Chapter 8: DNA and the Language of Life

Fredrick Griffith In 1928, Fredrick Griffith was studying two forms or strain of a bacterial species: one strain was fatal to mice, while the other strain was harmless. Strain 1 Strain 2

Griffith’s Experiment When he injected heat-treated bacteria into mice, the mice remained healthy. –Heat kills the deadly strain of bacterium, making it harmless. Strain 1 Strain 2Heated Strain 1

Griffith’s “Transforming Factor” When he injected mice with a mixture of the harmless strain and the heat-treated deadly strain, he expected the mice to survive. However, the mixture killed the mice. Some of the harmless bacteria had been “transformed”, becoming deadly. Strain 1 Strain 2Heated Strain 1 Strain 2+ heated Strain1

DNA or Protein????? After Griffith’s experiment, scientists began to search for the “transforming factor”. Attention focused on two types of chemicals: protein and DNA. In 1952, biologists Alfred Hershey and Martha chase provided more evidence to distinguish between the two possibilities. They conducted a series of experiments using viruses.

Virus A virus is package of nucleic acid wrapped in a protein coat. Unlike living things, viruses are not made of cells. A virus can only reproduce by infecting a living cell with its genetic material. A virus that infects bacteria is called a bacteriophage. Phage consists of a protein coat that encloses the genetic material. When a phage infects a bacterium, it inserts its genetic material into the bacterium, while its coat remains outside.

Hershey and Chase’s Experiment In the first experiment, phages with radioactive-labeled DNA, infected bacteria. In a second experiment, phages with radioactive-labeled protein infected bacteria. In both experiments, bacteria were separated from the phage coats by blending. In the first experiment, most radioactivity was found in the infected bacteria, while in the second experiment most radioactivity was found in the phage coat. These experiments demonstrated that DNA is the genetic material of phage and that protein does not transmit genetic information.

DNA Structure The heritable genetic information of an organism is stored in DNA. The DNA molecule is made up of two strands that are held together by hydrogen bonds. These strands are parallel to each other but run in opposite directions, called antiparallel. Each strand of DNA consists of a large number of nucleotides.

DNA Structure Each nucleotide is made up of a deoxyribose (sugar), a phosphate group and a nitrogenous base. There are 4 kinds of nitrogenous bases, Thymine (T), Cytosine (C), Adenine (A), and Guanine (G). Bases Thymine (T) and Cytosine (C) are single-ring structure called pyramidines. Bases Adenine (A) and Guanine (G) are double-ring structures called purines. In the double stranded DNA, A always pairs with T and C always pairs with G. This is called complementary base pairing.

DNA Strands Nucleotides are joined to one another by covalent bonds that connect the sugar of one nucleotide to the phosphate group of the next. This repeating pattern of sugar-phosphate is called a sugar-phosphate backbone. Knowing the main components of DNA, Watson and Crick tried to figure out how the elements fit together? One clue came from X-ray photographs of DNA taken by Rosalind Franklin suggested that the structure of DNA was a double helix.

DNA Replication The process of copying the DNA molecule. This process can be divided into 3 major parts: 1.Binding of enzymes to existing DNA 2.Unwinding the double helix 3.Synthesis of a new matching strand for each existing strand

DNA Replication 1. What do the yellow strands of DNA represent? new DNA strands 2. What will the two daughter DNA molecules consist of? Each consists of one original (parent) strand and one new strand.

RNA DNA Single-stranded Double-stranded Ribose Deoxyribose A, C, G and U A, C, G and T

Types of RNA: 1. mRNA - messenger RNA - carries information from DNA to the ribosome where the protein is made. 2. tRNA - transfer RNA - carries amino acids to mRNA at the ribosome to assembly the protein being made. 3. rRNA - ribosomal RNA - major structural component of the ribosome where protein synthesis occurs.

The Central Dogma: DNA is maintained by DNA replication, DNA is transcribed into RNA, RNA is translated into protein.

What are proteins? We are protein. Our hair, our nails, our skin, our blood, our enzymes and hormones are protein; indeed, our bodies contain some ten thousand to fifty thousand kinds of protein.

Genetic Alphabets: Genetic "Alphabets" - there are three alphabets involved in the entire process of protein synthesis 1) DNA - A, C, G and T 2) RNA - A, C, G and U 3) Protein - Twenty different amino acids Triplet Code - three nucleotides code for one amino acid 1. Codon – a triplet in mRNA, pairs with triplet on a tRNA molecule carrying the correct amino acid. 2. Anticodon – a triplet in tRNA

The Genetic Code: Example #1: 1) mRNA Codon = AUG 2) Amino Acid = Met Example #2: C U A G G C A A C U U A Amino Acids #2: Leu - Gly - Asn - Leu Example #3: UUACGCCGUAAG Leu – Arg – Arg - Lys

Transcription: Purpose: to synthesize RNA from a DNA template It starts when the enzyme RNA polymerase attaches to a specific region of the DNA. As a result, a single complementary strand of RNA is made.

Editing the mRNA message: Transcribed mRNA must first be edited before it can leave the nucleus for the cytoplasm. The initial RNA transcripts have stretches of noncoding nucleotides that interrupt nucleotide sequences that actually code for amino acids.

Splicing: Splicing - Introns are removed and Exons are joined together. Intron - segment of mRNA which does NOT code for protein; therefore, it is removed. Exon - segment of mRNA which does code for protein; therefore, it remains for expression in protein.

Translation: It is the final step on the way from DNA to protein. It is the synthesis of proteins directed by a mRNA template. tRNA translates the three-letter codons of mRNA to the amino acids that make up proteins. It happens on ribosomes.

tRNA during Translation: 1.A tRNA molecule must become bound to the appropriate amino acid. 2.It has to recognize the appropriate codon in the mRNA. 3.During translation, the anticodon on tRNA recognizes a particular codon on mRNA by using base-pairing rules.

Ribosome: A ribosome has two subunits: –Small subunit: binding site for mRNA –Large subunit: consist of two binding sites for tRNA “P” site: holds the tRNA carrying the growing polypeptide chain. “A” site: holds the tRNA carrying the next amino acid to be added to the chain.

Steps of Translation: First, the ribosome attaches at a specific site on the mRNA. This site is the start codon, AUG. Next, amino acids are added one by one to the growing chain of amino acids. During translation, the ribosome moves down the mRNA, codon by codon, until translation is completed. This process continues until the ribosome reaches a stop codon: UAA, UAG, or UGA.

Mutation A mutation is any change in the nucleotide sequence of DNA. Mutations can change the meaning of genes. Mutations can involve large regions of a chromosome or just a single nucleotide. Mutation can be divided into 2 general categories.

1. Base Substitution 1.Base substitution: replacement of one base or nucleotide with another. It results in a change that affects the function of a protein.

2. Base Insertion or Deletion 2. Base insertion or deletion: adding or subtracting nucleotides. It’s usually more disastrous than the effects of base substitutions.

What Causes Mutation? May occur when errors are made during DNA replication. May occur when errors happen during chromosome crossovers in meiosis. Physical or chemical agents that cause mutations are called mutagens. Most common physical mutagen is high-energy radiation. Ex: X-rays Mutations are the ultimate source of genetic diversity in the living world.

EXTRAS!!!!!!!!!!!!!

Transcription & Translation nscribe/ nscribe/ Translation video- tein_synthesis.htm Protein synthesis- online.com/objects/index_tj.asp?objID=AP130 2

Sickle cell disease Sickle cell disease is an example of a disorder caused by inheritance of a genetic mutation. In sickle cell disease, the hemoglobin in red blood cells tends to bind together when oxygen levels are low. The hemoglobin crystals deform the red blood cells into sickle, or crescent shapes. The sickle shaped cells clog tiny blood vessels, dangerously blocking the normal flow of blood.

Replication of the Double Helix More than a dozen enzymes are involved in DNA replication. Each “incoming” nucleotide pairs with its complementary nucleotide on the parent strand. Enzymes called DNA polymerase make the covalent bonds between the nucleotides of the new strand. DNA replication begins at specific sites called origins of replication. The copying proceeds outward