Discovery and Structure of DNA (chapter 9)

What jobs must genetic material be able to carry out?

1. Duplicate itself

2. Control development of rest of cell in specific way

When was DNA discovered?

April 25, 1953

Friedrich Miescher

Isolated nuclei from white blood cells in pus on soiled bandages- since material is in nuclei, named it nuclein

Frederick Griffith

1928- identified DNA as genetic material after studying bacterial pneumonia after 1918 flu pandemic by transferring killing ability between types of bacteria

What did Griffith’s experiments show?

Mice with certain form of pneumonia had 1 of 2 types of streptococcus pneuomoniae bacteria- Type R bacteria was rough texture

Type R bacteria

Mouse could recognize it and kill it

Type S bacteria

Smooth bc enclosed in polysaccharide capsule- mouse can’t recognize it

What happens with mouse injected with Type R bacteria?

Didn’t get pneumonia

Why did Type S bacteria give them pneumonia?

The polysaccharide-shielded bacteria caused severe (virulent) infection

Type S heated

Killed bacteria, no pneumonia in mice

Type R + heat killed Type S

Mice died of pneumonia, bodies had live type S bacteria encased in polysaccharide

Protease

enzyme that dismantles protein

DNase (deoxyribonuclease)

Enzyme that dismantles DNA

U.S Physicians Oswald Avery, Colin MacLeod, Maclyn McCarty

Treated bacteria with DNase disrupted transformation, so DNA is genetic material (DNA transmits killing ability in bacteria)

Avery, MacLeod, McCarty

1944: confirmed DNA transformed bacteria by isolating DNA from heat-killed type S bacteria + injected with w/ type R bacteria into mice so mice died and bodies had active type S bacteria

Avery, MacLeod, McCarty conclusion

DNA passed from type S to type R , so type R can make smooth coat needed for infection

Once type R bacteria encases themselves in smooth coats…

no longer type R

Alfred Hershey + Martha Chase

1953: infected escherichia coli bacteria w/ virus that had large protein head to prove protein isn’t heredity material, nucleic acid is

What do viruses do?

Infect bacterial cells by injecting DNA/RNA into them, protein coats remain outside bacterial cells

Protein contains (which element)

sulfur

Protein DOESN’T contain (which element)

phosphorus

Nucleic acids have

sulfur, not phosphorus

Do radioactive forms exist for sulfur and phosphorus?

Yes

When Hershey and Chase grew viruses in presence of radioactive sulfur…

viral protein coats took up and emitted radioactivity

When Hershey and Chase grew viruses in presence of radioactive phosphorus…

viral DNA emitted radioactivity

If protein is genetic material, then infected bacteria would have radioactive sulfur

true

DNA genetic material, bacteria would have radioactive phosphorus

true

Phoebus Levene

identified 5’ carbon-sugar ribose and deoxyribose in other nucleic acids

Levene discovered…

RNA has ribose, DNA has deoxyribose

RNA

carries info from DNA molecule that instructs cell to connect amino acids to form certain protein

4 main parts of nucleotide

5-carbon sugar, nitrogenous base, phosphate, hydroxyl (OH) group- all present in abt equal proportions

Covalent phophodiester bonds

phosphate of 1 group w/ hydroxyl group of another nucleotide (holds together strands of DNA or RNA)

Erwin Chargaff

Found that DNA had equal amount of C+G, A+T

Bonds between DNA bases

hydrogen bonds

Watson and Crick

DNA was double helix, 3-D structure

Phoebus Levene, Erwin Chargaff, Maurice Wilkins, Roaslind Franklin

DNA components, proportions, positions

James Watson

had his genome sequenced

Gene

section of DNA whose order of bases specifies sequence of amino acids in protein

Nucleotide

single building block of DNA, containing 1 deoxyribose sugar, phosphate group, nitrogenous base

Purines

A+G, 2 ring structure

Pyrimidines

T + C, 1 ring stricture

Gene length

100s- millions of nucleotides long

Phosphodiester bonds

Form between hydorxyl group and phosphates

Pho..bonds

create sugar-phosphate backbone

Antiparallelism

opposing orientation of 2 polypeptide chains of DNA

Complementary base pairs

A+T, C+G

H bond attaches?

Hydrogen atom of 1 molecule attaches to oxygen or nitrogen atom apart of other molecule

H bonds A + T

2

H bonds C + G

3

Histones

what DNA coils around

Nucleosome

DNA “bead” coiled around octet of histone

Nucleosome composed of

8 histone proteins (pair of each 4 types) , 147 nucleotides of DNA wrapped around it

Chromatin

DNA + associated material (30% histone proteins, 30% scaffold proteins, 30% DNA, 10% RNA)

CTCF

“anchor” protein brings parts of DNA structure together within same long DNA molecule to form “loop-ome” structure

Why does DNA need to be repliacted?

So it can be passed on to future cell generations

Semiconservative

Each new DNA strand double helix conserves half of the original

Heavy + light double helices

differed from daughter DNA double helix built of entirely heavy labeled nucleotides (conservative)

Dispersive mechanism

both strands joined of “heavy” and “light”