Molecular Biology Notes: DNA, RNA, Replication, Transcription, Translation, and Operons (copy)

DNA

A double helix made of two long polynucleotide chains running anti-parallel, containing nucleotides with a phosphate group, deoxyribose sugar, and nitrogenous bases.

Nucleotide

The basic building block of DNA and RNA, consisting of a phosphate group, a sugar (deoxyribose in DNA, ribose in RNA), and a nitrogenous base.

Phosphate Group

A chemical group consisting of a phosphorus atom bonded to four oxygen atoms; part of the backbone of DNA and RNA.

Nitrogenous Base

The part of a nucleotide that varies between different nucleotides; in DNA, the bases are adenine (A), thymine (T), guanine (G), and cytosine (C).

Phosphodiester Bond

The bond formed between the phosphate group of one nucleotide and the sugar of another during DNA and RNA synthesis.

Double Helix

The structure of DNA, consisting of two strands coiled around each other.

A-T Pairing

In DNA, adenine (A) pairs with thymine (T) via two hydrogen bonds.

G-C Pairing

In DNA, guanine (G) pairs with cytosine (C) via three hydrogen bonds.

Euchromatin

A less condensed form of chromatin that is transcriptionally active.

Heterochromatin

A more condensed form of chromatin that is transcriptionally inactive.

RNA Polymerase

An enzyme that synthesizes RNA from a DNA template during transcription.

mRNA

Messenger RNA; the RNA copy of a gene that is translated into protein.

tRNA

Transfer RNA; carries amino acids to ribosomes for protein synthesis.

Ribosome

A cellular structure composed of rRNA and proteins that synthesizes proteins from mRNA.

Okazaki Fragments

Short DNA fragments synthesized on the lagging strand during DNA replication.

Semi-conservative Replication

A process of DNA replication where each new DNA molecule consists of one old strand and one new strand.

Constitutive Gene

A gene that is continuously expressed under normal cellular conditions.

Facultative Gene

A gene that is expressed only under specific conditions depending on the cell's requirements.

Operon

A cluster of genes that are co-transcribed from a single promoter as a polycistronic mRNA.

Attenuation

A regulatory mechanism in prokaryotic operons, where premature termination of transcription occurs depending on the availability of specific metabolites.

Quorum Sensing

A process where bacteria coordinate behavior based on the density of their population, often involving signaling molecules.