Multicellular Life

Key concept: Cells work together to carry out complex

functions.

Human!

*Multicellular organisms depend on interactions among

different cell types.*

*Multicellular organisms depend on interactions among

different cell types.*

CELL TISSUE ORGAN

vascular tissue

leaf

stem

lateralroots primary

root

roo

t sy

stem

sho

ot

syst

em

*Specialized cells perform specific functions.*

It is easy to see that a skin cell can divide to make a new skin cell, but how does a complex organism like you develop?

Your body begins as a single fertilized egg, if the egg simply divided to make lots of identical cells it would not form a baby.

To form intricate structures that make up your body, cells must be specialized.

Specialized cells perform specific functions.

Cells develop into their mature forms and functions through the process of cell differentiation.

Cells differ because different combinations of genes are expressed. Every cell in your body has a full set of DNA but each type of cell

uses only the specific genes it needs to carry out its function- like a cookbook!

A cell’s location in an embryo helps determine how it will differentiate.

Outer: skin cells Middle: bone cells Inner: intestines

A cell’s location in an embryo helps determine how it will differentiate.

In animals, an egg undergoes many rapid divisions after it is fertilized.

The resulting cells can migrate to a specific area, and the cells quickly begin to differentiate.

The early animal embryo usually takes the shape of a hollow ball. As the embryo develops, part of the ball folds inward, forming an inner layer and creating an opening in the outer cell layer. A middle layer of cells then forms between the two.

Outer: skin cells Middle: bone cells

Inner: intestines

Outer

middle

inner

A cell’s location in an embryo helps determine how it will differentiate.

As shown in the figures, the outer cell layer differentiates to form the outer layer of skin and elements of the nervous system such as the spinal cord and brain.

The middle cell layer forms bones, muscles, kidneys, and the inner layer of skin

The inner cell layer forms internal organs such as the pancreas, lungs, and digestive systems.

Outer: skin cells Middle: bone cells Inner: intestines

Outer

middle

inner

What are stem cells, and why are they

important? Stem cells have the ability to

divide and renew themselves remain undifferentiated in form develop into a variety of specialized cell types

When a stem cell divides, it forms either 2 stem cells or 1 stem cell + 1 specialized cell.

Stem cells are classified into three types.– totipotent, or growing into any other cell type– pluripotent, or growing into any cell type but a totipotent

cell– multipotent, or growing into cells of a closely related cell

family

Stem cells come from adults and embryos.

Embryonic stem cells as their name suggests, are derived from embryos. Most embryonic stem cells are derived from embryos

that develop from eggs that have been fertilized by the in vitro process with the consent of the donors.

They are not derived from eggs fertilized in a woman's body.

can be grown indefinitely in culture Can turn into almost any type of Cell, so it is preferred over adult stem cells

The use of embryonic stem cells raises ethical issues

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.

Stem cells come from adults and embryos.

– Adult stem cells– The primary role in a living organism is to maintain and repair the

tissue in which they are found.– Where are adult stem cells found, and what do they normally

do?– Adult stem cells have been identified in many organs and tissues,

including brain, bone marrow, skeletal muscle, skin, teeth, heart, gut and liver.

– They are thought to reside in a specific area of each tissue (called a "stem cell niche").

– Stem cells may remain quiescent (non-dividing) for long periods of time until they are activated by a normal need for more cells to maintain tissues, or by disease or tissue injury.

– Typically, there is a very small number of stem cells in each tissue, and once removed from the body, their capacity to divide is limited, making generation of large quantities of stem cells difficult.

Adult stem cells continued…

– Scientists in many laboratories are trying to find better ways to grow large quantities of adult stem cells in cell culture and to manipulate them to generate specific cell types so they can be used to treat injury or disease.

– Some examples of potential treatments include regenerating bone using cells derived from bone marrow, developing insulin-producing cells for type 1 diabetes, and repairing damaged heart muscle following a heart attack with cardiac muscle cells.

Adult stem cell differentiation

Stem Cell developments UK, Japan scientists have discovered ways to

create tissues that would act like embryonic cells, without the need to collect the cells from embryos.

Cells grown by the same scientists above are thought to be linked to possibly killing cancer and other major diseases.

A new method for generating brain cells from urine samples is in the development stages. Skin like cells in the urine can be reprogrammed, via a

pluripotent state, into neurons, glia, liver cells and heart muscles.

Funding Stem Cell Research The U.S. Federal Court of Appeals has

overturned an August 2010 ban on federal funding of embryonic stem cell research . The ruling has been welcomed by the Obama Administration.

Private funding is also available through programs, universities, companies, etc…