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ASU / Biology / BIO 340 / What did beadle and tatum discover?

What did beadle and tatum discover?

What did beadle and tatum discover?


Test 3 Study Guide

What did beadle and tatum discover?

DNA Structure and Analysis

1.) Definition of a gene: Fundamental units of inheritance in living organisms.  Together, they old all the info necessary to reproduce a given organism and to pass on  genetic traits to its offspring

2.) Scientist to Know

a. Frederik Griffiths Transformation Experiment 1928

i. First accepted demonstration of bacterial  

transformation where bacteria changes its form and  

function. Showed that Diplococcus pneumoniae could  Don't forget about the age old question of What do plants do for soil?

transform from one strain to a different strain.

ii. Living IIIS into a mouse  the mouse died; Living IIR into a  mouse  the mouse lived; Heat killed IIIS into a mouse 

What did the experiments of avery macleod and mccarty show?

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mouse lives; Living IIR and heat-killed IIIS  mouse dies  

because the living IIIS recovered.

b. Barbara McMlintock 1929

i. Genetic linkage corresponds to physical locations on  


c. Beadle and Tatum 1941

i. Mutations in genes could cause defects in steps in  

metabolic pathways. The “one gene, one enzyme” view  

that lead to the “one gene, one polypeptide”.  

d. Avery, McLeod and Mcarty 1944- Test tube assay instead of mice i. DNA is the “transforming factor” not proteins or other  

materials and the transforming principle (that genes are  

now made of DNA) was demonstrated by this  

ii. DNA is the transforming factor. “a nucleic acid of the deoxyribose type is the fundamental unit of the  

What did hershey and chase discover in 1952?

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transforming principle…”

e. The Hershey Chase Experiment 1952

i. Helped to confirm that DNA was the genetic material.  

Showed that when bacteriophages infect bacteria, the  

DNA enters the host bacterial cell but most of their  protein does not.  

ii. DNA contains Phosphorus and Proteins contain sulfur.  

f. Erwin Chargaff 1949-1953

i. Showed that the amount of A is proportional to the amount of T and that the amount of G is proportional to the amount of G. But the percent od A+T does not necessarily equal  We also discuss several other topics like What is the americans with disabilities act?

the percentage of G+C.  

g. Rosalind Franklin and Maurice Wilkins- Kings College, UK i. DNA has an Helical Structure

h. Francis Crick and Jim Watson- Cambridge, Uk  

i. DNA is a right-handed double helix in which the two  strands are antiparallel and the bases are stacked on one

another. The two strands are connected by A-T and G-C  

base pairing.  

ii. Explained how DNA could function as the molecule of  heredity Don't forget about the age old question of What is the step in turning glucose into pyruvate?

iii. Base pairing explained how genetic information could be  copied

i. Linus Pauling- Caltech, US  

j. Encode Project 1010

i. Identification of all functional elements in human genome ii. The gene is now replaced with open reading frames  (ORF) sequence patterns.  

iii. Identification of most genes is based either on their  similarity to other known genes or the statistically  

significant signature of a protein coding sequence.  

k. Thomas Kornberg discovered DNA polymerase II and III  l. Arthur Kornberg discovered DNA polymerase I  

3.) DNA

a. Nucleotides are the building blocks of DNA. They consist of a nitrogen base, a  pentose sugar, and a phosphate group. 

b. There are two types of nitrogenous bases: Pyrimidines (Thymine (T), Cytosine ©, and Uracil (U)) and Purines (Adenine  (A), and Guanine (G))

c. A­T base pairs form two hydrogen bonds, and G­C base pairs form three  hydrogen bonds

d. Central Dogma of Molecular Biology

i. DNA   RNA   Protein  → →

ii. Transcription   Splicing   translation   post translational modification    → → → → finished protein

e. DNA is reproduced by semiconservative replication i. The complementarity of DNA strands allows each strand to  serve as a template for synthesis of the other

f. Three modes of DNA replication are possible

i. Conservative- original helix is conserved and two newly  synthesized strands come together

ii. Semiconservative- each replicated DNA molecule  

consists of one “old” strand and one new strand

iii. Dispersive- parental strands are dispersed into two new  double helices.

g.) Meselson and Stahl Experiment 1958­ used E. Coli to demonstrate that DNA  replication is semiconservative in prokaryotes; each new DNA consists of one old strand and one newly synthesized strand.

a. Semiconservative replication became the rule in every species that  was studied. 

h.) DNA Polymerase­ enzymes that helps catalyze the polymerization of dNTPs  (deoxyribonucleoside triphosphates) into DNA strands. 

i.) Nucleotides arrive as nucleosides

a. DNA has its own energy from its P­P­P bonding

b. Bonded by DNA polymerase

j.) Chain elongation occurs in the 5' to 3' direction by addition of one nucleotide  at a time to the 3' end 

k.) • As the nucleotide is added, the two terminal phosphates are cleaved off,  providing a newly exposed 3'­OH group that can participate in the addition of  another nucleotide as DNA synthesis proceeds

a. Bacteria have many DNA polymerase

b. DNA polymerase III is the enzyme responsible for the 5’  to 3’ polymerization essential in vivo

c. DNA polymerase II and III are the main DNA builders d. DNA polymerase I is in charge of editing, repair and  primer removal

l.) DNA replication is Fast and Accurate!

m.) Seven key issues that must be resolved during DNA  replication

a. Unwinding of the helix

b. Reducing increased coiling generated during  


c. Synthesis of RNA primer for initiation

d. Discontinuous synthesis of the second strand

e. Removal of the RNA primers

f. Joining of the gap-filling DNA to the adjacent strand g. Proofreading

n.) DNA polymerase uses sliding clamps to move along the  template without falling off. Sliding Clamps are loaded onto  DNA by Clamp loaders which are ATP-fueled molecular  machines that open the sliding clamp, load then onto primed  DNA and unload them at the appropriate time

o.) RNA Primer- DNA polymerase III needs a primer to elongate  a polynucleotide chain.  

a. Primase synthesizes a RNA primer that provides the  free 3’- hydroxyl required by DNA polymerase III.  b. Priming is a universal phenomenon during  initiation of DNA synthesis

p.) Eukaryotic DNA is like that in prokaryotes but it is more  complex

a. There is more DNA in Eukaryotes

b. The chromosomes are linear

c. DNA is complexed with proteins

d. Eukaryotic chromosomes contain multiple origins of  replication

q.) Telomeres provide structural support at chromosome ends but are hard to replicate. They consist of long stretches of  short repeating sequences and preserve the integrity of the  chromosome.

r.) Telomerase- maintains structures called telomeres, which are composed  of repeated segments of DNA found at the ends of chromosomes. 

a. Telomeres protect chromosomes from abnormally s2cking together or  breaking down (degrading)

b. Telomeres become shorter as the cell divides which  

leads to apoptosis but, Telomerase counteracts the shortening of 

telomeres by adding small repeated segments of DNA to the ends of 

chromosomes each 2me the cell divides.

c. Telomerase is abnormally active in cancer cells.  

d. Telomerase is made of telomeres reverse transcriptase  (TERT) which adds the new DNA segment to  

chromosome ends and telomerase RNA (TR) which  

provides a template for creating the repeated sequence  

of DNA

Eukaryotic Chromosomal organization

1.) The amount of DNA that eukaryotes have varies; the amount of DNA is not necessarily  related to the complexity and most eukaryotes are diploid. 

2.) Two types of Chromatin

a. Euchromatin­ uncoiled and active. Usually areas where gene expression is  occurring

b. Heterochromatin­ condensed areas and inactive because they lack genes or they contain genes that are repressed

3.) Histone Proteins­ abundant, highly conserved among eukaryotes. 

a. Provide first level of packaging for chromosome

b. DNA is wound around histone proteins to produce nucleosomes

4.) Nucleosomes are connected by linker DNA H1 histone to produce the “beads­on­a string” extended form of chromatin 

5.) The 30 nm Fiber­ DNA is further compacted when the nucleosomes associated with one  another produce 30 nm chromatin. 

6.) Compaction continues by forming looped domains from the 30 nm chromatin a. Loops are arranged so that the DNA condensation can be independently  controlled for gene expression 

b. MARs are known to be near regions of the DNA that are actively expressed  7.) SWI/SNF Complex­ ATP­dependent chromatin remodeling complex 8.) Histone modifications­ covalently attached groups usually to histone tails a. Reversible: enzyme that add or remove modification signals 

b. Histone Tails­ 

i. Acetylation (any lysine; gene activation) activates transcription; opens up  chromatin

ii. Methylation (lys9­ gene repression; lys4 – gene activation; lys36­ 

transcription elongation) 

RNA transcription

1.) RNA is produced by copying part of the nucleotide sequence of DNA into  complementary sequence in RNA

a. During transcription, RNA polymerase binds to DNA and separates the DNA  strands. RNA polymerase then uses one strand of DNA as a template from which nucleotides are assembled into a strand of mRNA. 

b. No primer is required for initiation, and the enzyme uses ribonucleotides instead  of deoxy ribonucleotides

2.) Eukaryotic mRNAs have three main parts

a. 5’ untranslated region (5’UTR)

1. Varies in length

b.) The coding sequence (open reading Frame)

2. Specifies the amino acid sequence of the protein that will be 

produced during translation. It varies in length according to the 

size of the protein that it encodes.

c.) 3’ untranslated region (3’UTR)

3. Also varies in length and contains info influencing the stability of 


3.) Transcription in prokaryotes

a. Transcription begins at the transcription start site, where DNA double helix is  unwound to make the template strand accessible to the action of RNA  polymerase

b. Transcriptional termination­ 

1. Rho­dependent: a protein factor helicase called “rho” binds the 

RNA and destabilizes the interaction between the template and 

the mRNA, thus releasing the newly synthesized mRNA from the 

elongation complex. 

2. Rho­independent: RNA transcription stops when the newly 

synthesized RNA molecule forms a hairpin loop, followed by a 

run of Us. this destabilizes RNAP and makes it detach from the 

DNA template. 

4.) Eukaryotic Transcription

a. Promoter: a region of DNA that “promotes” the transcription of a particular gene.  Promoters are upstream from the genes that they regulate and on the same  strand. 

5.) Three types of RNA

a. Messenger RNA(mRNA)­ transfers DNA code to ribosome for translation b. Transfer RNA (tRNA)­ brings amino acids to ribosomes for protein synthesis c. Ribosomal RNA (rRNA)­ ribosomes are made of rRNA and protein. 

6.) The TATA box is a core promoter element that binds the TATA­binding protein (TBP)  and determines the start site of transcription

7.) 5’ cap addition

a. It is a modified guanine structure: called 7­methyl G5’ ppp5’ N (m7G) which is  added to the front of the 5’ end of all mRNAs

b. It consist of a terminal 7­methylguanosine residue which is linked through a 5’­5’­ triphosphate bond to the first transcribed nucleotide. 

c. The cap has three functions

i. Transport­ export from cytosol from nucleus

ii. Protection­ prevents 5’­3’ RNA digestion

iii. Activity­ serves as a docking site for ribosomes

8.) Splicing­ taking out introns and connecting exons. 

a. Splicing is done in a series of reactions which are catalyzed by the spliceosome.

i. The spliceosome constantly re­arranges during a pre­mRNA splicing  cycle

ii. The major components of the spliceosome are specific pre­formed RNA protein complexes that bind together with other proteins to different 

regions of the introns

9.) Alternative splicing­ different combinations of exons could be spliced together to produce different mRNA isoforms of a gene. 

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