1. A molecule of DNA is composed of 2 strands that develop a double helix framework.
You are watching: Which of the following statements about the dna double helix is true?
DNA is a macromolecule consisting of two strands that twist about a prevalent axis in a shape called a double helix. The double helix looks prefer a twisted ladder—the rungs of the ladder are composed of pairs of nitrogenous bases (base pairs), and also the sides of the ladder are comprised of alternating sugar molecules and phosphate teams.
Molecules of DNA selection in length from hundreds of thousands to countless base pairs. The smallest chromosome in the human genome, Chromosome 21, has actually roughly 48 million base pairs.
DNAA molecule of DNA has actually 2 strands, created of nucleotides, that form a double helix shape.
Downfill DNA Lab Activities
2. Each DNA strand also is composed of nucleotides—units comprised of a sugar (deoxyribose), a phosphate group, and also a nitrogenous base.
Each strand also of DNA is a polynucleotide written of devices referred to as nucleotides. A nucleotide has 3 components: a sugar molecule, a phosphate group, and also a nitrogenous base.
The sugar in DNA’s nucleotides is called deoxyribose—DNA is an abbreviation for deoxyribonucleic acid. RNA molecules usage a various sugar, dubbed ribose. Covalent bonds sign up with the sugar of one nucleotide to the phosphate team of the next nucleotide, creating the DNA strand’s sugar-phosphate backbone.
A nitrogenous base is an organic molecule that consists of nitrogen and has actually the chemical properties of a base. There are four nitrogenous bases that take place in DNA molecules: cytosine, guanine, adenine, and thymine (abbreviated as C, G, A, and also T). RNA molecules contain cytosine, guanine, and adenine, yet they have actually a different nitrogenous base, uracil (U) rather of thymine.
3. The sequences of nitrogenous bases on the two strands of a DNA molecule are complementary.
The sequence of nitrogenous bases on one strand of a DNA molecule’s double helix matches up in a specific means via the sequence on the other strand. Adenine pairs through thymine and cytosine pairs via guanine.
Why carry out the nitrogenous bases pair in this specific way? The bases on each strand also are joined to the bases on the various other strand also via hydrogen bonds, however various bases have various chemical frameworks. Cytosine and thymine (and uracil in RNA) are pyrimidines, containing one ring. Adenine and also guanine are purines, containing 2 rings. The pyrimidines pair with the purines: cytosine and guanine create 3 hydrogen bonds, and adenine and thymine develop two.
4. Specific sequences of nitrogenous bases that code for certain proteins or regulatory RNA molecules are referred to as genes.
Each strand of DNA is choose a recipe book for manufacturing proteins. Certain sequences of nitrogenous bases along the strand encode particular RNA molecules. These sequences are referred to as genes. mRNA molecules transcribed from genes are interpreted into proteins later.
Chromosomes have the right to differ commonly in their variety of base pairs and genes. The longest chromosome in huguy cells, Chromosome 1, is about 249 million base pairs long and has actually between 2000 and also 2100 distinct genes. Chromosome 21, the shortest humale chromosome, is composed of 48 million base pairs and has in between 200 and 300 genes. Overall, prokaryotic cells have shorter chromosomes through fewer genes. For instance, the bacterium Carsonella rudii has actually just 159,662 base pairs and 182 genes in its entire genome.
Although genes get many of the crmodify for what DNA does, they make up just around 1% of DNA (in humans). Genes are separated from one one more by sequences of nitrogenous bases that don’t carry out instructions for RNA synthesis. These are called intergenic areas. Even within genes, tright here are areas of noncoding DNA called introns.
See more: Modelo De Carta De Invitacion Para Visa De Visitantes, Carta De Invitacion Rusia
Noncoding regions of DNA are vital because they carry out binding sites for proteins that assist activate or deactivate the procedure of transcription. They have the right to likewise provide security for the coding regions. For circumstances, telomeres consist of repeated sequences that defend the hereditary indevelopment on each DNA molecule from being damaged in the time of cell division.