Cell Specialization

Prokaryote  eukaryote? Prokaryotes dominated life on Earth from 3.5 – 1.5 bya

Prokaryote  eukaryote? First eukaryotes Development of internal membranes ~1.5 bya Create internal micro-environments Advantage = specialization = increased efficiency infolding of the plasma membrane DNA cell wall plasma membrane Prokaryotic cell Prokaryotic ancestor of eukaryotic cells Eukaryotic cell endoplasmic reticulum (ER) nuclear envelope nucleus

Endosymbiosis Evolution of eukaryotes Origin of mitochondria Engulfed aerobic bacteria, but did not digest it Mutually beneficial relationship Ancestral eukaryotic cell Eukaryotic cell with mitochondrion internal membrane system aerobic bacterium mitochondrion Endosymbiosis

Evolution of eukaryotes Origin of chloroplasts Engulfed photosynthetic bacteria, but did not digest them Mutually beneficial relationship Eukaryotic cell with mitochondrion photosynthetic bacterium Endosymbiosis chloroplast Eukaryotic cell with chloroplast & mitochondrion

Endosymbiont Hypothesis Evidence Structural Mitochondria & chloroplasts resemble bacterial structures  Have 70S ribosomes Genetic Mitochondria & chloroplasts have their own circular DNA  Different from nuclear DNA Functional Mitochondria & chloroplasts move freely within cells Mitochondria & chloroplasts reproduce independently from the cell Lynn Margulis

Cell Specialization Different cells have specialized structures Different structures give cells specialized functions Specialized function depends upon unique environment of the cell

Cell Specialization The specific form (structure) of a cell allows it to perform a specific function FORM RELATES TO FUNCTION Ex. – nerve cells are long and thin to transmit messages

Important to remember … All cells within an organism have identical DNA All cells contain the complete genome As the organism develops, genes within specific cells turn off/on

Where does the process start? Stem cells A cell that has the ability to continuously divide and differentiate into various other types of cells

Stem cell characteristics “Blank cells” Capable of dividing and renewing themselves for long periods of time Proliferation & renewal Have the potential to give rise to specialized cell types Differentiation

Kinds of stem cells Stem cell typeDescriptionExamples Totipotent Each cell can develop into a new individual Cells from early embryos (1-3 days) Pluripotent Cells can form any cell type (over 200) Some cells of blastocyst (5-14 days) Multipotent Cells differentiated, but can form a number of other tissues Fetal tissue, cord blood, and adult stem cells

Fully mature This cell can form the embryo and placenta This cell can form the embryo only

Kinds of stem cells Embryonic stem cells 5-6 day old embryo Tabula rosa Embryonic germ cells Derived from the part of the embryo that will ultimately produce sperm or eggs (gametes) Adult stem cells Undifferentiated cells found among specialized tissues or organs after birth Pluripotent Multipotent

Pluripotent stem cells More potential to become any type of cell

Multipotent stem cells Limited in what the cell can become

Embryonic stem cells Obtained mainly from IVF Use inner cell mass

Stages of Embryogenesis blastocystBlastocyst inner mass cells 8-cell stage cleavage

Blastocyst diagram

Adult stem cells Found in tissue and organs Sometimes called somatic stem cells Skin, fat cells, bone marrow, brain, & more Can differentiate to yield some major cell types of that tissue/organ

Bone marrow Found in spongy bone where blood cells form Used to replace damaged or destroyed bone marrow with healthy marrow stem cells Treats patients with leukemia, aplastic anemia, & lymphomas Need histological immunocompatibility

Blood cell formation

Umbilical cord stem cells Also known as Wharton’s Jelly Less invasive than bone marrow Greater compatibility Procedure is less expensive Cost of maintaining cells ???

Are stem cells the next “big thing” in genetic research? Though controversial, a very active area of research Applications Tissue repair Nerve Heart Skin Cancer Autoimmune diseases Diabetes Multiple sclerosis Rheumatoid arthritis

Tissue repair Regenerate spinal cord, heart tissue or any other major tissue in the body Replace skin Bone marrow stem cells injected into hearts are believed to improve cardiac function in heart failure or heart attack victims

Leukemia and cancer Studies have shown leukemia patients treated with stem cells emerge free of disease Chance of delayed rejection Injections of stem cells have also reduced pancreatic cancer in some patients Eliminating cancer stem cells directly Control cell differentiation Proliferation of white cells

Rheumatoid arthritis Adult stem cells may be helpful in repairing eroded cartilage

Type I diabetes Pancreatic cells do not produce insulin Embryonic stem cells might be trained to become pancreatic islets cells needed to secrete insulin

Stargardt’s disease Inherited progressive vision loss Affects ~1:10,000 Retinal stem cells are used Highly successful in rats, clinical trials started in humans

Stem cells in the adult brain

Can we reprogram cells?

Importance of stem cell research

Stem cells can replace diseased or damaged cells Stem cells allow us to study development and genetics Stem cells can be used to test different substances (drugs and chemicals)

So, what’s the problem? Ethical concerns about stem cell research center around the source of the stem cells A significant number of people believe removing cells from an embryo, whether or not the embryo formed in a lab, is destroying human life

So, what’s the problem? This raises an ethical question about when life begins, and whether it is ethical to sacrifice that life (if it has begun) to potentially save another life via research or cell- based therapies

So, what’s the problem? Technical challenges Source – cell lines may have mutations Delivery to target areas Prevention of rejection Suppressing tumors

So, what’s the problem? Mutations can lead to leukemia

Any Questions??