Chapter #12 – DNA, RNA, & Protein Synthesis

I. DNA – experiments & discoveries A. Griffith and Transformation Frederick Griffith – British scientist who experimented with bacterial strains of pneumonia in mice & discovered transformation. Transformation – process in which one strain of bacteria is changed by a gene or genes from another strain of bacteria, ex : rough, harmless bacteria becoming smooth & disease-causing.

Griffith & Transformation

B. Avery and DNA Oswald Avery – Canadian biologist who repeated Griffith’s work & found that DNA causes transformation in bacteria. -His work showed that DNA stores & transmits genetic info from one generation of an organism to the next.

C. The Hershey-Chase Experiment Alfred Hershey & Martha Chase – American scientists who experimented with radioactive markers in viruses & concluded that the genetic material of the bacteriophage was DNA, not protein. Virus – nonliving particles smaller than a cell that can infect living organisms. Bacteriophage – (“bacteria eater”) type of virus that infects bacteria. -Scientists conclude that genes are made of DNA.

Alfred Hershey & Martha Chase

D. Components & Structure of DNA DNA – (Deoxyribonucleic acid) nucleic acid that contains the sugar deoxyribose; the molecule of heredity. -DNA (nucleic acid) is made up of nucleotides. Nucleotides of DNA have 3 basic parts : 1. A 5-carbon sugar called deoxyribose. 2. A phosphate group. 3. A nitrogenous (nitrogen-containing) base. -There are 4 kinds of nitrogenous bases found in DNA : 1. Adenine (A) 2. Guanine (G) 3. Cytosine (C) 4. Thymine (T)

Structure of DNA

The 4 bases can be divided into 2 major groups : Purines – have 2 rings in their structures & include adenine & guanine. Pyrimidines – have 1 ring in their structure & include cytosine & thymine. -The backbone of the DNA molecule is formed by sugar & phosphate groups of each nucleotide & the nitrogenous bases stick out sideways from the chain. -Nucleotides can be joined together in any order to make different sequences of bases. Chargaff’s Rule : In any sample of DNA, the percentages of guanine & cytosine bases are nearly equal & the percentages of adenine & thymine bases are nearly equal.

Rosalind Franklin Rosalind Franklin – British scientist who used a technique called X-ray diffraction to Record information about the structure of DNA. -Her work revealed that DNA is shaped like a helix (twisted strands like the coils of a spring).

James Watson and Francis Crick James Watson & Francis Crick – American biologist & British physicist who built the first accurate structural model of DNA, after viewing Rosalind Franklin’s work. -Watson & Crick’s model of DNA was a double helix, in which 2 strands were wound around each other.

The Twisted Ladder -A double helix looks like a twisted ladder or a spiral staircase. -In DNA, hydrogen bonds only form between certain nitrogenous bases in the double helix to hold it together, this is known as base pairing. -Every adenine molecule binds with a thymine and every cytosine molecule binds with a guanine.

Applying Concepts : *Given this sequence, determine the bases that would match it in a double helix : A C G T C T G C A G