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Chapter 12 Molecular Genetics

Section 1: DNA: The Genetic Material

Section 2: Replication of DNA

Section 3: DNA, RNA, and Protein

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12.1 DNA: The Genetic Material

Molecular Genetics

Chapter 12

Griffith

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Avery

 _{Identified the molecule that transformed the}

R strain of bacteria into the S strain

 _{Concluded that when the S cells were killed,}

DNA was released

 _{R bacteria incorporated this DNA into their}

cells and changed into S cells. 12.1 DNA: The Genetic Material

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Hershey and Chase

 Used radioactive labeling to trace the DNA and protein

 Concluded that the viral DNA was injected into the cell and provided the

genetic information needed to produce new viruses

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DNA Structure

 Nucleotides

 Consist of a five-carbon sugar, a phosphate group, and a nitrogenous base

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Chargaff

 _{Chargaff’s rule:}

C = G and T = A 12.1 DNA: The Genetic Material

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X-ray Diffraction

 _{X-ray diffraction data helped solve the}

structure of DNA

 _{Indicated that DNA was a}_{double helix}

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Watson and Crick

 _{Built a model of the double helix that}

conformed to the others’ research

1. two outside strands consist of alternating deoxyribose and phosphate

2. cytosine and guanine bases pair to each other by three hydrogen bonds

3. thymine and adenine bases pair to each other by two hydrogen bonds

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DNA Structure

 _{DNA often is compared to a twisted ladder.}  _{Rails of the ladder are represented by the}

alternating deoxyribose and phosphate.

 _{The pairs of bases (cytosine–guanine or}

thymine–adenine) form the steps. 12.1 DNA: The Genetic Material

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Orientation

 On the top rail, the strand is said to be oriented 5′ to 3′.  The strand on the bottom runs in the opposite

direction and is oriented 3′ to 5′. 12.1 DNA: The Genetic Material

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Chromosome Structure

 DNA coils around histones to form nucleosomes, which coil to form chromatin fibers.

 The chromatin fibers supercoil to form chromosomes that are visible in the metaphase stage of mitosis.

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Classwork & Homework

• _Classwork

– _{Section 1 Review}

• _{Page 332} • _{#1 - 6}

• _Homework

– _{Read 12.2 & 12.3}

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12.2 Replication of DNA

Semiconservative Replication

 _{Parental strands of}

DNA separate, serve as templates, and

produce DNA

molecules that have one strand of

parental DNA and

one strand of new DNA.

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Unwinding

 _{DNA helicase, an enzyme, is responsible for}

unwinding and unzipping the double helix.

 _{RNA primase adds a short segment of RNA,}

called an RNA primer, on each DNA strand. 12.2 Replication of DNA

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Base pairing

 _{DNA polymerase continues adding appropriate}

nucleotides to the chain by adding to the 3′ end of the new DNA strand.

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 _{One strand is called the leading strand}

and is elongated as the DNA unwinds.

 _{The other strand of DNA, called the}

lagging strand, elongates away from the replication fork.

 _{The lagging strand is synthesized}

discontinuously into small segments, called Okazaki fragments.

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Joining

 _{DNA polymerase removes the RNA primer}

and fills in the place with DNA nucleotides.

 _{DNA ligase links the two sections.}

 _{Replication Video Link:}

https://www.youtube.com/watch? v=vNXFk_d6y80

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Comparing DNA Replication in Eukaryotes and Prokaryotes

 _{Eukaryotic DNA unwinds in multiple areas}

as DNA is replicated.

 _{In prokaryotes, the circular DNA strand is}

opened at one origin of replication.

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12.3 DNA, RNA, and Protein

Central Dogma  _RNA

 _{Contains the sugar ribose and the}

base uracil

 _{Usually is single stranded}

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Messenger RNA (mRNA)

 _{Long strands of RNA nucleotides that are}

formed complementary to one strand of DNA

Ribosomal RNA (rRNA)

 _{Associates with proteins to form ribosomes}

in the cytoplasm

Transfer RNA (tRNA)

 _{Smaller segments of RNA nucleotides that}

transport amino acids to the ribosome 12.3 DNA, RNA, and Protein

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 DNA is unzipped in the nucleus and RNA

polymerase binds to a specific section where an mRNA will be synthesized.

Transcription

 _{Through transcription,}

the DNA code is

transferred to mRNA in the nucleus.

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RNA Processing

 The code on the DNA is interrupted

periodically by sequences that are not in the final mRNA.

 Intervening sequences are called introns.

 Remaining pieces of DNA that serve as the coding sequences are called exons.

Chapter 12

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The Code

 _{Experiments during the 1960s demonstrated}

that the DNA code was a three-base code.

 _{The three-base code in DNA or mRNA is}

called a codon.

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Translation

 In translation, tRNA molecules act as the

interpreters of the mRNA codon sequence.

 _{At the middle of the folded} strand, there is a three-base coding sequence called the anticodon.

 Each anticodon is

complementary to a codon on the mRNA.

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One Gene—

One Enzyme

 _{The Beadle and Tatum}

experiment showed that one gene codes for one enzyme. We now know that one gene codes for one polypeptide.

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Classwork & Homework

• _Classwork

• _{Page 335 # 1 - 5}

• _{Page 341 # 1 - 4}

– _{Data Analysis 12.1}

• _{Page 340}

• _Homework

– _{Read 12.4}

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12.4 Gene Regulation and Mutation

Prokaryote Gene Regulation

 Ability of an organism to control which genes are transcribed in response to the environment

 An operon is a section of DNA that contains

the genes for the proteins needed for a specific metabolic pathway.

 _Operator  Promoter

 Regulatory gene

 Genes coding for proteins

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The Trp Operon

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The Lac Operon

Chapter 12

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Eukaryote Gene Regulation  _{Controlling transcription}

 _{Transcription factors ensure that a gene}

is used at the right time and that proteins are made in the right amounts

 _{The complex structure of eukaryotic}

DNA also regulates transcription. 12.4 Gene Regulation and Mutation

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Hox Genes

 _{Hox genes are}

responsible for the general body pattern of most animals.

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RNA Interference

 _{RNA interference can stop the mRNA from}

translating its message.

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Mutations

 _{A permanent change that occurs in a cell’s}

DNA is called a mutation.

 _{Types of mutations}  _{Point mutation}

 _Insertion  _Deletion

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Protein Folding and Stability

 _{Substitutions also can lead to genetic}

disorders.

 _{Can change both the folding and stability}

of the protein

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Causes of Mutation

 _{Can occur spontaneously}

 _{Chemicals and radiation also can}

damage DNA.

 _{High-energy forms of radiation, such as X rays}

and gamma rays, are highly mutagenic. 12.4 Gene Regulation and Mutation

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Body-cell v. Sex-cell Mutation

 _{Somatic cell mutations are not passed on}

to the next generation.

 _{Mutations that occur in sex cells are passed}

on to the organism’s offspring and will be present in every cell of the offspring.

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Classwork & Homework

• _Classwork

– _{Data Analysis 12.2}

• _{Page 348}

• _{Page 349 # 1 - 6}

• _Homework

– _{Chapter Review}

• _{Pages 353 – 355 #1-9, 12 – 17, 22 – 28, 31 - 36}