CHAPTER 12

DNA & RNA

Griffith & Transformation

Discovered transformation using bacteria that causes pneumonia

Transformation Process in which part of the nucleotide sequence of

DNA is copied into a complementary sequence in RNA

Avery & DNA

Retested Griffith’s experiment to determine what caused transformation

Discovered that the nucleic acid in DNA stores and transmits the genetic information from one generation of an organism to the next

Hershey-Chase Experiment

Studied virusesConcluded that DNA was the genetic material

of bacteriophages, not protein

Components & Structure of DNA

• DNA is made up of Nucleotides• Each nucleotide is made up of 3 basic

components:– 5 carbon sugar (deoxyribose)– A phosphate group– Nitrogenous base

• 4 nitrogen bases– Adenine– Guanine– Cytosine – thymine

Chargaff’s Rule

The observation that [A] = [T] & [G] = [C]Found that in 4 different types of organisms

the amount of A & T were nearly the same as well as the amount of G & C were nearly the same.

Double Helix

• Watson & Crick built a 3-D model of DNA based on the evidence found by Franklin using X-ray.

• Found that DNA was a double helix, in which two strands were wound around each other resembling a spiral staircase

• Hydrogen bonds hold the two strands together but only formed between A&T and G&C

• This is called base pairing

12-2 Chromosomes & DNA Replication

DNA Replication

Each strand of the DNA double helix has all the information needed to reconstruct the other half by the mechanism of base pairing.

Replications proceeds in both directions until each chromosome is completely copied

Duplicating DNA

Before a cell divides it duplicates DNADuring duplication, the DNA molecule

separates into 2 strands, produces 2 new complementary strands based on base pairing.

How Replication Works

Replication is carried about by many enzymes, the principle enzyme is DNA polymerase It joins individual nucleotides to produce a DNA

molecule Proofreads each new DNA strand

12-3 RNA & Protein Synthesis

The Structure of RNA

Consists of a long chain of nucleotides3 main differences between RNA & DNA

The 5 carbon sugar is ribose, not deoxyribose RNA is generally single stranded RNA contains uracil instead of thymine

Types of RNA

RNA has many functions, but in the majority of cells most RNA molecules are involved in only one thing – PROTIEN SYNTHESIS

3 main types of RNA Messenger RNA (mRNA) Ribosomal RNA (rRNA) Transfer RNA (tRNA)

Types of RNA

Genes contain instructions for assembling amino acids into proteins

RNA molecules that carry copies of these instructions are known as mRNA

Proteins are assembled on the ribosomes. Ribosomes are made up of several dozen proteins as well as a form of RNA called rRNA

During protein construction, a third type of RNA molecule transfers each amino acid to the ribosome as it is specified by coded messages in mRNA. This is known as tRNA.

Transcription

RNA molecules are produced by copying part of the nucleotide sequence of DNA into a complementary sequence in RNA. This is called transcription.

Requires RNA polymeraseRNA polymerase binds to DNA and separates

the DNA strands. RNA polymerase then uses one strand of DNA as a template from which nucleotides are assembled into a strand of RNA.

RNA Editing

DNA of eukaryotic genes contains sequences of nucleotides called introns that are not involved in coding for proteins.

The DNA sequence that code for proteins are called exons because the are expressed in the synthesis of proteins.

When RNA molecules are formed they copy both the introns and exons.

The Genetic Code

The language of mRNA instructions is called the genetic code.

A codon consists of 3 consecutive nucleotides that specify a single amino acid that is to be added to the polypeptide

There are 64 possible the base codonsDuring translation, the cell uses information

from mRNA to produce proteins

Mutations & Gene Regulation

Kinds of Mutations

Mutations are changes in the genetic material

Point Mutations = gene mutations involving changes in one or few nucleotides Include:

Substitutions Insertions Deletions

Frameshift Mutations = shift the “reading frame” of the genetic message

Examples

PointThe fat cat ate the wee rat.The fat hat ate the wee rat.

FrameshiftThe fat cat ate the wee rat.The fat caa tet hew eer at.

Chromosomal Mutations

Involve changes in the number or structure of chromosomes

May change locations of genes on chromosomes

4 types Deletions Duplications Inversions Translocations

Examples

OriginalOriginalABCDEFABCDEF

Deletions ACDEF

Duplications ABBCDEF

Inversion AEDBBF

Translocations ABCJKL GHIDEF