Download 10.1 Cell growth and division Lesson Objectives Explain the

10.1 Cell growth and division
Lesson Objectives
Explain the problems that growth causes for cells.
Lesson Summary
Limits to Cell Size There are two main reasons why cells divide:
Information “overload”: The larger a cell gets, the more demands it places on its DNA. Eventually,
the cell’s DNA cannot meet the cell’s needs.
Exchange of materials: Cells take in nutrients and eliminate wastes through the cell membrane.
 The larger a cell’s volume, the more materials it needs to function and the more waste it creates.
 A cell’s volume increases at a faster rate than its surface area. As a cell grows, its surface-area-tovolume ratio becomes too small.
 The larger a cell gets, the harder it is for enough materials to move across its cell
membrane.
Cell division solves the information overload and materials exchange problems.
10.2 The process of cell division
Lesson Objectives
Describe the role of chromosomes in cell division.
Name the main events of the cell cycle.
Describe what happens during the four phases of mitosis.
Describe the process of cytokinesis
Lesson Summary
Chromosomes Packages of DNA called chromosomes hold a cell’s genetic information.
Prokaryotic chromosomes consist of a single, circular strand of DNA.
Eukaryotic chromosomes are highly organized structures.
 The DNA winds around histone proteins, forming chromatin.
 Chromosomes make the precise separation of DNA possible during cell division.
The Cell Cycle The cell cycle is the series of events in the growth and division of a cell.
In the prokaryotic cell cycle, the cell grows, duplicates its DNA, and divides by pinching in the cell
membrane.
The eukaryotic cell cycle has four stages (the first three of which are referred to as interphase):
 In the G1 phase, the cell grows.
 In the S phase, the cell replicates its DNA.
 In the G2 phase, the cell produces organelles and materials for division.
 In the M phase, the cell divides in two stages—mitosis, the division of the nucleus, and
cytokinesis, the division of the cytoplasm.
Mitosis The division of the nucleus, mitosis, occurs in four stages:
Prophase : a cell’s genetic material condenses, a spindle starts to form, and the nuclear envelope
breaks down.
Metaphase : the duplicated chromosomes line up and spindle fibers connect to the
centromeres.
Anaphase : sister chromatids separate and move toward the centrioles.
Telophase : the chromosomes begin to unwind and a nuclear envelope reforms.
Cytokinesis Division of the cytoplasm differs in plant cells and animal cells.
In animal cells, the cell membrane draws in and pinches off.
In plant cells, a cell plate forms, followed by a new cell membrane, and finally a new cell wall
forms.
10.3 Regulating the Cell Cycle
Lesson Objectives
Describe how the cell cycle is regulated.
Explain how cancer cells are different from other cells.
Lesson Summary
Cancer: Uncontrolled Cell Growth Cancer is a disorder in which cells divide uncontrollably,
forming a mass of cells called a tumor.
Cancers are caused by defects in genes that regulate cell growth.
Treatments for cancer include:
 removal of cancerous tumors.
 radiation, which interferes with the copying of DNA in multiplying cancer cells.
 chemotherapy, which is the use of chemicals to kill cancer cells.
10.4 Cell Differentiation
Lesson Objectives
Describe the process of differentiation
Define stem cells and explain their importance.
Identify the possible benefits and issues relating to stem cell research.
Lesson Summary
From One Cell to Many Multicellular organisms produced via sexual reproduction begin life as a
single cell.
Early cell divisions lead to the formation of an embryo.
Then, individual cells become specialized in both form and function through the process of
differentiation.
Once cells of a certain type, such as nerve cells or muscle cells, have formed, the cells cannot
develop into a different type of cell.
Stem Cells and Development During an organism’s development, some cells differentiate to
become a wide variety of body cells.
A fertilized egg and the first few cells in an embryo are able to form any kind of cell and tissue.
Such a cell is termed totipotent.
A blastocyst is an embryonic stage that consists of a hollow ball of cells. These cells are able to
become any type of body cell. Such cells are termed pluripotent.
Unspecialized cells that can develop into differentiated cells are called stem cells. Stem cells are
found in embryos and in adults.
 Embryonic stem cells are the pluripotent cells of an early embryo.
 Adult stem cells are multipotent, which means they can produce many, but not all, types of
differentiated cells.
Frontiers in Stem Cell Research Scientists want to learn about the signals that tell a cell to
become either specialized or multipotent.
Potential benefits of stem cell research include the repair or replacement of damaged cells and
tissues.
Research with human stem cells is controversial because it involves ethical issues of life and death.
12.2 The Structure of DNA
Lesson Objectives
Identify the chemical components of DNA.
Discuss the experiments leading to the identification of DNA as the molecule that carries the
genetic code.
Describe the steps leading to the development of the double-helix model of DNA.
Lesson Summary
The Components of DNA DNA is a nucleic acid made up of nucleotides joined into long strands or
chains by covalent bonds. Nucleotides may be joined in any order.
A DNA nucleotide is a unit made of a nitrogenous base, a 5-carbon sugar called deoxyribose, and a
phosphate group.
DNA has four kinds of nitrogenous bases: adenine, guanine, cytosine, and thymine.
Solving the Structure of DNA
Erwin Chargaff showed that the percentages of adenine and thymine are almost always equal in
DNA. The percentages of guanine and cytosine are also almost equal.
Rosalind Franklin’s X-ray diffraction studies revealed the double-helix structure of DNA.
James Watson and Francis Crick built a model that explained the structure of DNA.
The Double-Helix Model The double-helix model explains Chargaff’s rule of base pairing and how
the two strands of DNA are held together. The model showed the following:
The two strands in the double helix run in opposite directions, with the nitrogenous bases in the
center.
Each strand carries a sequence of nucleotides, arranged almost like the letters in a fourletter
alphabet for recording genetic information.
Hydrogen bonds hold the strands together. The bonds are easily broken allowing DNA strands to
separate.
Hydrogen bonds form only between certain base pairs–adenine with thymine, and cytosine with
guanine. This is called base pairing.
12.3 DNA Replication
Lesson Objectives
Summarize the events of DNA replication.
Compare DNA replication in prokaryotes with that of eukaryotes.
Lesson Summary
Copying the Code Each strand of the double helix has all the information needed to reconstruct the
other half by the mechanism of base pairing. Because each strand can be used to make the other
strand, the strands are said to be complementary. DNA copies itself through the process of
replication:
The two strands of the double helix unzip, forming replication forks.
New bases are added, following the rules of base pairing (A with T and G with C).
Each new DNA molecule has one original strand and one new strand.
DNA polymerase is an enzyme that joins individual nucleotides to produce a new strand of
DNA.