Structure and function of dna pdf

This strand is synthesized continuously and grows from 5' to 3'. Open navigation menu. Close suggestions Search Search. User Settings. Skip carousel. Carousel Previous. Carousel Next. What is Scribd? Explore Ebooks. Bestsellers Editors' Picks All Ebooks. Explore Audiobooks. Bestsellers Editors' Picks All audiobooks. Explore Magazines. Editors' Picks All magazines. Explore Podcasts All podcasts. Difficulty Beginner Intermediate Advanced. Explore Documents. Structure and Function of DNA.

Uploaded by Matthew Justin Villanueva Gozo. Did you find this document useful? Is this content inappropriate? Report this Document. Home » General Science » Biology. Download Post as PDF. Table of Contents. Continue Reading in App. Next Post. More from testbook. No more posts found! Replicates and stores genetic information like a blueprint.

The four nitrogenous bases are Adenine, Uracil, Guanine, or Thymine. The four nitrogenous bases are Adenine, Uracil, Guanine, or Cytosine. RNA contains ribose sugar molecules, without the hydroxyl modifications of deoxyribose. The early x-ray diffraction results indicated that DNA was composed of two strands of the polymer wound into a helix.

The observation that DNA was double-stranded was of crucial significance and provided one of the major clues that led to the Watson-Crick structure of DNA. Only when this model was proposed did DNA's potential for replication and information encoding become apparent. In this section we examine the structure of the DNA molecule and explain in general terms how it is able to store hereditary information.

A DNA molecule consists of two long polynucleotide chains composed of four types of nucleotide subunits. Hydrogen bonds between the base portions of the nucleotides hold the two chains together Figure As we saw in Chapter 2 Panel , pp.

In the case of the nucleotides in DNA, the sugar is deoxyribose attached to a single phosphate group hence the name deoxyribonucleic acid , and the base may be either adenine A , cytosine C , guanine G , or thymine T. Because only the base differs in each of the four types of subunits, each polynucleotide chain in DNA is analogous to a necklace the backbone strung with four types of beads the four bases A, C, G, and T.

These same symbols A, C, G, and T are also commonly used to denote the four different nucleotides—that is, the bases with their attached sugar and phosphate groups.

DNA and its building blocks. DNA is made of four types of nucleotides, which are linked covalently into a polynucleotide chain a DNA strand with a sugar-phosphate backbone from which the bases A, C, G, and T extend. A DNA molecule is composed of two more The way in which the nucleotide subunits are lined together gives a DNA strand a chemical polarity.

The three-dimensional structure of DNA — the double helix —arises from the chemical and structural features of its two polynucleotide chains. Because these two chains are held together by hydrogen bonding between the bases on the different strands, all the bases are on the inside of the double helix, and the sugar -phosphate backbones are on the outside see Figure In each case, a bulkier two-ring base a purine ; see Panel , pp.

This complementary base-pairing enables the base pairs to be packed in the energetically most favorable arrangement in the interior of the double helix.

In this arrangement, each base pair is of similar width, thus holding the sugar-phosphate backbones an equal distance apart along the DNA molecule. To maximize the efficiency of base-pair packing, the two sugar-phosphate backbones wind around each other to form a double helix, with one complete turn every ten base pairs Figure Complementary base pairs in the DNA double helix.

The shapes and chemical structure of the bases allow hydrogen bonds to form efficiently only between A and T and between G and C, where atoms that are able to form hydrogen bonds see Panel , pp.

The DNA double helix. A A space-filling model of 1. Each turn of DNA is made up of The coiling of the two strands around more The members of each base pair can fit together within the double helix only if the two strands of the helix are antiparallel —that is, only if the polarity of one strand is oriented opposite to that of the other strand see Figures and A consequence of these base-pairing requirements is that each strand of a DNA molecule contains a sequence of nucleotides that is exactly complementary to the nucleotide sequence of its partner strand.

Genes carry biological information that must be copied accurately for transmission to the next generation each time a cell divides to form two daughter cells. Two central biological questions arise from these requirements: how can the information for specifying an organism be carried in chemical form, and how is it accurately copied?

The discovery of the structure of the DNA double helix was a landmark in twentieth-century biology because it immediately suggested answers to both questions, thereby resolving at the molecular level the problem of heredity.