DNA Chapter 11

What is it? Deoxyribonucleic Acids Contains information to create proteins. Proteins control all the reactions that occur in your body. Instructions for life. Found in nucleus and mitochondria.

The discoverers… Hershey and Chase (1950’s) What is the genetic material DNA or proteins? Injected viruses with radioactive elements and infected bacteria. Viruses will transfer their genetic material to other organisms. They transferred their DNA not proteins.

Watson and Crick (1953) Constructed the first DNA model Double Helix shape (spiral staircase) A-T, G-C are always together Rungs held together by Hydrogen bonds Rosalind Franklin

Structure Made up of nucleotides (which are made of 3 things): Deoxyribose – sugar , same in all nucleotides Phosphate group – bonds sugars together, same in all nucleotides. Nitrogenous Base (4 possibilities): Carbon ring with one or more nitrogen atoms. Purines: 2 larger bases – Adenine, Guanine Pyrimidines: 2 smaller bases – Cytosine, Thymine

There is always the same amount of Adenine (A) and Thymine (T) in any DNA sequence. There is always the same amount of Cytosine (C) and Guanine (G) in any DNA sequence. Why? Complimentary Bases Pairs

DNA Replication All organisms undergo DNA replication. Why? Name some instances you would need to do this. Why do viruses transfer their DNA to other cells?

Recall… During what phase of the cell cycle is DNA replicated? Why must this happen during every cell cycle?

How it works… The DNA untwists itself. An enzyme comes along (RNA polymerase) and break the Hydrogen bonds between the nucleotides. There are free floating nucleotides in the nucleus. The nucleotides match up with their partners. What bases pair up together?

The unzipping and pairing up of the extra nucleotides continues until both sides are the DNA are copied. Essentially, one DNA strand becomes two DNA strands. We use this copied DNA to make more cells, or to create reproductive cells.

DNA Replication Errors? What happens if there is an error in replication? Mutations – Cancer is the most influential mutation to most of our lives.

Computer Simulation Go to: http://nobelprize.org/education_games/medicine/dna_double_helix/ Click on Play the DNA

Creation of Proteins Proteins are a string of amino acids all gathered together. DNA create proteins to control the functions of cells. Cells job unique to location in body Speed

RNA Our cells create proteins from DNA with the help of RNA (Ribonucleic Acids). Single stranded Contains four bases: Adenine, Cytosine, Guanine, and Uracil (instead of Thymine). Uracil does bond with Adenine . (Remember the U from the simulation?)

Why use RNA? DNA is very important to our cells. Why would we not want it to leave the safety of the nucleus? Proteins are very large and cannot be created in the nucleus because they would not be able to leave it. RNA is a copy of the DNA they can leave the nucleus and we don’t have to worry about it being damaged.

3 Types of RNA mRNA – messenger RNA rRNA – Ribosome An opposite copy of DNA that leaves the nucleus and enters the cytoplasm (carries instructions). Goes towards the ribosomes. rRNA – Ribosome This attaches itself the mRNA and uses the instructions to make sure the amino acids are in the right order. tRNA – transfer RNA These line up with mRNA in the ribosome and carry along with them amino acids.

Transcription Occurs in the nucleus. DNA unwinds and unzips. (Same as in replication) An enzyme travels down the unzipped DNA and grabs nucleotides that are free floating in the nucleus. (Same as in replication) But instead of T’s we use U’s. Once the single stranded mRNA is made from the DNA it detaches itself and leaves the nucleus. This messenger RNA is an opposite copy of the original.

Transcription

Translation The mRNA is now in the cytoplasm heading towards a ribosome (where proteins are made). The ribosome wraps itself around the mRNA like a clothespin on a clothesline. It reads the mRNA 3 bases at a time. We call these 3 bases a codon.

Codons Ex. AUG, CAG, GGC There are certain sets of bases that are always found at the beginning of mRNA (AUG – start codon). Certain bases located at the ends of mRNA (UAA – is the stop codon). Each codon will match up with a corresponding tRNA. What tRNA will match up with UCG? AGC

tRNA The tRNA are free floating in the cytoplasm. They carry amino acids with them. The consist of 3 bases called anticodons. These are the bases that match up with the codons.

Translation continued… Each anticodon will line up with the correct mRNA codon. Each anticodon carries a specific amino acid. If the mRNA consist of UCA then the corresponding tRNA carries a serine with it. If the mRNA is CGU then the tRNA that matches it carries what? Arginine

Translation continued… As the anticodons match up with the correct codons the amino acids they carry start to bond with each other. When they reach the stop codon the long amino acid chain that has been formed is released, and will twist itself into a protein, and become an enzyme.

Mutations Mutation – any change to a DNA sequence. How might mutations positively or negatively affect us? If one cell mutates every cell it creates will have the same mutation. Aging One type of mutation is when a cell’s cycle is affected and it creates unnecessary cells. Cancer is unnecessary cells.

Types of Mutations Point Mutation – one base is incorrect in the sequence. Can or cannot affect amino acid used. What base in a codon (most often) would not affect the DNA’s ability to create the correct protein?

Types of Mutations Frameshift Mutation – When every codon is shifted or changed by one base. Insertion – adding an extra base. Deletion – when a base is removed. Which one would affect DNA the most?

Chromosome Mutations A chromosome is a DNA coiled together. We have 46 chromosomes in our cells. Deletion – When DNA is removed. Insertion – When a repeat of DNA is added. Inversion – When DNA is replicated backwards. Translocation – When a section of DNA is moved to a different spot on the chromosome.

Causes of Mutations Mutagens – something in the environment that causes mutations in DNA Radiation – X rays, UV radiation, chemicals (tar in cigarettes), asbestos, formaldehyde. Chemical mutagens usually cause substitution mutations. (When an incorrect base is used).

Repairing DNA There are repair enzymes in the cell that check DNA and try to fix mistakes. We also have lysosomes in the cell that will destroy the cell if there are mistakes in the DNA before the cell replicates. However, our cells are not perfect and mistakes are made. The more mutagens the cells encounter the more mistakes are made, and the more likely a mistake will not be caught.