640 likes | 1.95k Views
DNA Structure, Replication, and Organization (DNA 구조 , 복제 그리고 체계 ). Chapter 14. DNA 의 디지털 모형 (X- 선 구조 데이터에 근거 ). Why It Matters. Deoxyribonucleic acid (DNA) molecule forms the genetic material of all living organisms. 그림 14.1. 1953 년 DNA 구조의 모형을 보여주고 있는 왓슨과 크릭 .
E N D
DNA Structure, Replication, and Organization (DNA 구조, 복제 그리고 체계) Chapter 14
Why It Matters • Deoxyribonucleic acid (DNA) molecule forms the genetic material of all living organisms 그림 14.1. 1953년 DNA 구조의 모형을 보여주고 있는 왓슨과 크릭.
14.1 Establishing DNA as the Hereditary Molecule • Griffith found a substance that could genetically transform pneumonia bacteria (폐렴균 박테리아) • Avery and coworkers identified DNA as the molecule that transforms rough Streptococcus to the infective form • Hershey and Chase found the final evidence establishing DNA as the hereditary molecule
Griffith’s Experiments • A substance derived from killed infective pneumonia bacteria could transform (형질전환) noninfective living pneumonia bacteria to the infective type
Avery’s Experiments • Showed that DNA (not protein or RNA) was the molecule responsible for transforming pneumonia bacteria into the infective form
Hershey and Chase’s Experiments • Showed that phage DNA (not protein) enters bacterial cells to direct the life cycle of the virus • Together, Griffith, Avery and coworkers, and Hershey and Chase established that DNA is the hereditary molecule
그림 14.3. DNA가 유전물질이라는 것을 보여주는 허시와 체이스의 실험.
14.2 DNA Structure • Watson and Crick brought together information from several sources to work out DNA structure • New model proposed that two polynucleotide chains wind into a DNA double helix
Watson and Crick • Discovered that a DNA molecule consists of two polynucleotide chains twisted around each other into a right-handed double helix • Each nucleotide of the chains consists of • Deoxyribose • A phosphate group • A base (adenine, thymine, guanine, or cytosine)
The Double Helix • Deoxyribose sugars are linked by phosphate groups to form a sugar–phosphate backbone (당-인산 골격) • Two strands are held together by base pairs • Adenine–Thymine, Guanine–Cytosine • Each full turn of double helix is 10 base pairs
그림 14.4. 4개의 뉴클레오티드로 구성된 DNA 폴리뉴클레오티드 사슬.
14.3 DNA Replication • Meselson and Stahl showed that DNA replication is semiconservative (반보존적) • DNA polymerases are the primary enzymes of DNA replication • Helicases unwind DNA to expose template strands for new DNA synthesis
14.3 (cont.) • RNA primers provide the starting point for DNA polymerase to begin synthesizing a new DNA chain • One new DNA strand is synthesized continuously; the other, discontinuously • Multiple enzymes coordinate their activities in DNA replication
14.3 (cont.) • Telomerases solve a specialized replication problem at the ends of linear DNA molecules • DNA replication begins at replication origins
Semiconservative Replication • Two strands of parental DNA molecule unwind • Each is a template for the synthesis of a complementary copy
그림 14.8. DNA 복제의 반보존적(a), 보존적(b), 분산적(c) 모형.
그림 14.9-1. 반보존적 모형을 증명하는 메셀슨과 스탈의 실험.
그림 14.10. DNA 중합효소가 5’→3’방향으로 상보적인 사슬을 만드는 반응.
Two Antiparallel Strands • As DNA helix unwinds, one template strand runs in a direction allowing new DNA strand to be made continuously in the direction of unwinding • Other template strand is copied in short lengths that run in the direction opposite to unwinding • Discontinuous replication produces short lengths, then linked into a continuous strand
그림 14.11. 역평행인 주형가닥들은 분기점에서 어떻게 복제 되는가?
Enzymes of DNA Replication • Helicase unwinds the DNA • Primase synthesizes RNA primer (starting point for nucleotide assembly by DNA polymerases) • DNA polymerases assemble nucleotides into a chain, remove primers, and fill resulting gaps • DNA ligase closes remaining single-chain nicks
그림 14.12-1. 헬리카제, 프리마제, DNA 중합효소, DNA 리가제 등의 활성을 포함하는 DNA 복제의 단계들.
Telomeres • Ends of eukaryotic chromosomes • Short sequences repeated hundreds to thousands of times • Repeats protect against chromosome shortening during replication
Telomerase • Chromosome shortening is prevented in some cell types which have a telomerase enzyme (adds telomere repeats to chromosome ends)
그림 14.13. 복제 과정 5’ 말단에서 프라이머가 제거되면 공백이 남게 됨.
그림 14.14. 진핵생물 염색체가 짧아지는 것을 방지하는 텔로미어 반복들.
DNA Synthesis • Begins at sites that act as replication origins • Proceeds from the origins as two replication forks moving in opposite directions
14.4 Mechanisms That Correct Replication Errors • Proofreading (교정) depends on the ability of DNA polymerases to reverse and remove mismatched (불일치) bases • DNA repair (수선) corrects errors (오류들) that escape proofreading
Proofreading • If a replication error causes a base to be mispaired, DNA polymerase reverses and removes the most recently added base • The enzyme then resumes DNA synthesis in the forward direction
DNA Repair Mechanisms • DNA polymerase enzymes • Recognize distorted regions caused by mispaired base pairs • Remove DNA section with mispaired base from the newly synthesized nucleotide chain • Resynthesize the section correctly, using original template chain as a guide (길잡이)
14.5 DNA Organization (체계; 조직)in Eukaryotes and Prokaryotes • Histones pack eukaryotic DNA at successive levels of organization • Many nonhistone proteins have key roles in the regulation of gene expression • DNA is organized more simply in prokaryotes than in eukaryotes
Eukaryotic Chromosomes • Consist of DNA complexed with histone and nonhistone proteins • DNA wraps around a nucleosome (two molecules each of histones H2A, H2B, H3, H4) • Linker DNA connects adjacent nucleosomes • Binding of histone H1 causes nucleosomes to package into a coiled structure (solenoid) • Nonhistone proteins help control the expression of individual genes
그림 14.18. 진핵생물 염색질과 염색체에서의 조직화 단계.
Chromatin • Distributed between: • Euchromatin (진정염색질)(loosely packed region, genes active in RNA transcription) • Heterochromatin (이질염색질)(densely packed masses, genes are inactive) • Folds and packs to form thick, rodlike chromosomes during nuclear division
The Bacterial Chromosome • Closed, circular molecule of DNA packed into nucleoid (핵양체) region of cell • Replication begins from a single origin, proceeds in both directions • Plasmids (in many bacteria) replicate independently of the host chromosome
Bacterial DNA • Organized into loops through interaction with proteins • Proteins similar to eukaryotic nonhistones regulate gene activity in prokaryotes
그림 14.19. 원핵생물의 원형 DNA에서 단일 원점으로부터의 복제.