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LT5.2 Nucleic Acids (DNA & RNA)
- 1. Unit 5: MOLECULAR BIOLOGY (DNA & Protein Synthesis) LT5.1: Nucleic Acids (DNA & RNA) Biology Mrs. DeFord
- 2. Recall from First Semester… • UNIT 1: One of the characteristics that all living organisms share is that they are made of one or more cells that contain DNA. • UNIT 3: DNA (and RNA) are examples of nucleic acids. The monomers (building blocks) of nucleic acids are nucleotides, which are composed of the elements carbon, hydrogen, oxygen, nitrogen, and phosphorus (CHONP). Nucleic acids perform a vital function in genetic information and heredity.
- 3. DNA • DNA is considered the Molecule of Life • DNA stands for DeoxyriboNucleic Acid • DNA is a double-stranded molecule that encodes genetic information • The discovery of DNA was the most important event in biological science of the 20th century
- 4. Discovery of DNA’s Existence Miescher – While studying white blood cells in 1869, he isolated a previously unknown type of molecule that was slightly acidic and contained a high percentage of phosphorus. This molecule eventually became called DNA. At the time, this molecule was not thought to be the carrier of hereditary information because it was believed to lack the variability necessary to account for the incredible diversity among organisms.
- 5. Discovery of DNA’s Function Griffith – Experimented on mice and observed that some harmless strains of bacteria could change into harmful strains. He called this process of one strain of bacteria being changed by a gene (or genes) from another strain of bacteria transformation. VIDEO #1
- 6. Discovery of DNA’s Function • Avery – Altered Griffith’s experiment by adding enzymes to destroy all the major macromolecules, which led to the discovery that DNA was the “transforming factor”, making it the best candidate for the hereditary material.
- 7. DNA Discovery of Function • Hershey & Chase – Used viruses to study DNA and was able to confirm/conclude that the genetic material in bacteria was DNA, not proteins.
- 8. Function/Purpose of DNA 1. Storage of genetic information DNA’s major function is to code for proteins – Recall that proteins are very important molecules in our cells. They are involved in virtually all cell functions! Each protein within the body has a specific function. Some proteins are involved in structural support, while others are involved in bodily movement and in defense against germs. Proteins are also responsible for determining all of an organism’s traits, such as eye color! 2. Self-duplication of genetic information (DNA Replication) 3. Transmission of genetic information (Cellular Reproduction)
- 9. VIDEO #2
- 10. DNA Structure DNA is made up of millions of tiny subunits (monomers) called nucleotides. Each nucleotide consists of three parts: – Pentose Sugar (Deoxyribose) – Phosphate Group – Nitrogenous Base • Adenine • Cytosine • Guanine • Thymine
- 11. DNA Structure • Purines and Pyrimidines are nitrogenous bases that make up the two different kinds of nucleotide bases in DNA. • The two-carbon nitrogen ring bases (adenine and guanine) are purines, while the one- carbon nitrogen ring bases (thymine and cytosine) are pyrimidines. • Bases code for your traits!
- 12. DNA Structure • Chargaff – Discovered how the nitrogenous bases bond together. He discovered that Adenine (A) always bonds with Thymine (T), and that Cytosine (C) always bonds with Guanine. The observation that A=T and C=G became known as Chargaff’s rule. He also noted that DNA composition varies from species to species. 23%
- 13. DNA Structure DNA consists of two molecules that are arranged into a twisted, ladder-like structure called a double-helix. • Franklin – Used a technique called X-ray diffraction to get information about the structure of the DNA molecule. Her pictures of DNA fibers were key to the discovery of the structure of DNA; although she didn’t recognize it, her pictures showed that the strands in DNA are twisted around each other and that DNA is made up of two strands.
- 14. DNA Structure • Watson & Crick – Made physical models to narrow down the possibilities and eventually create an accurate model of the DNA molecule. Proposed the double helical structure of DNA in 1953 using Franklin’s pictures.
- 15. The Watson & Crick DNA Model • DNA is composed of 2 chains of nucleotides that form a double helix shape. • The backbone is formed by covalent bonds between the sugar of one nucleotide and the phosphate group of the • next. The backbone has directionality (polarity): – 5’ End – phosphate end – 3’ End – sugar end • The two strands are antiparallel (they run side-by-side in opposite directions).
- 16. Watson & Crick Model • Each base will only bond with one other specific base (A=T, C=G). Hydrogen bonds are formed between the bases. These are fairly weak bonds, having just enough force to hold the two strands of DNA together (DNA strands have to be able to separate easily to function). The order (or sequence) of the bases determines what proteins are made!
- 17. DNA Complementarity • When Watson and Crick discovered the structure of DNA, they immediately recognized that each strand of the double helix has all the information needed to make the other strand. Because each strand can be used to make the other strand, the strands are said to be complementary. This is essential for DNA replication. – For example, the complementary strand of the DNA sequence 5’ A G T C A T G 3’ is 3’ T C A G T A C 5'
- 18. DNA Complementarity Practice • Write the complementary strand of DNA for: – ATG TGA CAG – AAT CCG TAG
- 19. MAKE a DNA MOLECULE using Manipulatives black 5 carbon sugar = deoxyribose white tube = phosphate red tube = Guanine blue tube = Thymine green tube = Adenine black tube = Cytosine small clearish tubes = hydrogen bonds A C G T T C A G
- 20. DNA Concept Check 1. DNA is called a double helix, what does this mean? 2. What are the sides of DNA made of? 3. What are the “rungs” of DNA made of? 4. List the 3 parts of every DNA molecule. 5. List the 4 nitrogenous bases. 6. How do the bases bond? 7. How is every organism different from all others?
- 21. RNA – Ribonucleic Acid
- 22. VIDEO #3
- 23. Unit 5 Foldable: DNA Deoxyribonucleic Acid vs RNA Ribonucleic Acid TYPES LOCATION STRUCTURE FUNCTION
Editor's Notes
- Every living thing has DNA. That means that you have something in common with a zebra, a tree, a mushroom, and a beetle! DNA controls all the chemical changes which take place in cells. The kind of cell which is formed, (muscle, blood, nerve etc) is controlled by DNA. The kind of organism which is produced (buttercup, giraffe, herring, human etc) is controlled by DNA.
- DNA is too small to be seen in detail, but under a microscope it looks like a twisted-up ladder. If you uncoiled the DNA from one of your cells it would be @ 6 foot long; all the DNA in your body weights 7.5 grams (1/4 ounce) and is worth about 9 million dollars.
- Miescher (PRONOUNCED MEESHER) wanted to study the chemistry of cells. He chose to study white blood cells, which are abundant in pus, and were easily available to him in bandages from a hospital near his university. Miescher isolated a material rich in phosphorus from the cells and called it nuclein. He found nuclein in other types of cells as well, including salmon sperm. The name nuclein was changed to nucleic acid, then later to deoxyribonucleic acid. At the time, this molecule was not thought to be the carrier of hereditary information because it was believed to lack the variability necessary to account for the incredible diversity among organisms. Rather, like most scientists of his time, Miescher believed that proteins were responsible for heredity, because they existed in such a wide variety of forms.
- How do genes work? That was the question many scientists were asking themselves. They needed to know what genes were made up of to answer the question. The first scientist to help figure this out was Frederick Griffith. [show video] The heat-killed bacteria in his experiments on mice had made the harmless bacteria deadly. Discovering the molecule responsible for this transformation would be the key to understanding heredity.
- In 1944, a team led by Oswald Avery tried to find out what this hereditary molecule was. Because of Griffith, scientists knew that some types of these bacteria (called "S type") had an outer layer called a capsule, but other types (called "R type") did not. Avery’s team altered Griffith’s experiment by adding enzymes to destroy all the major macromolecules. Through a series of experiments with treatments to mixtures of heat-killed bacteria molecules showed that if they destroyed proteins, lipids, carbohydrates, and RNA, one at a time, transformation still occurred, but when they destroyed the DNA it did not. Avery and his colleagues had found that only DNA could change R type bacteria into S type. This meant that something about DNA allowed it to carry instructions from one cell to another. This was not true of any other substances within the bacteria, including protein. This result highlighted DNA as the "transforming factor," thereby making it the best candidate for the hereditary material.
- Avery's findings were largely unaccepted as evidence for DNA as the hereditary material until separate experiments were performed by other scientists. Thus, eight years later, Alfred Hershey and Martha Chase further confirmed that protein was not the hereditary material through their work with bacteriophages, which are viruses that infect bacteria. Bacteriophages are composed of only two substances: protein and DNA. By using radioactive labels that would integrate specifically into either DNA or protein, but not both, Hershey and Chase were able to show that DNA is the only material transferred directly from bacteriophages into bacteria when the bacteria are infected by these viruses. Thus, In 1952, Alfred Hershey and Martha Chase confirmed Avery’s discovery that DNA is the hereditary material.
- Everything the organism is and will become is because of the DNA, or the information stored in the DNA. Information is stored in the DNA. The instructions for physical characteristics, for patterns of development, for telling the cell what it will be and how to do its job…these instructions must be protected. A cell must make a complete copy of every one of its genes before the cell divides, so that each new cell has a complete set of instructions. We know that genes are passed down from parent to offspring. Therefore, DNA must be carefully sorted and passed along when cells divide (especially when gametes are formed when the loss of any DNA might mean a loss of valuable genetic information that offspring might need to survive).
- We will watch this video over DNA structure, then I will recap the information for our notes!
- By the late 1940s DNA was largely accepted as the genetic molecule. Scientists still needed to figure out this molecule's structure to be sure, and to understand how it worked.
- Pyrimidines have a Y like cytosine and thymine Purines (guanine and adenine have the double letters, so they are double ringed)
- According to Chargaff, if a sample of DNA has 23% adenine it would have 23% thymine (because A=T). If we add these together we see that 46% of the DNA is composed of A=T…leaving 54% for C=G. That means the sample has 27% C and 27% G.
- Watson and Crick took a crucial conceptual step, suggesting the molecule was made of two chains of nucleotides, each in a helix as Franklin had found, but one going up and the other going down (we call this antiparallel). Crick had just learned of Chargaff's findings about base pairs in the summer of 1952. He added that to the model, so that matching base pairs interlocked in the middle of the double helix to keep the distance between the chains constant. Watson and Crick showed that each strand of the DNA molecule was a template for the other. During cell division the two strands separate, and build a new "other half" on each strand, just like the one before. This way DNA can reproduce itself without changing its structure -- except for occasional errors, called mutations. The structure so perfectly fit the experimental data that it was almost immediately accepted. DNA's discovery has been called the most important biological work of the last 100 years, and the field it opened may be the scientific frontier for the next 100. By 1962, when Watson, Crick, and Wilkins won the Nobel Prize for physiology/medicine, Franklin had died. The Nobel Prize only goes to living recipients, and can only be shared among three winners. Were she alive, would she have been included in the prize?
- Watch this DNA vs RNA video, then we will create a foldable with the information!