HomeUnderstanding DNA Basics of DNA DNA stands for deoxyribonucleic acid. It's the chemical that all of the genetic material in a cell is made up from. It contains coded information - basically all the instructions to put an organism together and make it work. So is what's in your DNA that determines what in herited characteristics you have. DNA is found in the nucleus of animal and plant cells, in really long structures called chromosomes. Chromosomes normally come in pairs. DNA is a polymer. It's made up of two strands coiled together in the shape of a double helix. Importance of DNA Every living organism has DNA. Remember, DNA contains all the instructions to 'build' an organism. The instructions are different for each type of organism on Earth (otherwise all living things would be the same). There's a lot more about DNA and chromosomes coming up in this topic so make sure you understand this page before you move on. Genes and Proteins Function of Genes A gene is a small section of DNA found on a chromosome. Each gene codes for (tells the cells to make) a particular sequence of amino acids which are put together to make a specific protein. Only 20 amino acids are used, but they make up thousands of different proteins. Genes simply tell cells in what order to put the amino acids together (more on this on the next page). DNA also determines what proteins the cell produces, e.g. haemoglobin, keratin. That in turn determines what type of cell it is, e.g. red blood cell, skin cell. The Genome Understanding the Genome Genome is just the fancy term for the entire set of genetic material in an organism. Scientists have worked out the complete human genome. Understanding the human genome is a really important tool for science and medicine for many reasons. Applications of Genome Research It allows scientists to identify genes in the genome that are linked to different types of diseases. Knowing which genes are linked to inherited diseases could help us to understand them better and could help us to develop effective treatments for them. Scientists can look at genomes to trace the migration of certain populations of people around the world. Human Migration and Genetics All modern humans are descended from a common ancestor who lived in Africa, but humans can now be found all over the planet. The human genome is mostly identical in all individuals, but as different populations of people migrated away from Africa, they gradually developed tiny differences in their genomes. By investigating these differences, scientists can work out when new populations split off in a different direction and what route they took. The Structure of DNA and Protein Synthesis Composition of DNA DNA molecules contain a genetic code that determines which proteins are built. DNA strands are polymers made up of lots of repeating units called nucleotides. DNA Molecules and Nucleotides DNA molecules contain a genetic code that determines which proteins are built. DNA strands are polymers made up of lots of repeating units called nucleotides. Each nucleotide consists of a sugar, a phosphate group and one 'base'. The sugar and phosphate groups in the nucleotides form a backbone to the DNA strands. The sugar and phosphate groups alternate. One of four different bases - A, T, C or G — joins to each sugar. Each base links to a base on the opposite strand in the helix. A always pairs up with T, and C always pairs up with G. This is called complementary base pairing. It's the order of bases in a gene that decides the order of amino acids in a protein. Each amino acid is coded for by a sequence of three bases in the gene. mRNA and Ribosomes Proteins are made in the cell cytoplasm on tiny structures called ribosomes. To make proteins, ribosomes use the code in the DNA. DNA is found in the cell nucleus and can't move out of it because it's really big. The cell needs to get the code from the DNA to the ribosome. This is done using a molecule called mRNA - which is made by copying the code from DNA. The mRNA acts as a messenger between the DNA and the ribosome - it carries the code between the two. The correct amino acids are brought to the ribosomes in the correct order by carrier molecules. Functions of Proteins When a chain of amino acids has been assembled, it folds into a unique shape which allows the protein to perform the task it's meant to do. ENZYMES — act as biological catalysts to speed up chemical reactions in the body. HORMONES — used to carry messages around the body. E.g. insulin is a hormone released into the blood by the pancreas to regulate the blood sugar level. STRUCTURAL PROTEINS — are physically strong. E.g. collagen is a structural protein that strengthens connective tissues (like ligaments and cartilage). Mutations Overview of Mutations Sometimes the sequence of DNA bases can change. These changes are called mutations. A mutation is a random change in an organism's DNA. They can sometimes be inherited. Mutations occur continuously. They can occur spontaneously, e.g. when a chromosome isn't quite replicated properly. The chance of mutation is increased by exposure to certain substances or some types of radiation. Mutations change the sequence of the DNA bases in a gene, which produces a genetic variant (a different form of the gene). Most mutations have very little or no effect on the protein. Some will change it to such a small extent that its function or appearance is unaffected. However, some mutations can seriously affect a protein. Sometimes, the mutation will code for an altered protein with a change in its shape. This could affect its ability to perform its function. Effects of Mutations on Proteins If the shape of an enzyme's active site is changed, its substrate may no longer be able to bind to it. Structural proteins like collagen could lose their strength if their shape is changed, making them pretty useless at providing structure and support. If there's a mutation in non-coding DNA, it can alter how genes are expressed. Types of Mutations Insertions are where a new base is inserted into the DNA base sequence where it shouldn't be. An insertion changes the way the groups of three bases are read, which can change the amino acids that they code for. Deletions are when a random base is deleted from the DNA base sequence. Substitution mutations are when a random base in the DNA base sequence is changed to a different base.

Understanding DNA Basics of DNA DNA stands for deoxyribonucleic acid. It's the chemical that all of the genetic material in a cell is made up from. It contains coded information - basically all the instructions to put an organism together and make it work. So is what's in your DNA that determines what in herited characteristics you have. DNA is found in the nucleus of animal and plant cells, in really long structures called chromosomes. Chromosomes normally come in pairs. DNA is a polymer. It's made up of two strands coiled together in the shape of a double helix. Importance of DNA Every living organism has DNA. Remember, DNA contains all the instructions to 'build' an organism. The instructions are different for each type of organism on Earth (otherwise all living things would be the same). There's a lot more about DNA and chromosomes coming up in this topic so make sure you understand this page before you move on. Genes and Proteins Function of Genes A gene is a small section of DNA found on a chromosome. Each gene codes for (tells the cells to make) a particular sequence of amino acids which are put together to make a specific protein. Only 20 amino acids are used, but they make up thousands of different proteins. Genes simply tell cells in what order to put the amino acids together (more on this on the next page). DNA also determines what proteins the cell produces, e.g. haemoglobin, keratin. That in turn determines what type of cell it is, e.g. red blood cell, skin cell. The Genome Understanding the Genome Genome is just the fancy term for the entire set of genetic material in an organism. Scientists have worked out the complete human genome. Understanding the human genome is a really important tool for science and medicine for many reasons. Applications of Genome Research It allows scientists to identify genes in the genome that are linked to different types of diseases. Knowing which genes are linked to inherited diseases could help us to understand them better and could help us to develop effective treatments for them. Scientists can look at genomes to trace the migration of certain populations of people around the world. Human Migration and Genetics All modern humans are descended from a common ancestor who lived in Africa, but humans can now be found all over the planet. The human genome is mostly identical in all individuals, but as different populations of people migrated away from Africa, they gradually developed tiny differences in their genomes. By investigating these differences, scientists can work out when new populations split off in a different direction and what route they took. The Structure of DNA and Protein Synthesis Composition of DNA DNA molecules contain a genetic code that determines which proteins are built. DNA strands are polymers made up of lots of repeating units called nucleotides. DNA Molecules and Nucleotides DNA molecules contain a genetic code that determines which proteins are built. DNA strands are polymers made up of lots of repeating units called nucleotides. Each nucleotide consists of a sugar, a phosphate group and one 'base'. The sugar and phosphate groups in the nucleotides form a backbone to the DNA strands. The sugar and phosphate groups alternate. One of four different bases - A, T, C or G — joins to each sugar. Each base links to a base on the opposite strand in the helix. A always pairs up with T, and C always pairs up with G. This is called complementary base pairing. It's the order of bases in a gene that decides the order of amino acids in a protein. Each amino acid is coded for by a sequence of three bases in the gene. mRNA and Ribosomes Proteins are made in the cell cytoplasm on tiny structures called ribosomes. To make proteins, ribosomes use the code in the DNA. DNA is found in the cell nucleus and can't move out of it because it's really big. The cell needs to get the code from the DNA to the ribosome. This is done using a molecule called mRNA - which is made by copying the code from DNA. The mRNA acts as a messenger between the DNA and the ribosome - it carries the code between the two. The correct amino acids are brought to the ribosomes in the correct order by carrier molecules. Functions of Proteins When a chain of amino acids has been assembled, it folds into a unique shape which allows the protein to perform the task it's meant to do. ENZYMES — act as biological catalysts to speed up chemical reactions in the body. HORMONES — used to carry messages around the body. E.g. insulin is a hormone released into the blood by the pancreas to regulate the blood sugar level. STRUCTURAL PROTEINS — are physically strong. E.g. collagen is a structural protein that strengthens connective tissues (like ligaments and cartilage). Mutations Overview of Mutations Sometimes the sequence of DNA bases can change. These changes are called mutations. A mutation is a random change in an organism's DNA. They can sometimes be inherited. Mutations occur continuously. They can occur spontaneously, e.g. when a chromosome isn't quite replicated properly. The chance of mutation is increased by exposure to certain substances or some types of radiation. Mutations change the sequence of the DNA bases in a gene, which produces a genetic variant (a different form of the gene). Most mutations have very little or no effect on the protein. Some will change it to such a small extent that its function or appearance is unaffected. However, some mutations can seriously affect a protein. Sometimes, the mutation will code for an altered protein with a change in its shape. This could affect its ability to perform its function. Effects of Mutations on Proteins If the shape of an enzyme's active site is changed, its substrate may no longer be able to bind to it. Structural proteins like collagen could lose their strength if their shape is changed, making them pretty useless at providing structure and support. If there's a mutation in non-coding DNA, it can alter how genes are expressed. Types of Mutations Insertions are where a new base is inserted into the DNA base sequence where it shouldn't be. An insertion changes the way the groups of three bases are read, which can change the amino acids that they code for. Deletions are when a random base is deleted from the DNA base sequence. Substitution mutations are when a random base in the DNA base sequence is changed to a different base.