Genetics: The Molecular Basis of Inheritance

Nucleotide

The fundamental unit of life's genetic code, consisting of a five-carbon sugar, a phosphate group, and a nitrogenous base.

Deoxyribose

The five-carbon sugar found in DNA that lacks an oxygen at the 2' carbon.

Ribose

The five-carbon sugar found in RNA that has an -OH group at the 2' carbon.

Phosphate Group

The chemical group attached to the 5' carbon of the sugar in a nucleotide, giving DNA its negative charge.

Nitrogenous Base

One of the components of a nucleotide, which can be a purine or pyrimidine.

Purines

Nitrogenous bases with a double-ring structure; examples include adenine and guanine.

Pyrimidines

Nitrogenous bases with a single-ring structure; include cytosine, thymine (DNA only), and uracil (RNA only).

Complementary Strands

The two strands of DNA that are paired according to base pairing rules, with adenine pairing with thymine and guanine pairing with cytosine.

Antiparallel

Describes the opposite orientation of the two strands of DNA, running in 5' to 3' and 3' to 5' directions.

Chargaff's Rules

Rules that state adenine pairs with thymine and guanine pairs with cytosine, determining base pairing in DNA.

Prokaryotes

Single-celled organisms that typically have a circular chromosome found in a nucleoid region.

Eukaryotes

Organisms composed of cells that contain a nucleus and multiple linear chromosomes.

Histones

Positively charged proteins around which DNA wraps to form nucleosomes.

Nucleosomes

The structure formed by DNA wrapping around histones, resembling 'beads on a string'.

Euchromatin

Loosely packed DNA that is active and available for transcription.

Heterochromatin

Tightly packed DNA that is generally inactive.

Semiconservative Replication

The process of DNA replication in which each new molecule consists of one original strand and one newly synthesized strand.

Helicase

The enzyme that unzips the double helix of DNA by breaking hydrogen bonds during replication.

Topoisomerase

An enzyme that relieves the strain and supercoiling ahead of the replication fork by cutting and rejoining DNA strands.

Primase

An enzyme that synthesizes a short RNA primer for DNA polymerase to initiate DNA replication.

DNA Polymerase III

The enzyme that adds DNA nucleotides to the 3' end of the growing DNA strand.

DNA Polymerase I

The enzyme that removes RNA primers and replaces them with DNA during replication.

Ligase

An enzyme that joins DNA fragments together by forming phosphodiester bonds.

Leading Strand

The DNA strand synthesized continuously toward the replication fork during DNA replication.

Lagging Strand

The DNA strand synthesized discontinuously away from the replication fork in short segments called Okazaki fragments.

Telomeres

Repetitive non-coding sequences at the ends of linear chromosomes that protect against deterioration.

Transcription

The process of synthesizing RNA using a DNA template.

RNA Polymerase

The enzyme that synthesizes RNA during the process of transcription.

Promoter

A region where RNA polymerase binds to initiate transcription; often contains the TATA box in eukaryotes.

Elongation

The phase in transcription where RNA polymerase unwinds DNA and adds RNA nucleotides to the growing strand.

Splicing

The process of removing introns and joining exons together in pre-mRNA processing.

Codon

A three-nucleotide sequence on mRNA that codes for a specific amino acid.

Start Codon

The codon AUG, which signals the start of translation and codes for Methionine.

Stop Codons

Codons (UAA, UAG, UGA) that signal the termination of translation.

mRNA

The type of RNA that carries the genetic message from DNA to the ribosome for protein synthesis.

tRNA (Transfer RNA)

The type of RNA that brings amino acids to the ribosome and contains an anticodon.

Ribosome

The cellular machinery that facilitates the translation of mRNA into proteins, composed of rRNA and proteins.

Operon

A group of related genes regulated together under a single promoter in prokaryotes.

Repressible Operon

An operon that is usually active (ON) and can be inhibited (turned OFF) by a corepressor.

Inducible Operon

An operon that is usually inactive (OFF) and can be activated (turned ON) by an inducer.

Epigenetics

The study of changes in gene expression not involving alterations to the DNA sequence.

Mutations

Changes in the genetic material of a cell that can affect gene function.

Point Mutations

Mutations that involve a single base change in the DNA sequence.

Frameshift Mutations

Mutations caused by insertions or deletions of nucleotides that shift the reading frame.

PCR (Polymerase Chain Reaction)

A technique used to amplify specific DNA segments rapidly.

CRISPR-Cas9

A gene-editing technology that allows scientists to modify specific DNA sequences with high precision.