4: DNA Structure

Part 4

Describe the structure of a nucleotide

pentose sugar + phosphate + base

What are the four nitrogenous bases found in DNA?

Adenine, Thymine, Cytosine, Guanine (A, T, C, G)

Rules of complementary base pairing:

• Adenine always pairs with Thymine (A + T), held together by 2 hydrogen bonds

• Guanine always pairs with Cytosine (G + C), held together by 3 hydrogen bonds

Describe the overall structure of the DNA double helix, including the major and minor grooves

DNA is in the shape of a Double Helix:

• bases facing inward

• Antiparallel strands

• Major/minor grooves for protein binding

• Sugar-phosphate backbone outward

Predict how a mutation that disrupts base pairing might affect DNA stability

A mutation that disrupts base pairing DNA significantly reduces thermodynamic stability and creates local structural disruptions.

• Disrupts base pairing —> reduces stability & affects DNA function