DNA: Structure + Replication

HideShow resource information
  • Created by: amy_br0
  • Created on: 07-05-14 20:33

DNA: Structure

DNA:

  • a complex molecule containing the genetic information of an organism. 
  • a polymer made up of necleotides

One nucleotide ~ sugar, phosphate group & nitrogen base

  • SUGAR - Deoxyribose
  • NITROGEN BASES - A, T, C, G

Nucleotides join together in a condesation reation - forms polynucleotide chains

DOUBLE HELIX STRUCTURE - sugar phosphate backbone

held together by the bases + hydrogen bonds

A --> T : TWO HYDROGEN BONDS 

G --> C : THREE HYDROGEN BONDS

1 of 3

DNA: Replication

For cells to divide, DNA needs to replicate. It does this by the following process:

  • HELICASE enzymes BREAK hydrogen bonds holding the two strand of DNA together (UNZIPS)
  • Each polynucleotide strand acts a template ~ complementary nucleotides are attracted
  • ENERGY used to activate nucleotides
  • activated nucleotides join together ~  BY DNA POLYMERASE 
  • these form the missing polynucleotide strand on each of the original strands of DNA

Process called: SEMI-CONSERVATIVE REPLICATION because:

  • each NEW DNA molecule contains one of the original DNA strands
  • so half the original DNA has been saved and built into each of the new DNA molecule
2 of 3

PROOF: SEMI-CONSERVATIVE REPLICATION

SEMI-CONSERVATIVE REPLICATION was proved by MENDELSOHN + STAHL:

  • bacterial was collected in a medium of 'heavy' nitrogen ~ mean DNA strands would be heavy
  • a sample of bacterial DNA was taken
  • bacteria then transferred to a medium contain normal nitrogen and allowed to divide
  • sample of bacterial DNA was taken again
  • bacterial was allowed to divide again, a third sample was then taken. 

the three samples were analysed using CENTRIFUGATION ~ separates molecules by density

  • parent strands ~ gave a single band in the lower region, contained only heavy nitrogen
  • first gen, ~ gave a band of intermediate density, rules out conservative replication
  • second gen. ~ gave two bands, one light and one intermediate, rules out dispersive replication
3 of 3

Comments

No comments have yet been made

Similar Biology resources:

See all Biology resources »See all DNA, genetics and evolution resources »