How do cells know when to divide? Cell division can be turned on and off Cyclins regulate the cell cycle Family of proteins names after cyclin – the oroginal molecule discovered This was just the start…. There is a whole host of regulatory proteins both inside and outside the cell

Internal vs External regulators Internal regulators Respond to events occurring inside a cell Cell cycle only proceeds when certain events have happened Ensure cell division only occurs after mitosis Cells will not anaphase until the spindle fibers attach to the chromosome External regulators Direct cells to speed up or slow down cell cycle Growth factors stimulate growth and division of cells Important during wound healing, embryo development Some regulators on neighbouring cells inhibit cell growth

Apoptosis As cells are produced other cells die Cells can die due to damage or injury or Cells can be programed to die – apoptosis Once triggered leads to self destruction Cell and chromatin shrink Cell membrane breaks off Neighboring cells clean up remains

What is cancer? A condition where body cells become unable to control growth Cancer cells do not respond to normal growth regulation signals Cancer cells form a tumor Benign tumors – does not spread to surrounding healthy tissue Malignant tumors – invade and destroy surrounding healthy tissues Tumor absorb nutrients needed by other cells, block nerve connections and prevent organs from functioning properly

What causes cancer? Defects in genes that regulate cell growth Smoking Radiation Other defective genes Certain viral infections Common factor – control over the cell cycle has broken down Defect in p53 genes most common

Cancer treatment Tumors can be removed by surgery As cancer cells replicate so quickly they are vulnerable to radiation damage Carefully targeted beams of radiation can treat cancer Chemotherapy – Chemical compounds that kill cancer cells/inhibit growth But also effect normal healthy cells Lots of side effects Conquering cancer requires detail understanding of the cell cycle

Cell differentiation Section 10.4

How do cells become specialized? Humans have 100000000000000 cells Only 47 rounds of mitosis All multicellular organisms have an embryonic stage Over time cells get specialized for specific functions Termed cell differentiation Over development, cells differentiate into many types

Mapping differentiation Differentiation determines a cells ultimate identity In some organisms it’s role is determined by the cells development In a microscopic worm, the outcome of every cell has been mapped out

Cell differentiation in mammals The process is more flexible Cell differentiation is controlled by a number of factors in the embryo Adult cells however reach a point where their differentiation is complete Can’t become new types of cells

Stem cells Zygotes are totipotent ( they can literally become any body cell!) After 4 days, an embryo forms into a blastocyst – a hollow ball of cells with a cluster of cells inside known as inner cell mass Even this early cells have begun to specialize Outer part attaches to the mother Inner part becomes embryo

Stem cells The inner cells are pluripotent – they can become any of the body’s cells – just not tissues that surround the embryo Stem cells – undifferentiated cells from which all other cells develop

Adult vs Embryonic stem cells Adult stem cells Cells in tissues in an adult body need to be constantly replaced Pools of adult stem cells found in various locations produce the new cells needed for these tissues Example – blood cells from bone marrow, skin stem cells in hair follicles Adult stem cells are multipotent – types of differentiated cells that can form are limited to the tissues where they are found Embryonic stem cells Pluripotent – can produce every cell in the body Since 1998 they have been able to be grown in a culture in a lab

Benefits of stem cell research Large potential for treating human conditions and diseases Heart attack damage can be reversed using stem cell therapy Same idea for brain damage, damage nerves, or repair organs damaged by chemicals or disease Could lead to a new field of regenerative medicine Damaged cells are replaced by new, undifferentiated cells

Ethical issues Adult stem cells can be harvested from a willing donor – no real issues Harvesting of embryonic stem cells generally will destroy the embryo Some people argue that destruction of human embryonic life is unethical Others argue that it is essential for saving human life It is a controversial topic, as arguments for and against it involve ethical issues of life and death

Other approaches Understanding why stem cells are so versatile Can artificial stem cells be made? Proteins that bind to bind to DNA and activate genes (transcription factors) are used Promising, but early stages of research Other research has created ’artificial’ pluripotent cells from human fibroblast cells May make it possible for treatments to be tailored to a patient by using their own cells