How does cell size affect how efficiently materials get to all parts of a cell?
How much longer would it take nutrients to get to the center of the larger cell compared to the smaller cell?
4 Reasons why cells divide 1. EfficiencyAs cell grows bigger demand for transport across membrane is too great http://www.animationlibrary.com
4 Reasons why cells divide 2. DNA OverloadAs cell grows bigger, DNA can’t send out instructions fast enough to instruct organelles on work to do http://www.adc.state.az.us/images/Off-Library.JPG
4 Reasons why cells divide 3) Growth 4) Cells divide to replace worn out or damaged cells http://www.adc.state.az.us/images/Off-Library.JPG
Cell Division in Prokaryotes • Called Binary Fission • DNA is copied then cell divides
Cell Division in Eukaryotes • Called Mitosis • Cell Grows & Copies its DNA before it can divide
The series of events that cells go through as they grow & divide ~ The Cell Cycle
2 Phases of the Cell Cycle • Interphase • “M” Phase • Includes Mitosis & Cytokinesis
The Cell Cycle: Interphase • G1 • S • G2 • Prophase • Metaphase • Anaphase • Telophase Mitosis
Interphase: a growth period • G1 (Growth/Gap 1) - Cell grows in size, makes new organelles & performs assigned function; DNA is relaxed in chromatin and is not visible • S phase (Synthesis) - duplicates DNA to prepare for mitosis • G2 (Growth/Gap 2) – cell prepares for mitosis
Mitosis occurs in 4 phases • Prophase • Metaphase • Anaphase • Telophase
Vocab Terms • Chromatin DNA “scrunched up” in the nucleus & is not visible • Chromosomecell structure that carries the genetic material • Sister chromatidsidentical halves of the duplicated parent chromosome • Centromerecell structure that joins the two sister chromatids of a chromosome
Prophase • DNA organizes • chromatin condense into visible chromosomes. • Chromosomes are paired with their identical copies and are called sister chromatids. • Sister chromatids are held together as a pair by a centromere. • Nuclear membrane & nucleolus disappear. • Spindle fibers form between the pairs of centrioles, which have moved to opposite ends of the cell
Metaphase • Chromosomes line up in the middle of the cell. • Each chromatid is attached to a separate spindle fiber by its centromere.
Anaphase • Sister chromatids are pulled apart to opposite poles of the cell.
Telophase • 2 identical daughter cells are formed. • Cytokinesis occurs (the division of the cytoplasm) as the plasma membrane pinches in along the equator. • Nucleolus and nuclear membrane reappear, chromosomes begin to uncoil & relax back into chromatin
Picture of cytokinesis *Image courtesy Indigo Instruments. Visit indigo.com for more original content like this. Reprint permission is granted with this footer included.*
In plants… • Because plant cells have a cell wall, the plasma membrane does not pinch in. • Rather a structure known as the cell plate forms across the cell’s equator.
Plant in cytokinesis It’s hard to see, but there is a cell plate forming in the middle of the cell, next to the arrow.
Finally… • After mitosis is complete, each new daughter cell is an identical copy of the parent cell. Both cells enter interphase to carry out their assigned function until they are ready to divide.
Cell Cycle Video Lingering Questions…. • How long does the cell spend in each phase? • What is the life span of human cells? • What happens when the cell is NOT growing or dividing? • Does the cell continue in the cell cycle indefinitely?
Think-Pair-Share:Explain why damage to heart muscle cells are permanent Explain why spinal cord injuries are irreversible
What happens when the cell is not growing or dividing? Cell is resting
When cells are damaged and need repair or need to be replaced, cell will reenter the cell cycle
Section 10-3 Talk to a Partner: Do Cells Grow Indefinitely? If center cells are removed,cells near the space will start to grow again. SHOWS: Cell division genes can be turned on and off Cells grow until they touch other cells
Controlling Cell Growth Through Gene Regulation • Cell division stops when cells touch • Can resume if space is available (injury) • Cell division stops when they cannot absorb enough nutrients
What happens when the genes that control cell division become damaged? • Some cells do not respond to the signals that regulate the growth • Result ~ uncontrolled cell growth: cancer • Causes of cancer: • cigarette & tobacco use • radiation exposure (X-ray & UV light) • genetics • some viruses
Stem Cells • Stem cells - unspecialized cells • Through cell differentiation – stem cells become specialized in structure and function • Two Types: Embryonic and Adult Stem Cells