Cell Growth

Cells have distinct phases of growth, reproduction, and normal functions. Just as all species (humans) have life cycles, cells also have a life cycle. The Cell Cycle is the 1 regular pattern of growth, 2 DNA duplication, and 3 cell division that occurs in eukaryotic cells. Cell division is the process by which 2 new cells are produced from one cell. The new cells are identical to each other and to the original cell. Parent produces 2 daughter cells

The Cell Cycle The cell cycle is divided into 4 phases: The G 1 Phase The S Phase The G 2 Phase The M Phase Interphase

The Cell Cycle Phases G 1 : Gap 1 Cells grow, carry out normal functions, and replicate their organelles Cell spends most of its time in this phase S: Synthesis A new set of DNA is created from the original G 2 : Gap 2 Additional growth of cell and normal functions (job of cell) is carried out M: Mitosis and Cytokinesis Cell division occurs. ***Mitosis occurs only if the cell is large enough and the DNA is undamaged.

Cells divide at different rates Rates of cell division vary widely. The prokaryotic cell cycle is similar but not identical to that of eukaryotic cells. This is because prokaryotic cells have no nucleus and organelles, so they divide much faster than eukaryotic cells. The rate at which your cells divide is linked to your body’s need for those cells. In human cells, the S, G2, and M stages together usually take about 12 hours. The rate of cell division is greater in embryos and children than it is in adults

The rate of cell division also varies within different tissues of the adult body Some cells are unlikely to divide (G 0 ). Example- Neuron cells This explains why most people are unable to recover from brain injuries.

Cell size is limited Like most living things, cells have upper and lower size limits. If cells were to small, they could not contain all the necessary organelles & molecules. i.e. a cell with too few mitochondria wouldn’t have enough energy to live Cell also can’t grow beyond a certain size, even if it were surround by plenty of nutrients. Upper limit size is due to the RATIO OF CELL SURFACE AREA TO VOLUME.

Cell size is limited Remember materials are transported via the cell membrane Transportation of materials must happen in adequate amounts with adequate speed to keep cell functioning. But as cell size increases, its volume increases even faster. Therefore, a further increase in size (volume) could result in a surface area too small for adequate exchange of materials.

Some cells, however, must be large. Example: A neuron running down a giraffe’s neck to it’s legs may be several meters long The neuron can grow to a large size because of it’s shape- long and thin- instead of a cube or sphere. This structure gives the neuron a large surface area with a relatively small increase in volume. Cell size is limited

SO… To maintain a suitable size, growth & division must be coordinated! If a cell doubles its size before division, the daughter cells would get larger & larger with each generation. Quickly becoming too large to live On the flip side, if cell size was too small before division, the daughter cells would get smaller & smaller with each generation. Quickly becoming too small to live **So a cell must have a balance of both growth and division to stay functional**