Human Genetics - DNA Structure and Replication (2)

Vocabulary flashcards for key terms in DNA structure and replication.

Carbon Numbering in DNA

The carbons in the sugar of DNA are numbered from 1 to 5, always moving clockwise from the Oxygen on the Deoxyribose.

Purines

A and G; Have a double-ring structure.

Pyrimidines

C and T; Have a single-ring structure.

X-ray diffraction 'X' pattern

Indicates that X-rays passing through a molecule diffract at angles perpendicular to the helix, suggesting an equal diameter helix in DNA.

Length of one turn of the DNA helix

34 Angstroms

Distance between base pairs in DNA

3.4 Angstroms

Width of the DNA helix

20 Angstroms

Three parts of a nucleotide

DNA and RNA Pentose Sugar, Phosphate, Nitrogen base

Antiparallel

Two polynucleotide chains run in opposite directions.

Semiconservative Replication

Each new DNA double helix conserves half of the original, parental double helix.

Conservative Model (DNA replication)

The parental double helix remains intact, and a second, all-new copy is made.

Semiconservative Model (DNA replication)

The two strands of the parental molecule separate, and each functions as a template for synthesis of a new complementary strand.

Dispersive Model (DNA replication)

Each strand of both daughter molecules contains a mixture of old and newly synthesized parts.

Replication Fork

A site where DNA is locally opened.

Helicase

Catalyzes the untwisting of the DNA at the replication fork.

Binding Proteins

Stabilizes separate strands of DNA

Primase

Adds short primer to template strand.

DNA Polymerase

Binds nucleotides to form new strands.

Ligase

Joins Okazaki fragments and seals other nicks in the sugar-phosphate backbone.

Topoisomerase

Breaks the DNA strands and prevents excessive coiling.

Primase

Synthesizes the RNA primers and starts the replication.

DNA Polymerase

Adds DNA nucleotides to the RNA primer at the 3’ end; also has proofreading activity.

Leading Strand

Strand synthesized continuously in a 5’ to 3’ direction.

Lagging Strand

Synthesis produces Okazaki fragments on the 5’ to 3’ template.

DNA synthesis

DNA synthesis proceeds in both directions from a point of origin.

Helicase

Separates DNA strand

Primase

Creates RNA primers

Single Stranded Binding Protein

Prevents reannealing

DNA Polymerase

Extends DNA strand