BIOB11H3 Lecture Notes - Lecture 3: Deoxyribonucleotide, Ribonucleotide, Gene Expression
BIOB11
LEC 3 - An overview of transcription. rRNA synthesis & maturation
January 10, 2017
→ The Relationship Between Genes and Proteins
→ Evidence that DNA is the Genetic Material
● Beadle and Tatum
○ Studied bread mold (Neurospora)
○ Grows in simple medium with a single organic carbon source, inorganic salts, and biotin
○ Plan: to expose mold spores to radiation and screen them for mutations that caused cells
to lack a particular enzyme
■ Radiation damaged the DNA → changed DNA sequence (mutations)
■ Irradiated spores were tested for their ability to grow in a minimal medium that
lacked the essential compounds synthesized by this organism
■ If a spore is unable to grow in minimal medium BUT a genetically identical spore
can grow in a medium supplemented with a particular metabolic compound (eg:
pantothenic) → can conclude that the cells are missing an enzyme that prevents
them from making this essential compound **
○ Experiment: isolation of genetic mutants in Neurospora
1. Spores irradiated to induce mutations
2. Allowed to grow into colonies in tubes containing supplemented medium
3. Genetically identical spores tested for their ability to grow on either
supplemented/minimal medium
● Those that failed to grow on minimal medium = mutant
4. Sample of mutant cells found to grow in medium supplement with vitamins, but
wouldn’t grow in medium supplemented with aa
● Indicates deficiency in enzyme leading to formation of a vitamin
5. Growth of these same cells in minimal medium supplemented with other vitamins
indicates→ deficiency resides in a gene involved in formation of
PANTOTHENIC acid (part of coenzyme A)
○ Results: gene carrie s info for the production of a particular enzyme → ONE GENE-ONE
ENZYME HYPOTHESIS
■ BUT became modified when it was discovered that enzymes are composed of
more than one polypeptide, each of which is encoded by its own gene → one
gene-one polypeptide
● genes→ segment of DNA that contains info for either a single polypeptide chain OR for one or more
functional RNAs
→ Flow of Info Through the Cell
● Gene expression: production of a functional product using the info encoded in a gene
○ Info i the segment of DNA is made available to the cell through formation of RNA
● Transcription: synthesis of RNA from DNA template
○ Info encoded in the the 4 deoxyribonucleotide letters of DNA is transcribed (rewritten) into
a similar language composed of 4 ribonucleotide letters of RNA
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Lec 3 - an overview of transcription. rrna synthesis & maturation. Evidence that dna is the genetic material. Grows in simple medium with a single organic carbon source, inorganic salts, and biotin. Plan: to expose mold spores to radiation and screen them for mutations that caused cells to lack a particular enzyme. Radiation damaged the dna changed dna sequence (mutations) Irradiated spores were tested for their ability to grow in a minimal medium that lacked the essential compounds synthesized by this organism. Experiment: isolation of genetic mutants in neurospora: spores irradiated to induce mutations, allowed to grow into colonies in tubes containing supplemented medium, genetically identical spores tested for their ability to grow on either supplemented/minimal medium. Those that failed to grow on minimal medium = mutant: sample of mutant cells found to grow in medium supplement with vitamins, but wouldn"t grow in medium supplemented with aa.
