A1.2 Nucleic Acid
DNA & Nucleotides
DNA (Deoxyribonucleic Acid):
is the hereditary molecule that carries genetic instructions for the growth, development, functioning, and reproduction of all known living organisms and many viruses. It is a macromolecule composed of repeating units called nucleotides and is found primarily in the nucleus of eukaryotic cells and in the cytoplasm of prokaryotic cells
Nucleotide:
Is the smallest unit of a DNA molecule, that is composed of Nitrogenous basis, Pentose sugars & phosphate groups.
Structure of Nucleotides
Structure of DNA double strand
RNA
RNA (Ribonucleic Acid) is a single-stranded nucleic acid that plays a central role in coding, decoding, regulation, and expression of genes. Unlike DNA, which stores genetic information long-term, RNA is more involved in the transfer and execution of that information to build proteins.
RNA also consists of nucleotides but contains Uracil instead of Thymine.
RNA vs DNA
RNA vs DNA
Complimentary Base Pairing
Complimentary Base Pairing is the feature that allows DNA to be replicated easily.
Base pairing is essentially:
Adenine and Thymine binding.
Guanine and Cytosine binding.
Due to their similar complimentary shapes and charges.
Purines & Pyramidines
Purines are adenine and guanine
Pyrimidines are cytosine, thymine & uracil.
Despite different base sequences, DNA maintains the same 3D structure. That is because a purine (adenine and guanine) is always connected to a Pyrimidine (cytosine and thymine), so the structure remains the same.​
Higher Level
Features of dna that make it good at storing information
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DNA is endlessly long
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DNA is thin/with a large storage area/helical shape supports
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Infinite base sequence varieties
DNA is the molecule of life used by all organisms, suggesting evolution from a common ancestor.
Higher Level
Histones & Eukaryotic DNA
In eukaryotic cells, DNA is wrapped around histone proteins to form structures called nucleosomes, each consisting of eight histone proteins. The negatively charged DNA is attracted to the positively charged histones, allowing it to coil tightly around them. Linker DNA, approximately 2 nm thick, connects one nucleosome to the next, creating a chain-like structure. When these nucleosomes group together, they form a chromatin fiber, which undergoes further supercoiling to become increasingly compact. This progressive coiling and condensation ultimately leads to the formation of visible chromosomes during cell division.
Higher Level
Important for 1B - Hershey & Chase
Hershey and Chase conducted an experiment to determine whether DNA or protein was the genetic material. At the time, many believed protein carried genetic information due to its complexity, while DNA was thought too simple, based on the tetranucleotide hypothesis.
To test this, they used bacteriophages and labeled their DNA with radioactive phosphorus and their protein with radioactive sulfur. After the phages infected bacteria, only the radioactive DNA entered the cells —while the labeled protein remained outside. This showed that DNA, not protein, was the hereditary material.
Their findings were supported by advances in radioisotope tracking and by Chargaff’s rule (A = T, G = C), which disproved the idea that DNA had a repetitive, non-informational structure.