Describe the structure and complementary base pairing of...

Key Concepts

Sugar-Phosphate Backbone

The nucleotides are linked together through covalent bonds between the sugar and phosphate groups to form a sugar-phosphate backbone. This backbone provides structural integrity and creates polarity in the DNA strand.

Antiparallel Orientation

The two strands of the DNA double helix run in opposite directions, an arrangement known as antiparallel orientation. This orientation is critical for the enzymatic activities involved in DNA replication and repair.

Nucleotides

The basic building blocks of DNA are nucleotides, each consisting of a phosphate group, a deoxyribose sugar, and one of four nitrogenous bases. The specific sequence of these bases encodes the genetic instructions for the organism.

Double Helix Structure

DNA is organized as a double helix, which consists of two long strands twisting around each other. This structure offers stability and compactness along with an elegant way to store genetic information within a cell.

Complementary Base Pairing

DNA base pairing is based on the specific pairing between adenine and thymine, and cytosine and guanine. These pairings occur through the formation of hydrogen bonds, ensuring accuracy in genetic replication and transcription processes.

Transcript

00:01 So on this screen, i show you a general ribbon molecule model of a dna, and then i also show you some detailed structure of the nucleotides and the nitrogen base and the base parent root.

00:13 So let's start from the left -hand side figure, which is a ribbon model of a dna molecule.

00:18 A single dna molecule is composed of two dna strands.

00:22 The two dna strands are inter -parallel.

00:25 That means according to the direction of sugar phosphate backbone, the two strands are facing opposite.

00:30 Direction.

00:32 So this is why we sometimes call one strand go from five to three, the other is three to five.

00:37 And i would explain the five prime end and three prime end a little later.

00:41 The bottom line is the two dna strand and they are connected by hydrogen bonds between the nitrogen base of the nucleotides and they twist it into this double helix structures.

00:55 So this is a general bigger view of a dna molecule.

00:59 Let's break down the small details and then look at those details and you will have a better understanding.

01:05 So on the bottom of the figure, i show you a single nucleotide.

01:10 Remember, dna has four nucleotides, right? so they are a, t, c, and g.

01:19 So it doesn't matter which nucleotide, they all have something in common.

01:24 So all the nucleotides have a five carbon sugar, and they have a phosphate group.

01:30 So according to the position of the carbon, each carbon is named one, two, three, four, and five.

01:39 So at the fifth carbon, there is always a phosphate group connect to it.

01:44 And then at the third position of the carbon, there is a hydroxyl group, oh...

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