Regulating the Cell Cycle Regulating the Cell Cycle

Regulating the Cell Cycle

Regulating the Cell Cycle • How do cells know when to divide? • Cell growth and division is carefully controlled! – Some cells divide more quickly than others; some cells rarely divide once the organism is developed! Time to divide!!!

Regulating the Cell Cycle • In a lab, cells will divide until they come in contact with nearby cells. – If cells are scraped away, cell division begins again! • Similar things happen in our bodies! – What happens if you get a cut or broken bone?

Regulating the Cell Cycle • Scientists have found many proteins that regulate the cell cycle (cyclins) • Some are present inside the cell; others are outside the cell

Regulating the Cell Cycle • Internal Regulators– Respond to events within the cell – Control the stages of the cell cycle • Ex: Makes sure DNA has been copied before mitosis starts

Regulating the Cell Cycle • External Regulators– Respond to events outside the cell – Direct cells to speed up or slow down the cell cycle – One group is growth factors • Wound healing • Development of embryo – Others cause cells to slow down or stop the cell cycle • Prevents too much cell growth

Regulating the Cell Cycle • Cells die every day in a multi-cellular organism in one of two Death of nerve cell ways • May die by accident – Due to damage or injury • Some cells are programmed to die – Apoptosis is programmed cell death – Cell undergoes series of steps leading to self-destruction • Shapes the structure of tissues and organs Apoptosis

Uncontrolled Cell Growth • Cancer – Disorder in which some cells lose ability to control growth – Cells do not respond to signals that regulate growth of most cells – Result > divide uncontrollably and form masses of cells called tumors

Uncontrolled Cell Growth • Tumors – Cancerous tumors invade and destroy healthy tissue around them – As cancer cells spread, they: • use nutrients needed by other cells • block nerve connections • stop invaded organs from functioning properly tumor

• Cancer is caused by damage to a cell’s DNA • Defects are in genes that regulate cell growth and division – Several sources of defects: • Smoking or chewing tobacco • Radiation exposure • Viral infection Cancerous lung

Treatments for Cancer • Three main treatments: – Surgery • If the tumor hasn’t spread, it can often be removed by surgery • Ex: Melanomas (skin cancer) – Radiation • Since cancer cells divide quickly, beams of radiation can kill them – Chemotherapy • Chemical compounds that either kill cancer cells or slow their growth • Chemo can also interfere with cell division in normal, healthy cells

Cell Differentiation • Your body began as one cell… Now it contains about 100 trillion!! • The human body has hundreds of types of cells, yet each developed from the same individual cell! • We (and many other organisms) go through a developmental stage as an embryo • As we develop, cells go through differentiation and become more specialized (for different functions).

Cell Differentiation • During the development of an organism, cells differentiate into many types of cells

Stem Cells and Development • A cell that can develop into any type of cell is called totipotent. • In humans, only the fertilized egg and the cells produced by the first few cell divisions are totipotent • After about 4 days of development, human embryo forms blastocyst, a hollow ball of cells with a cell cluster inside • Cells in the blastocyst have already begun specialization!

Stem Cells and Development • Outer cells of the blastocyst form tissues that attach to the mother • Inner cells of the blastocyst are called pluripotent, because they can develop into most (but not all) of the body’s cell types

Stem Cells and Development • Unspecialized cells from which differentiated cells develop are called stem cells. Called “stem” cells because they are at the base of a branching “stem” of development Because they have potential to become any type of cell, there is a lot of research being done

Stem Cells and Development • Embryonic Stem Cells – Pluripotent cells found in the early embryo – Researchers have found a way to grow these in a lab! • Adult Stem Cells – Differentiate to renew and replace cells in the adult body, such as skin and blood cells – Because they can make some (but not most) types of cells, they are called multipotent, meaning they can become several cell types – Usually stem cells of specific tissues produce only cells that are in that tissue

Stem Cell Research • Potential Benefits – Importance for human health – Cells are often damaged (heart attacks, stroke, injury, etc. ) – Prospect of using stem cells to repair damaged cells has excited researchers

Stem Cell Research Ethical Issues • Taking stem cells from an embryo requires destruction of the embryo – Very controversial!! – Arguments involve ethics of life and death • Technology may someday lead to a way to take just a few stem cells from embryos without damaging the embryo – This will allow research to continue without the ethical concerns – Other research has shown we may be able to “re-program” adult stem cells to look & function like embryonic stem cells

Stem Cells https: //www. youtube. com/watch? v=o. QKL 5 N 1 Uwp. E https: //www. youtube. com/watch? v=j. F 2 i. Xpo. G 5 j 8