Deoxyribonucleic Acid DNA Chapter 12 Page 287 Mystery

Deoxyribonucleic Acid DNA Chapter 12 Page 287

Mystery DNA was a mystery. Many steps were taken to un-solve the mystery. The first step was in the form of finding a vaccine for pneumonia. Vaccine- a substance that is prepared from killed or weakened micro-organisms and is introduced into the body to protect the body against future infections by the same microorganisms.

Boosters On your mom and dad, they have a scar on their arm. This is a booster. It is also a vaccine for Polio. Many kids that were born in Mexico have the same scar. Polio boosters are a vaccine in which your body creates antibodies to kill the organisms that cause polio. Virulent means that a micro-organism is able to cause disease or death.

1928—Griffith’s Experiment Griffith was working to find a vaccine for pneumonia. He was working with the bacteria Streptococcus pnuemoniae. He had 2 different strains— 1 was round with smooth edges (S-bacteria) and was disease causing. (caused pneumonia) The 2 nd strain was rough edged (R-bacteria) and did not cause pneumonia.

Griffith’s Griffith killed all of the S-Bacteria by heating them so that they couldn’t reproduce. He then mixed the R-bacteria (the one that didn’t cause pneumonia) with the heat killed S-bacteria (the one that couldn’t cause pneumonia anymore. ) When he injected this mixture (R and dead S) into mice, the mice developed pneumonia and died. Why?

Griffith's Somehow, the heat-killed bacteria had passed the disease causing ability to the harmless strain. Griffith was the first one to think of “Transformation” Transformation-the process in which one strain of bacteria is changed by a gene or genes from another strain of bacteria.

Figure 12– 2 Griffith’s Experiment Section 12 -1 Disease-causing bacteria (smooth colonies) Harmless bacteria Heat-killed, disease(rough colonies) causing bacteria (smooth colonies) Dies of pneumonia Go to Section: Lives Control (no growth) Live, disease-causing bacteria (smooth colonies) Heat-killed, disease -causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Dies of pneumonia

1944 - Avery’s Experiment Avery was a scientist who wanted to know, which molecule in the heat-killed bacteria extract was most important for transformation? Carbohydrates? Lipids? Nucleic Acids? Proteins? Avery made an extract from the heat killed S bacteria.

Extracts, Extracts… He treated the extract with enzymes that destroyed proteins, lipids, carbohydrates and other molecules including the RNA. Guess what happened? Transformation still occurred. What did that mean? Proteins, Lipids, & carbohydrates are not responsible for the transformation to harmful bacteria.

More Extracts… He made another extract. This time he treated it with an enzyme that broke down DNA (nucleic acid). When the nucleic acid was destroyed, Transformation did not occur! What did this mean? Avery discovered that DNA is the nucleic acid that stores and transmits the genetic information from one generation of an organism to the next generation.

1949—Chargaff Rules! Chargaff was another scientist who noticed that Adenine always equaled the amount of Thymine. A = T He also noticed the Guanine always equaled the amount of Cytosine. G = C In the structure of DNA, you will always pair an A with a T and a G with a C.

1952– Hershey-Chase Experiment Hershey and Chase were experimenting with Bacteriophages. (Bacteria eaters) A virus that infects and kills bacteria is called a bacteriophage. The virus attaches to the surface of the cell and injects its DNA into it. The viral genes act to produce more viruses. Once the viruses have taken over the bacteria, the viruses burst out.

Figure 12– 4 Hershey-Chase Experiment Section 12 -1 Go to Section: Bacteriophage with phosphorus-32 in DNA Phage infects bacterium Radioactivity inside bacterium Bacteriophage with sulfur-35 in protein coat Phage infects bacterium No radioactivity inside bacterium

It’s Radioactive! Hershey-Chase used different radioactive markers to see if the DNA (nucleic acid) went into the bacterium or if the protein went into the bacterium. PROTEINS DO NOT CONTAIN Phosphorus DNA DOES NOT CONTAIN Sulfur. What does this tell you?

Sulfur or Phosphorus? If sulfur were found in the bacteria, it would mean that the proteins would have been injected into the bacteria. If the phosphorus was found, then the DNA was injected into the bacteria. What do you think they found?

Yep, You got it! They found phosphorus. Hershey and Chase concluded that the genetic material of the bacteriophage was DNA and not protein.

Ladies—you’re about to get angry! 1952— Rosalind Franklin 1 st person to x-ray the double helix

1953—Watson & Crick These two scientists took Rosa Franklin’s picture and made a 3 D model out of tin and wire to show the double helix structure. A double helix looks like 2 strands twisted around each other, like a twisted ladder or a winding staircase.

Nucleotides The double helix is also made up of; Nucleotides—the building block of DNA. Consists of: 1) a phosphate group 2) a 5 carbon sugar called DEOXYRIBOSE and 3) a NITROGEN BASE—either Adenine, Thymine, Guanine, or Cytosine.

Nucleotides Continued… The sugar molecule (deoxyribose) and the phosphate group are the same for each molecule or handles in the ladder. However, the nitrogen base may be any one of the 4 bases of Adenine, Thymine, Guanine, or Cytosine. These are the rungs or steps in the ladder.

P & P Purines—Adenine & Guanine Pyrimindines—Thymine & Cytosine

Figure 12– 5 DNA Nucleotides Section 12 -1 Purines Adenine Guanine Pyrimidines Cytosine Thymine Phosphate group Deoxyribose Go to Section:

Analogy When picturing the DNA structure… Think of a ladder that is made up of phosphate groups (The outside of the ladder or where you put your hands). Then you have a sugar molecule attached to the ladder (phosphates). (So far we have phosphates and sugar attached together to make the area where you put your hands or the backbone)

Twisted… To the sugar molecule, we attach the nitrogen bases (in what ever order we want). In between the nitrogen bases is a Hydrogen bond. These bonds hold the nitrogen bases together forming the rungs of the ladder. So phosphate, sugar, whatever nitrogen base and a hydrogen bond to hold them together. –Now twist it! Viola! DNA

Figure 12– 7 Structure of DNA Section 12 -1 Nucleotide Hydrogen bonds Sugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G) Go to Section:

DNA Replication Section: 12 -2—pg-295

Replication or Duplication –making a copy of the DNA This occurs during S phase of the Cell Cycle 3 steps—

Step 1 The double helix unwinds by enzymes called DNA Helicases, which open the double helix by breaking the Hydrogen bonds. Once the strand is separated—other proteins attach to each strand to keep them separated. These 2 separated areas are called replication forks because of their Y shape. The Zipper Model

Figure 12– 11 DNA Replication Section 12 -2 New strand Original strand DNA polymerase Growth Replication fork Nitrogenous bases Replication fork New strand Go to Section: Original strand

Step 2 At the replication fork, enzymes known as DNA polymerases move along each of the exposed DNA strand adding the corresponding nucleotides/nitrogen bases. As the enzymes move along, two new double helixes are formed. The main function of DNA polymerase is to make DNA from nucleotides, the building blocks of DNA. There are several forms of DNA polymerase that play a role in DNA replication and they usually work in pairs to copy one molecule of double-stranded DNA into two new double stranded DNA molecules.

Step 3 Once the DNA polymerase starts adding nucleotides/nitrogen bases, it goes until the entire DNA is copied. DNA ligase is a specific type of enzyme, a ligase, (EC 6. 5. 1. 1) that facilitates the joining of DNA strands together by catalyzing the formation of a phosphodiester bond.

RNA Primase DNA polymerase is the enzyme responsible for adding the daughter nucleotides to the parent DNA strand. In order to help it get started in its process, an RNA primer is built upon the parent strand at the base of the replication fork. The enzyme responsible for building that RNA primer is RNA primase. Since primase produces RNA molecules, the enzyme is a type of RNA polymerase. Primase functions by synthesizing short RNA sequences that are complementary to a single-stranded piece of DNA, which serves as its template. It is critical that primers are synthesized by primase before DNA replication can occur.

Figure 12– 11 DNA Replication Section 12 -2 New strand Original strand DNA polymerase Growth Replication fork Nitrogenous bases Replication fork New strand Go to Section: Original strand

Protein Synthesis Section 12 -3 pg-300

Traits… Traits such as eye color, are determined by proteins that are built according to instructions specified by DNA. How are the DNA instructions carried out? Proteins are not built directly from DNA— RNA is involved.

Traits continued… A double helix structure explains how DNA can be replicated but not how a gene works. Genes are coded DNA instructions that control the production of proteins in the cell.

disposable copy of a segment of DNA

B. 3 Types of RNA 1. Messenger RNA or m. RNA—these are the RNA molecules that has the codes to make proteins. 2. Ribosomal RNA or r. RNA—Proteins are assembled in the ribosomes which are made up of proteins and r. RNA 3. Transfer RNA or t. RNA—During the construction of a protein for a trait, this RNA molecule transfers each amino acid to the ribosome as it says in the coded message from m. RNA.

Messenger RNA or m. RNA Looks like a message. Has the genetic codes (codons) to make the protein in its’ proper sequence. Codons

Transfer RNA or t. RNA TRANSFERS the amino acid to the ribosome to assemble the proteins Amino acids are the building blocks of proteins Anticodons on t. RNA match up with the codons on m. RNA

Ribosomal or r. RNA is the RIBOSOME Ribosomes make ____? Ribosomes don’t know the correct order of the amino acids. They just put together the amino acids that TRANSFER RNA brings to it

3 Types of RNA Section 12 -3 Nucleus Messenger RNA is transcribed in the nucleus. Phenylalanine t. RNA The m. RNA then enters the cytoplasm and attaches to a ribosome. Translation begins at AUG, the start codon. Each transfer RNA has an anticodon whose bases are complementary to a codon on the m. RNA strand. The ribosome positions the start codon to attract its anticodon, which is part of the t. RNA that binds methionine. The ribosome also binds the next codon and its anticodon. Ribosome Go to Section: m. RNA Transfer RNA Methionine m. RNA Lysine Start codon

Hmmm…. Section 12 -3 The Polypeptide “Assembly Line” The ribosome joins the two amino acids— methionine and phenylalanine—and breaks the bond between methionine and its t. RNA. The t. RNA floats away, allowing the ribosome to bind to another t. RNA. The ribosome moves along the m. RNA, binding new t. RNA molecules and amino acids. Lysine Growing polypeptide chain Ribosome t. RNA m. RNA Completing the Polypeptide m. RNA Go to Section: Ribosome Translation direction The process continues until the ribosome reaches one of the three stop codons. The result is a growing polypeptide chain.

C. Transcription This is a PROCESS in protein synthesis in which the information in DNA (for making a protein that shows a trait) is transferred to an RNA molecule. 1. RNA polymerase binds on the start signal on the DNA code. 2. The polymerase unwinds the DNA to get that specific code of protein for a specific trait (Hair color, Eye color, etc. )

Transcription 3 -4 3. The m. RNA reads the code off of the gene, but this time it uses Uracil instead of Thymine. EXCEPTION in RNA, Uracil is paired with Adenine. NOT THYMINE! So, U=A in RNA only! 4. m. RNA goes until it reaches a stop CODON. Then it moves into the next step of making a protein, which is translation.

Transcription 5 -6 5. In DNA replication, you are making 2 strands of DNA again. 6. In transcription, you have made messenger RNA, which is only one part of the 2 strands.

Transcription 7 -8 7. Prokaryotic cells—Transcription & Translation occur Only in the cytoplasm 8. Eukaryotic cells—Transcription occurs in the nucleus and Translation occurs in the cytoplasm.

D. The Genetic Code 1. Proteins are made by joining amino acids into long chains called polypeptides. 2. The “language” of m. RNA is called the Genetic Code. There are only 4 bases. (G, U, A, & C) So, how can you get 20 different amino acids with only 4 bases?

The Genetic Code Continued… ****The genetic code is read 3 letters at a time. 3. A CODON consists of 3 consecutive nitrogen bases on m. RNA that specify a single amino acid that is to be added to the polypeptide/ protein chain.

Figure 12– 17 The Genetic Code Section 12 -3 Go to Section:

Genetic Code—Square

Translation In this process, the language of RNA gets translated into the language of Amino Acids or the final product of proteins. Amino Acids are the building blocks of proteins It is the de-coding of an m. RNA message into a polypeptide chain or a protein.

Figure 12– 18 Translation Section 12 -3 Nucleus Messenger RNA is transcribed in the nucleus. Phenylalanine t. RNA The m. RNA then enters the cytoplasm and attaches to a ribosome. Translation begins at AUG, the start codon. Each transfer RNA has an anticodon whose bases are complementary to a codon on the m. RNA strand. The ribosome positions the start codon to attract its anticodon, which is part of the t. RNA that binds methionine. The ribosome also binds the next codon and its anticodon. Ribosome Go to Section: m. RNA Transfer RNA Methionine m. RNA Lysine Start codon

Process of Translation 1. m. RNA must be transcribed from DNA in the nucleus and released into the Cytoplasm. 2. Translation begins when m. RNA attaches to a ribosome in the Cytoplasm. As the CODON on m. RNA moves through the ribosome—t. RNA brings the ANTICODON to match up with the codon.

Translation 2 completed The Ribosome does not know which amino acid on each anticodon is needed to match on each codon. The t. RNA knows the matching anticodon that goes with the codon. ANTICODON—a group of three bases on a t. RNA molecule that are complementary to an m. RNA codon.

Figure 12– 18 Translation (continued) Section 12 -3 The Polypeptide “Assembly Line” The ribosome joins the two amino acids— methionine and phenylalanine—and breaks the bond between methionine and its t. RNA. The t. RNA floats away, allowing the ribosome to bind to another t. RNA. The ribosome moves along the m. RNA, binding new t. RNA molecules and amino acids. Lysine Growing polypeptide chain Ribosome t. RNA m. RNA Completing the Polypeptide m. RNA Go to Section: Ribosome Translation direction The process continues until the ribosome reaches one of the three stop codons. The result is a growing polypeptide chain.

Translation 3 The Ribosome does not know which amino acid on each anticodon is needed to match on each codon. The t. RNA knows the matching anticodon that goes with the codon. ANTICODON—a group of three bases on a t. RNA molecule that are complementary to an m. RNA codon.

Translation 3 & 4 Once the 2 amino acids are in both the “P” and “A” sites, they hook together forming a bond between them which forms the start of the protein chain. 4. This assembly line stops once it reaches the stop codon and the newly made protein is released in the cell to be used.

G. The Roles of DNA and RNA When constructing a building, you don’t bring the master plan to the job site do you? NO! You leave it in a safe place. You make a disposable copy of the master plan to take to the job site. DNA is the master plan. RNA is the disposable copy of blue prints.

H. Genes & Proteins What do proteins have to do with the color of a flower? Most proteins are enzymes. A gene that codes for an enzyme to produce pigment controls the color of the flower