DNARNA

& Proteins

James Watson & Francis Crick and Their DNA Model

Winning the Nobel Prize

Watson & Crick on the 50th anniversary of their discovery

Rosalind Franklin’s Famous Photo 51 of DNA

Rosalind Franklin’s Lab

Erwin Chargaff, Jerry Donahue, Lawrence Bragg

DNA• Polymer of nucleotides

(phosphate group bonded to deoxyribose bonded to a nitrogen base)

DNA Nucleotide

A Nucleotide

4 Nitrogen Bases of DNA

• Adenine (A)

• Thymine (T)

• Guanine (G)

• Cytosine (C)

• Adenine and guanine are purines

• Cytosine and thymine are pyrimidines

Purines

Pyrimidines

Nucleotides Bond Together in Long Chains

The two chains of nucleotides are bonded in the middle by the paired bases

Base Pairing Rule• Adenine bonds to Thymine

• Guanine bonds to Cytosine

BASES THAT BOND ARE CALLED COMPLEMENTARY BASES

Bases Bond by Hydrogen Bonds

The 2 DNA Chains are Anti-Parallel

DNA Replication

Before cell division, cells copy (replicate) their DNA

• An enzyme breaks the hydrogen bonds holding the paired bases together (unzips the DNA)

• Complementary nucleotides bond to the separated DNA chains (A to T and G to C)

• DNA polymerase enzymes bond new DNA nucleotides to the original DNA strands

• The original strand serves as a template for the new strand

DNA Replication

• At the end of DNA replication, there are two identical DNA molecules

• Each DNA molecule contains an original strand and a new strand (semi-conservative)

Proofreading enzymes check for mistakes during replication (bonding 50 base pairs per second means mistakes will be made!)

http://www.youtube.com/watch?v=Bju4C5GxeQs&feature=related

RNA

• Ribonucleic acid

• A polymer of nucleotides

• The sugar in RNA is ribose (instead of deoxyribose, as in DNA)

Comparison of Ribose and Deoxyribose

• RNA nucleotides do not have thymine, but contain uracil instead

• RNA is one strand of nucleotides (DNA is two chains of nucleotides)

• So RNA is a single helix, but DNA is a double helix

3 Types of RNA

• tRNA (transfer RNA)

• mRNA (messenger RNA)

• rRNA (ribosomal RNA)http://www.dnatube.com/video/1017/Compare-DNA-and-RNA-in-structural-basis

tRNA

TRANSCRIPTION (RNA Synthesis)

• A gene for a specific protein is turned on

• DNA “unzips” and unwinds (as in replication)

• Complementary RNA nucleotides bond to one strand of DNA (function of RNA polymerase)

• Bases must be complementary

C on DNA bonds to G on RNA

G on DNA bonds to C on RNA

T on DNA bonds to A on RNA

A on DNA bonds to U on RNA

• RNA breaks away from the DNA template

• DNA strands reform the hydrogen bonds

• RNA can then exit the nucleus via pores in the nuclear membrane

Transcription

Transcription

Transcription

http://www.youtube.com/watch?v=vJSmZ3DsntU&feature=related

Translation – the making of a protein

• Begins when mRNA attaches to a ribosome

• The genetic code of mRNA is read three bases at a time (codons)

• Each codon specifies a particular amino acid that will be placed in the chain to build the protein molecule

• The tRNA with its specific amino acid pairs to the codon of the mRNA

• When a second tRNA with its specific acid pairs to the next codon, the attached amino acid breaks from the first tRNA and attaches to the amino acid of the 2nd tRNA

• The ribosome forms a peptide bond between the amino acids

• The empty tRNA moves off and picks up another matching amino acid from the cytoplasm in the cell

• This sequence is repeated until the ribosome reaches a stop codon on the mRNA, which signs the end of protein synthesis

Beginning of Translation

Translation

Termination of Translation

http://www.youtube.com/watch?v=NJxobgkPEAo

The Central Dogma of Biochemistry

The Central Dogma of Biochemistry

• http://www.dnatube.com/video/1027/Central-Dogma