The Cell The basic unit of life

The Cell Theory The cell is the basic unit of life. All living things are composed of cells. New cells come from existing cells.

Who? When? Antonie von Leeuwenhoek, from Holland has long been given credit for inventing the first microscope. When? He used a microscope in 1673!

Who? When? However, Robert Hooke, from Britain, is credited with viewing with a microscope much earlier. When? His work was recorded in 1665.

What? Robert Hooke viewed the cells of cork wood, while Antonie von Leeuwenhoek viewed living microscopic organisms under the microscope.

This is a sketch of the cork cells, which Hooke drew in his notes. These are actual cork cells as viewed through a microscope.

Leeuwenhoek viewed “bee mouth parts and stings” as well as fungus and human louse. He also viewed bacteria, such as the ones pictured below.

Early discoveries about cells: 1838 Schleiden announced that all plant tissue is composed of cells. 1839 Schwann describes animal cells as being similar to plant cells. 1840 Virchow determined that cells come only from existing cells.

There are many different kinds of cells: Bacteria Red Blood Cells Single Celled Animals Plant Cells Skin Cells

Out of all these kinds of cells, there are actually only two types of cells: Prokaryotes and Eukaryotes

Characteristics of the two types of cells: Prokaryotes Eukaryotes Capsule Single circular chromosome No membrane bound nucleus No organelles Small (0.25mm-3mm) Cell division by fission* Plasma membrane Linear molecule chromosomes Well defined nucleus Membrane-bound organelles Larger (4.6mm+)* Cell division by mitosis* Example: Everything else! (plants, animals, protists, fungi) Example: Bacteria

Prokaryote means: Pro = before Karyon = nucleus

Eukaryote means: Eu = true Karyon = “Kernel” or nucleus

Prokaryote Cells:

Eukaryotic Cells:

There are two types of Eukaryotic Cells: Animal Cells and Plant Cells

Cell Growth Does the adult bear have larger cells than the bear cub? …Or does the adult bear have more cells than the baby bear?

On average, the adult animal’s cells are no larger than the baby’s. The adult just has more cells than the baby. The same thing is true for any living organism! Including this huge oak tree and this tiny oak sapling!

Why do cells stay small? As cells grow, the surface area to volume ratio decreases. (This means that there will be less surface area per unit of volume inside the cell. )

Why does this matter? Because the surface of cells are covered with signaling proteins, which communicate between the inside of the cell and the outside of the cell. These proteins tell the membrane what can come into the cell and what can go out of the cell.

Animal Cells: Nucleolus Nucleus 8. Smooth Endoplasmic Reticulum Ribosome Vesicle Rough Endoplasmic Reticulum Golgi Body Microtubule 8. Smooth Endoplasmic Reticulum 9. Mitochondria 10. Lysosome 11. Cytoplasm 12. Peroxisome 13. Centriole

Animal cells have cell membranes: Fluid mosaic model of the cell membrane Lipid Bilayer

Inside the nucleus of an animal cell:

Electron micrograph of the nucleus: nucleolus

Organelles of the animal cell: The “E.R.” – The smooth endoplasmic reticulum functions in synthesis of lipids and phospholipids. Proteins are synthesized by ribosomes which are on the rough E.R.

Golgi Apparatus- or complex, functions in storage, modification, and packaging of protein products, especially secretory products. These vesicles may add complex carbohydrates to protein molecules. These vesicles bud off the “maturing face” of the complex. (ex. lysosomes)

The Golgi works with the E.R.

Mitochondria – enzymes located on the cristae carry out energy-yielding steps of aerobic metabolism.

Cytoskeleton – this is the structural part of the cell. It provides support and a means of locomotion of organelles within the cell. The cytoskeleton is made up of several kinds of tubules and filaments: Microtubules – These are composed of a protein called tubulin. Microfilaments - These are made up of proteins called actin and myosin Intermediate filaments – There are five Biochemically distinct types. They vary based on what type of cell in which they are found.

The Centrisome – this is made up of two centrioles at right angles to each other. Microtubules radiating from here are called the aster. This is the microtubule organizing center. centrisome centriole

Cell surfaces and their specializations: Cilia – motile extensions of the cell surface that sweep materials past the surface of the cells. (Usually short and numerous like many fine hairs.) Flagella – also motile extensions. (Usually long and single or only two or three.) Both cilia and flagella are similar in internal structure. They are composed of a long cylinder of nine pairs of microtubules enclosing a central pair. At the base of each cilium or flagella is a basal body, Which is identical in structure to a centriole.

cilia

flagella

Microvilli – these are fingerlike projections which increase the surface area of the cell for absorption.

Methods of cell locomotion: Cilia and flagella are able to propel single- celled or small creatures. Amoeboid movement – single-celled organisms use extensions of the cytoplasm as “false feet,” or Pseudopodia. The cytoplasm streams and the action of the microfilaments contracting moves the cell. pseudopodia

Cell membranes – function to communicate between neighboring cells. They also serve as a selectively permeable barrier. It functions in cellular metabolism.

Ways materials can pass through the cell membrane: Diffusion – movement of particles from an area of high concentration to an area of lower concentration. (Concentration gradient – when a difference exists between the concentration inside and outside the cell.) Osmosis – water molecules move through a selectively permeable barrier across a concentration gradient. Mediated transport – special proteins called transporters or permeases move biologically important molecules into and out of the cell. (These are usually macromolecules.)

Two kinds of mediated transfer: Facilitated diffusion – permease assists a molecule permeate a membrane that it would not normally be able to penetrate. Active transport – energy is supplied to the transporter system to transport molecules in the direction opposite the concentration gradient.

Endocytosis – the ingestion of material by cells. (Ex. 1 Phagocytosis – “cell eating.” Common among protozoa. Ex. 2 Potocytosis – small areas of the surface membrane are invaginated to form tiny vesicles called caveolae. Ex 3 Pinocytosis = cell drinking.) Exocytosis - membranes of vesicles within the cell fuse with the plasma membrane in order to let wastes exit the cell.

Plant Cells

Plant cells differ from animal cells: cellulose cell walls Plant cells have cell walls made of cellulose.

Plant cells have pores for transport between cells:

Plants have a large storage vacuole:

Plant cells have chloroplasts used for photosynthesis. These convert light energy into chemical bond energy. This is how plants manufacture their own food.

Chloroplasts visible in real plant cells:

Cells can be differentiated to perform different functions within the same organism: For example, in an eight week old fetus, there are: heart cells fat cells muscle cells bone cells skin cells bone marrow cells All are cells, but they all do different things!

What is the largest cell on Earth? Answer : An unfertilized Ostrich egg!

The End