PROKARYOTIC & EUKARYOTIC CELLS

As you have already learned, everything is made up of living cells.

And the cells themselves are made up of many different parts .

There are many different cells that do many different things, but all of these cells fall into one of the two main categories:

Prokaryotic cells

&

Eukaryotic cells

WHAT THE WORDS MEAN

Prokaryotes

Pro = before

Karyose = kernel, which represents the nucleus

So prokaryotes occurred before cells with a nucleus

Ex. Bacteria

Eukaryotes

Eu = true

Karyose = kernel, the nucleus

So eukaryotes are the cells with a true nucleus

Ex. Found in animals, plants, and fungi (yeast)

WHAT THEY HAVE IN COMMON

DNA

Cell (plasma) membrane

Ribosomes

Simple in Prokaryotic, complex in Eukaryotic

Cytoplasm

Allow the flow of nutrients and wastes to enter and leave the cell

Have similar metabolic ( life processes) like photosynthesis and respiration

Require a supply of energy

Made from the same basic chemicals

Carbohydrates, proteins, nucleic acid, fats, minerals, and vitamins

DIFFERENCES

That’s what they have in common, but there are significant differences too.

The two main ones are age and structure.

AGE DIFFERENCES

Scientists believe that prokaryotic cells (in the form of bacteria) were the first life forms on earth. They are considered “primative” and originated 3.5 billion years ago. That is 2 billion years before eukaryotic cells and billions of years before our earliest ancestor, the hominids.

4.6 billion years ago – Earth was formed

3.5 billion years ago – the first life arose: prokaryotic bacteria

1.5 billion years ago – eukaryotic cells arose

500 million years ago – multi-celled eukaryotes arose

3 million years ago – our earliest ancestor, the hominids, appeared

STRUCTURAL DIFFERENCES

Eukaryotic cells contain two important things that prokaryotic cells do not:

A nucleus

Membrane bound organelles

DNA

Although both contain DNA:

The DNA in eukaryotic cells in in the membrane bound nucleus

The DNA in prokaryotic cells floats around in the cell in what we call a Nucleoid – not a real structure, just a word to

describe the inside of the cell where the nuclear material sits

ORGANELLES

The organelles in eukaryotic cells allow them to perform more complex functions than prokaryotic cells.

Prokaryotic cells do not have organelles like eukaryotic cells.

Both have ribosomes, but they are much more complex in Eukaryotic cells.

CHLOROPLASTS AND MITOCHONDRIA

Evidence suggests that chloroplasts and mitochondria were once bacteria that developed a symbiotic relationship with cells that have a nucleus

Chloroplasts and mitochondria have their own DNA that is not a part of the cells.

Yes, plants have both chloroplasts and mitochondria.

SIZE

Eukaryotic cells are about 10 times larger than prokaryotic cells.

CELL WALL

Both have a cell wall, but they are made up of different substances. Well, eukaryotic plant cells do.

FLAGELLA & CILIA

Flagella and cilia are the structures that help cells move.

Eukaryotic flagella are more complex than prokaryotic flagella.

CHECK FOR UNDERSTANDING

Eukaryotic and Prokaryotic Cell Structure

Cell Structure Prokaryotic Cell Typical Animal Eukaryotic Cell

Cell Membrane Yes Yes

Cell Wall Yes No

Cilia or Flagella Yes, simple Yes, complex

Endoplasmic Reticulum No Yes

Golgi Complex No Yes

Lysosomes No Yes

Mitochondria No Yes

Nucleus No Yes

Ribosomes Yes, simple Yes, complex

NEW DISCOVERIES

Until recently, it was thought that only eukaryotic cells existed in multi-celled groups like in organs and tissue. Recent discoveries suggest that some prokaryotic cells do too.

This is just one more example of how new discoveries are always changing what we know – or think we know.

But that is what makes science so exciting!

http://www.ted.com/talks/lang/eng/bonnie_bassler_on_how_bacteria_communicate.html