The Cell Cycle

Why do cells divide? - Smaller cells are more efficient at: - Obtaining O 2 H 2 O Nutrients (glucose amino acids, etc.) - Ridding themselves of CO 2 wastes Reproduction Replace damaged cells/Repair Allows organism to grow Density Dependent Inhibition - Space fills, division stops

Cell Cycle So cells divide to stay small and efficient. Let’s look at their life cycle: G Phases = intense growth intense activity S Phases = DNA synthesis How long does this all take? Depends on the type of cell! Skin cells – 2 or less hrs Digestive – 6 hrs Nerves – don’t Chromosome division and separation Interphase: G 1, S, G 2 Mitosis: Cell division

Chromosome Changes During Cell Cycle Chromosome Sister Chromatids joined by a Centromere Chromosomes headed for 2 separate daughter cells Chromatin

Cell Division Cell Division occurs in two ways: to produce two different kinds of cells for two different functions Mitosis produces genetically identical daughter cells that will take over the job of the parent cell Meiosis produces genetically different cells that will be used in sexual reproduction,egg + sperm

Mitosis Occurs in 4 (5) stages: Prophase Metaphase Anaphase Telophase ( Cytokinesis ) Describe changes involving DNA Describes changes involving cytoplasm and the rest of the cell

Interphase Centrioles Cell is full sized Nucleus is intact DNA has already been replicated Centrioles (animal cells only) are prepared to assist in division Animal Cell Plant Cell

Prophase Plant Cell Early Late Animal Cell Chromosomes form Nuclear envelope breaks up Nucleolus breaks up Spindle apparatus forms Centrioles (animal cells only) move to opposite ends of the cell

Metaphase Animal Cell Plant Cell Chromosomes line up in the middle of the cell Centrioles (animal cells only) are as far apart as possible Spindle attaches to centromeres

Anaphase Animal Cell Plant Cell Sister chromatids separate Spindle shortens Cytokinesis begins Animal Cells = “pinching” Plant Cells = cell plate forms

Telophase Animal Cell Plant Cell Chromosomes have moved to opposite ends of the cell Chromosomes begin to unwind into chromatin Nuclear envelope begins to reform Spindle apparatus dissociates Cytokinesis continues Animal Cells = pinching more Plant Cells = cell plate grows until wall is complete EarlyLate

Cytokinesis Cell will separate throughout anaphase and telophase Daughter cells result; half the size as parent cell at the end of G 2 Animal Cell Plant Cell

Mathematical Proof: Surface Area Volume cm 2 cm 3 Compare: 1cm 3cm Surface Area = 1x6 = 6 Volume 1x1x1 1 Surface Area = 1x6(9) = 54 = 2 Volume 3x3x More surface area per unit of volume Less surface area per unit of volume

Multicellular organisms depend on interactions among different cell types. Tissues are groups of cells that perform a similar function. Organs are groups of tissues that perform a specific or related function. Organ systems are groups of organs that carry out similar functions. CELLTISSUEORGAN

Specialized cells perform specific functions. Cells develop into their mature forms through the process of cell differentiation. Cells differ because different combinations of genes are expressed. A cell’s location in an embryo helps determine how it will differentiate. Outer: skin cells Middle: bone cells Inner: intestines

Stem cellsStem cells are unique body cells. Stem cells have the ability to –divide and renew themselves –remain undifferentiated in form –develop into a variety of specialized cell types

Stem cells are classified into three types. –totipotent, or growing into any other cell type –pluripotent, or growing into any cell type but a totipotent cell –multipotent, or growing into cells of a closely related cell family

Cell cycle regulation is necessary for healthy growth.

Internal and external factors regulate cell division. External factors include physical and chemical signals. Growth factors are proteins that stimulate cell division. –Most mammal cells form a single layer in a culture dish and stop dividing once they touch other cells.

–a normal feature of healthy organisms –caused by a cell’s production of self-destructive enzymes –occurs in development of infants webbed fingers Apoptosis is programmed cell death.

Cell division is uncontrolled in cancer. Cancer cells form disorganized clumps called tumors. cancer cell bloodstream normal cell –Benign tumors remain clustered and can be removed. –Malignant tumors metastasize, or break away, and can form more tumors.

Cancer cells do not carry out necessary functions. Cancer cells come from normal cells with damage to genes involved in cell-cycle regulation.

Carcinogens are substances known to promote cancer. Standard cancer treatments typically kill both cancerous and healthy cells.

Binary fission is similar in function to mitosis. Asexual reproduction is the creation of offspring from a single parent. –Binary fission produces two daughter cells genetically identical to the parent cell. –Binary fission occurs in prokaryotes. parent cell DNA duplicates cell begins to divide daughter cells