one. A molecule of Deoxyribonucleic acid consists of two strands that form a double helix structure.
Dna is a macromolecule consisting of two strands that twist effectually a mutual axis in a shape called a
double helix. The double helix looks like a twisted ladder—the rungs of the ladder are composed of pairs of nitrogenous bases (base pairs), and the sides of the ladder are made upwardly of alternate saccharide molecules and phosphate groups.
Molecules of DNA range in length from hundreds of thousands to millions of base pairs. The smallest chromosome in the man genome, Chromosome 21, has around 48 million base of operations pairs.
ii. Each DNA strand is equanimous of nucleotides—units made up of a sugar (deoxyribose), a phosphate group, and a nitrogenous base.
Each strand of Dna is a polynucleotide composed of units called
nucleotides. A nucleotide has three components: a carbohydrate molecule, a phosphate grouping, and a nitrogenous base.
The saccharide in DNA’southward nucleotides is called deoxyribose—DNA is an abbreviation for deoxyribonucleic acid. RNA molecules use a unlike sugar, called ribose. Covalent bonds join the sugar of 1 nucleotide to the phosphate group of the next nucleotide, forming the Dna strand’due south
is an organic molecule that contains nitrogen and has the chemical properties of a base. There are four nitrogenous bases that occur in Dna molecules: cytosine, guanine, adenine, and thymine (abbreviated as C, Thousand, A, and T). RNA molecules contain cytosine, guanine, and adenine, but they have a unlike nitrogenous base, uracil (U) instead of thymine.
iii. The sequences of nitrogenous bases on the two strands of a DNA molecule are complementary.
The sequence of nitrogenous bases on 1 strand of a DNA molecule’southward double helix matches up in a particular way with the sequence on the other strand. Adenine pairs with thymine and cytosine pairs with guanine.
Why do the nitrogenous bases pair in this specific manner? The bases on each strand are joined to the bases on the other strand with hydrogen bonds, but different bases have different chemical structures. Cytosine and thymine (and uracil in RNA) are pyrimidines, containing i ring. Adenine and guanine are purines, containing two rings. The pyrimidines pair with the purines: cytosine and guanine form iii hydrogen bonds, and adenine and thymine form ii.
four. Specific sequences of nitrogenous bases that lawmaking for detail proteins or regulatory RNA molecules are called genes.
Each strand of DNA is like a recipe volume for synthesizing proteins. Certain sequences of nitrogenous bases forth the strand encode particular RNA molecules. These sequences are called genes. mRNA molecules transcribed from genes are translated into proteins later on.
Chromosomes can vary widely in their number of base pairs and genes. The longest chromosome in human being cells, Chromosome 1, is around 249 meg base pairs long and has betwixt 2000 and 2100 distinct genes. Chromosome 21, the shortest human chromosome, consists of 48 million base pairs and contains between 200 and 300 genes. Overall, prokaryotic cells have shorter chromosomes with fewer genes. For instance, the bacterium
has only 159,662 base pairs and 182 genes in its unabridged genome.
Although genes go most of the credit for what Deoxyribonucleic acid does, they brand up only well-nigh 1% of DNA (in humans). Genes are separated from one some other past sequences of nitrogenous bases that don’t provide instructions for RNA synthesis. These are chosen intergenic regions. Fifty-fifty inside genes, there are regions of noncoding Deoxyribonucleic acid chosen introns.
Noncoding regions of DNA are important because they provide bounden sites for proteins that help activate or deactivate the procedure of transcription. They can too provide protection for the coding regions. For case, telomeres consist of repetitive sequences that protect the genetic information on each Deoxyribonucleic acid molecule from being damaged during jail cell partition.
The Structure of Dna Resembles a Twisted Ladder