DNA and RNA Chapters 12 & 13

Hershey and Chase Performed two experiments to show that DNA is genetic material. Worked with viruses to determine if it was the protein or the DNA that contained the genetic information.

Experiment One Bacteria were grown with a radioisotope of sulfur. The sulfur was used as a tracer. Viruses (bacteriophages) were allowed to infect the bacterial cells. Viral proteins were made within the host cell and contained the sulfur tracer.

The viruses were then allowed to infect a group of bacteria without the tracers. The colonies were spun in a blender to remove the viral protein coat. There was no tracer in the fluid medium, but there was still tracer within the bacterial cells.

Experiment Two This was a repeat of experiment one, but phosphorous was added as a trace.

Watson and Crick Working with everything they knew about the chemical properties of DNA, they were able to construct a model of DNA out of wire and metal pieces.

Parts of a nucleotide 5-Carbon Sugar called deoxyribose (in DNA) or ribose (in RNA) Phosphate Group Nitrogenous Base – these are what make the nucleotides different.

Purines are 2 ringed: Adenine or Guanine

Pyrimidines are 1 ringed: Thymine or Cytosine

Adenine binds to Thymine Guanine binds to Cytosine A purine will always bind to a pyrimidine to produce a base pair

Two strands of nucleotides are held together by hydrogen bonds between bases. They coil to form a Double Helix.

Replication of DNA occurs during the S-phase of Interphase 1) Proteins and enzymes (helicase) break the hydrogen bond between the bases causing the helix to unwind and expose the bases 2) Free Nucleotides (those within the nucleus) pair with the exposed bases with the help of DNA polymerase. 3) DNA Ligase (enzyme) ensures that all parts of the DNA strand are connected.

4. The DNA Strands will coil again creating two new identical strands. Result: Each strand will have one side from the original DNA and one side that is new.

RNA Single Strand – not a double helix The four bases are different – adenine, cytosine, guanine, uracil Adenine bonds to uracil Guanine bonds to cytosine RNA gets its code from the DNA code

3 types of RNA Messenger (mRNA) – carries protein building instructions. Goes from the DNA in the nucleus to the ribosome Ribosomal (rRNA) – makes up the ribosome Transfer (tRNA) – delivers amino acids to the ribosomes. Has an anticodon specific to the amino acid.

Protein Synthesis Occurs in 2 processes: Transcription – mRNA forms from DNA code in the nucleus and moves to the ribosome Translation – tRNA matches its anticodon to the codons on mRNA creating an amino acid chain.

Transcription 1. One gene on the DNA strand “unzips” and is copied with RNA bases 2. Transcription begins at a promoter – a sequence of bases that tells the RNA to begin binding. 3. When the DNA is transcribed, mRNA leaves the nucleus and goes to the ribosome for translation.

Translation mRNA is “translated” into a protein 1) mRNA arrives at the ribosome - 3 bases of mRNA = 1 codon (initiation) 2) tRNA comes to the ribosome and the anticodon matches to the codon on mRNA (elongation) 3) Amino Acids break off to form proteins (termination)

Mutations An inheritable change in genetic code, which may or may not cause a change in the proteins made.

Deletion – one or more base pairs are removed from the DNA sequence Example: A T G G C A C C G A T T T A A with deletion A T G G C G A T T T A A

Insertion – one or more base pairs are inserted into the gene sequence Example: A T G G C A C C G A T T T A A A T G G C C A C A C C G A T T T A A

Base Pair Substitution - one or more base pairs are replaced with other base pairs Example: A T G G C A C C G A T T T A A base pair substituted A T G G G G T C C G A T T T A A

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