Give an example of changes that take place as cells in a multicellular organism differentiate

Cells function differently in unicellular and multicellular organisms, but in every organism, each cell has specialized cell structures, or organelles, of which there are many. These organelles are responsible for a variety of cellular functions, such as obtaining nutrients, producing energy, and making proteins. Unicellular organisms are made up of only one cell that carries out all of the functions needed by the organism, while multicellular organisms use many different cells to function.

Unicellular organisms include bacteria, protists, and yeast. For example, a paramecium is a slipper-shaped, unicellular organism found in pond water. It takes in food from the water and digests it in organelles known as food vacuoles. Nutrients from the food travel through the cytoplasm to the surrounding organelles, helping to keep the cell, and thus the organism, functioning.

Multicellular organisms are composed of more than one cell, with groups of cells differentiating to take on specialized functions. In humans, cells differentiate early in development to become nerve cells, skin cells, muscle cells, blood cells, and other types of cells. One can easily observe the differences in these cells under a microscope. Their structure is related to their function, meaning each type of cell takes on a particular form in order to best serve its purpose. Nerve cells have appendages called dendrites and axons that connect with other nerve cells to move muscles, send signals to glands, or register sensory stimuli. Outer skin cells form flattened stacks that protect the body from the environment. Muscle cells are slender fibers that bundle together for muscle contraction.

The cells of multicellular organisms may also look different according to the organelles needed inside of the cell. For example, muscle cells have more mitochondria than most other cells so that they can readily produce energy for movement; cells of the pancreas need to produce many proteins and have more ribosomes and rough endoplasmic reticula to meet this demand. Although all cells have organelles in common, the number and types of organelles present reveal how the cell functions.

Cellular differentiation is the process by which a less specialized cell becomes a more specialized cell type.

Differentiation occurs numerous times during the development of a multicellular organism as the organism changes from a simple zygote to a complex system of tissues and cell types.

Differentiation is a common process in adults as well: adult stem cells divide and create fully-differentiated daughter cells during tissue repair and during normal cell turnover.

Differentiation dramatically changes a cell's size, shape, membrane potential, metabolic activity, and responsiveness to signals. These changes are largely due to highly-controlled modifications in gene expression.

With a few exceptions, cellular differentiation almost never involves a change in the DNA sequence itself. Thus, different cells can have very different physical characteristics despite having the same genome.

A cell that is able to differentiate into all cell types of the adult organism is known as pluripotent. Such cells are called embryonic stem cells in animals and meristematic cells in higher plants.

A cell that is able to differentiate into all cell types, including the placental tissue, is known as totipotent.

In mammals, only the zygote and subsequent blastomeres are totipotent, while in plants many differentiated cells can become totipotent with simple laboratory techniques.

Understanding:

•  Specialised tissues can develop by cell differentiation in multicellular organisms

•  Differentiation involves the expression of some genes and not others in a cell’s genome

    
Differentiation

Differentiation is the process during development whereby newly formed cells become more specialised and distinct from one another as they mature

All cells of an organism share an identical genome – each cell contains the entire set of genetic instructions for that organism

The activation of different instructions (genes) within a given cell by chemical signals will cause it to differentiate 

Cell Specialisation via Differential Gene Expression

Gene Packaging

Within the nucleus of a eukaryotic cell, DNA is packaged with proteins to form chromatin

• Active genes are usually packaged in an expanded form called euchromatin that is accessible to transcriptional machinery
• Inactive genes are typically packaged in a more condensed form called heterochromatin (saves space, not transcribed)

Differentiated cells will have different regions of DNA packaged as euchromatin and heterochromatin according to their specific function

Euchromatin versus Heterochromatin

What are some changes that take place as cells in a multicellular organism differentiate?

How do multicellular organisms differentiate?

How a multicellular organism goes from a single cell to hundreds of different types of cells with different structure and functions?

What type of organism has differentiated cell?