Chapter 12 Notes

A. First Discoveries1.Griffith- experiment showed that live uncoated bacteria acquired the ability to make coats from dead coated bacteria. He called the process transformation.

Disease-causing bacteria (smooth

colonies)

Harmless bacteria (rough colonies)

Heat-killed, disease-causing bacteria (smooth colonies)

Control(no growth)

Heat-killed, disease-causing bacteria (smooth colonies)

Harmless bacteria (rough colonies)

Dies of pneumonia Lives Lives Live, disease-causingbacteria (smooth colonies)

Dies of pneumonia

Section 12-1Figure 12–2 Griffith’s Experiment

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2. Avery- discovered that DNA is the nucleic acid that stores and transmits the genetic information from one generation to the next.

3. Hershey & Chase- used radioactive labeling to identify DNA. They showed that DNA, not protein, is the genetic material of a bacteriophage (virus).

Bacteriophage with phosphorus-32 in DNA

Phage infectsbacterium

Radioactivity inside bacterium

Bacteriophage with sulfur-35 in protein coat

Phage infectsbacterium

No radioactivity inside bacterium

Figure 12–4 Hershey-Chase ExperimentSection 12-1

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DNA Structure1. DNA is composed of subunits called nucleotides.2. Nucleotides have three parts: a) sugar

b) phosphate group c) basea. The sugar is a 5 carbon sugar called deoxyribose.b. There are four kinds of nitrogenous bases- these form the “rungs” of the ladder

1. Adenine 2. Guanine

3. Cytosine4. Thymine

Purines Pyrimidines

Adenine Guanine Cytosine Thymine

Phosphate group Deoxyribose

Figure 12–5 DNA NucleotidesSection 12-1

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DNA Structure

c. The two larger bases- adenine and guanine are called purines.d. The two smaller bases- cytosine and thymine are called

pyrimidines.

e. The backbone of the DNA chain is formed by all sugar and phosphates, the bases hook onto

the sugar part of the chain3. Chargaff’s Rule

a. A (adenine) always equals (joins) to T (thymine)b. G (guanine) always equals (joins) to C (cytosine)

Hydrogen bonds

Nucleotide

Sugar-phosphate backbone

Key

Adenine (A)

Thymine (T)

Cytosine (C)

Guanine (G)

Figure 12–7 Structure of DNASection 12-1

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DNA RNA

4. Rosalind FranklinUsed a technique called X-ray diffraction to

determine DNA was helical.5. Watson and Crick

Built a 3 dimensional model of a DNA molecule which was called a double helix

6. DNA is tightly coiled around a protein called histones. The coil then forms your Chromatin. Coiled chromatin forms your chromosomes.

Figure 12-10 Chromosome Structure of Eukaryotes

Chromosome

Supercoils

Coils

Nucleosome

Histones

DNA

double

helix

Section 12-2

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C. DNA Replication1. Before a cell divides DNA is copied (replicated)2. During DNA replication, the DNA molecule separates into 2 strands. Each new strand will hook up with it’s complementary base partner, making 2 new complementary strands. The strands follow Chargaff’s rule on base pairing.

3. The sites where separation and replication occur are called replication forks.

4. The replication is carried out by enzymes that “unzip” the DNA called DNA polymerase.

Figure 12–11 DNA ReplicationSection 12-2

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Growth

Growth

Replication fork

DNA polymerase

New strand

Original strand DNA

polymerase

Nitrogenous bases

Replication fork

Original strand

New strand

DNA

DNA Replication• Complementary base pairs form new strands.

DNA

from to to make up

Concept MapSection 12-3

also called which functions to also called also called which functions towhich functions to

can be

RNA

Messenger RNA Ribosomal RNA Transfer RNA

mRNA Carry instructions rRNACombine

with proteins tRNABring

amino acids toribosome

DNA Ribosome Ribosomes

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III. RNA Structure

A. RNA Structure1. Nucleic Acid made of single chains of

nucleotides2. The sugar is called Ribose3. Base pairs are cytosine & guanine,

adenine & Uracil.4. Uracil replaces the Thymine

B. Types of RNA1. Messenger RNA (mRNA)- carries the instructions to make a particular protein from DNA2. Ribosomal RNA (rRNA)- makes up the major part of ribososmes3. Transfer RNA (tRNA)- transfers the amino acids to ribosomes during protein synthesis

III. Transcription

A. The process of producing mRNA from DNA.1. RNA polymerase binds to the DNA and separates the strands.2. RNA polymerase uses one strand of DNA as a template to form a strand of mRNA.3. RNA polymerase enzymes will only bind to regions of DNA called promoters (it has a specific base sequence).

RNADNA

RNApolymerase

Figure 12–14 TranscriptionSection 12-3

Adenine (DNA and RNA)Cystosine (DNA and RNA)Guanine(DNA and RNA)Thymine (DNA only)Uracil (RNA only)

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B. RNA Editing

1. Intron- intervening sequences that are removed from the mRNA molecules before they become functional.

2. Exons- the remaining portions that are spliced back together to form the final mRNA.

IV. Genetic Code

A. Three bases long, called codons (Ex. GCA)B. Proteins are made of long chains called

polypeptidesC. Codons specify a single amino acid that is to

be added to the polypeptideD. D. Polypeptides are made by joining the

amino acids.

Figure 12–17 The Genetic Code

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V. Translation (Protein synthesis)A. The decoding of an mRNA message into a proteinB. Takes place in the ribosomesC. Steps involved:

1. mRNA is transcribed from DNA and released in the cytoplasm2. Translation begins when mRNA attaches to a ribosome in the cytoplasm at the start codon (AUG)3. Each transfer RNA as an anticodon whose bases are complementary to a codon on the mRNA. This has an amino acid attached to one end.

4. The ribosome positions the start codon to attract its anticodon, which is part of tRNA and binds them together.

5. Once the first and second codon and anticodon are bound, the ribosome joins the two amino acids and the tRNA breaks away.

6. Chains of amino acids continue to grow until the ribosome reaches a stop codon on the mRNA strand. Then it replaces the chain.

Messenger RNA

Messenger RNA is transcribed in the nucleus.

Transfer RNA

The mRNA then enters the cytoplasm and attaches to a ribosome. Translation begins at AUG, the start codon. Each transfer RNA has an anticodon whose bases are complementary to a codon on the mRNA strand. The ribosome positions the start codon to attract its anticodon, which is part of the tRNA that binds methionine. The ribosome also binds the next codon and its anticodon.

mRNA Start codon

Ribosome

Methionine

Phenylalanine tRNALysine

Nucleus

Figure 12–18 TranslationSection 12-3

mRNA

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The Polypeptide “Assembly Line”The ribosome joins the two amino acids—methionine and phenylalanine—and breaks the bond between methionine and its tRNA. The tRNA floats away, allowing the ribosome to bind to another tRNA. The ribosome moves along the mRNA, binding new tRNA molecules and amino acids.

mRNARibosome

Translation direction

Lysine tRNA

tRNA

Ribosome

Growing polypeptide chain

mRNA

Completing the PolypeptideThe process continues until the ribosome reaches one of the three stop codons. The result is a growing polypeptide chain.

Figure 12–18 Translation (continued)Section 12-3

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http://www.pbs.org/wgbh/aso/tryit/dna/#

Substitution InsertionDeletion

Gene Mutations:Substitution, Insertion, and Deletion

Section 12-4

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Deletion

Duplication

Inversion

Translocation

Figure 12–20 Chromosomal Mutations

Section 12-4

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