DNA-notes. A. First Discoveries 1.Griffith- experiment showed that live uncoated bacteria acquired the ability to make coats from dead coated bacteria.

DNA-notes

A. First Discoveries

1.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

Go to Section:

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

Go to Section:

Chargaff’s Rule Erwin Chargaff discovered:

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

4. Rosalind FranklinUsed a technique called X-ray diffraction to determine DNA was helical.

5. Watson and CrickBuilt 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.

DNA Replication-see how it works

DNA Replication

DNA Replication

DNA Replication

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 helicase.

Figure 12–11 DNA ReplicationSection 12-2

Go to Section:

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

RNA Structure

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

nucleotides2. The sugar is called Ribose.3. Base pairs are cytosine & guanine,

adenine & uracil.4. Uracil replaces the thymine.

Compare DNA to RNACompare DNA to RNA

Structure: DNA RNA

Strands of nucleotides

Double Single

Sugars Deoxyribose Ribose

Nitrogen bases

A, T, C, G A, U, C, G

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

TranscriptionA. 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

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

Go to Section:

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.

Genetic Code

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

polypeptides.C. Codons specify a single amino acid that is to

be added to the polypeptideD. Polypeptides are made by joining the amino acids.

Figure 12–17 The Genetic Code

Go to Section:

Translation (Protein synthesis)A. The decoding of an mRNA message into a protein.B. Takes place in/on the ribosomes.C. Steps involved:

1. mRNA is transcribed from DNA and released in the cytoplasm 2. Translation begins when mRNA attaches to a ribosome in the cytoplasm at the start codon (AUG) 3. Each transfer RNA has 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

Go to Section:

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

Go to Section:

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

Carry instructions rRNACombine

with proteins tRNA

Ribosome

Go to Section: