Information storage and transfer

Information storage and flow are dynamic and interactive

Students should be able to explain and apply core concepts of biological information, including the genome, the manner in which the information it contains is encoded and translated, and the mechanisms by which it is transmitted and maintained across generations.

The learning goals below are categorized as introductory A, intermediate B and upper C.

1. The genome

A genome is an organism’s complete set of DNA, including all of its genes. Each genome contains all of the information needed to build and maintain that organism. Some noncoding sequences enable our cells to produce different amounts of proteins at different times. For example, control sequences contain instructions to tell the cell how to switch genes on and off. Other noncoding sequences are part of genes but do not directly code for proteins. These are thought to help the cell generate a number of different proteins from one gene. More than half of the DNA in our genome is made up of repeated sequences, which appear to stabilize chromosomes; noncoding regions may have a role in spacing out the coding sequences so that they can be activated independently.

Associated learning goals

  • Students should be able to define what a genome consists of and how the information in the various genes and other sequence classes within each genome is used to store and express genetic information. A
  • Students should be able to discuss how the genome is organized and packaged in prokaryotes and eukaryotes. A
  • Students should be able to discuss tools used to study expression, conservation and structure of an organism at the genome level. B
  • Students should be able to explain the role of repetitive and non-repetitive DNA and how its relative abundance varies from prokaryotes to eukaryotes. B

2. Information in the gene: nucleotide sequence to biological function

The information contained in the nucleotide sequence of a genome is organized into various elements, including coding regions, which contain three base codons coding for amino acids, which are transcribed to messenger RNA. The messenger RNA is translated to give the primary sequence of a protein and regulatory elements. The transcribed coding region for a given protein may contain introns and exons in eukaryotic cells. The amino acid sequence of a protein gives rise to biological function through stably folded regions and/or intrinsically disordered regions.

Associated learning goals

  • Students should be able to explain the central dogma of biology and relate the commonality of the process to all of life. A
  • Students should be able to explain the process of gene regulation connecting how extracellular signals can result in a change of gene expression. A
  • Students should be able to discuss how genes are organized and contrast the different approaches used in prokaryotic and eukaryotic organisms. B
  • Students should be able to explain how mRNA processing occurs and how splicing affects the diversity of gene products in eukaryotic organisms. B

3. Genome transmission from one generation to the next

The primary concern of cell division is the maintenance of the original cell's genome. The genomic information that is stored in chromosomes must be replicated, and the duplicated genome must be separated cleanly between cells. Somatic cell lines are diploid (2n chromosome complement), and mitotic division normally results in two daughter cells, each with chromosomes and genes identical to those of the parent cell. Germline cells, called gametes, are haploid (having the haploid or the n chromosomal complement) and reproduce by meiosis.

Associated learning goals

  • Students should be able to explain the differences of mitosis and meiosis and relate them to the process of cellular division. A
  • Students should be able to illustrate how DNA is replicated A and genes are transmitted from one generation to the next in multiple types of organisms including bacteria, eukaryotes, viruses and retroviruses. B
  • Students should be able to apply the concepts of segregation and independent assortment to traits inherited from parent to offspring B and discuss how they increase genetic variation. C

4. Genome maintenance

Throughout its lifetime, the DNA in a cell is under constant metabolic and environmental assault leading to damage. The ultraviolet (UV) component of sunlight, ionizing radiation and numerous genotoxic chemicals, including the (by)products of normal cellular metabolism (e.g. reactive oxygen species such as superoxide anions, hydroxyl radicals and hydrogen peroxide), constitute a permanent enemy to DNA integrity. Hydrolysis of nucleotide residues leaves non-instructive abasic sites. Spontaneous or induced deamination of cytosine, adenine, guanine or 5-methylcytosine converts these bases to the miscoding uracil, hypoxanthine, xanthine and thymine, respectively. Left unchecked, the resulting genomic instability initiates cancer and other age-related disorders. Inherited or acquired deficiencies in genome maintenance systems contribute significantly to the onset of cancer. Over time, DNA accumulates changes that activate proto-oncogenes and inactivate tumor-suppressor genes. Cells have evolved nucleotide- and base-excision repair mechanisms, homologous recombination, end joining, mismatch repair and telomere metabolism as mechanisms to maintain the integrity of the genome.

Associated learning goals

  • Students should be able to state how the cell ensures high fidelity DNA replication A and identify instances where the cell employs mechanism for damage repair. B
  • Students should be able to explain what a mutation is at the molecular level, how it arises A and how it could potentially affect the organism from gene expression to fitness. B
  • Students should be able to construct relationships between chromosome and cellular structures (e.g. telomere, centromeres and centrosomes) and explain how these structures are responsible for and/or involved in genomic stability. B
  • Students should be able to relate how the cell cycle and genome maintenance are coordinated and how disruptions in this coordination could affect the organism. C
  • Students should be able to list events that result in genomic instability and explain how the cell responds to restore order and stability. C