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Inheritance and the Structure of DNA
Deoxyribonucleic Acid
DNA Discovery
• 1928-Frederick Griffith
– transforming factor
• 1944-James Watson and Francis Crick
– discovered that DNA was the transforming factor
• 1952-Rosalind Franklin and Maurice Wilkins
– took x-ray photographs of the DNA molecule
• 1953-Watson and Crick
– created a three-dimensional 3-D model of DNA
• 1962-Watson, Crick, and Wilkins
– received the Nobel Prize in Medicine
What is DNA?
• Genetic material used to express traits
• Nucleotide units
– Deoxyribose (sugar)
– Phosphate
– Base
• Purines (double ring)
– Thymine ( T )
– Cytosine ( C )
• Pyrimidine (one ring)
– Adenine ( A )
– Guanine ( G )
Complementary Strands
• Order of bases on the nucleotides in one
strand of DNA complements the order of
bases on the opposite strand
– base sequence
DNA Replication
• DNA stores and transmit information that tells
cells which proteins to make and when to
make them.
• DNA located in the nucleus and cannot leave.
• Duplication of DNA
DNA Helicase and DNA Polymerase
5”  3” refers to location of carbon on sugar, bases added to C with OH attached,
work forward from there, refer to DNA handout. Bases attach to C #2, C#5 Phosphate
Deoxyribose vs Ribose sugars
• 2-Deoxy-Ribose in DNA is replaced by Ribose in RNA.
• The difference is a hydroxy group ( -OH ) in RNA versus a
single proton ( -H ) in DNA.
• The extra -O- in the ribose backbone prevents formation of
stable double-helices in RNA.
RNA (Ribonucleic Acid)
• RNA differs from DNA
– Sugar is ribose
– The nitrogen base THYMINE is replaced by URACIL
– RNA is single-stranded
• There are three types of RNA
– Messenger RNA (mRNA)
– Transfer RNA (tRNA)
– Ribosomal RNA (rRNA)
RNA
• Messenger RNA (mRNA)
– copies the information from the DNA in the
nucleus
• Transfer RNA (tRNA)
– reads the information from mRNA
– carries amino acids to the ribosome
• Ribosomal RNA (rRNA)
Transcription vs Translation
• Transcription
– DNA to mRNA
– in nucleus
• Translation
– mRNA to tRNA and rRNA to make proteins
– in cytoplasm
Transcription
• Reading the gene
• RNA polymerase (mRNA)
Translation
• RNA to proteins
• Cytoplasm
– tRNA, rRNA, and mRNA
– assemble proteins
• Genetic Code
– Three letter word (codon)
– Codon codes for amino acid
– 64 mRNA
Translation
• Specific amino acid on one end of each tRNA.
– anticodon on tRNA is complementary codon on
mRNA.
• mRNA joins with a rRNA and tRNA
– first tRNA is released from the ribosome
– Amino acids bond creating a polypeptide chain
– This process is repeated until one of three stop
codons is reached