Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Regulating the Cell Cycle Controls on Cell Division • Most cells divide until they come in contact with other cells • Injury in body stimulates cells to divide – As healing processes nears completion the rate of cell division slows Cyclins – family of proteins that regulate the timing of the cell • The cell cycle is controlled by regulatory proteins both inside and outside the cell – Internal regulators (inside): allow cell cycle to proceed only when certain events have occurred in the cell itself • Keeps cell from dividing if DNA has not been replicated – External regulators (outside): direct cells to speed up or slow down the cell cycle • Growth factors – stimulate growth & division of cells – Embryonic development or wound healing • Some cause cells to slow down or stop their cell cycles – Prevents cells from over growing environment – Keeps body tissues from disrupting on another Apoptosis • # of cells is closely regulated – Not just by regulating cell cycle, but also by controlling when a cell dies – If cells are not needed then they will activate an intracellular death program (programmed cell death or apoptosis) • Key role in developing structures Cancer • Occurs when cell growth/division is not carefully regulated • Cancer cells do not respond to the signals that regulate the growth of most cells – Cells divide uncontrollably and form a tumor – Several have a defect in p53 gene – Several do not respond to external or internal regulators • Treatment – Radiation, chemotherapy, surgery Cell Differentiation From One Cell to Many • All living things pass through a developmental stage called an embryo – As organisms develop the cells become more differentiated and specialized for specific functions • Determines the cell’s ultimate identity • Controlled chemically Stem Cells and Development • Totipotent – cells that have the ability to everything, to develop into any type of cell – Only first few divisions • Blastocyte – a hollow ball of cells with a cluster of cells on the inside – Outer cells become tissues that attach embryo to mother – Inner cells become the embryo itself • Pluripotent – can develop into most cells, but cannot form the tissues surrounding embryo • Pluripotent cells can develop into most, but not all, of the body’s cells – They cannot form the tissues surrounding an embryo STEM CELLS • The unspecialized cells from which differentiated cells develop are known as stem cells • Embryonic stem cells – pluripotent • Adult stem cells – multipotent – They can develop into many types of differentiated cells – More limited than pluripotent – Bone maroow can develop into different types of blood cells˜ Stem Cell Research • Potential Benefits – Repair or replace badly damaged cells and tissues • Ethical issues – Human embryonic stem cells are harvested causing destruction of an embryo