Cell Growth and Division Chapter 10

Cell growth limiting factors Limiting factors- conditions that prevent endless expansion. Cell growth limiting factors Diffusion DNA content Surface area-to-volume ratio Cells range from 2 to 200 micrometers in diameter.

DNA Limits DNA in the nucleus is the blueprint for all protein production in the cell. DNA replicates protein blueprints very slowly. The larger the cell, the more protein needed. The more protein needed the more DNA is required. The nucleus can only contain a small amount of DNA. Larger cells contain multiple nuclei.

Diffusion Rate Limits Diffusion rate Nutrients move about the cell primarily by passive transport. Diffusion is very slow through cytoplasm. It would take over one week to diffuse glucose across a 2cm stretch of cytoplasm!

Surface area-to-volume ratio Limits As the cells surface area doubles its volume increases 8 times. A cell with a surface area of 6 mm has a volume of 1 cubic mm. Double length of each side and the volume goes to 8 cubic mm. In other words, you have a greater area for materials to diffuse throughout.

Ratio of Surface Area to Volume in Cells Cell Size Volume (length x width x height) Ratio of Surface Area to Volume

Solution to Limits Cell division As a cells volume increases, the diffusion rate becomes too slow to carry essential nutrients to the organelles and the DNA cannot replicate plans fast enough. So the solution is Cell Division

Cell Cycle Every cell goes through a sequence of growth and division. Two general periods Growth Division Interphase- the longest period of a cell’s life cycle. Growth and metabolism take place in interphase.

Cell Cycle Interphase – 3 steps G1 - “gap 1” - first growth phase; cell gets larger S - “synthesis” - DNA is replicated and chromosomes are copied for division G2 - “gap 2” - second growth phase; final preparation for division

Cell Cycle Cell Division Short period of time. This is divided into phases. The nucleus is divided during mitosis The cytoplasm is divided last in cytokinesis

Figure 10–4 The Cell Cycle Section 10-2 G1 phase M phase S phase

Concept Map Cell Cycle Section 10-2 includes M phase (Mitosis) Interphase is divided into is divided into G1 phase S phase Prophase G2 phase Metaphase Telophase Anaphase

Interphase There are three stages of interphase: G1 S stage G2

Interphase G1-stage Rapid growth. Cells do the majority of growing during this phase. Cells make new proteins and organelles during this phase. Chromosomes not visible because they are loosely wound.

Interphase S-stage Occurs after the G1-phase Chromosomes are replicated. DNA is duplicated along with key proteins the chromosomes need.

Interphase G2-stage Occurs after S-phase is complete. The shortest of three interphases. Any organelles left to be duplicated are duplicated in this phase.

Figure 10–5 Mitosis and Cytokinesis Section 10-2 Spindle forming Centrioles Chromatin Centromere Nuclear envelope Centriole Chromosomes (paired chromatids) Interphase Prophase Spindle Cytokinesis Centriole Metaphase Telophase Individual chromosomes Anaphase Nuclear envelope reforming

Cell Division Consists of mitosis (period of nuclear division) and cytokinesis (division of the cytoplasm). Two daughter cells are produced each with a complete set of chromosomes. 4 stages of mitosis Prophase Metaphase Anaphase Telophase

Centromeres

Prophase Prophase is the 1st and longest stage of mitosis. Characterized by the tightening up of the loosely wound chromatin into sister chromatids. The disappearance of the nucleolus & nuclear membrane. You find the appearance of centromeres and spindles.

Prophase Metaphase Early mitotic spindle Centrosome Centromere Fragments of nuclear envelope Chromosome, consisting of two sister chromatids Spindle microtubules Spindle Figure 8.7.2

Figure 10–5 Mitosis and Cytokinesis Section 10-2 Spindle forming Centrioles Chromatin Centromere Nuclear envelope Centriole Chromosomes (paired chromatids) Interphase Prophase Spindle Cytokinesis Centriole Metaphase Telophase Individual chromosomes Anaphase Nuclear envelope reforming

Metaphase Metaphase is the 2nd stage in mitosis. In this short phase the centromeres connect to the spindle fibers. The chromosomes align themselves along the “equator” of the cell.

Figure 10–5 Mitosis and Cytokinesis Section 10-2 Spindle forming Centrioles Chromatin Centromere Nuclear envelope Centriole Chromosomes (paired chromatids) Interphase Prophase Spindle Cytokinesis Centriole Metaphase Telophase Individual chromosomes Anaphase Nuclear envelope reforming

Anaphase Anaphase is the 3rd stage of mitosis. In anaphase the chromosomes are split apart. Each identical copy gets pulled toward the “poles” of the cell by the spindle fibers.

Figure 10–5 Mitosis and Cytokinesis Section 10-2 Spindle forming Centrioles Chromatin Centromere Nuclear envelope Centriole Chromosomes (paired chromatids) Interphase Prophase Spindle Cytokinesis Centriole Metaphase Telophase Individual chromosomes Anaphase Nuclear envelope reforming

Telophase Telophase is the last stage of mitosis. Most of the other characteristics of the previous stages are reversed. Cell begins to divide.

Figure 10–5 Mitosis and Cytokinesis Section 10-2 Spindle forming Centrioles Chromatin Centromere Nuclear envelope Centriole Chromosomes (paired chromatids) Interphase Prophase Spindle Cytokinesis Centriole Metaphase Telophase Individual chromosomes Anaphase Nuclear envelope reforming

Click the image to play the video segment. Animal Cell Mitosis Click the image to play the video segment.

Cytokinesis The division of cytoplasm. Differs in plant & animal cells. Animal cells simply pinch into two cells. Plant cells lay down a cell plate at which point the cell divides.

Figure 10–5 Mitosis and Cytokinesis Section 10-2 Spindle forming Centrioles Chromatin Centromere Nuclear envelope Centriole Chromosomes (paired chromatids) Interphase Prophase Spindle Cytokinesis Centriole Metaphase Telophase Individual chromosomes Anaphase Nuclear envelope reforming

Click the image to play the video segment. Animal Cell Cytokinesis Click the image to play the video segment. Video 2

Cell Division Controls You have many ways cell growth can be controlled. External Regulators Outside signals that tell the cell to divide. I.e. a cut wound Internal Regulators Proteins that respond to signals inside cells that tell the cell to grow. I.e. cyclins

Control of Cell Division Section 10-3

Figure 10–8 Effect of Cyclins Section 10-3 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.

What Is Cancer? What is cancer? Cancer is caused by a breakdown in control of the cell cycle

Uncontrolled Cell growth From time to time the cell growth regulators do not work. This is essentially what cancer is.

Cancer cells divide excessively Cancer cells spread from a malignant tumor Metastasis is the spread of cancer Lymph vessels Tumor Glandular tissue Metastasis A tumor grows from a single cancer cell. Cancer cells invade neighboring tissue. Cancer cells spread through lymph and blood vessels to other parts of the body Figure 8.9

Cancer cells are often grown in culture for study Figure 8.10

Cancer Treatment Cancer treatment Radiation therapy disrupts cell division Chemotherapy involves drugs that disrupt cell division