Ch 4 Sec 4: DNA connection Key Concepts: Key Terms: What forms the genetic code? How does a cell produce proteins? How can mutations affect an organism? Key Terms: Messenger RNA Transfer RNA Mutation

DNA bases DNA is made up of four different nitrogen bases – adenine (A), thymine (T), guanine (G), and cytosine (C). They form the “rungs” of the ladder. A gene is a section of a DNA molecule that contains the information to code for one specific protein.

Order of the bases The order of the nitrogen bases along a gene forms a genetic code that specifies what type of protein will be produced. Proteins are long-chain molecules made of amino acids. In the code, a group of three DNA bases codes for one protein. For example, CGT always codes for the amino acid alanine. The order of the three base code determines the order of the amino acids which build a protein.

How cells make proteins During protein synthesis, the cell uses information from a gene on a chromosome to produce a specific protein. This occurs on the ribosomes in the cytoplasm of the cell.

RNA Like DNA with a different sugar (instead of deoxyribose it’s just ribose) and a different nitrogen base (instead of thymine there is uracil). It acts like a messenger, carrying the code from the DNA inside the nucleus into the cytoplasm

Types of RNA Messenger RNA copies the encoded message from the DNA in the nucleus and carries the message to the ribosome in the cytoplasm. Transfer RNA carries amino acids to the ribosome and adds them to the growing protein.

Translating DNA’s code 1. DNA unzips, then directs the production of messenger RNA. RNA bases pair with DNA. 2. Messenger RNA leaves the nucleus and enters the cytoplasm. It then attaches to a ribosome. On the ribosome, RNA provides the code for the protein that will form. The ribosome moves along the messenger RNA strand.

continued 3. Transfer RNA attaches to messenger RNA. The transfer RNA reads the message by pairing up three letter codes to bases on messenger RNA. 4. The protein grows longer as each transfer RNA molecule puts amino acids along the protein chain.

Mutations A mutation is any change in a gene or chromosome. It happens when mistakes are made  but sometimes it is  It can really go either way, and sometimes depends on the organism’s environment as to whether the mutation will be noticed or harmful or beneficial. Mutations can cause a cell to produce incorrect proteins.