Scope, Sequence, and Coordination

A Framework for High School Science Education

Based on the National Science Education Standards


The Watson-Crick Model of DNA Structure

DNA, RNA and Genetic Engineering
Cells store and use information to guide their functions. The genetic information stored in DNA is used to direct the synthesis of the thousands of proteins that each cell requires.

Cells can differentiate, and complex multicellular organisms are formed as a highly organized arrangement of differentiated cells. In the development of these multicellular organisms, the progeny from a single cell form an embryo in which the cells multiply and differentiate to form the many specialized cells, tissues and organs that comprise the final organism. This differentiation is regulated through the expression of different genes.

Cell functions are regulated. Regulation of cells occurs both through changes in the activity of the functions performed by proteins and through the selective expression of individual genes. This regulation allows cells to respond to their environment and to control and coordinate cell growth and division.


Further Description:

The language of life is based upon the chemical composition of DNA. This macromolecule spells out codes that dictate messages which are translated by cells into the traits of organisms. Messages are in the form of RNA, a single-stranded nucleic acid. RNA carries the messages in the form of triplet-sequence codons. These sequences are composed of specific chemical molecules called nitrogenous basesCadenine, guanine, cytosine, and uracil. The arrangement of these bases into triple combinations results in the production of 64 possible codons. These sequences of three bases correspond to specific amino acids. Amino acids are the building blocks of proteins, and proteins are expressed as traits. In the cell the process of building proteins is controlled by DNA, which is transcribed to form RNA, which in turn is translated to form proteins. All organisms are made up of thousands of characteristics or traits coded for by DNA.

Control of cellular function is generated by genetic components within the nucleus of each cell. This control is indirect: the nucleus sends messages into the cytoplasm where they are translated into proteins. Proteins then perform thousands of chemical reactions in the cell.

The production of all proteins is regulated by the nucleus of each cell. It is believed that a gene regulatory system in the nucleus can "switch on" or "switch off" protein production; therefore, only essential proteins will be produced for needed activities of the cell.

Development is the process whereby a fertilized egg divides and differentiates into tissues, organs, organ systems, and ultimately the organism. The process of development is different in animals and plants. In animals the development of the embryo can be divided into the following stages: cleavage, germ layer formation, and organ development. By the action of cell division the fertilized egg will divide into masses of cells that will then develop into discrete germ layers. Germ layers will further develop into specific organs and organ systems. This complex process is under the control of gene mechanisms of the female parent as well as those of the developing embryo.

In higher plants the differentiation of the zygote is activated by hormones produced in the embryo. Through cell division embryonic regions will form the first root, stem, and leaf structures. Upon germination the embryo will again begin to divide and differentiate into a seedling.


Concepts Needed:

Grade 9

Growth, mitosis

Grade 10

Codes, characteristics, traits, nucleus, mitosis

Grade 11

Replication, double helix, DNA, codon, polymer, translation, transcription, nitrogen bases, triplets, templates, proteins, amino acids, RNA, protein synthesis

Grade 12

Intron, exon, permease, operator gene, regulation gene, repressor protein, inducer substance, structural gene, differentiation, fertilization, germ layers


Empirical Laws or Observed Relationships:

The genetic code, base pair complementarity, feedback mechanisms, the process of developmental onset, semiconservative replication, chronologically triggered development, embryo germ layer processes, organogenesis


Theories or Models:

One gene-one enzyme theory, gene theory, operon theory, genetic control of cell processes


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Micro-Unit Description:

The Watson-Crick Model of DNA Structure
Students should understand the universality of the DNA molecule. They should become familiar with the Watson-Crick Model of DNA structure, recognizing the significance of the nucleotide sequence in that it directs the activities of cells and determines the traits of the organism.Students should examine the relationship between DNA, genes, chromosomes, and inheritable traits.


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