Genetics

Chapter Twelve: The Code of Life 12.1 The Role of DNA in Heredity 12.2 DNA and Technology

Investigation 12A What is the structure of the DNA molecule? The DNA Molecule

12.1 The role of DNA in heredity A DNA molecule looks like a twisted ladder. Its shape is called a double helix.

12.1 The role of DNA in heredity The two sides of the DNA ladder are made of sugar molecules alternating with phosphate molecules. The rungs of the DNA molecule are made of chemical building blocks called bases. The four bases found in DNA are adenine (A), thymine (T), cytosine (C), and guanine (G). Can you pronounce the names of the four bases?

12.1 DNA replication DNA replication is the process of a DNA molecule making a copy of itself.

12.1 DNA replication DNA replication ensures that each daughter cell has an exact copy of the DNA from the parent cell.

12.1 DNA replication 1.Replication begins with the partial unwinding of the double helix. 2.The base pairs separate. 3.A special molecule moves along each original strand of DNA and “reads” the bases. 4.A new strand is assembled along each original strand. (New pieces come from the cytoplasm.) 5.The strands re-twist and two daughter molecules are produced.

12.1 Protein synthesis In total, the DNA in one of your cells contains about 3 billion base pairs! The order of base pairs along a gene is called its base sequence. What is the base sequence of this gene segment?

12.1 Protein synthesis Genes control the production of proteins. For example, the color of your eyes is determined by a protein. The production of proteins in the cell is called protein synthesis.

12.1 Protein synthesis The order of base pairs along a gene forms a code that tells a cell which protein to make. Sets of three bases along a strand of DNA form three-letter codes that tell the cell which amino acids make up the protein. There are 20 different amino acids, so these amino acids can be put together in many ways to make millions of different proteins!

12.1 Protein synthesis 1.Messenger RNA copies the gene and carries it out of the nucleus. 2.Transfer RNA from the cytoplasm decodes the three letters. 3.Transfer RNA matches the right amino acid to messenger RNA sequence. 4.The amino acids are linked together on the ribosome to form a protein strand.

12.1 Mutations A mutation is a change in the hereditary material of an organism Mutations can happen in any cell and in any gene.

12.1 Genetic disorders A genetic disorder is an abnormal condition that an organism inherits from its parents. One chromosome pair has a mutated extra chromosome. Can you find it?

12.1 Mutations Doctors use a procedure called amniocentesis to find out if a baby could have Down’s syndrome. The doctor removes a small amount of the fluid that surrounds the developing baby and examines the chromosomes.