Be able to: Explain the problems that growth causes for cells. Describe how cell division solves the problems of cell growth. Name and describe the main events of the cell cycle.

Let’s do some math! Calculate the surface area of each sphere.                    Let’s do some math! Calculate the surface area of each sphere. Calculate the volume of each sphere. Then, calculate the surface area to volume ratio. Round #’s up or down to make it easier. S.A. = 4 (pi) r 2 Radius 2cm S.A. = ________ V = __________ Ratio SA:V = ________ Radius 2cm S.A. = ___50cm2__ V = __33cm3____ Ratio SA:V = 50:33_or 1.51:1

S.A. = 4 (pi) r 2 Radius 1cm S.A. = _____ V = ______ Ratio SA:V = ___ S.A. = __13cm2___ V = __4cm3____ Ratio SA:V = _13:4 or 3.25:1__ Radius 2cm S.A. = ___50cm2__ V = __33cm3____ Ratio SA:V = 50:33_or 1.51:1 Radius 3cm S.A. = __113cm2_ V = ___113cm3___ Ratio SA:V = _113:113 or 1:1__ Radius 3cm S.A. = _____ V = ______ Ratio SA:V = ___ S.A. = 4 (pi) r 2 As the spheres get larger what happens to the SA:V ratio?

1st problem: Cell size and material exchange The larger a cell grows the more trouble it has… moving enough nutrients in Moving all the waste materials out

2nd problem: DNA overload A larger cell makes greater demands on its genetic library.

Checkpoint! What are two problems that cell growth causes for cells? The larger a cell becomes, the more demands the cell places on its _____ and the more trouble the cell has moving enough _________and _________ across the cell membrane. What is viable solution for cells solve these problems? Cell Division – A larger cell splits into two smaller daughter cells.

The Cell Cycle - series of events that cells go through as they grow and divide The cell cycle is divided into two halves Interphase - period of the cell cycle between cell divisions M phase – period of time when mitosis and cell division occurs

Parts of Interphase G1 Phase Growing Synthesize new proteins and organelles Doing their jobs Longest phase of cell cycle S Phase Chromosomes(DNA) are replicated Key proteins associated with replication are made (centromeres) G2 Phase Shortest of the 3 phases of interphase Organelles and molecules for cell division are produced (centrioles) Check-up phase before mitosis

Chromatin and Chromosomes Chromatin - A complex of DNA and proteins in the cell nucleus that condenses to form chromosomes during cell division. Chromosomes – Condensed Chromatin They are the same stuff, just in different forms

Chromatin condenses in chomosomes before mitosis begins Chromosomes

Chromosomes Different organisms have different #’s of chromosomes Humans cells – 46 Fruit Fly cells – 8 Carrot cells – 18 King Crab cells - 208 Note: Chromosomes are not visible in most cells except during cell division.

Chromosomes Replication During the cell cycle (before cell division can take place) chromosomes are replicated to form an identical copy of itself. Two identical copies of a chromosome are called “sister” chromatids – (one of two identical “sister” parts of a duplicated chromosome) Centromere - area where each pair of the chromatids of a chromosome are attached

M Phase, Cell Division and Mitosis

Mitosis (PMAT) Prophase 1. Chromosomes become visible 2. Centrioles take up positions on opposite sides of the nucleus Metaphase 1. Chromosomes line up across center of cell (Metaphase-Middle) Anaphase 1. The chromosomes move until they form two groups near the poles of the spindle (guides that help separate the chromosomes) Telophase 1. A nuclear envelope re-forms around each cluster of chromosomes 2. The nucleolus becomes visible in each daughter nucleus

Cytokinesis Cytoplasmic division and other changes exclusive of nuclear division that are a part of mitosis or meiosis In animal cells the cell membrane is drawn inward until the cytoplasm is pinched into two nearly equal parts In plant cells a cell plate forms midway between the divided nucleus

In plant cells, a cell plate forms In plant cells, a cell plate forms. The cell plate is synthesized by the fusion of multiple membrane-bounded vesicles. Their fusion supplies new plasma membrane for each of the two daughter cells. Synthesis of a new cell wall between the daughter cells then occurs at the cell plate.

Controls on Cell Division

Answer The cells would form more layers but would probably begin to die off when space and nutrients ran short and wastes accumulated.

How do cells know when to divide and when not to? Internal regulators – proteins that respond to events inside the cell. Some proteins make sure cells do not enter mitosis until all of the chromosomes have been replicated. What stage of the cell cycle do you think these proteins work? G2 phase Cyclins – (internal regulator) one of a family of closely related proteins that regulate the cell cycle in eukaryotic cells

Cyclins

External Regulators External regulators - Proteins that respond to events outside the cell are called external regulators. External regulators direct cells to speed up or slow down the cell cycle. Growth factors are among the most important external regulators, which tell cells to speed up division. When is this important? (Answer: During embryonic development and wound healing) Molecules found on the surfaces of neighboring cells often have an opposite effect, causing cells to slow down or stop their cell cycles.

Uncontrolled Cell Growth Cancer cell Various forms of cancer have many causes Smoking Radiation Viral infections The common thread in all cancers is that control over the cell cycle has broken down. Many cancer cells have a defect in the p53 gene which makes a protein that stops the cell cycle if the chromosomes have not been replicated properly

Checkpoint! 1. The break down of a cell’s entire life is the _______ ________. 2. The phase of the cell cycle when the cell is growing, replicating DNA and getting ready for mitosis is _____________. 3-6. What are the four phases of Mitosis? 7. The process of a cell actually splitting in two is called _______________.