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