Standard B-2.4 Cell Differentiation

The student will be able to: Explain the process of cell differentiation as the basis for the hierarchical organization of organisms.

Key Concepts Cell Organization Cell Differentiation Stem Cells

It is essential for you to know: In the development of most multicellular organisms, a single cell (fertilized egg) gives rise to many different types of cells, each with a different structure and corresponding function. Nearly all of the cells of a multicellular organism have exactly the same chromosomes and DNA. Stem cells are unspecialized cells that continually reproduce themselves and have, under appropriate conditions, the ability to differentiate into one or more types of specialized cells.

TODAY’S OBJECTIVES: Explain the process of cell differentiation. Recall that all of the cells of a particular organism contain all of the genetic code. Summarize the unique characteristics of embryonic and adult stem cells.

How do we get from ….. ATOM to ANTONIO? (a person)

Organization Levels of Life Atom to Organism

Levels of Organization Nonliving Levels: ATOM (element) MOLECULE (atoms joining together to create compounds like carbohydrates & proteins) ORGANELLES (nucleus, ER, Golgi …)

Levels of Organization Living Levels: CELL (makes up ALL organisms) TISSUE (cells working together) ORGAN (heart, brain, stomach …) ORGAN SYSTEMS (respiratory, circulatory, digestive…) ORGANISM (you, frog, tree)

Levels of Organization Living Levels continued: POPULATION (one species in an area) COMMUNITY (several populations in an area ECOSYSTEM (forest, prairie …) BIOME (Tundra, Tropical Rain forest…) BIOSPHERE (all living and nonliving things on Earth)

Nonliving levels….. Atom ---------- Molecule -------

LIFE STARTS AT THE CELLULAR LEVEL!! Organelles ------ Cell -------

Living levels Tissue ------- Organs ----

Living levels cont’d… Organ Systems ---- Organism

Let’s go back to where life started… LIFE STARTS AT THE CELLULAR LEVEL!

Now that we have learned how living things are organized, what’s next? We will learn more about the lowest level or organization: cells What is the first thing that we need to know about cells? All cells fall into one of the 2 major classifications: PROKARYOTIC or EUKARYOTIC

Prokaryotic vs. Eukaryotic

What’s the difference b/w prokaryotes and eukaryotes? Prokaryotic cells were here 1st and for billions of years, they were the only form of life on Earth. All prokaryotic organisms are unicellular. Eukaryotic cells appeared on Earth long after prokaryotic cells but they are much more advanced. Unlike prokaryotic organisms, eukaryotic organisms can be uni- or multicellular.

Characteristics of Prokaryotes Simplest type of cell. Oldest type of cell: appeared 4 billion yr ago. Largest group of organisms. (more prokaryotes than eukaryotes) Unicellular organisms that are found in all environments. (commonly called bacteria)

Characteristics of Prokaryotes Prokaryotes DO NOT have a nuclear membrane: have a single, circular chromosome in a place called the nucleoid region. (middle of cell) DO NOT have membrane bound organelles: have ribosomes to make proteins, but they don’t have a membrane.

Characteristics of Prokaryotes Are much smaller in size than the eukaryotic cells. Very simple internal structure. So what do these simple cells look like?

Prokaryotic cell

Characteristics of Eukaryotes Most complex type of cell. Appeared about 1 billion yr ago. Generally more advanced than prokaryotes. Nuclear membrane surrounds linear genetic material (DNA).

Characteristics of Eukaryotes Eukaryotic cells have several different parts which means they have a complex internal structure. Larger in size than prokaryotic cells. 2 main types of Eukaryotic cells: Plants Animals

Eukaryotic Cell

How are they different? Organelles lack a membrane. Ribosomes are the only organelles. Genetic info floats around uncontained. Organelles have a membrane. Multiple organelles including ribosomes. Genetic info is contained within the nucleus. PROKARYOTIC CELLS EUKARYOTIC CELLS

How are they different? Circular DNA Unicellular Cells are small in size Has large # of organisms 4 billion yr ago Linear DNA Uni- or multicellular Cells are large in size Has smaller # of organisms. 1 billion yr ago PROKARYOTIC CELLS EUKARYOTIC CELLS

How are they similar? Have cell membranes (outer covering of the cell) Both: Have cell membranes (outer covering of the cell) Have ribosomes Have DNA Have a liquid environment within called the cytoplasm

Cells Differentiate…..

Life Begins… All life begins with a single cell, a fertilized egg called a zygote.

Differentiation The fertilized egg gives rise to many different types of cells in a multicellular organism. Each cell has a special shape and job (structure/function)

As cells differentiate, they organize themselves into tissues, then organs, then organ systems. Working together, the whole organism is complete.

Not so fast, though…. Even though cells are differentiated, they contain the same DNA in their nuclei. During differentiation, only some parts of that DNA are activated (turned on) Since all cells have the same DNA, they all have the potential to become any type of cell. Once a cell specializes, it cannot be reversed.

Stem Cells A type of cell that is UNSPECIALIZED. They have not yet differentiated into a certain cell type. 2 types of stem cells: Embryonic stem cells Adult stem cells

Embryonic stem cells Found in embryos Can give rise to any type of cell You kill the embryo when harvesting embryonic stem cells Very controversial

Adult stem cells Found in human adults. Bone marrow can give rise to blood or bone cells. Not controversial b/c the human doesn’t die when adult stem cells are harvested.

HOMEWORK: Make a Venn Diagram showing the SIMILARITIES and DIFFERENCES between Prokaryotic and Eukaryotic cells.