A1.2 nucleic acids

What is the role of DNA? Are viruses living?

All living things use DNA as genetic material to store genetic info (genes). Some viruses use RNA as their genetic material, but are not considered to be living because they need a host to reproduce and be active.

what are components of a nucleotide (structure of DNA)?

Phosphate group: circle

Pentose sugar: pentagon; deoxyribose OR ribose sugar

Nitrogenous base: recatngle; base that contains nitrogen

what is sugar-phosphate bonding and the sugar-phosphate "backbone" of DNA and RNA?

The sugar-phosphate backbone is formed when nucleotides in the same direction connect via phosphodiester covalent bonds between the 5' phosphate and the 3' sugar of the next (C3), creating a strong chain that carries and protects genetic information in DNA/RNA. Each addition to the hydroxyl side requires an input of energy and releases one molecule of water.

what are the bases in each nucleic acid that form the basis of a code?

Purines are one-ring bases, and pyrimidines are two-ring bases (atom rings). Purines (adenine & guanine) only pair with pyrimidines (thymine and cytosine) G & C require 3 hydro bonds, A & T require 2.

what is RNA as a polymer?

RNA, like DNA, is formed by a polymerization reaction (nucleotides connected) to make a large chain (polymer). It produces a molecule of water and has a phosphodiester covalent bond like DNA. RNA is single-stranded while DNA is double-stranded because it does not have hydrogen bonds with another strand.

what is DNA as a double helix?

DNA double-strands are in a helical shape, with each strand running anti-parallel to each other, linked together by complementary base pairing, bonded by weak hydrogen bonds.

what are similarities of DNA and RNA?

• composed of nucleotides

• backbones joined by phosphodieter bonds

• contains a phosphate group

what are the differences of DNA and RNA?

• thymine is present in DNA, uracil (different base) is in RNA.

• double stranded vs single stranded

• DNA deoxyribose sugar as only H, ribose in RNA has OH

• DNA in the nucleus only vs RNA throughout cells

what is the role of complementary base pairing in allowing genetic info to be replicated & expressed?

• Base pairing: A-T (2 H-bonds) and C-G (3 H-bonds) → only correct pairs fit stably.

• Many H-bonds = stable double helix; individual H-bonds = easy strand separation.

• Ensures accurate DNA replication (only correct bases bond).

• Ensures mRNA matches the DNA template during transcription.

what are the diversities of possible DNA base sequences and the limitless capacity of DNA for storing information?

DNA uses 4 nitrogenous bases (A, T, C, G). The possible sequences grow as 4ⁿ (where n = sequence length), giving huge variation. Since the double helix is only 2 nm wide, DNA stores vast information in a very compact space.

how is the conservation of the genetic code across all life forms evidence of universal common ancestry?

There are 64 codons in the genetic code, coding for 20 amino acids or stop signals. Since codons have the same meaning in almost all organisms, the genetic code is universal (with rare exceptions). This universality is strong evidence that all life shares a common ancestor.

what is the importance of the directionality of RNA and DNA?

DNA and RNA have directionality: bases are always read in the 5' → 3' direction. This ensures accuracy so the same DNA or protein is produced each time. During replication, DNA polymerase reads the template 3' → 5' and adds new nucleotides to the 3' end. During transcription, RNA polymerase also reads DNA 3' → 5'. During translation, ribosomes move along mRNA in the 5' → 3' direction.

what is purine-to pyrimidine bonding as a component of DNA helix stability?

Each base pair in DNA has one purine and one pyrimidine, making the distance between the sugar-phosphate backbones constant. This maintains the uniform, stable structure of the DNA double helix. Length "mismatches" can be detected to ensure proper pairing.

what is the structure of a nucleosome?

DNA wraps around eight histone proteins twice. Bacteria do not have histone proteins.

H histone (protein): Binds DNA to the nucleosome core and helps package chromosomes for cell division.

Linker DNA: A short DNA section between adjacent nucleosomes.

what was the Hersey-Chase Experiment?

label phage → bacteria → blender → pellet vs. liquid = After infection and separation, only phosphorus (DNA) entered bacteria. This proved DNA is the genetic material.

what is the importance of radioisotopes?

They allowed DNA (³²P) and protein (³⁵S) to be labeled separately (in HS experiment), making it clear that only DNA entered bacteria. This shows how technological advances enable new discoveries in science.

what is the significance of Chargraffs Data?

Tetranucleotide hypothesis: Proposed that nucleotide bases repeated, meaning that there were equal amounts of each base (C, G, A, and T). Chargraff's data found that the number of A = T and the number of C = G, and base number ratios vary between species, falsifying the tetranucleotide hypothesis.