3.genes and dna(1)

8/8/2019 3.Genes and Dna(1)

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WHAT DO GENES DO?


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BEADLEAND TATUMEXPERIMENT

Experiment done at StanfordUniversity 1941

The hypothesis: One gene specifiesthe production of one enzyme

They chose to work with bread mold(Neurospora) biochemistry alreadyknown (worked out by Carl C.Lindegren)

Easy to grow, maintain

short life cycle easy to induce mutations

easy to identify and isolatemutants


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BEADLEANDTATUMEXPERIMENT

PROCEDURE 2 different growth media:

Complete - consists of agar, inorganic salts, malt &

yeast extract, and glucose

Minimal - consists of agar, inorganic salts, biotin,disaccharide and fat

X-ray used to irradiate Neurospora to induce

mutation

Mutated spores placed onto minimal medium


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BEADLEANDTATUMEXPERIMENTPROCEDURE


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BEADLEANDTATUMEXPERIMENTCONCLUSIONS

Irradiated Neurospora survived whensupplemented with Vitamin B6

X-rays damaged genes that produces a proteinresponsible for the synthesis of Vitamin B6

three mutant strains - substances unable tosynthesize (Vitamin B6, Vitamin B1 and Para-aminobenzoic acid) essential growth factors


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crosses between normal and mutant strainsshowed differed by a single gene

hypothesized that there was more than onestep in the synthesis of Vitamin B6 and thatmutation affects only one specific step

Evidence: One gene specifies the productionof one enzyme!


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GENESMAKEPROTEINS

genome-> genes ->protein(forms cellular structural & life

functional)->pathways & physiology


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Proteins work together with other proteins or nucleicacids as "molecular machines"

structures that fit together and function in highly

specific, lock-and-key ways


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DISCOVERYOFDNA D

NA Sequences Chargaff and Vischer, 1949

DNA consisting of A, T, G, C

Adenine, Guanine, Cytosine,

Thymine Chargaff Rule

Noticing #A}#T and #G}#C

A strange but possibly meaningless

phenomenon. Wow!! A Double Helix

Watson and Crick, Nature, April 25, 1953 Crick Watson


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WATSON & CRICK- |uTHESECRETOF

LIFE Watson: a zoologist, Crick: a physicist

In 1947 Crick knewno biology andpracticallyno organic chemistry orcrystallography..

Applying Chagraffs rules and the X-rayimage from Rosalind Franklin, theyconstructed a tinkertoy model showingthe double helix

Their 1953Nature paper: It has notescapedournotice that the specific pairingwe have postulated immediately suggestsa possible copying mechanism for thegenetic material.

Watson & Crick with DNA model

Rosalind Franklin with X-ray image ofDNA


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DNA:THEBASISOFLIFE Deoxyribonucleic Acid (DNA)

Double stranded with complementary strands A-T, C-G

DNA is a polymer

Sugar-Phosphate-Base

Bases held together by H bonding to the opposite strand


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DNA:THEBASISOFLIFE

Humans have about3

billion basepairs.

How do you package it into a cell?

How does the cell know where inthe highly packed DNA where tostart transcription?

Special regulatory sequences DNA size does not mean more

complex

Complexity ofDNA

Eukaryotic genomes consist ofvariable amounts ofDNA

Single Copy or Unique DNA

Highly Repetitive DNA


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THESTRUCTUREOFDNA


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DNA Stores all information of life 4 letters base pairs. AGTC (adenine, guanine, thymine,

cytosine ) which pair A-T and C-G on complimentary

strands.


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DNA,CONTINUED

DNA has a double helix structure. However, it

is not symmetric. It has a forward and

backward direction. The ends are labeled 5

and 3 after the Carbon atoms in the sugarcomponent.

DNA always reads 5 to 3 for transcriptionreplication


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DNA COMPONENTS

Nitrogenous Base:

N is important for hydrogen bonding

between basesA adenine with T thymine (double H-

bond)

C cytosine with G guanine (triple H-

bond)


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Sugar:

Ribose (5

carbon)Base covalently bonds with 1 carbon

Phosphate covalently bonds with 5 carbon

Normal ribose (OH on 2 carbon) RNA

deoxyribose (H on 2 carbon) DNAdideoxyribose (H on 2 & 3 carbon) used in

DNA sequencing

Phosphate:

negatively charged


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BASICSTRUCTURE

Phosphate

Sugar


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BASICSTRUCTUREIMPLICATIONS

DNA is (-) charged due to phosphate:

gel electrophoresis, DNA sequencing

H-bonds form between specific bases: hybridization replication, transcription, translation

DNA microarrays, hybridization blots, PCR

C-G bound tighter than A-T due to triple H-bond


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DNA-protein interactions (via major & minorgrooves): transcriptional regulation

DNA polymerization:

5 to 3 phosphodiester bond formedbetween 5 phosphate and 3 OH


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The Purines The Pyrimidines


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Double helix of DNA


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CONTINUED

3.genes and dna(1)

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