Transcript 28.1 Levels of Organization

28.1 Levels of Organization
LEQ: How do cells become committed to specialized
functions in bodies?
• Key terms – stem cell, cell determination,
• Reading – 28.1, 5.5, 8.6 (eukaryotic gene regulation)
• Lab due 5/3
• Test/note cards Friday 5/4
28.1 Levels of Organization
• Activator:
– Complete epigenome survey
28.1 Levels of Organization
Stem cells add new cells to a body when they divide
• Stem cells have the ability to
– divide and renew themselves via mitosis
- Stochastic (top)
- Asymmetric (bottom)
– Daughter cells can specialize in biological tasks
28.1 Levels of Organization
Specialized cells of the body develop from stem cells
28.1 Levels of Organization
A stem cell divides and forms specialized populations of
cells
• Cell Determination is
committing to become
one cell type.
• Factors affecting
determination:
• Cell position in the
body
• Signaling
• Gene expression
28.1 Levels of Organization
Determination gives rise to related cell populations in a
body
28.1 Levels of Organization
• The use of stem cells has biomedical applications
First, an egg is fertilized by a sperm cell in a petri dish. The egg divides, forming an inner cell
mass. These cells are then removed and grown with nutrients. Scientists try to control how the
cells specialize by adding or removing certain molecules.
28.1 Levels of Organization
Summary:
• What are the characteristics of stem cells?
• Explain how a stem cell’s fate is “determined,” what
factors influence the future jobs these cells will perform?
• Discuss the potential to use stem cells in medical therapy
– Is using human embryos essential for medical
therapy? Why or why not?
28.1 Levels of Organization
Chromosomes are imprinted with epigenetic marks
• The epigenome is a pattern of
chemical modifications on
chromatin that control gene
expression
• Imprinting involves placing
epigenetic marks on
chromosomes
– Sex cell formation
• Goal: single gene expression
for certain genes that direct
development & metabolism
– Male vs. female
– Diploidy is essential
28.1 Levels of Organization
Changes to the epigenome alter how cells use their DNA
– Histone modifications – chemically modify “tails”
– DNA methylation – CpG islands: CG rich DNA
28.1 Levels of Organization
Epigenetic marks impart a genetic memory on cells
“determining” their fate
• Genes can be switched on or off permanently
28.1 Levels of Organization
Changes in epigenetics can result in disease
• (A) previously unmethylated tumor suppressor gene such
as p53 becomes methylated suppressing gene
expression
• (B) A protooncogene is demethylated, allowing TFs
express the protein product.
28.1 Levels of Organization
Epigenetic marks can change over time
• Development
– Cell differentiation
• Imprinting
– Chromosomes can be
permanently tagged
– Reversible
– Age correlation
– Disease correlation
28.1 Levels of Organization
Summary:
• A cell has undergone determination to become an
endocrine gland cell. If it is transplanted to a leg muscle,
what do you think will happen to this cell?