DNA, genes and chromosomes — University of Leicester
The cell's nucleus contains chromosomes made from long DNA molecules. shows the relationship between the cell, its nucleus, chromosomes in the nucleus . A DNA (deoxyribonucleic acid) double helix is the fundamental unit of our genetic molecule of DNA is made up of a sugar group (deoxyribose), a phosphate. Every factor in inheritance is due to a particular gene. Genes specify the Think of it this way: DNA is in genes, genes are on chromosomes.
Difference Between DNA and Genes | Difference Between | DNA vs Genes
DNA was known to be a long polymer composed of only four types of subunits, which resemble one another chemically. Early in the s, DNA was first examined by x-ray diffraction analysis, a technique for determining the three-dimensional atomic structure of a molecule discussed in Chapter 8. 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. Hydrogen bonds between the base portions of the nucleotides hold the two chains together Figure As we saw in Chapter 2 Panelpp.
In the case of the nucleotides in DNA, the sugar is deoxyribose attached to a single phosphate group hence the name deoxyribonucleic acidand the base may be either adenine Acytosine Cguanine Gor 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. Figure 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 Panelpp.
This complementary base-pairing enables the base pairs to be packed in the energetically most favorable arrangement in the interior of the double helix.
The Structure and Function of DNA - Molecular Biology of the Cell - NCBI Bookshelf
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 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 Panelpp. Figure 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.
The Structure of DNA Provides a Mechanism for Heredity 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: 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.
We discuss briefly the answers to these questions in this sectionand we shall examine them in more detail in subsequent chapters.
Difference Between DNA and Genes
DNA encodes information through the order, or sequence, of the nucleotides along each strand. Each base —A, C, T, or G —can be considered as a letter in a four-letter alphabet that spells out biological messages in the chemical structure of the DNA.
As we saw in Chapter 1, organisms differ from one another because their respective DNA molecules have different nucleotide sequences and, consequently, carry different biological messages.
Info DNA, genes and chromosomes Your genes are part of what makes you the person you are. You are different from everyone alive now and everyone who has ever lived.
DNA But your genes also mean that you probably look a bit like other members of your family. For example, have you been told that you have 'your mother's eyes' or 'your grandmother's nose'? Genes influence what we look like on the outside and how we work on the inside. They contain the information our bodies need to make chemicals called proteins. Proteins form the structure of our bodies, as well playing an important role in the processes that keep us alive. Genes are made of a chemical called DNA, which is short for 'deoxyribonucleic acid'.
The DNA molecule is a double helix: The DNA double helix showing base pairs The sides are sugar and phosphate molecules. The rungs are pairs of chemicals called 'nitrogenous bases', or 'bases' for short.
There are four types of base: These bases link in a very specific way: A always pairs with T, and C always pairs with G. The DNA molecule has two important properties. It can make copies of itself.
If you pull the two strands apart, each can be used to make the other one and a new DNA molecule. It can carry information.