KEY CONCEPT DNA was identified as the genetic material through a series of experiments.

1. KEY CONCEPT DNA was identified as the genetic material through a series of experiments.

2. Griffith finds a ‘transforming principle.’ • Griffith experimented with the bacteria that cause pneumonia. • He used two forms: the S form (deadly) and the R form (not deadly). • A transforming material passed from dead S bacteria to live R bacteria making them deadly. *Note: heating bacteria to 60℃ can kill the bacteria without denaturing their DNA. DNA can remain unchanged up to 90℃. Therefore, the S bacteria died, but their DNA remained intact. Analyze:What were the variables in Griffith’s experiment? Infer: What evidence suggested that there was a transforming principle?

3. Avery identified DNA as the transforming principle. • Avery isolated and purified Griffith’s transforming principle. • Enzyme tests showed: • Enzymes that broke down proteins still transformed R bacteria to S bacteria. • Enzymes that broke down DNA stopped transformation.

4. Hershey and Chase confirm that DNA is the genetic material. • Hershey and Chase studied viruses that infect bacteria, or bacteriophages. • They tagged viral DNA with radioactive phosphorus. • They tagged viral proteins with radioactive sulfur. • Tagged DNA was found inside the bacteria; tagged proteins were not. Apply: How did Hershey and Chase build upon Avery’s analysis results? Fig. 1.3 – This micrograph shows the protein coat of a bacteriophage (orange) after it has injected its DNA into an E. coli bacterium (blue). TM: 115,000X

5. KEY CONCEPT DNA structure is the same in all organisms.

6. phosphate group nitrogen-containing base deoxyribose (sugar) DNA is a nucleic acid composed of four types of nucleotides. • DNA stands for deoxyribonucleic acid • DNA is made up of a long chain of nucleotides. • Each nucleotide has three parts. • a phosphate group • a deoxyribose sugar • a nitrogen-containing base Summarize: How do four DNA nucleotides differ in structure?

7. The nitrogen containing bases are the only difference in the four nucleotides. They are divided into to two classes: Pyrimidines and Purines based on their structures.

8. Watson and Crick determined the three-dimensional structure of DNA by building models. • They realized that DNA is a double helixthat is made up of a sugar-phosphate backbone on the outside with bases on the inside.

9. Watson and Crick’s discovery built on the work of Rosalind Franklin and Erwin Chargaff. • Franklin’s x-ray images suggested that DNA was a double helix of even width. • Chargaff’s rules stated that A=T and C=G. Apply: How did the Watson and Crick model explain Chargaff’s rules?

10. G C A T Nucleotides always pair in the same way • The base-pairing rules show how nucleotides always pair up in DNA (Chargaff’s rule) • A pairs with T • C pairs with G • Because a pyrimidine (single ring) pairs with a purine (double ring), the helix has a uniform width. Apply: What complementary sequence of bases would pair with the sequence TGACTA? Apply: If a DNA sequence is made up of 15% Thymine, then what is the percentage of each of the other three bases?

11. covalent bond hydrogen bond • The backbone is connected by covalent bonds (stronger). • The bases are connected by hydrogen bonds (weaker). Analyze: How many rings are there in each base pair?

12. KEY CONCEPT DNA replication copies the genetic information of a cell.

13. Replication copies the genetic information. • A single strand of DNA serves as a template for a new strand. • The rules of base pairing directreplication. • DNA is replicated during theS (synthesis) stage of thecell cycle. • Each body cell (somatic cell) gets a complete set ofidentical DNA.

14. nucleotide The DNA molecule unzips in both directions. Proteins (enzymes) carry out the process of replication. • DNA serves only as a template. • Enzymes and other proteins do the actual work of replication. • The enzyme helicaseunzips the double helix. This proceeds in two directions at the same time. • Free-floating nucleotides form hydrogen bonds with the template strand.

15. nucleotide new strand DNA polymerase • DNA polymerasedoes 2 jobs. First, enzymes bond the nucleotides together to form the double helix. Second, DNA polymerase checks for errors and corrects them. • Note: there’s only about one error per 1 billion nucleotides. • Note: human cells take about 8 hours to complete DNA replication.

16. new strand original strand Two molecules of DNA • Two new molecules of DNA are formed, each with an original strand and a newly formed strand. • This is why we say that DNA replication is semiconservative.

17. There are many origins of replication in eukaryotic chromosomes. Replication is fast and accurate. • DNA replication starts at many points in eukaryotic chromosomes. Infer: Why is it important that DNA have many origins of replication?

18. Differences in DNA replication Prokaryotes Eukaryotes DNA is in linear chromosomes Occurs in the nucleus Several replication starting points that meet together • DNA is in circular chromosomes called plasmids • Occurs in cytoplasm • One replication starting point

19. KEY CONCEPT Transcription converts a gene into a single-stranded RNA molecule.

20. replication transcription translation • The central dogma states that information flows in one direction from • DNA to RNA to proteins. • The central dogma includes three processes. • Replication • Transcription • Translation • RNA is a link between DNA and proteins.

21. RNA differs from DNA in three major ways. • RNA has a ribose sugar. DNA has a deoxyribose sugar. • RNA has uracil as a base. DNA has thymine instead. • RNA is a single-stranded structure. DNA is double stranded.

22. transcription complex start site nucleotides Transcription makes three types of RNA. • Transcription begins by RNA polymerase binding to the DNA and forming a transcription complex. • Transcription copies DNA to make a strand of RNA. • The transcription complex recognizes the start of a gene and unwinds a segment of it.

23. DNA RNA polymerase moves along the DNA • Nucleotides pair with one strand of the DNA lining up a complementary RNA strand. • RNA polymerase bonds the RNA nucleotides together. • The DNA helix reforms again as the gene is transcribed.

24. RNA • The RNA strand detaches from the DNA once the gene is transcribed. Discuss: Why must the DNA strands unwind and separate before transcription can take place? Practice: Using the following DNA sequence: CATACG create the complementary RNA sequence.

25. Transcription makes three types of RNA. • Messenger RNA (mRNA) carries the message from the nucleus to ribosome to be translated to form a protein. • Ribosomal RNA (rRNA) forms part of ribosomes where proteins are made. • Transfer RNA (tRNA) brings amino acids from the cytoplasm to a ribosome. Analyze: Explain why transcription occurs in the nucleus of eukaryotes. Critical viewing: How is the nucleotide sequence of the RNA transcript different or the same as the non-template strand of DNA?

26. one gene growing RNA strands DNA The transcription process is similar to replication. • Transcription and replication both involve complex enzymes, complementary base pairing and take place in the nucleus of eukaryotic cells. • The two processes have different end results. • Replication copiesall the DNA;transcription copiesa gene. • Replication makesone copy;transcription canmake many copies.

27. KEY CONCEPT Translation converts an mRNA message into a polypeptide, or protein.

28. codon for methionine (Met) codon for leucine (Leu) Amino acids are coded by mRNA base sequences. • Translation converts mRNA messages into polypeptide chains. Reminder: one or more polypeptide make up a protein. • A codon is a sequence of three nucleotides that codes for an amino acid. Amino acids are the monomer for building proteins.

29. The genetic code matches each RNA codon with its amino acid or function. • The genetic code matches each codon to its amino acid or function. • three stop codons • one start codon, codes for methionine (met)

30. A change in the order in which codons are read changes the resulting protein. • Regardless of the organism, codons code for the same amino acid. Calculate: Suppose an mRNA molecule in the cytoplasm had 300 nucleotides. How many amino acids would be in the resulting protein?

31. Amino acids are linked to become a protein. • An anticodon is a set of three nucleotides that is complementary to an mRNA codon. For example: the anticodon CCC pairs with the mRNA codon GGG. • An anticodon is carried by a tRNA.

32. Ribosomes consist of two subunits. • The large subunit has three binding sites for tRNA. • The small subunit binds to mRNA.

33. For translation to begin, tRNA binds to a start codon and signals the ribosome to assemble. • A complementary tRNA molecule binds to the exposed codon, bringing its amino acid close to the first amino acid.

34. The ribosome helps form a polypeptide bond between the amino acids. • The ribosome pulls the mRNA strand the length of one codon.

35. The now empty tRNA molecule exits the ribosome. • A complementary tRNA molecule binds to the next exposed codon. • Once the stop codon is reached, the ribosome releases the polypeptide chain and disassembles. Practice: Determine the mRNA codon transcribed from the DNA sequence: CAT. Then determine the tRNA anticodon and the amino acid that is translated.

36. KEY CONCEPT Mutations are changes in DNA that may or may not affect phenotype.

37. mutated base Some mutations affect a single gene, while others affect an entire chromosome. • A mutation is a change in an organism’s DNA. • A point mutationsubstitutes one nucleotide for another. A substitution is a type of point mutation. DNA polymerase often catches these substitutions and corrects them. If the substitution is not caught it may permanently change the organism’s DNA.

38. Many kinds of mutations can occur, especially during replication. • A frameshift mutationinserts or deletes a nucleotide in the DNA sequence. An insertion or deletion mutation tends to affect the polypeptide much more than a substitution. Practice:Imagine a short sentence of 3-letter “codons”: THE CAT ATE THE RAT If the first letter E has a deletion mutation, how would the reading frame shift? How would the new sentence of “codons” read?

39. Point mutations and frameshift mutations affect a single gene. Some mutations affect an entire chromosome. The four types of chromosomal mutations are deletion, duplication, inversion, and translocation.

40. Chromosomal mutations affect many genes. A gene is a section of DNA that codes for a trait. • Chromosomal mutations may occur during crossing over of meiosis. These usually occur in gametes (germ cells).

41. Translocation results from the exchange of DNA segments between non-homologous chromosomes.

42. blockage no blockage Mutations may or may not affect phenotype. • Chromosomal mutations tend to have a big effect. • Some gene mutations change phenotype (the physical appearance of a trait). • A mutation may cause a premature stop codon. • A mutation may change protein shape or the active site. • A mutation may change gene regulation. Fig 7.1: Cystic fibrosis (CF) is a genetic disease that is most commonly caused by a specific deletion mutation. It causes the overproduction of thick, sticky mucus. Although CF cannot be cured, it is treated in a number of ways, including oxygen therapy (above).

43. Some gene mutations do not affect phenotype. • A mutation that does not cause a change is called a silent mutation. • A mutation may occur in a noncoding region. • A mutation may not affect protein folding or the active site.

44. Mutations in body cells (somatic cells) do not affect offspring. • Mutations in sex cells (gametes or germ cells) can be harmful or beneficial to offspring. • Natural selection often removes mutant alleles from a population when they are less adaptive (do not help an organism to survive). Apply: Why aren’t mutations in body cells (somatic cells) passed on to offspring?

45. Mutations can be caused by several factors. • Errors is cellular processes such as: Replication errors, transcription errors and translation errors can cause mutations. • Mutagens, such as UV rays and chemicals, can cause mutations. • Some cancer drugs use mutagenic properties to kill cancer cells. Fig. 7.4 – Rachel Carson was one of the first ecologists to warn against the widespread use of pesticides and other potential mutagens and toxins. Summarize: Explain why mutagens can damage DNA in spite of repair enzymes.