Hereditary Material - DNAIn 1952, Alfred Hershey and Martha Chase studied the genetic material of the virus called T2 that infects the bacterium E.Coli.

They concluded that T2 injects its DNA into the host cell leaving the protein outside, proving DNA is the hereditary material (genetic material) of cells.

The Hershey-Chase Experiment

Bacteriophages A virus that infects bacteria is known as a bacteriophage.

Bacteriophages are composed of a DNA or RNA core and a protein coat.

DNA and RNA DifferencesDNA and RNA are made up of nucleotides.

A nucleotide is a monomer of nucleic acids made up of a five-carbon sugar, a phosphate group, and a nitrogenous base. DNA & RNA are polymers.

DNA RNA

•Deoxyribose•Thymine•Double strand

•Ribose•Uracil•Single strand

There are four kinds of bases in DNA:

adenine

guanine

cytosine

thymine

RNARNA replaces the base thymine with uracil replaces the base thymine with uracil

The DNA chain is formed by sugar and phosphate backbone.

The nucleotides can be joined together in any order.

Chargaff's Rules for Base pairing

•The percentages of guanine [G] and cytosine [C] bases are almost equal in any sample of DNA.

•The percentages of adenine [A] and thymine [T] bases are almost equal in any sample of DNA.

X-Ray Evidence 

Rosalind Franklin used X-ray diffraction to identify the structure of DNA.

The Double Helix 

Using clues from Franklin’s pattern, James Watson and Francis Crick built a model that explained how DNA carried information and could be copied.

Watson and Crick's model of DNA was a double helix, in which two strands were wound around each other.

Watson and Crick discovered that weak hydrogen bonds can form only between certain base pairs — adenine and thymine, and

guanine and cytosine.

This principle is called base pairing

ReplicationChromosomes and DNA Replication

In prokaryotic cells, DNA is located in the cytoplasm.

Most prokaryotes have a single DNA molecule containing nearly all of the cell’s genetic information.

Eukaryotic cellsMany eukaryotes have 1000 times the

amount of DNA as prokaryotes.

Eukaryotic DNA is located in the cell nucleus inside chromosomes.

The number of chromosomes varies widely from one species to the next.

99.9% of the genes in humans are exactly the same

Chromosome Structure

Eukaryotic chromosomes contain DNA and protein, tightly packed together to form chromatin.

Chromatin consists of DNA tightly coiled around proteins called histones.

DNA and histone molecules form nucleosomes.

Nucleosomes pack together, forming a thick fiber.

Duplicating DNA  Replication occurs during the S-phase of

cell division DNA molecule separates into two strands Produces two new complementary strands Each strand of the double helix of DNA serves as a

template for the new strand.

ReplicationHow Replication Occurs:

DNA replication is carried out by the enzyme Helicase that “unzips” a molecule of DNA.

Weak hydrogen bonds between base pairs are broken and the two strands of DNA unwind.

DNA replication

The principal enzyme involved in DNA replication is DNA polymerase.

DNA polymerase joins individual nucleotides to produce a DNA molecule and then “proofreads” each new DNA strand.

DNA Replication - unwinding

Genes are coded DNA instructions that control the production of proteins.

Genetic messages can be decoded by copying part of the nucleotide

sequence from DNA into RNA.

RNA contains coded information for making proteins.

RNA

Types of RNA

There are three main types of RNA:

messenger RNA

ribosomal RNA

transfer RNA

Types of RNA

• Ribosomes are made up of proteins and ribosomal RNA (rRNA).

Ribosome

Ribosomal RNA

Exons and Introns

RNA EditingThe DNA of eukaryotic genes contains sequences of nucleotides, called introns, that are not involved in coding for proteins. The DNA sequences that code for proteins are called exons.When RNA molecules are formed, introns and exons are copied from DNA.

The Genetic CodeA codon consists of three consecutive nucleotides on mRNA that specify a particular amino acid.

Amino AcidsEach codon specifies a particular amino acid that is to be placed on the polypeptide chain.

Some amino acids can be specified by more than one codon.

There are twenty different amino acids

There are 64 different combinations of bases that code for the twenty amino acids

Start and Stop CodonsThere is one codon AUG that can either specify the amino acid methionine or serve as a “start” codon for protein synthesis.

There are three “stop” codons that do not code for any amino acid. These “stop” codons signify the end of a polypeptide. UGA, UAA, UAG

TranslationTranslation is the decoding of an mRNA message into a polypeptide chain (protein).

Translation takes place on ribosomes.

During translation, the cell uses information from messenger RNA (mRNA) to produce proteins.

Each tRNA molecule carries only one kind of amino acid.

In addition to an amino acid, each tRNA molecule has three unpaired bases.

These bases, called the anticodon, are complementary to one mRNA codon.

DNA & RNA

The cell uses the DNA “master plan” to prepare RNA “blueprints.” The DNA stays in the nucleus.

The RNA molecules go to the protein building sites in the cytoplasm—the ribosomes.