1. A molecule the DNA is composed of two strands that type a twin helix structure.

You are watching: In the spiral staircase model of dna the rungs are

DNA is a macromolecule consists of two strands that twist roughly a usual axis in a shape dubbed a double helix. The twin helix looks choose a twisted ladder—the rungs that the ladder are composed of pairs of nitrogenous bases (base pairs), and the political parties of the ladder are made up of alternative sugar molecules and phosphate groups.

Molecules that DNA variety in length from thousands of thousands to countless base pairs. The smallest chromosome in the person genome, Chromosome 21, has about 48 million base pairs.


A molecule the DNA has two strands, written of nucleotides, that form a double helix shape.

Download DNA lab Activities

2. Each DNA strand is written of nucleotides—units made up of a sugar (deoxyribose), a phosphate group, and also a nitrogenous base.

Each strand of DNA is a polynucleotide created of units dubbed nucleotides. A nucleotide has three components: a street molecule, a phosphate group, and a nitrogenous base.

The street in DNA’s nucleotides is called deoxyribose—DNA is an abbreviation because that deoxyribonucleic acid. RNA molecules usage a different sugar, called ribose. Covalent bonds join the street of one nucleotide to the phosphate team of the next nucleotide, creating the DNA strand’s sugar-phosphate backbone.

A nitrogenous base is an essential molecule that contains nitrogen and has the chemical properties the a base. Over there are 4 nitrogenous bases that take place in DNA molecules: cytosine, guanine, adenine, and also thymine (abbreviated as C, G, A, and T). RNA molecules contain cytosine, guanine, and adenine, but they have a various nitrogenous base, uracil (U) instead of thymine.


3. The order of nitrogenous bases top top the 2 strands that a DNA molecule space complementary.

The succession of nitrogenous bases on one strand of a DNA molecule’s dual helix matches up in a particular means with the succession on the other strand. Adenin pairs with thymine and cytosine pairs with guanine.

Why execute the nitrogenous bases pair in this details way? The bases on every strand space joined come the bases ~ above the various other strand through hydrogen bonds, however different bases have various chemical structures. Cytosine and also thymine (and uracil in RNA) are pyrimidines, comprise one ring. Adenine and also guanine room purines, containing two rings. The pyrimidines pair with the purines: cytosine and guanine type three hydrogen bonds, and adenine and also thymine type two.

4. Certain sequences of nitrogenous bases that password for certain proteins or regulation RNA molecules are referred to as genes.

Each strand of DNA is like a recipe publication for synthesizing proteins. Particular sequences of nitrogenous bases follow me the strand encode particular RNA molecules. This sequences are dubbed genes. MRNA molecule transcribed from gene are analyzed into protein later.

Chromosomes can vary extensively in their variety of base pairs and also genes. The longest chromosome in human cells, Chromosome 1, is approximately 249 million base pairs long and has in between 2000 and also 2100 distinct genes. Chromosome 21, the shortest person chromosome, consists of 48 million basic pairs and also contains between 200 and also 300 genes. Overall, prokaryotes cells have much shorter chromosomes v fewer genes. For example, the bacterium Carsonella rudii has actually only 159,662 base pairs and 182 gene in its whole genome.

Although genes gain most of the credit transaction for what DNA does, they comprise only about 1% of DNA (in humans). Genes room separated native one one more by sequences of nitrogenous bases the don’t carry out instructions because that RNA synthesis. This are called intergenic regions. Even within genes, over there are areas of noncoding DNA dubbed introns.

See more: Is The Square Root Of 144 Rational Or Irrational ? Is The Square Root Of 144 Rational Or Irrational

Noncoding areas of DNA space important because they provide binding sites for proteins that aid activate or deactivate the procedure of transcription. They deserve to also provide protection for the coding regions. Because that instance, telomeres consists of repeated sequences that defend the genetic information on each DNA molecule from gift damaged throughout cell division.