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Lesson Overview 12.1 Identifying the Substance of Genes.

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1 Lesson Overview 12.1 Identifying the Substance of Genes

2 Lesson Overview Lesson Overview Identifying the Substance of Genes Griffith’s Experiments Griffith isolated two different strains of the same bacterial species. Only one of the strains caused pneumonia.

3 Lesson Overview Lesson Overview Identifying the Substance of Genes Griffith’s Experiments When injecting mice with disease-causing bacteria, the mice developed pneumonia and died. When injecting mice with harmless bacteria, the mice stayed healthy.

4 Lesson Overview Lesson Overview Identifying the Substance of Genes Griffith’s Experiments First, Griffith took the S strain, heated the cells to kill them, and then injected the heat-killed bacteria into mice. Mice survived, suggesting that the cause of pneumonia was not a toxin from disease-causing bacteria.

5 Lesson Overview Lesson Overview Identifying the Substance of Genes Griffith’s Experiments In Griffith’s next experiment, mixed the heat-killed S-strain with live, harmless R strain and injected the mixture into mice. The injected mice developed pneumonia, and died.

6 Lesson Overview Lesson Overview Identifying the Substance of Genes Transformation Process called transformation - one type of bacteria is changed permanently into another. Because the ability to cause disease was inherited by the transformed bacteria, Griffith concluded that the transforming factor had to be a gene.

7 Lesson Overview Lesson Overview Identifying the Substance of Genes The Molecular Cause of Transformation Avery extracted molecules from heat-killed bacteria and destroyed proteins, lipids, carbohydrates, and RNA. Transformation still occurred.

8 Lesson Overview Lesson Overview Identifying the Substance of Genes The Molecular Cause of Transformation Then destroyed DNA and transformation did not occur. Therefore, DNA was the transforming factor. This led to the discovery that DNA stores and transmits genetic information.

9 Lesson Overview Lesson Overview Identifying the Substance of Genes Bacteriophages Bacteriophage - virus that infects bacteria

10 Lesson Overview Lesson Overview Identifying the Substance of Genes The Hershey-Chase Experiment Hershey and Chase studied a bacteriophage with a DNA core and a protein coat. Wanted to determine if the protein coat or the DNA core entered the bacterial cell Hershey and Chase grew viruses containing radioactive isotopes of phosphorus-32 (P-32) and sulfur-35 (S-35)

11 Lesson Overview Lesson Overview Identifying the Substance of Genes The Hershey-Chase Experiment Bacteria contained phosphorus P-32, the marker found in DNA. Hershey and Chase concluded that the genetic material of the bacteriophage was DNA, not protein. Experiment confirmed Avery’s results - that DNA was the genetic material found in genes.

12 Lesson Overview Lesson Overview Identifying the Substance of Genes The Role of DNA DNA can store, copy, and transmit genetic information

13 Lesson Overview 12.2 The Structure of DNA

14 Lesson Overview Lesson Overview Identifying the Substance of Genes Nucleic Acids and Nucleotides Located in the nucleus. Made up of nucleotides, linked to form long chains. Three components: a 5-carbon sugar called deoxyribose, a phosphate group, and a nitrogenous base.

15 Lesson Overview Lesson Overview Identifying the Substance of Genes Nucleic Acids and Nucleotides Nucleotides joined by covalent bonds DNA has four nitrogenous bases: adenine, guanine, cytosine, and thymine, or AGCT

16 Lesson Overview Lesson Overview Identifying the Substance of Genes Chargaff’s Rules Chargaff discovered the percentages of [A] and [T] bases are almost equal in any sample of DNA. The same thing is true for the other two nucleotides, guanine [G] and cytosine [C]. The observation that [A] = [T] and [G] = [C] became known as one of “Chargaff’s rules.”

17 Lesson Overview Lesson Overview Identifying the Substance of Genes Franklin’s X-Rays Rosalind Franklin used X-ray diffraction that showed: -DNA has 2 strands that are twisted around each other. -The nitrogen bases are near the center.

18 Lesson Overview Lesson Overview Identifying the Substance of Genes The Work of Watson and Crick Franklin’s X-ray pattern enabled Watson and Crick to build a model of the specific structure and properties of DNA. Built three-dimensional model of DNA in a double helix

19 Lesson Overview Lesson Overview Identifying the Substance of Genes Antiparallel Strands DNA strands are “antiparallel”— they run in opposite directions. Enables the nitrogenous bases to come into contact at the center. It also allows each strand to carry nucleotides.

20 Lesson Overview Lesson Overview Identifying the Substance of Genes Hydrogen Bonding Hydrogen bonds form between certain nitrogenous bases, holding the two DNA strands together. Hydrogen bonds are weak forces that allow the two strands to separate. Ability to separate is critical to DNA’s functions.

21 Lesson Overview Lesson Overview Identifying the Substance of Genes Base Pairing Watson and Crick realized that base pairing explained Chargaff’s rule. It gave a reason why [A] = [T] and [G] = [C]. Fit between A–T and G–C nucleotides called base pairing.

22 12-3 DNA REPLICATION FEDEROFF

23 EUKARYOTIC DNA REPLICATION Step 1 – Helicase unzips the DNA molecule.

24 Step 2 – DNA Polymerase adds on complementary nucleotides in a 5’ to 3’ direction.

25 Step 3 – The lagging strand continues to replicate in fragments instead of continually like the leading strand. Leading StrandLagging Strand

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30 OKAZAKI FRAGMENTS

31 Step 4 – Since the fragments still aren’t joined, the enzyme ligase joins the fragments.

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33 Step 5 – As replication continues, the leading and lagging strand twist back into their helical form.

34 TELOMERES Are the tips of chromosomes that make it less likely important genes will be lost with replication.

35 PROKARYOTIC DNA REPLICATION Starts at a single point, and proceeds in 2 directions until the entire chromosome is copied.

36 PROKARYOTIC VS. EUKARYOTIC DNA Replication Process [3D Animation] – Biology / Medicine Animations HD https://www.youtube.com/watch?v=27TxKoFU2Nw

37 Lesson Overview Lesson OverviewFermentation Lesson Overview 13.1 RNA

38 Lesson Overview Lesson OverviewFermentation The Role of RNA First step in decoding genetic instructions is to copy DNA into RNA. RNA, like DNA, is a nucleic acid that consists of a long chain of nucleotides. RNA uses the base sequence copied from DNA to produce proteins.

39 Lesson Overview Lesson OverviewFermentation Comparing RNA and DNA Each nucleotide in both DNA and RNA is made up of a 5-carbon sugar, a phosphate group, and a nitrogenous base. Three important differences between RNA and DNA: (1) Sugar in RNA is ribose (2) RNA is single-stranded. (3) RNA contains uracil (U) in place of thymine (T).

40 Lesson Overview Lesson OverviewFermentation Comparing RNA and DNA The cell uses DNA “master plan” to prepare RNA “blueprints.” DNA stays in the cell’s nucleus, while RNA goes to the ribosomes.

41 Lesson Overview Lesson OverviewFermentation Functions of RNA RNA is like a disposable copy of a segment of DNA, a working copy of a single gene. RNA controls the assembly of amino acids into proteins.

42 Lesson Overview Lesson OverviewFermentation Functions of RNA Three main types of RNA: messenger RNA, ribosomal RNA, and transfer RNA.

43 Lesson Overview Lesson OverviewFermentation Messenger RNA The RNA molecules that carry copies of instructions to other parts of the cell are known as messenger RNA (mRNA)

44 Lesson Overview Lesson OverviewFermentation Ribosomal RNA Ribosomal RNA (rRNA) make up ribosomes and assemble proteins.

45 Lesson Overview Lesson OverviewFermentation Transfer RNA Transfer RNA (tRNA) transfers each amino acid to the ribosome as specified by the mRNA to make proteins.

46 Lesson Overview Lesson OverviewFermentation Making RNA - Transcription Transcription – DNA serves as templates to produce complementary RNA molecules.

47 Lesson Overview Lesson OverviewFermentation Transcription In prokaryotes, RNA synthesis and protein synthesis take place in the cytoplasm. In eukaryotes, RNA is produced in the nucleus and moves to the cytoplasm to produce proteins.

48 Lesson Overview Lesson OverviewFermentation Transcription Requires RNA polymerase, which separates DNA strands, then uses one strand of DNA as a template to assemble complementary strand of RNA.

49 Lesson Overview Lesson OverviewFermentation Promoters RNA polymerase binds to promoters - regions of DNA with specific base sequences. Promoters show RNA polymerase where to begin making RNA. Similar signals cause transcription to stop when a new RNA molecule is completed.

50 Lesson Overview Lesson OverviewFermentation RNA Editing Portions of RNA are cut out and stay in the nucleus are called introns. The remaining pieces, known as exons, are spliced together to form the final mRNA, which exits the nucleus.

51 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis Lesson Overview 13.2 Ribosomes and Protein Synthesis

52 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis The Genetic Code First step in decoding genetic messages is to transcribe DNA to RNA. Transcribed information contains a code for making proteins. The genetic code is read three “letters” at a time, so that each “word” is three bases long and corresponds to a single amino acid.

53 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis The Genetic Code Proteins are made by joining amino acids together into long chains, called polypeptides. There are about 20 amino acids.

54 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis The Genetic Code The amino acids and their order determine the properties of proteins. Sequence of amino acids affects the shape of the protein, which determines its function.

55 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis The Genetic Code Each three-letter “word” in mRNA is known as a codon. A codon consists of three consecutive bases that specify a single amino acid.

56 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis Start and Stop Codons The methionine codon AUG serves as the “start” codon for protein synthesis. Following the start codon, mRNA is read, three bases at a time, until it reaches one of three different “stop” codons, which end translation.

57 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis Translation The decoding of mRNA into amino acids and eventually a protein is known as translation.

58 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis Steps in Translation mRNA is transcribed in the nucleus and then translated in the cytoplasm.

59 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis Steps in Translation Translation begins when a ribosome attaches to mRNA. As the ribosome reads each codon of mRNA, it directs tRNA to bring the amino acid to the ribosome.

60 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis Steps in Translation Each tRNA molecule carries one amino acid. In addition, each tRNA has three unpaired bases, called the anticodon — which is complement to one mRNA codon.

61 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis Steps in Translation The ribosome forms a peptide bond between the amino acids At the same time, the bond holding tRNA to its amino acid is broken.

62 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis Steps in Translation The polypeptide chain grows until the ribosome reaches a “stop” codon. When it reaches a stop codon, it releases both the newly formed polypeptide and the mRNA molecule, completing translation.

63 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis The Roles of tRNA and rRNA in Translation rRNA holds ribosomal proteins in place and locates the beginning of mRNA. They may even join amino acids together.

64 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis The Molecular Basis of Heredity Genes contain instructions for assembling proteins.

65 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis The Molecular Basis of Heredity Gene expression - the way DNA, RNA, and proteins put genetic information into action in living cells.

66 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis The Molecular Basis of Heredity There is a near-universal nature in the genetic code. Although some organisms show slight variations in the amino acids assigned to particular codons, the code is always read three bases at a time and in the same direction. Despite their enormous diversity in form and function, living organisms display remarkable unity at life’s most basic level, the molecular biology of the gene.

67 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis Lesson Overview 13.3 Mutations

68 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis Types of Mutations Now and then cells make mistakes in copying their own DNA, inserting the wrong base or even skipping a base as a strand is put together. These variations are called mutations Mutations are heritable changes in genetic information.

69 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis Types of Mutations All mutations fall into two basic categories: Gene mutations - produce changes in a single gene Chromosomal mutations - produce changes in whole chromosomes.

70 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis Gene Mutations Point mutations - involve changes in one or a few nucleotides. If a gene in one cell is altered, the alteration can be passed on to every cell that develops from the original one.

71 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis Gene Mutations Point mutations include substitutions, insertions, and deletions.

72 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis Substitutions In a substitution, one base is changed to a different base. Usually affect a single amino acid, and sometimes they have no effect at all.

73 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis Insertions and Deletions Insertions and deletions are point mutations in which one base is inserted or removed. Called frameshift mutations because they shift the “reading frame” of the genetic message and can change the protein so much that it won’t be functional.

74 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis Chromosomal Mutations Chromosomal mutations involve changes in the number or structure of chromosomes. Can change the location of genes and the number of copies of some genes. Four types: deletion, duplication, inversion, and translocation.

75 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis Chromosomal Mutations Deletion involves the loss of all or part of a chromosome.

76 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis Chromosomal Mutations Duplication produces an extra copy of all or part of a chromosome.

77 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis Chromosomal Mutations Inversion reverses the direction of parts of a chromosome.

78 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis Chromosomal Mutations Translocation occurs when part of one chromosome breaks off and attaches to another.

79 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis Effects of Mutations Genetic material can be altered by natural or artificial means. Resulting mutations may or may not affect an organism, most do not. Some mutations that affect individual organisms can also affect a species or even an entire ecosystem.

80 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis Effects of Mutations Many mutations are produced by errors in genetic processes. During DNA replication, an incorrect base is inserted roughly once in every 10 million bases. Small changes in genes can accumulate over time.

81 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis Mutagens Some mutations arise from mutagens - chemical or physical agents in the environment. Chemical mutagens include certain pesticides, plant alkaloids, tobacco smoke, and environmental pollutants. Physical mutagens include forms of electromagnetic radiation, such as X-rays and UV light. Stress can also be a factor.

82 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis Harmful Effects The most harmful mutations dramatically change protein structure or gene activity. Example: Sickle Cell Disease

83 Lesson Overview Lesson Overview Ribosomes and Protein Synthesis Beneficial Effects Some mutations can be highly advantageous to an organism or species. Example: Pesticide Resistance and Polyploidy


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