Cell Growth and Division Chapter 10

Limits to Cell Size Cells grow as the organism grows. However cells only grow to a certain extent then divide. Why? - The larger the cell the more demands on its dna - a large cell has more trouble moving food in and waste out Do you remember what the largest cell is?

Demands on DNA and exchanging materials As a cell grows the DNA (deoxyribose Nucleic Acid) stays the same size - DNA can meet all the cells needs when it is small, but if it becomes too big the cell’s DNA could not keep up with the information the cell needs. As a cell grows it needs to move more nutrients in and more waste out - the ratio of the surface area of the cell membrane to volume of the cell changes. - This difference means the cell has more trouble moving nutrients in and waste out. Can you think of an analogy to demonstrate the limits on the size of a cell?

Cell Division and Reproduction Cell division Is the process by which a cell divides into two new daughter cells. How does cell division solve the two limits on cell size? Types of reproduction: - asexual reproduction, e.g. Hydras (multicellular organisms that Undergo “budding”) - Sexual Reproduction, some unicellular organisms surprisingly

Advantages and Disadvantages Asexual Reproduction Sexual Reproduction Advantages: Quick Genetically identical offspring Disadvantages: Lack of genetic diversity Why does this matter in terms of evolution? Advantages: Genetically different offspring Disadvantages: Slower

Chromosomes Prokaryotic chromosomes are free floating in the cytoplasm in the shape of a circle Eukaryotic chromosomes are made up of DNA and found in the nucleus - Humans have 46 chromosomes

Organization of genetic material

The cell cycle Prokaryotic cells Eukaryotic cells Asexual reproduction in unicellular organisms called binary fission: - Cell growth - Dna replicates - Cell membrane indents - cell divides 4 phases: - G1 (interphase) - S (interphase) - G2 (interphase) - M (cell division): ~Mitosis ~Cytokinesis

4 Phases of the Eukaryotic cell cycle G1 (interphase) – increase in size and produces new proteins and organelles S (interphase) – New dna synthesized/chromosomes replicated G2 (interphase) – organelles and molecules needed for division are produced M (cell division): ~Mitosis – (Prophase, metaphase, anaphase, telophase) Nucleus divides ~Cytokinesis – cytoplasm divides

Cell division Mitosis Cytokinesis Prophase – Dna Condenses, nuclear envelope breaks down, Spindle forms Metaphase – Chromosomes line up in center of cell and spindle fibers connect to the centromere Anaphase – Centromeres split and sister chromatids separate and move to opposite sides of the cell Telophase – chromosomes unwind into chromatin, nuclear envelopes reform, and spindle breaks down Cytokinesis Animal cells – cell membrane is pulled toward the center of the cell and pinches to form two identical cells Plant cells – cell plate forms and develops into new cell membranes and a cell wall forms between the two new membranes to form the two new cells