Cell Communication & Cell Cycle

1.1.3

Explain how instructions in DNA lead to cell differentiation and result in cells specialized to perform specific functions in multicellular organisms

Unpacked:

• Compare a variety of specialized cells and understand how the functions of these cells vary. (Possible examples could include nerve cells, muscle cells, blood cells, sperm cells, xylem and phloem.)

• Explain that multicellular organisms begin as undifferentiated masses of cells and that variation in DNA expression and gene activity determines the differentiation of cells and ultimately their specialization.

o During the process of differentiation, only specific parts of the DNA are activated; the parts of the DNA that are activated determine the function and specialized structure of a cell.

o Because all cells contain the same DNA, all cells initially have the potential to become any type of cell; however, once a cell differentiates, the process cannot be reversed.

o Nearly all of the cells of a multicellular organism have exactly the same chromosomes and DNA.

o Different parts of the genetic instructions are used in different types of cells, influenced by the cell's environment and past history.

• Recall that chemical signals may be released by one cell to influence the development and activity of another cell.

• Identify stem cells as unspecialized cells that continually reproduce themselves and have, under appropriate conditions, the ability to differentiate into one or more types of specialized cells.

o Embryonic cells which have not yet differentiated into various cell types are called embryonic stem cells.

o Stem cells found in organisms, for instance in bone marrow, are called adult stem cells.

o Scientists have recently demonstrated that stem cells, both embryonic and adult, with the right laboratory culture conditions, differentiate into specialized cells.

Note: It is not essential for students to understand the details of how the process of transcriptional regulation in a cell produces specific proteins, which results in cell differentiation.

1.2.2

Analyze how cells grow and reproduce in terms of interphase, mitosis and cytokinesis.

Unpacked:

• Outline the cell cycle – Growth1, Synthesis, Growth2, Mitosis, and Cytokinesis.

• Recognize mitosis as a part of asexual reproduction. (middle school review)

• Organize diagrams of mitotic phases and describe what is occurring throughout the process.

Note: When students learn about meiosis (Bio.3.2.1), they should compare it to the process of mitosis.

3.1.1

Explain the double-stranded, complementary nature of DNA as related to its function in the cell.

Unpacking:

• Develop a cause-and-effect model relating the structure of DNA to the functions of replication and protein synthesis:

o The structure of DNA is a double helix or “twisted ladder” structure. The sides are composed of alternating phosphate-sugar groups and “rungs of the DNA ladder” are composed of complementary nitrogenous base pairs (always adenine, A, to thymine, T, and cytosine, C, to guanine, G) joined by weak hydrogen bonds.

o The sequence of nucleotides in DNA codes for proteins, which is central key to cell function and life.

o Replication occurs during the S phase of the cell cycle and allows daughter cells to have an exact copy of parental DNA.

o Cells respond to their environments by producing different types and amounts of protein.

o With few exceptions, all cells of an organism have the same DNA but differ based on the expression of genes.

• Infer the advantages (injury repair) and disadvantages (cancer) of the overproduction, underproduction or production of proteins at the incorrect times.

3.2.1

Explain the role of meiosis in sexual reproduction and genetic variation

Unpacking:

• Recall the process of meiosis and identify process occurring in diagrams of stages. (middle school review) Note: Students are not expected to memorize the names of the steps or the order of the step names.

• Infer the importance of the genes being on separate chromosomes as it relates to meiosis.

• Explain how the process of meiosis leads to independent assortment and ultimately to greater genetic diversity.

• Exemplify sources of genetic variation in sexually reproducing organisms including crossing over, random assortment of chromosomes, gene mutation, nondisjunction, and fertilization.

• Compare meiosis and mitosis including type of reproduction (asexual or sexual), replication and separation of DNA and cellular material, changes in chromosome number, number of cell divisions, and number of cells produced in a complete cycle.