Biological and Biochemical Foundations of Living Systems: Content Category 1B

Transmission of genetic information from the gene to the protein
Biomolecules and biomolecular assemblies interact in specific, highly-regulated ways to transfer sequence information between biopolymers in living organisms. By storing and transferring biological information, DNA and RNA enable living organisms to reproduce their complex components from one generation to the next. The nucleotide monomers of these biopolymers, being joined by phosphodiester linkages, form a polynucleotide molecule with a “backbone” composed of repeating sugar-phosphate units and “appendages” of nitrogenous bases. The unique sequence of bases in each gene provides specific information to the cell.

DNA molecules are composed of two polynucleotides that spiral around an imaginary axis, forming a double helix. The two polynucleotides are held together by hydrogen bonds between the paired bases and van der Waals interactions between the stacked bases. The pairing between the bases of two polynucleotides is very specific, and its complementarity allows for a precise replication of the DNA molecule.

The DNA inherited by an organism leads to specific traits by dictating the synthesis of the biomolecules (RNA molecules and proteins) involved in protein synthesis. While every cell in a multicellular organism inherits the same DNA, its expression is precisely regulated such that different genes are expressed by cells at different stages of development, by cells in different tissues, and by cells exposed to different stimuli.

The topics included in this category concern not only the molecular mechanisms of the transmission of genetic information from the gene to the protein (transcription and translation), but also the biosynthesis of the important molecules and molecular assemblies that are involved in these mechanisms. The control of gene expression in prokaryotes and eukaryotes is also included.

Broadly speaking, the field of biotechnology uses biological systems, living organisms, or derivatives thereof, to make or modify products or processes for specific use. The biotechnological techniques emphasized in this category, however, are those that take advantage of the complementary structure of double-stranded DNA molecules to synthesize, sequence, and amplify them, and to analyze and identify unknown polynucleotide sequences. Included within this treatment of biotechnology are those practical applications which directly impact humans, such as medical applications, human gene therapy, and pharmaceuticals.

Content in this category covers the biopolymers, including ribonucleic acid (RNA), deoxyribonucleic acid (DNA), proteins, and the biochemical processes involved in carrying out the transfer of biological information from DNA.

Topic Level Key:

The abbreviations found in parentheses indicate the course(s) in which undergraduate students at many colleges and universities learn about the topics and associated subtopics. The course abbreviations are:

BC = first-semester biochemistry
BIO = two-semester sequence of introductory biology

Please note topics that appear on multiple content lists will be treated differently. Questions will focus on the topics as they are described in the narrative for the content category.
Nucleic Acid Structure and Function (BIO, BC)
  • Description
  • Nucleotides and nucleosides
    • Sugar phosphate backbone
    • Pyrimidine, purine residues
  • Deoxyribonucleic acid (DNA): double helix, Watson–Crick model of DNA structure
  • Base pairing specificity: A with T, G with C
  • Function in transmission of genetic information (BIO)
  • DNA denaturation, reannealing, hybridization
DNA Replication (BIO)
  • Mechanism of replication: separation of strands, specific coupling of free nucleic acids
  • Semi-conservative nature of replication
  • Specific enzymes involved in replication
  • Origins of replication, multiple origins in eukaryotes
  • Replicating the ends of DNA molecules
Repair of DNA (BIO)
  • Repair during replication
  • Repair of mutations
Genetic Code (BIO)
  • Central Dogma: DNA → RNA → protein
  • The triplet code
  • Codon–anticodon relationship
  • Degenerate code, wobble pairing
  • Missense, nonsense codons
  • Initiation, termination codons
  • Messenger RNA (mRNA)
Transcription (BIO)
  • Transfer RNA (tRNA); ribosomal RNA (rRNA)
  • Mechanism of transcription
  • mRNA processing in eukaryotes, introns, exons
  • Ribozymes, spliceosomes, small nuclear ribonucleoproteins (snRNPs), small nuclear RNAs (snRNAs)
  • Functional and evolutionary importance of introns
Translation (BIO)
  • Roles of mRNA, tRNA, rRNA
  • Role and structure of ribosomes
  • Initiation, termination co-factors
  • Post-translational modification of proteins
Eukaryotic Chromosome Organization (BIO)
  • Chromosomal proteins
  • Single copy vs. repetitive DNA
  • Supercoiling
  • Heterochromatin vs. euchromatin
  • Telomeres, centromeres
Control of Gene Expression in Prokaryotes (BIO)
  • Operon Concept, Jacob–Monod Model
  • Gene repression in bacteria
  • Positive control in bacteria
Control of Gene Expression in Eukaryotes (BIO)
  • Transcriptional regulation
  • DNA binding proteins, transcription factors
  • Gene amplification and duplication
  • Post-transcriptional control, basic concept of splicing (introns, exons)
  • Cancer as a failure of normal cellular controls, oncogenes, tumor suppressor genes
  • Regulation of chromatin structure
  • DNA methylation
  • Role of non-coding RNAs
Recombinant DNA and Biotechnology (BIO)
  • Gene cloning
  • Restriction enzymes
  • DNA libraries
  • Generation of cDNA
  • Hybridization
  • Expressing cloned genes
  • Polymerase chain reaction
  • Gel electrophoresis and Southern blotting
  • DNA sequencing
  • Analyzing gene expression
  • Determining gene function
  • Stem cells
  • Practical applications of DNA technology: medical applications, human gene therapy, pharmaceuticals, forensic evidence, environmental cleanup, agriculture
  • Safety and ethics of DNA technology

To support your studies, see the following video tutorials below from the Khan Academy MCAT Collection. The videos and associated questions were created by the Khan Academy in collaboration with the AAMC and the Robert Wood Johnson Foundation.