Molecular Library

Look up the science behind every challenge.

Deoxyribonucleic acid — the double-helix molecule that stores genetic information using bases A, T, C, G.

Two antiparallel strands held together by complementary base pairs: A–T and C–G. Each strand is a template for replication.

Ribonucleic acid — a single-stranded copy of genetic information that uses Uracil (U) instead of Thymine (T).

Messenger RNA (mRNA) carries instructions from DNA to the ribosome. Transcription pairing: A→U, T→A, C→G, G→C.

The rules that keep the genetic code accurate.

DNA: A–T, C–G. RNA complement: A–U, C–G. These rules make replication and transcription reliable.

Copying DNA before cell division.

Strands separate, complementary nucleotides are added to each template, and two identical double helices form.

Making mRNA from a DNA template.

RNA polymerase reads the template strand and builds complementary mRNA, which then leaves the nucleus.

Building a protein from mRNA.

Ribosomes read mRNA in codons (groups of 3). tRNA brings matching amino acids until a stop codon ends the chain.

Three-base units that specify amino acids.

A codon on mRNA pairs with a complementary tRNA anticodon. AUG is the start codon; UAA, UAG, UGA are stop codons.

Nuclear division that produces two identical diploid cells for growth and repair.

Phases: prophase, metaphase, anaphase, telophase, then cytokinesis. Chromosome number stays 2n → 2n.

Two divisions that produce haploid gametes with genetic diversity.

Homologs pair and may cross over in Prophase I. Meiosis I reduces 2n → n; Meiosis II separates sister chromatids.

How alleles pass from parents to offspring.

Genotype is the allele pair; phenotype is the trait. Dominant alleles mask recessive ones in heterozygotes. Punnett squares predict ratios.

A change in DNA sequence that can alter proteins or stay silent.

Substitutions, insertions, and deletions create variation. Repair systems catch many errors; remaining changes feed evolution and sometimes disease.

Change in allele frequencies in a population over generations.

Mutation and recombination create variation; natural selection, drift, and gene flow change which alleles become common.