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1.3Unit 1 — Cell Biology

DNA and the Production of Proteins

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Section 1 of 4DNA structure and the genetic code

generalized amino acid structure
DNA Base Pairing
DNA Base Pairing
DNA Nucleotide Structure
DNA Nucleotide
DNA Nucleotide
DNA Nucleotide
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DNA double helix structure
DNA Base Pairing and Hydrogen Bonds
DNA and RNA nucleotide comparison
Structure of DNA and complementary base pairs
DNA base pairing (A-T, C-G)
DNA Base Sequence Comparison
Genetic Code Chart
Bioinformatics: DNA, mRNA, proteins and databases
Structure of RNA
Structure of RNA
Nucleotide and DNA polynucleotide strand structure
Substitution mutation changes one codon/amino acid
DNA Nucleotide Structure
DNA structure and the genetic code
DNA (Deoxyribonucleic acid)
  • Double-stranded molecule twisted into a double helix.
  • Composed of repeating nucleotide units with a sugar-phosphate backbone and nitrogenous bases facing inwards.
  • Carries the genetic instructions for making proteins needed by all living organisms.
Complementary base pairing rules
  • Adenine (A) pairs strictly with Thymine (T).
  • Cytosine (C) pairs strictly with Guanine (G).
  • Bases are held together by weak hydrogen bonds.
The genetic code
  • The sequence of bases along a DNA strand specifies the sequence of amino acids in a polypeptide chain.
  • Every triplet of bases (a codon) codes for one specific amino acid.
  • The order of amino acids determines the 3D shape and specific function of the resulting protein.

Section 2 of 4The role of mRNA in protein synthesis

Translation at the ribosome (protein synthesis)
DNA to PROTEIN: Transcription and Translation Simulation
nuclear envelope dna isis rna processing peon
DNA Transcription and Translation — Full Simulation
Amino Acids to Proteins — Step-by-Step Simulation
Amino Acids to Protein
Amino Acids to Proteins — Step-by-Step Simulation
Transcription in the nucleus
Transcription in the nucleus (DNA to mRNA)
Transcription in the nucleus (DNA to mRNA)
Genetic code is degenerate (leucine codons)
Ribosome Subunits and mRNA
Ribosome Subunits and mRNA
Ribosome Translation
Translation at the Ribosome
Translation at the Ribosome — Animated 2D Simulation
Ribosome Translation
Translation at the ribosome
Translation: ribosome reading mRNA codons to build a protein
The role of mRNA in protein synthesis
DNA is confined to the nucleus and is too large to pass through nuclear pores to the cytoplasm.
Messenger RNA (mRNA)
  • Single-stranded molecule complementary to one DNA strand.
  • Synthesised in the nucleus during transcription (in RNA, Uracil (U) pairs with Adenine instead of Thymine).
  • Carries a complementary copy of the genetic code from DNA in the nucleus out through nuclear pores to a ribosome in the cytoplasm.
Assembly at the ribosome (translation)
  • The ribosome reads the mRNA base sequence in triplets.
  • Amino acids are brought in and joined in the specified correct order by peptide bonds, assembling the completed protein.

Section 3 of 4Key terms

TermMeaning
Double helixThe structural shape of double-stranded DNA formed by two anti-parallel helical strands.
Base pairComplementary nitrogenous bases (A with T, and C with G) linked by hydrogen bonds.
mRNAMessenger RNA; a single-stranded molecule carrying genetic code from nucleus to ribosome.
RibosomeThe cytoplasmic organelle where amino acids are linked into proteins according to mRNA instructions.

Section 4 of 4Exam technique

Avoid these mistakes
Writing Uracil in DNA — Uracil is present ONLY in RNA; DNA contains Thymine.
Saying DNA leaves the nucleus — DNA remains permanently in the nucleus; only mRNA travels from nucleus to ribosomes.
البيولوجيا الجزيئية — أسرار تخليق البروتين مقارنة اتجاهات الإنزيمات

قواعد اتجاهات البلمرة ومضاد الكودون

  • إنزيم بلمرة RNA: يبني دائماً في الاتجاه 5′ → 3′، ويقرأ شريط القالب فقط في الاتجاه 3′ → 5′.
  • كودون البدء: AUG يقابله مضاد كودون UAC ويشفر للميثيونين أول حمض أميني.
  • كودونات الوقف: UAA, UAG, UGA ليس لها tRNA يقابلها، بل يرتبط بها بروتين عامل الإطلاق (Release Factor) لإنهاء الترجمة.