Telomeres and centromeres typically contain few genes but are important for the function and stability of chromosomes. In many speciesonly a small fraction of the total sequence of the genome encodes protein.
The lambda repressor helix-turn-helix transcription factor bound to its DNA target . The set of chromosomes in a cell makes up its genome ; the human genome has approximately 3 billion base pairs of DNA arranged into 46 chromosomes.
For example, UV light can damage DNA by producing thymine dimerswhich are cross-links between pyrimidine bases. The relationship between the nucleotide sequences of genes and the amino-acid sequences of proteins is determined by the rules of translationknown collectively as the genetic code.
Deamination converts 5-methylcytosine into thymine. These protein interactions can be non-specific, or the protein can bind specifically to a single DNA sequence. Transmission of genetic information in genes is achieved via complementary base pairing. In eukaryotes, this structure involves DNA binding to a complex of small basic proteins called histoneswhile in prokaryotes multiple types of proteins are involved.
Genes contain an open reading frame that can be transcribed, and regulatory sequences such as promoters and enhancerswhich control transcription of the open reading frame.
The double helix is unwound by a helicase and topoisomerase. There is, further, crosstalk between DNA methylation and histone modification, so they can coordinately affect chromatin and gene expression. Mutagens include oxidizing agentsalkylating agents and also high-energy electromagnetic radiation such as ultraviolet light and X-rays.
Because of inherent limits in the DNA repair mechanisms, if humans lived long enough, they would all eventually develop cancer. The details of these functions are covered in other articles; here the focus is on the interactions between DNA and other molecules that mediate the function of the genome.
Next, one DNA polymerase produces the leading strand copy. These remaining DNA damages accumulate with age in mammalian postmitotic tissues.
Most intercalators are aromatic and planar molecules; examples include ethidium bromideacridinesdaunomycinand doxorubicin. A gene is a unit of heredity and is a region of DNA that influences a particular characteristic in an organism.
Structure of cytosine with and without the 5-methyl group. Base modifications and DNA packaging Further information: In alternative fashion, a cell may simply copy its genetic information in a process called DNA replication. Genes and genomes Further information: The type of DNA damage produced depends on the type of mutagen.
Base modifications can be involved in packaging, with regions that have low or no gene expression usually containing high levels of methylation of cytosine bases. DNA replication Cell division is essential for an organism to grow, but, when a cell divides, it must replicate the DNA in its genome so that the two daughter cells have the same genetic information as their parent.
Another DNA polymerase binds to the lagging strand.Cytoplasm is a watery, gel-like substance that fills the inside of a cell. It is what the other cellular objects float around in while they are in the cell. Fukuoka | Japan Fukuoka | Japan. DNA is a long polymer made from repeating units called nucleotides.
The structure of DNA is dynamic along its length, being capable of coiling into tight loops, and other shapes. In all species it is composed of two helical chains, bound to each other by hydrogen mi-centre.com chains are coiled round the same axis, and have the same pitch of 34 ångströms ( nanometres).