DNA Chapter 4 Section 3

What is DNA? Deoxyribonucleic acid Hereditary material of a cell. Chemical that stores information for the growth and function of an organism. Stores this info in the form of a code. Copied and passed on to new cells each time a cell divides.

What is DNA? Discovering DNA Mid-1800’s 1950 Scientists knew that the nuclei of cells contained large molecules called nucleic acids. 1950 Scientists knew what the nucleic acid DNA was made of but didn’t understand its structure

What is DNA? DNA’s Structure 1952 1953 Rosalind Franklin discovered DNA is two chains of molecules in a spiral form, similar to a twisted ladder. 1953 James Watson and Francis Crick made a model of DNA.

What is DNA? A DNA Model Each side of the ladder is made up of a sugar (deoxyribose) and a phosphate molecule.

What is DNA? A DNA Model Rungs of the ladder are made of 4 different nitrogen bases Adenine (A), Guanine (G), Cytosine (C), and Thymine (T) Bases always occur in pairs Guanine will only pair with cytosine Adenine will only pair with thymine So, Amount of cytosine in the cell always equals the amount of guanine. The amount of adenine in the cell always equals the amount of thymine.

What is DNA? Copying DNA The two sides of the DNA molecule unwind and separate. The nucleotides on each side pair with free nucleotides to form two new DNA strands.

Genes Gene A section of DNA on a chromosome. Contains instructions for making a specific protein. Proteins determine most of your characteristics (by building tissues and cells and controlling chemical reactions (enzymes). Each protein is made from multiple amino acids. Genes control the order of the amino acids used to make the protein.

Genes Making Proteins Genes are located in the nucleus. Proteins are made on ribosomes in the cytoplasm. So, codes for making the proteins have to be carried from the nucleus to the ribosomes by RNA.

Genes Ribonucleic Acid Made in the nucleus from the pattern of the DNA. Can be thought of as half of a DNA molecule. Has one side made of a sugar (ribose) and a phosphate group. Contains 4 bases: Adenine, Guanine, Cytosine, and Uracil (U) 3 types Messenger RNA (mRNA) Ribosomal RNA (rRNA) Transfer RNA (tRNA)

Genes Making Proteins mRNA is made in the nucleus from the DNA pattern and than sent to the cytoplasm. In the cytoplasm, a ribosome made from rRNA attaches to the mRNA. tRNA brings amino acids to the ribosome. Each tRNA molecule will only bind with a specific amino acid.

Genes Making Proteins Inside the ribosome, the three nitrogen bases on the tRNA molecule bind with matching bases on the mRNA. The ribosome slides down the mRNA chain to the next set of bases. A new tRNA molecule carrying a second amino acid pairs with the new bases.

Genes Making Proteins The two amino acids that are now adjacent to each other form a bond. The first tRNA releases its amino acid and moves back to the cytoplasm to get a new amino acid. Amino acids continue to be assembled in this manner until the protein is complete and released from the mRNA.

Genes Controlling Genes Codes contained in the mRNA determine the order that amino acids are assembled. Different orders of amino acids make different proteins. If amino acids are assembled in the wrong order, the protein won’t function properly.

Genes Controlling Genes Each cell uses only some of the thousands of genes that it has to make proteins. Each cell only makes the proteins that it needs. So, cells have to control genes by turning some genes on and some genes off. Cells can turn genes on and off in many ways, including: Twisting so tightly that no RNA can be made. Binding to chemicals so the DNA cannot be used

Mutations Mutation Any permanent change in the DNA sequence of a gene or a chromosome of a cell. Occur when DNA is not copied properly. Results in the production of the wrong proteins, malfunctioning proteins, etc. Mutations can be caused by extra or missing chromosomes or by outside factors such as X rays, sunlight, or chemicals.

Mutations Results of a mutation Can: If in a body cell: be harmful (most) or beneficial change the traits of the organism be fatal have no effect If in a body cell: mutation only affects those cells made from the body cell. If in a sex cell: mutation is passed on to all cells in the organism produced from the body cell.