DNA & Protein Synthesis

History Before the 1940’s scientists didn’t know what material caused inheritance. They suspected it was either DNA or proteins.

History A series of experiments proved that DNA was the genetic material responsible for inheritance.

History In 1952, Alfred Hershey and Martha Chase did an experiment using a virus that infects E. coli bacteria. The experiment proved that DNA and not protein is the factor that influences inheritance.

History Erwin Chargaff discovered the base pairing rules and ratios for different species. Adenine pairs with Thymine Cytosine pairs with Guanine.

History Rosalind Franklin & Maurice Wilkins had taken the 1 st pictures of DNA using X-ray crystallization

This proved that DNA had a helical shape.

History The Nobel Prize in Medicine 1962 Francis Harry Compton Crick James Dewey Watson Maurice Hugh Frederick Wilkins Rosalind Franklin (Died of cancer 1958)

Wilkins has become a historical footnote and Watson & Crick are remembered as the Fathers of DNA WatsonCrick

DNA O O=P-O OPhosphate Group Group N Nitrogenous base (A, T, G, C) (A, T, G, C) CH2 O C1C1 C4C4 C3C3 C2C2 5 Sugar Sugar(deoxyribose)

Nitrogen Bases 2 types of Nitrogen Bases –Purines Double ring –G & A –Pyrimidines Single ring –C & U & T PGA CUT PY

DNA - double helix P P P O O O P P P O O O G C TATA

DNA The genetic code is a sequence of DNA nucleotides in the nucleus of cells.

DNA DNA is a double- stranded molecule. The strands are connected by complementary nucleotide pairs (A-T & C-G) like rungs on a ladder. The ladder twists to form a double helix.

DNA During S stage in interphase, DNA replicates itself. DNA replication is a semi- conservative process.

DNA Semi-conservative means that you conserve part of the original structure in the new one. You end up with 2 identical strands of DNA.

DNA Gene - a segment of DNA that codes for a protein, which in turn codes for a trait (skin tone, eye color, etc.) A gene is a stretch of DNA.

DNA A mistake in DNA replication is called a mutation. Many enzymes are involved in finding and repairing mistakes.

Mutations What causes mutations? –Can occur spontaneously –Can be caused by a mutagen Mutagen: An agent, such as a chemical, ultraviolet light, or a radioactive element, that can induce or increase the frequency of mutation in an organism.

Mutations Some mutations can: Have little to no effect Be beneficial (produce organisms that are better suited to their environments) Be deleterious (harmful)

Mutations Types of mutations –Point Mutations or Substitutions: causes the replacement of a single base nucleotide with another nucleotide Missense- code for a different amino acid Nonsense- code for a stop, which can shorten the protein Silent- code for the same amino acid (AA)

Mutations Example: Sickle Cell Anemia

Mutations Types of mutations –Frame Shift Mutations: the number of nucleotides inserted or deleted is not a multiple of three, so that every codon beyond the point of insertion or deletion is read incorrectly during translation. Ex.: Crohn’s disease

InsertionDeletion

Mutations Types of mutations –Chromosomal Inversions: an entire section of DNA is reversed. –Ex.: hemophilia, a bleeding disorder

DNA Repair A complex system of enzymes, active in the G 2 stage of interphase, serves as a back up to repair damaged DNA before it is dispersed into new cells during mitosis.

RNA O O=P-O OPhosphate Group Group N Nitrogenous base (A, U, G, C ) (A, U, G, C ) CH2 O C1C1 C4C4 C3C3 C2C2 5 Sugar Sugar (ribose) (ribose)

RNA Function: obtain information from DNA & synthesizes proteins

3 differences from DNA 1.Single strand instead of double strand 2.Ribose instead of deoxyribose 3.Uracil instead of thymine

3 types of RNA 1.Messenger RNA (mRNA)- copies information from DNA for protein synthesis Codon- 3 base pairs that code for a single amino acid. codon

3 types of RNA 2. Transfer RNA (tRNA)- collects amino acids for protein synthesis Anticodon-a sequence of 3 bases that are complementary base pairs to a codon in the mRNA

3 types of RNA 3. Ribosomal RNA (rRNA)- combines with proteins to form ribosomes

DNA Replication During DNA replication, the DNA molecule separates into 2 strands, and then produces 2 new complementary strands following the rules of base pairing. Each strand of the double helix of DNA serves as a template, or model, for the new strand. fhttp:// /pub/flash/24/menu.sw f

Amino Acids Amino acids- the building blocks of protein At least one kind of tRNA is present for each of the 20 amino acids used in protein synthesis.

Transcription - mRNA is made from DNA & goes to the ribosome Translation - Proteins are made from the message on the mRNA

Transcription In order for cells to make proteins, the DNA code must be transcribed (copied) to mRNA. The mRNA carries the code from the nucleus to the ribosomes. class.unl.edu/biochem/gp2/m _biology/animation/gene/gen e_a2.htmlhttp://www- class.unl.edu/biochem/gp2/m _biology/animation/gene/gen e_a2.html

Translation At the ribosome, amino acids (AA) are linked together to form specific proteins. The amino acid sequence is directed by the mRNA molecule. class.unl.edu/biochem/ gp2/m_biology/animati on/gene/gene_a3.htmlhttp://www- class.unl.edu/biochem/ gp2/m_biology/animati on/gene/gene_a3.html ribosome Amino acids

Make A Protein DNA sequence ATG AAA AAC AAG GTA TAG mRNA sequence UAC UUU UUG UUC CAU AUC

Make mRNA mRNA sequence UAC UUU UUG UUC CAU AUC tRNA sequence AUG AAA AAC AAG GUA UAG