• DNA is a polymer made of repeating subunits called nucleotides.

• Nucleotides have three parts: a simple sugar, a phosphate group, and a nitrogenous base.

Phosphate group

Sugar (deoxyribose)

Nitrogenous base

The structure of nucleotidesThe structure of nucleotides

• The phosphate group is composed of one atom of phosphorus surrounded by four oxygen atoms.

• The simple sugar in DNA, called deoxyribose gives DNA its name—deoxyribonucleic acid.

The structure of nucleotidesThe structure of nucleotides

• A nitrogenous base is a carbon ring structure that contains one or more atoms of nitrogen.

• In DNA, there are four possible nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T).

Adenine (A) Guanine (G) Thymine (T)Cytosine (C)

The structure of nucleotidesThe structure of nucleotides

• In DNA, the amount of adenine is always equal to the amount of thymine, and the amount of guanine is always equal to the amount of cytosine.

• Adenine always pairs with thymine and cytosine always pairs with guanine!!!!

The structure of nucleotidesThe structure of nucleotides

• In 1953, Watson and Crick proposed that DNA is made of two chains of nucleotides held together by nitrogenous bases.

The structure of DNAThe structure of DNA

• Watson and Crick also proposed that DNA is shaped like a long zipper that is twisted into a coil like a spring.

• Because DNA is composed of two strands twisted together, its shape is called double helix.

Rosalind Franklin

Rosalind Franklin's crucial contribution to science went largely unrecognized at the time it was made. In 1952, while working as a research associate at King's college in Cambridge, England, she produced the first usable X-ray pictures of DNA ever taken. A year later, Francis Crick and James Watson used her pictures to determine that DNA spirals into a double helix.

Rosalind Franklin died in 1958 of ovarian cancer at the early age of thirty-seven. Four years later, her coworker Maurice Wilkins, along with Watson and Crick, were awarded the Nobel Prize for Physiology or Medicine for the double-helix model of DNA.

Some of Franklin's contributions to the discovery of the structure of DNA were posthumously acknowledged in Watson's book The Double Helix. "Since my initial impressions of her, both scientific and personal (as recorded in the early pages of this book), were often wrong, I want to say something here about her achievements. The X-ray work she did at King's is increasingly regarded as superb," Watson writes in the epilogue in 1968.

The importance of nucleotide sequencesThe importance of nucleotide sequences

Chromosome

The sequence of nucleotides forms the unique genetic information of an organism. The closer the relationship is between two organisms, the more similar their DNA nucleotide sequences will be.

The importance of nucleotide sequencesThe importance of nucleotide sequences

• Scientists use nucleotide sequences to determine evolutionary relationships among organisms, to determine whether two people are related, and to identify bodies of crime victims.

Replication of DNAReplication of DNA

• Before a cell can divide by mitosis or meiosis, it must first make a copy of its chromosomes.

• The DNA in the chromosomes is copied in a process called DNA replication.

• Without DNA replication, new cells would have only half the DNA of their parents.

Replication of DNA

Replication of DNA

DNA

Replication

Replication

DNA Replication

DNA contains the code that tells the cell which proteins to make. These proteins are responsible for maintaining the health of an

organism. Transcription and Translation are the processes that direct

the making of the proteins !!!!

RNA—ribonucleic acid•only 1 strand

•has ribose sugar

•contains the base uracil instead of thymine

•3 types: mRNA= messenger RNA

tRNA= transfer RNA

rRNA= ribosomal RNA

http://plantandsoil.unl.edu/croptechnology2005/weed_science/animationOut.cgi?anim_name=transcription.swfhttp://plantandsoil.unl.edu/croptechnology2005/weed_science/animationOut.cgi?anim_name=transcription.swf

View Transcription Animation

Transcription—from DNA to mRNA

•separation of DNA strands

•RNA nucleotides floating around and move to the DNA

•reaches the STOP signal

•mRNA leaves nucleus through nuclear pore to cytoplasm to ribosomes

http://plantandsoil.unl.edu/croptechnology2005/weed_science/animationOut.cgi?anim_name=translation.swfhttp://plantandsoil.unl.edu/croptechnology2005/weed_science/animationOut.cgi?anim_name=translation.swf

View Translation Animation

Translation—from mRNA to protein•mRNA and ribosome connect

•free amino acids in cytoplasm

•tRNA picks up specific amino acid

•codon on mRNA complements the anti-codon on tRNA—this brings in the correct a.a.