Chapter 10

Cell Growth and Divison

10.1 Cell growth, division, and reproduction

Limits to Cell SizeWe learned in Chapter 7, that small cells are more efficient than large cells.

•The larger a cell becomes, • the more demands the cell places on its DNA• the less efficient in moving nutrients and waste materials

across the cell membrane.

Cells need a high sa/v ratio

Cell Division

An adult produces 25 million new cells per second.

Why do cells divide?1. Asexual reproduction

2. Unicellular organism developing into a multicellular organism (growth)

3. Renewal and Repair of damaged cells

• In each situation DNA must be present in each new cell.

• When a cell divides the DNA is copied and distributed so that each cell ends up with an exact copy of the DNA.

Asexual Reproduction

• Prokaryotic cells reproduce by binary fission• Produces identical offspring where a parent passes exact copies

of its DNA to its offspring.

parent cell

DNA duplicates

cell begins to divide

daughter cells

Asexual reproduction

Eukaryotic organisms can also reproduce asexually.• Budding forms a new organism from a small projection

growing on the surface of the parent.• Fragmentation is the splitting of the parent into

pieces that each grow into a new organism.

bud

Hydra

Yeast

Sexual reproduction

• Involves the fusion of two parent cells• Offspring inherit some information from each

parent

10.2 THE PROCESS OF CELL DIVISION

CHROMOSOMES – condensed chromatin•A single molecule of DNA has thousands of genes•DNA is arranged into chromosomes

• Prokaryotes – single circular chromosome in cytoplasm• Eukaryotes – multiple chromosomes are located in the nucleus

Eukaryotic Chromosomes

• Each chromosome is made up of 2 sister chromatids

• The sister chromatids are attached at a centromere

Condensed, duplicated chromosome

chromatid

centromere

Chromosomes in Sexual Reproduction

• Somatic Cell – normal body cell, not a sperm or egg cell.• Diploid• In a normal human contains 46 chromosomes

• Gamete – sex cell, sperm or egg• Haploid • In a normal human contains 23 chromosomes• Why?

• When two haploid gametes fuse in fertilization, the result is a diploid zygote (the first cell of a new individual).

The Cell Cycle

The cell cycle is a regular pattern of growth, DNA replication, and cell division.

Stages of the Cell Cycle

• Interphase• G1: cell growth and normal

functions• S (synthesis): copies DNA• G2: additional growth and

preparation for division

• Cell Division (M phase)• Mitosis

• division of the cell nucleus

• Cytokinesis • division of the cell cytoplasm

interphase

Before cell division can begin the cell will go through interphase.

Parent cell in Interphase

centrioles

spindle fibers

centrosome

nucleus withDNA

Steps of Mitosis

• Step I: Prophase• chromosomes condense • Spindle fibers form from centrioles.• Nucleolus disappears and the nuclear envelope breaks down

• Step 2: Metaphase• Centromeres of chromosomes line up in the middle of the cell• Spindles attach to centromeres

• Step 3: Anaphase• sister chromatids separate and move along the spindle fibers to

opposite sides of the cell

• Step 4: Telophase the new nuclear envelopes form and chromosomes begin

to uncoil into chromatinMitosis is complete! (cell division still has one more step)

Cytokinesis

• In animal cells, the membrane pinches closed.

• After cytokinesis in all cells, each new cell begins interphase.

• Cells Alive Animation

• In plant cells, a cell plate forms.

Review Questions

Compare asexual and sexual reproduction.How does cytokinesis compare in plant and animal cells?Describe the relationship between the following terms: chromatin, chromosomes, chromatid, and centromere.

Mitosis song

10.3 regulating the Cell Cycle

• One of the most important internal factors that regulate the cell cycle are: • Cyclins (regulatory proteins)

External Factor• Normal cells stop

dividing when they touch each other.

Cancer cells

• If one of these factors is mutated regulation of growth and division can be disrupted.

• Cancer cells do not respond normally to the bodys control mechanisms.• As a result they divide uncontrollably and form a mass

of cells called a tumor.

Metastasis Animation

10.4 Cell Differentiation

• As a zygote grows into stem cells, and then an embryo, the cells become specialized through the process of differentiation.• Differentiated cells are specialized

to perform certain jobs.• Example: nerve cells, muscle cell,

blood cell, skin cell

Stem Cell Research

• Embryonic stem cells vs. adult stem cells

• Benefits• Fix damaged cells• Treat devastating

diseases (leukemia, diabetes)

• Issues• Ethics• Expensive