Chapter 9: Cellular Reproduction Section 1: Cellular Growth Ms. Diana and Ms. Su’ad

Cell Size Limitations Most cells are less than 100 x 10-6 m in diameter. The main factor that limits the size of a cell is the ratio of its surface area to its volume. Surface area – the area covered by the plasma membrane. Volume – the space taken up by the inner contents of the cell.

Surface Area to Volume Ratio If the cell continues to grow, the ratio of surface area to volume will continue to decrease. As the cell grows, its volume increases much more rapidly than the surface area. This means, the cell might have difficulty supplying nutrients and getting rid of waste products. By staying small, the cell has a higher surface area to volume ratio and can sustain itself more easily.

Transport of Substances The movement of substances can be managed more easily in a small cell. Substances inside the cell move by diffusion or by motor proteins pulling them along the cytoskeleton. Diffusion over long distances is slow and inefficient. Also, the transportation network inside the cytoskeleton becomes less efficient if the distance to travel becomes too large. Small cell size maximizes the ability of diffusion and motor proteins to transport nutrients and waste products.

Cellular Communications In order to move substances around the cell, proteins need to send signals throughout the cell, which also limits cell size. If the cell becomes too large, it becomes almost impossible for cellular communications to take place efficiently.

The Cell Cycle Once a cell reaches its size limit, something must happen – either it stops growing or it will divide. Cell division – prevents the cell from becoming too large and it’s the way the cell reproduces. Cellular reproduction allows you to grow and heal certain injuries.. Cell Cycle - cells are able to reproduce by this cycle of growing and dividing

The Cell Cycle Each time a cell goes through one complete cycle, it becomes two cells. If the cycle is continuous, the results are continuous productions of new cells. The Cell Cycle has 3 main stages: Interphase Mitosis Cytokinesis

The Cell Cycle Stage 1: Interphase During Interphase, the cell grows, carries out cellular functions, and replicates, or makes copies of its DNA to prepare it for the next stage of the cycle. Interphase is divided into 3 substages: G1 – cell grows and performs normal functions S (synthesis) – DNA is replicated G2 – cell prepares for mitosis

The Cell Cycle Stage 2: Mitosis During mitosis, the cell’s nucleus and nuclear material divide. Mitosis is divided into 4 substages: Prophase Metaphase Anaphase Telephase

The Cell Cycle Stage 3: Cytokinesis Cytokinesis – the method by which a cell’s cytoplasm divides, creating a new cell. This process begins at the end of mitosis.

The Cell Cycle Some eukaryote cells might complete the cell cycle in as few as 8 minutes. Other cells might take up to 1 year. For normal, actively dividing animal cells, it takes approximately 12-24 hours.

The Stages of Interphase Stage 1 of Interphase: G1 G1 is the time immediately after a cell divides. During G1, a cell is growing, carrying out normal cell functions, and preparing to replicate DNA. Some G1 cells such as muscle and nerve cells exit the cell cycle at this point and do not divide again.

The Stages of Interphase Stage 2 of Interphase: S The time when a cell copies its DNA in preparation for cell division. Chromosomes – structures that contain the genetic material that is passed from generation to generation. Chromatin – the relaxed form of DNA in the cell’s nucleus.

The Stages of Interphase Stage 3 of Interphase: G2 During G2, the cell prepares for the division of the nucleus. A protein that makes microtubules for cell division is synthesized at this time. Also, the cell makes sure it has everything it needs to continue with mitosis.

Prokaryotic Cell Division The cell cycle is the method that eukaryotic cells use to reproduce themselves. Prokaryotic cells reproduce by using a different method called, binary fission.

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