Chapter 4 Section 3: DNA

Bellringer: Where do you get your traits from? How are they passed on?

Genes, DNA and Chromosomes Chromosomes- structures within the cells that carry hereditary material. Found in the nucleus of the cell. Each of these chromosomes are made up of proteins and tightly wound strands of DNA. Deoxyribonucleic Acid (DNA)-Chemical that carries the “code” for an organisms growth and development. Exists in every cell in every organism to ever exist. Gene-Instructions for making a specific protein Specific portion of DNA on a chromosome

Genes, DNA and Chromosomes

Discovery of DNA By the 1800’s, scientists knew that cells contained large molecules called nucleic acids 1952-Rosalind Franklin Used X-Ray technology to determine that DNA is made up of 2 chains of molecules in spiral form. 1953-James Watson and Francis Crick “Using” Franklins work, Watson and Crick discovered the structure of DNA Called a double helix Looks like a twisted ladder Sides of the ladder represent combinations of phosphate groups and a sugar called deoxyribose Rungs of the ladder represent nitrogenous bases

Structure of DNA

Nucleotides A nucleotide is a segment of a nucleic acid which contains: 1 sugar 1 Phosphate group 1 Nitrogen base

Nitrogen Bases DNA contains 4 nitrogen bases: Adenine(A), Cytosine(C), Guanine (G), and Thymine(T). Adenine=Thymine, Cytosine=Guanine Complementary base paring- A only pairs with T and C only pairs with G A-T, G-C Which bases would pair with the following? A T G C A C G A T G C A T T A C G T G C T A C G T A A section of these bases is called a gene The letters (genes) are a code to make a certain protein

Copying DNA Remember, the DNA molecule resembles a ladder (2 sides connected by rungs) An enzyme called DNA helicase “unzips” the DNA molecule, separating the complementary nitrogen bases. This leaves 2 strands, each of which is ½ of the DNA double helix Another enzyme called DNA polymerase adds the nucleotide

Ribonucleic Acid RNA is made in the nucleus on a DNA pattern. Similar to DNA copying with a few major differences. While DNA is 2 strands, RNA is only 1 strand (like a ladder sawed in half) While DNA has A,C,G,T, RNA has A,C,G,U U=Uracil Uracil is similar to Thymine, but has differences in chemistry The sugar in DNA is deoxyribose, the sugar in RNA is ribose.

Types of RNA Messenger RNA (mRNA) Ribosomal RNA (rRNA) Transfer RNA (tRNA)

Protein Synthesis mRNA is made using a strand of DNA. This mRNA leaves the nucleus and moves into the cytoplasm where a ribosome attaches to it. Ribosomes are mostly made of rRNA The rRNA reads the code. tRNA brings Amino Acids to the right spot based on the bases present, and the Amino Acids become bonded together The Amino Acids are the building blocks of Proteins Once this process is complete, a protein has been made, and is ready to be shipped out to do a job.

From DNA to Proteins

Controlling Genes Every cell in an organism has the same DNA so each is able to make the same proteins. But they don’t need to. Each cell uses only the genes necessary for the job it does, so makes only these proteins. Muscle cells make muscle proteins, but nerve cells do not because they do not need them. Cells can turn off the genes it does not need.

Mutations Much like you can make mistakes in writing letters while taking notes or texting, mistakes can be made during these processes. A base can be missed, the string can be misread, or bases can be switched around. This results in the wrong proteins being made. This is called a mutation-a permanent change in the DNA sequence of a gene or chromosome of a cell. Outside factors, called mutagens, can cause these changes. Asbestos, tobacco, carbon dioxide, sunlight, and many others can cause these mutations.

Results of mutations Most mutations are harmful. They damage the cell, and cause harm to the organism. Cells will often die and the organism will not know that anything was wrong. Occasionally, however, they can cause the cell to begin to multiply out of control. This uncontrolled cell multiplication can lead to a tumor. This is called cancer. Some mutations are neutral. The protein may not form, or the ribosome may be able to correct it. Sometimes, mutations can even be beneficial to the organism (Important for future chapter) They give the organism something that it did not have before which helps it survive. Ex. Some plants may have a mutation that produces a chemical that makes pests not want to eat it. These mutation are what evolution by natural selection acts on.