Nucleic Acids: Structure and Composition of DNA & RNA

These vocabulary flashcards cover essential terms related to DNA and RNA structure, composition, replication, conformations, and functional RNA types, providing a comprehensive review of the lecture content.

DNA (Deoxyribonucleic Acid)

A double-helical polymer of nucleotides that stores genetic information in almost all living organisms.

Nucleotide

The basic building block of nucleic acids, consisting of a nitrogenous base, a pentose sugar, and a phosphate group.

Purine

A double-ring nitrogenous base; adenine (A) and guanine (G) are purines.

Pyrimidine

A single-ring nitrogenous base; thymine (T), cytosine (C), and uracil (U) are pyrimidines.

Deoxyribose

The five-carbon sugar in DNA that lacks an oxygen atom at the 2′ carbon.

Phosphodiester Bond

The linkage between the 5′ phosphate of one nucleotide and the 3′ hydroxyl of the next, forming the sugar-phosphate backbone.

Double Helix

The right-handed, spiral structure of two complementary DNA strands coiled around a common axis.

Antiparallel Strands

The orientation in which one DNA strand runs 5′→3′ while the complementary strand runs 3′→5′.

Complementary Base Pairing

Specific hydrogen-bonding between A–T (2 bonds) and G–C (3 bonds) that maintains helix uniformity.

Chargaff's Rule

In double-stranded DNA, [A]=[T] and [G]=[C]; total purines equal total pyrimidines.

Major Groove

The wider groove of the DNA helix that serves as a primary binding site for many DNA-binding proteins.

Minor Groove

The narrower groove of the DNA helix that also participates in protein and drug interactions.

Base Stacking

Hydrophobic, van der Waals interactions between adjacent bases that stabilize the DNA helix.

Hyperchromic Shift

Increase in UV absorbance at 260 nm when DNA strands separate during denaturation.

Hypochromic Shift

Decrease in UV absorbance at 260 nm when single strands reassociate into double-stranded DNA.

Tm (Melting Temperature)

The temperature at which half of a DNA sample is denatured (shows 50 % hyperchromicity).

Semi-Conservative Replication

DNA replication mechanism in which each daughter molecule contains one parental and one newly synthesized strand.

B-DNA

The most common, right-handed DNA conformation in cells; 10 base pairs per turn and 3.4 nm pitch.

A-DNA

A right-handed, dehydrated DNA form with 11 base pairs per turn, 2.8 nm pitch, and C3′-endo sugar pucker.

Z-DNA

A left-handed DNA helix with a zig-zag backbone, 12 base pairs per turn, and found in GC-rich, high-salt regions.

Sugar Pucker (C2′-endo)

Conformation of the deoxyribose ring typical of B-DNA.

Sugar Pucker (C3′-endo)

Conformation of the ribose/deoxyribose ring typical of A-DNA and RNA helices.

RNA (Ribonucleic Acid)

Single-stranded nucleic acid with ribose sugar and uracil that functions in coding, decoding, regulation, and catalysis.

mRNA (Messenger RNA)

RNA that carries genetic information from DNA to ribosomes for protein synthesis.

tRNA (Transfer RNA)

Adapter RNA that delivers specific amino acids to the ribosome via anticodon-codon pairing.

rRNA (Ribosomal RNA)

Structural and catalytic RNA component of ribosomes that forms peptide bonds during translation.

snRNA (Small Nuclear RNA)

RNA that partners with proteins in spliceosomes to remove introns from pre-mRNA.

snoRNA (Small Nucleolar RNA)

RNA guiding chemical modifications such as methylation on rRNA, tRNA, and snRNA in the nucleolus.

miRNA (MicroRNA)

~21–25 nt non-coding RNA that regulates gene expression by mRNA degradation or translational repression.

siRNA (Small Interfering RNA)

Double-stranded RNA that triggers sequence-specific mRNA degradation in RNA interference pathways.

lncRNA (Long Non-Coding RNA)

RNA longer than 200 nt that regulates gene expression at multiple levels, including chromatin remodeling.

Retrovirus

RNA virus that uses reverse transcriptase to synthesize DNA from its RNA genome (e.g., HIV).

Reverse Transcriptase

Viral enzyme that converts RNA into complementary DNA during retroviral replication.

Tobacco Mosaic Virus (TMV)

Plant virus whose RNA alone is infectious, demonstrating RNA can serve as genetic material.

Ribozyme

RNA molecule with catalytic activity, such as rRNA peptidyl transferase.

Right-Handed Helix

Helical structure twisting clockwise; characteristic of A-DNA and B-DNA.

Left-Handed Helix

Helical structure twisting counter-clockwise; characteristic of Z-DNA.

Base Pair

Two complementary nucleobases (A-T or G-C) connected by hydrogen bonds in DNA or RNA.