essential for the activity of physiological proteins such as enzymes, antibodies and hormones, and structural proteins such as collagen and keratin. The enzyme and substrate have a complementary shape. Anything that disrupts the intermolecular forces holding the enzyme together will affect its activity Explain why the complex shape of proteins is essential. Complete Protein Synthesis exam questions.

Learning Check LO: • Describe the structure of DNA using diagrams. • Explain how the bases on the two strands link together. • HT: Describe in simple terms how a protein is synthesised. • HT: Explain the importance of the shape of a protein for enzyme action and function. • HT: Describe what a mutation is and how a mutation could affect the formation of a protein. • HT: Explain that most mutations have little effect but a few have more serious effects on the function of the protein. Keywords: mutation, ribosome, base, complementary, double helix, genetic code, nucleotide, polymer, amino acids, gene mutation.

Higher Tier Only Mutations are changes that can occur in an organisms DNA. These can be on a chromosome level or changes to the base sequence of the DNA. These changes are random and can be caused by background radiation and chemicals that we come into contact with, e. g. the chemicals in cigarette smoke. They are errors that are made when a cell divides, or when the instructions to produce a protein are being copied. When do mutations in organisms DNA occur?

Sometimes changes caused by mutations can be so severe that the cell dies, sometimes the cell can divide uncontrollably and become cancerous in a body cell, and sometimes the changes are small and the cell survives. If a mutation occurs in cells that produce eggs and sperm, it may lead to a genetic disorder (e. g cystic fibrosis) in the offspring. . Very rarely, the changes may even be beneficial to us and produce new and useful characteristics which can help an organism survive. Higher Tier Only

Higher Tier Only

Higher Tier Only Mutation video Because we have two copies of each gene, it’s likely that, if one is faulty, the other will be normal; so the protein can be produced as normal. In the genetic code, there are instances where several combinations of base triplets code for the same amino acid. So, a change in a single letter may not lead to a change in the amino acid sequence in the protein. There are many instances where one amino acid is substituted for another; the protein is changed but is still able to carry out its function. If a mutation occurs in non-coding DNA, it may affect how a gene is expressed. Occasionally, mutations can be beneficial. Mutations are one of the driving forces of evolution. Why don’t all mutations lead to change in a protein?

Higher Tier Only Mutation Single gene mutations involve the alternation of a DNA nucleotide as a result of the substitution, insertion or deletion of nucleotides. How can the base sequences of a gene change in a mutation?

Higher Tier Only A change in the bases that code for a protein may lead to a different amino acid being assembled into the protein. If the protein is an enzyme, it may lose its active site and no longer function. Explain how can a change in an amino acid in an enzyme can affect its activity. Linked to Enzymes in Organisation

Learning Check LO: • Describe the structure of DNA using diagrams. • Explain how the bases on the two strands link together. • HT: Describe in simple terms how a protein is synthesised. • HT: Explain the importance of the shape of a protein for enzyme action and function. • HT: Describe what a mutation is and how a mutation could affect the formation of a protein. • HT: Explain that most mutations have little effect but a few have more serious effects on the function of the protein. Keywords: mutation, ribosome, base, complementary, double helix, genetic code, nucleotide, polymer, amino acids, gene mutation.

Higher Tier Only Mutation A few gene mutations can have serious effects. A change in the bases that code for a protein may lead to a different amino acid being assembled into the protein. Some base triplets are designed to terminate a protein. So, some mutations can lead to the synthesis of a shorter protein. With these changes, the protein will have a different shape.

Higher Tier Only Mutation Not all parts of DNA code for proteins. More than 98% of the human genome does not encode protein sequences. Non-coding parts of DNA can switch genes on and off, so variation in these areas of DNA may affect how genes are expressed. Explain what happens at noncoding parts of DNA junk video

5 marks

(mutation) changes from C to T DNA code or there is a change in the three bases / triplet from CAG to TAG 1 (mutation) changes the amino acid 1 (this could) change the protein 1 (so it) forms a different shape / changed active site accept different tertiary structure 1 (therefore) the enzyme no longer fits the substrate / carbohydrate 1

Learning Check LO: • Describe the structure of DNA using diagrams. • Explain how the bases on the two strands link together. • HT: Describe in simple terms how a protein is synthesised. • HT: Explain the importance of the shape of a protein for enzyme action and function. • HT: Describe what a mutation is and how a mutation could affect the formation of a protein. • HT: Explain that most mutations have little effect but a few have more serious effects on the function of the protein. Keywords: mutation, ribosome, base, complementary, double helix, genetic code, nucleotide, polymer, amino acids, gene mutation.

Plenary Fill in the gaps DNA Structure worksheet.

DNA has a structure like a twisted ladder. The structure is called double helix. DNA has two strands. Each strand is made up of units called nucleotides joined together. Each unit contains three parts: bases, phosphate group and sugar molecule . There are four different bases each represented by the letters ATCG. The two strands are complementary with A linked T and C linked to G. As there are many units, the whole structure is called a polymer. A sequence of three bases is the genetic code for a particular amino acid. The order of bases controls the order in which amino acids are assembled to produce a particular protein. When the protein chain is complete it folds up to form a unique shape. Mutations occur continuously. A few mutations code for an altered protein with a different shape.

Homework Complete DNA Structure exam questions.

Learning Check LO: • Describe the structure of DNA using diagrams. • Explain how the bases on the two strands link together. • HT: Describe in simple terms how a protein is synthesised. • HT: Explain the importance of the shape of a protein for enzyme action and function. • HT: Describe what a mutation is and how a mutation could affect the formation of a protein. • HT: Explain that most mutations have little effect but a few have more serious effects on the function of the protein. Keywords: mutation, ribosome, base, complementary, double helix, genetic code, nucleotide, polymer, amino acids, gene mutation. From 0 -10 write down how confident you feel about DNA Structure and write down what you need to do to increase your score. 0 = Not feeling confident 10 = I feel confident