Structure & Function
Introduction: All known forms of cellular life and some viruses are known to contain DNA, the primary system for encoding the organism's genetic information, which can be found inside the nucleus of a cell. DNA is made of up long strands of molecules inside a cell's nucleolus (the center of its nucleus) that are tightly wrapped around histone proteins and then further condensed into the coiled form known as chromatin. Densely packed chromatin is arranged into the chromosome structure, and humans have 46 chromosomes inside the nucleus of each of their cells. Each chromosome serves a unique purpose in encoding an individual organism's genetic (or heritable) information. We will break down the structural and functional elements of DNA from the most basic molecular level to its overall purpose as the building blocks to all life.
DNA stands for deoxyribonucleic acid, which provides insight into a DNA molecule's structure. DNA molecules are built from nucleotides, which are individual molecules that each contain a nitrogenous base, a 5-carbon sugar ring, and a phosphate group. Each DNA molecule contains thousands of nucleotides strung together.
DNA stands for deoxyribonucleic acid, which provides insight into a DNA molecule's structure. DNA molecules are built from nucleotides, which are individual molecules that each contain a nitrogenous base, a 5-carbon sugar ring, and a phosphate group. Each DNA molecule contains thousands of nucleotides strung together.
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There are four different kinds of bases that may be included in the nucleotide: thymine (T), adenine (A), cytosine (C) and guanine (G). A and G have a double-ring molecular structure, while C and T have a single-ring structure. In RNA, uracil (U) replaces T.
Chargaff's rules:
These bases accompany each other in complimentary pairs so that a single-ring pyrimidine is always paired with a double-ring purine: T bonds with A, and C bonds with G. This rule of pairing is universal except for when errors in the replication of DNA occurs, known as mutations, which are discussed in mutations section on this website. Purines and pyrimidines always occur in equal proportions.
Chargaff's rules:
These bases accompany each other in complimentary pairs so that a single-ring pyrimidine is always paired with a double-ring purine: T bonds with A, and C bonds with G. This rule of pairing is universal except for when errors in the replication of DNA occurs, known as mutations, which are discussed in mutations section on this website. Purines and pyrimidines always occur in equal proportions.
The Double Helix
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DNA molecules are arranged into a double helix with base pairs running antiparallel to one another with hydrogen bonds between base pairs.
From specific to broad, the organization of DNA goes:
histones->nucleosomes->30nm fiber->300nm looped domains ->metaphase chromosome.
DNA strands are known as nucleic acids, which are polymers comprised of many nucleotides attached together. Each nucleotide is covalently bonded by its 5-carbon sugar to the phosphate group of the next nucleotide, forming the sugar-phosphate backbone of the double helix. This backbone holds together the double-helix structure, and the nitrogenous bases are paired together inside of it. Weak hydrogen bonds hold together the bases, designed to be strong enough to hold the helix together but weak enough that the strand can unwind for use in DNA replication and transcription. Three hydrogen bonds bind together the G and C base pairings, and two hydrogen bonds bind the A and T pairings.
From specific to broad, the organization of DNA goes:
histones->nucleosomes->30nm fiber->300nm looped domains ->metaphase chromosome.
DNA strands are known as nucleic acids, which are polymers comprised of many nucleotides attached together. Each nucleotide is covalently bonded by its 5-carbon sugar to the phosphate group of the next nucleotide, forming the sugar-phosphate backbone of the double helix. This backbone holds together the double-helix structure, and the nitrogenous bases are paired together inside of it. Weak hydrogen bonds hold together the bases, designed to be strong enough to hold the helix together but weak enough that the strand can unwind for use in DNA replication and transcription. Three hydrogen bonds bind together the G and C base pairings, and two hydrogen bonds bind the A and T pairings.