Ch.2

The Molecular Nature of Genes

DNA 의 구조 연구History of Molecular Genetics

The nature of genetic material

( S 형 )

( R 형 )

유전물질의 발견 ; Miescher (1869)

• nuclein ; 염색질 (DNA + 단백질 )• 핵산 (nucleic acid)• 뉴클레오티드 : 염기 + 당 + 인산

형질전환 (transformation) : Griffith (1928)

• 박테리아의 형질전환 ; 죽은 S 형의 형질전환 물질이 R 형에 전달됨

Variants of Streptococcus pneumoniae

Transformation experiments

DNA ; The transforming Material

형질전환물질은 DNA 임을 증명 : Avery 등 (1944)

• DNA 가수분해효소에 의해 형질전환 능력 상실

• 물리 - 화학적 분석1. 초원심 분리법 ; 고분자량의 물질

2. 전기영동법 ; 높은 이동성

3. UV- 흡수분광도법 ; 260 nm 의 파장을 흡수

4. 화학적 원소분석법 ; N: P 의 비율이 낮음 (1.67)

• 박테리오파아지의 감염 : Hershey & Chase (1952)

• DNA 염기는 같은 비율로 존재하지 않음 : Chargaff (1950)

• DNA 이중나선 구조 모델 : Watson & Crick (1953)

Blender Experiment by Hershey - Chase

DNA Structure ; Double helix

• L. Pauling ; -helix 구조 , 수소결합

• Franklin ; X-ray diffraction ( 나선구조 )

• Watson & Crick : DNA double helix

The base pairs of DNA

균일한 구조의 이중나선을 이룸

Chargaff’s rules (A=T, G=C)

The Watson Crick DNA Double Helix (Nature : 1953)

James Watson and Francis Crick analyzed the X - ray crystallographic data of DNA fibers and proposed a model for the three dimensional structure of DNA. The major features of their model are :

1. Two helical polynucleotide chains are coiled around a common axis, i.e., double helix and the chains run in apposite directions.

2. The bases are on the inside of the helix, whereas the phosphate and deoxyribose units are on the outside. The planes of the bases are perpendicular to the helix axis.

3. The diameter of the helix is 20Å. Adjacent bases are separated by 3.4Å along the helix and related by a rotation of 36 degrees.

4. The two chains are held together by hydrogen bonds between pairs of basis , i.e., A = T, and G C.

5. The random sequence of the bases carries the genetic information.

DNA Structure (A-, B-, and Z-DNA)

A 형 B 형 Z 형

DNA pol

dNTP

The nucleic acids

Nucleoside (base + sugar)

Nucleotide (nucleoside + phosphate)

Phosphodiester bonds

Replication of DNA ; semi-conservative replication

Semi-conservative replication

Central Dogma

(from the slides by Dr.John Ryals)

Genomics