Cell growth, division, and reproduction Miller and Levine Biology Sams

Why divide? The larger a cell becomes, the more demands the cells places on it’s DNA The larger a cell becomes, the less efficient it becomes at moving nutrients in a wastes out.

Why divide? Surface area is important to a cell because its surface area is its membrane. Membrane is responsible for nutrient/waste exchange. For a growing cell. A decrease in the relative amount of cell membrane available creates issues.

Surface/area volume ratio

Cell division Before becoming too large, a cell must divide. This solves the problems of… increasing size by reducing cell volume Information overload by copying DNA

Asexual reproduction Single celled organisms (i.e. bacteria) undergo cell division as a sole means of survival. The two cells produced by this type of cell division are genetically identical.

Sexual reproduction Involves fusion of two separate parent cells. Offspring produced by sexual reproduction inherit some genetic information from each parent.

Advantages/disadvantages

The cell Cycle Cells go through a series of events known as the “cell cycle” as they grow and divide. During the cell cycle, a cell grows, prepares for division, and divides to form two daughter cells.

Binary fission This type of cell division is specific to single celled organisms such as bacteria.

Eukaryotic cell cycle The eukaryotic cell cycle consists of four phases: G1, S, G2, and M. The G1, S, and G2 phases are known as interphase.

Eukaryotic cell cycle In G1, cells increase in size and synthesize new proteins and organelles. This is where most of a cell’s growth takes place.

Eukaryotic cell cycle In the “S” phase, new DNA is synthesized as chromosomes are replicated. At the end of this phase, 2X as much DNA exists than there was initially.

Eukaryotic cell cycle After replication, the cell enters its shortest phase which is G2. Organelles and molecule required for division are produced.

Eukaryotic cell cycle The M phase, or mitotic phase, produces the daughter cells. It occurs in two stages : mitosis and cytokinesis.

Mitosis Mitosis is divided up into four stages Prophase Metaphase Anaphase Telophase Mitosis can last anywhere from a few minutes to several days depending on the cell type.

Prophase Genetic material inside the chromosome condenses as the nuclear envelope breaks down Spindle begins to form outside nucleus

Metaphase Centromeres of duplicated chromosomes line up across the center of the cell Spindle fibers connect the centromere of each chromosome to the two poles of the spindle

Anaphase Chromosomes separate and move along the spindle fibers to the opposite ends of the cell

Telophase Chromosomes begin to spread out into a tangle of chromatin Nuclear envelope reforms

Cytokinesis Cytokinesis completes the process of cell division by splitting one cell into two

Mitosis

Cell cycle regulation Not all cells move through the cell cycle at the same rate Most of our muscle and nerve cells do not divide once they’ve developed. However cells of the skin and digestive tract divide rapidly throughout life

Cell cycle regulation In “in vitro” experiments, cells will divide until they come into contact with one another and then stop. “In vivo”, cells divide rapidly immediately after a wound forms but slow down when the healing process nears completion.

Cell cycle regulation Cyclins are a family of proteins that regulate the timing of the cell cycle in eukaryotic cells

Cell cycle regulation Internal regulators respond to events occurring within the cell (i.e. proteins that regulate events of the cell cycle) External regulators respond to events occurring outside of the cell (i.e. growth factors that stimulate or slow growth and cell division)

Cell cycle regulation Unlike single celled organisms such as bacteria, cells in our body sacrifice themselves for the good of the “community”.

Cell cycle regulation Apoptosis is the process of programmed cell death

Cell cycle regulation

Cancer Cancer is defined as a disorder in which body cells lose the ability to control their growth Cancer cells do not respond to signals that regulate the growth of most cells, resulting in them dividing uncontrollably.

Cancer

Cancer Growth 1. A cell divides abnormally 2. The cancer cells produce a tumor which begins to displace normal cells/tissues 3. Cancer cells may spread throughout the body through bloodstream or lymph system. This is called metastasis

Cancer treatment Removal through surgery Treatment with radiation and/or radiation