Biology Part One: DNA Structure and Restriction Enzymes

Vocabulary flashcards covering DNA structure (double helix, base pairing, purines/pyrimidines, backbone), strand orientation, palindromes, and restriction enzyme concepts (recognition sites, sticky/blunt ends, EcoRI, RFLP, SNP effects, and gel electrophoresis).

Double helix

The two DNA strands twisted around each other with hydrogen-bonded bases on the inside and sugar–phosphate backbones on the outside.

Hydrogen bonds

Weak bonds between complementary bases (A–T has 2; G–C has 3) that allow the DNA strands to unzip during replication and transcription.

Phosphodiester backbone

The strong covalent linkages that form the sugar–phosphate backbone of each DNA strand.

Base pairing (A–T and G–C)

Adenine pairs with thymine (A–T) and guanine pairs with cytosine (G–C) via hydrogen bonds.

Purines

Bases with two rings: adenine (A) and guanine (G).

Pyrimidines

Bases with one ring: cytosine (C), thymine (T) in DNA, and uracil (U) in RNA.

Nucleotides

Building blocks of DNA composed of a sugar, a phosphate, and a nitrogenous base.

5' to 3' direction

DNA sequences are read in the 5' to 3' direction; strands are antiparallel to each other.

Antiparallel strands

Two DNA strands run in opposite directions (one 5'→3', the other 3'→5').

Palindromic sequence

A DNA sequence that reads the same 5'→3' on both strands; many restriction enzymes target such palindromes.

Restriction enzyme

Enzymes that cut DNA at specific recognition sites; cuts can be blunt or sticky ends.

Recognition site

The exact DNA sequence recognized and cleaved by a restriction enzyme.

Sticky end

A cut that leaves overhanging single-stranded ends which can anneal to complementary fragments.

Blunt end

A cut that yields straight ends with no overhangs.

EcoRI

A restriction enzyme from E. coli that recognizes GAATTC and produces sticky ends.

Restriction fragment length polymorphism (RFLP)

Variations in DNA fragment lengths after restriction digestion, caused by sequence differences such as SNPs.

SNP (Single Nucleotide Polymorphism)

A single base pair difference between individuals that can alter restriction sites and gene function.

Restriction site modification by SNP

A single nucleotide change can disrupt a restriction site, changing whether the enzyme cuts and affecting fragment patterns.

Gel electrophoresis (fragments)

Technique that separates DNA fragments by size; shorter fragments migrate faster and appear as bands.

Helicase

Enzyme that unwinds the DNA double helix to allow replication or transcription.

DNA unzipping

The process of separating the two strands by breaking hydrogen bonds so templates can be read or copied.