Cell Growth and Division Chapter 10 Cell Growth and Division

3. What is the advantage of cells being small? Getting Through Materials move through cells by diffusion. Oxygen and food move into cells, while waste products move out of cells. How does the size of a cell affect how efficiently materials get to all parts of a cell? Work with a partner to complete this activity. 1. On a sheet of paper, make a drawing of a cell that has the following dimensions: 5 cm x 5 cm x 5 cm. Your partner should draw another cell about one half the size of your cell on a separate sheet of paper. 2. Compare your drawings. How much longer do you think it would take to get from the cell membrane to the center of the big cell than from the cell membrane to the center of the smaller cell? 3. What is the advantage of cells being small?

How big can a cell get? • The largest human cell is an ovum (0.2mm) • As a organism grows, can the cells get bigger? – No, cells start to divide. – Cells can’t keep growing indefinitely. • There are Limits to Cell Size – The amount of DNA – The exchange of materials

DNA Overload = As cells increase in size, no extra DNA is made • Analogy: books in a library =

Exchanging Materials Food and oxygen need to enter, wastes need to exit. • The larger the volume of the cell, the smaller the surface area gets. – Surface Area = cell membrane

Surface Area to Volume Ratio • Surface Area (SA) = Length x Width x # of sides – 1 x 1 x 6 = 6 • Volume (V) = Length x Width x Height – 1 x 1 x 1 = 1 • Ratio = SA / V – 6 / 1 = 6:1

Surface Area to Volume Ratio Cell Size Surface Area (length x width x 6) Volume (length x width x height) Ratio of Surface Area to Volume • What happens to the V as SA goes up? – It increases much more rapidly • What happens to SA / V Ratio? – It decreases • This causes major problems for the cell – Analogy: Town and Traffic

Division of the Cell • Before a cell gets too large, it divides into two “daughter” cells. • Before cell division takes place, the cell must replicate all of its DNA. • The cell then divides and solves the problem of the cell becoming too large. http://www.cellsalive.com/qtmovs/ecoli_mov.htm

Chromosomes -Carriers of genetic information -made of DNA -# in different organisms varies -we have 46, squirrels have 40, dogs have 78, corn has 20

Events of The Cell Cycle Interphase G1 phase G1: cells increase in size & make new proteins S: Chromosomes replicated DNA synthesis takes place G2: Organelles required for division are produced M phase S phase G2 phase Mitosis The process of cell division

Interphase Cell grows and replicates its DNA and centrioles Interphase Nuclear envelope Chromatin Interphase Cell grows and replicates its DNA and centrioles

Chromosomes (paired chromatids) Prophase Spindle forming Centromere Chromosomes (paired chromatids) Prophase Longest phase Spindle begins to form Chromosomes become visible Nuclear envelope breaks Centrioles separate down

Metaphase Chromosomes line up across center of cell Centriole Metaphase Centriole Spindle Chromosomes line up across center of cell Microtubules connect centromeres to poles of cell

Individual chromosomes Anaphase Individual chromosomes Anaphase Sister chromatids separate into individual chromosomes Chromosomes move apart Spindle fibers shorten

Nuclear envelope reforming Telophase Telophase Nuclear envelope reforming Chromosomes gather at opposite ends of cell and lose shape Nuclear envelopes form

Cytokinesis Cytoplasm pinches in half Daughter cells has an identical duplicate set of chromosomes

Cytokinesis in plant cells

Control of Cell Division Cells will continue to grow in a petri dish until they come into contact with other cells. Controls can be turned on and off

Cell Cycle Regulators The sample is injected into a second cell in G2 of interphase. A sample of cytoplasm is removed from a cell in mitosis. As a result, the second cell enters mitosis. Cells in mitosis contain a protein that when injected into non-dividing cell causes spindle formation Protein = cyclin. The amount of cyclin in a cell rises and falls in time w/cell cycle

Internal regulators External regulators Proteins that respond to events inside the cell Allow cycle to proceed only when certain events inside the cell have happened -several make sure a cell doesn’t proceed with mitosis until all the chromosomes have been replicated External regulators Proteins that respond to events outside the cell Direct cells to speed up or slow down division -Ex: growth factors. Important in embryonic development and the wound healing

What happens when cell growth isn't controlled?