DNA Structure and Function

DNA Structure

• DNA stands for deoxyribonucleic acid
• DNA is a nucleic acid that carries genetic information
• A segment of DNA is called a gene. A gene codes for proteins.

DNA Structure Objectives

• Students will be able to explain the meaning of each letter in DNA
• Students will be able to discuss and label parts of a DNA molecule
• Students will be able to name the parts of a nucleotide
• Students will be able to identify the 4 bases
• Students will be able to explain the function of DNA in a cell

The Shape of DNA

• The shape of a DNA molecule is a double helix
• The shape of DNA can be thought of as a twisted ladder

A Closer Look at DNA

• DNA is more complex than a simple twisted ladder
• DNA has a complex molecular structure with various components and connections.

The Sides of the DNA Ladder

• Each side of the DNA ladder is called a sugar-phosphate backbone
• The sugar-phosphate backbone is connected by covalent bonds
• The backbone consists of a phosphate group (with a negative charge) and a deoxyribose sugar (a pentagon-shaped sugar).

The Rungs of the DNA Ladder

• The rungs of the DNA ladder are made up of nitrogenous bases
• Nitrogenous bases are bonded to the sugar
• There are four different kinds of bases in DNA

The Bases: Purines and Pyrimidines

• Purines (adenine and guanine) have a double ring structure
• Pyrimidines (cytosine and thymine) have a single ring structure
• A purine always pairs with a pyrimidine (A with T, G with C)

Nucleotide

• A nucleotide is the building block of DNA
• A nucleotide comprises a deoxyribose sugar, a phosphate group, and a nitrogenous base.

Putting it Together

• The deoxyribose sugar of one nucleotide bonds to the phosphate group of another to form the sugar-phosphate backbone
• All bases are directly attached to a deoxyribose sugar
• The nitrogenous bases from one sugar-phosphate backbone bond to the bases of the other backbone to create base pairs
• Adenine (A) forms two hydrogen bonds with Thymine (T)
• Guanine (G) forms three hydrogen bonds with Cytosine (C)

Quick Practice and Complementary Strands

• If given a strand of DNA, the complementary strand can be determined based on the base pairing rules (A with T, G with C)
• Example: If one strand is ATAGGCAT, then the complementary strand is TATCCGTA

One Final Look

• DNA has a precise structure with a double helix shape
• DNA has a characteristic distance and width
• The double helix is also described as antiparallel, meaning the two strands run in opposite directions.
• Hydrogen bonds form between complementary base pairs(A-T, G-C) connecting the two strands of the DNA double helix

Function of DNA

• DNA stores genetic information
• The sequence of bases on the DNA strand acts as a blueprint for creating hundreds of thousands of different proteins.
• These proteins are essential components of living organisms.