CH.7 CELL STRUCTURE AND FUNCTION

THE DISCOVERY OF THE CELL It was not until the mid-1600’s that scientists began to use microscopes to observe cells. In 1665, Englishman Robert Hooke used an early compound microscope to look at a slice of cork, plant material.

CORK CELLS

Hooke saw thousands of empty chambers which he called cells Hooke saw thousands of empty chambers which he called cells. They reminded him of a monastery’s tiny rooms, which were called cells. In Holland around the same time, Anton van Leeuwenhoek used a single-lens microscope to observe pond water and other things. He discovered that living things seemed to be everywhere, even in the water he was drinking.

Paramecium Spirogyra

THE CELL THEORY In 1838, German botanist Matthias Schleiden concluded that all plants were made of cells. In 1839, German biologist Theodor Schwann stated that all animals were made of cells.

In 1855, German physician Rudolf Virchow concluded that new cells could be produced only from the division of existing cells. These discoveries, confirmed by other biologist, are summarized in the cell theory.

CELL THEORY STATES… 1. All living things are composed of cells. 2. Cells are the basic units of structure and function in living things. 3. New cells are produced from existing cells.

THE CHANGE OF THE MICROSCOPE Hooke, Virchow, and others used crude microscopes to study the cells. Today scientist can use a variety of different techniques.

High resolution video to make movies of cells as they grow. Transmission electron microscope electrons pass through thin slices of cell parts Cells must be dead and in a vacuum

CONFOCAL LIGHT TEM TEM CHLOROPLAST

Scanning electron microscope produces three-dimensional images of cells Do not have to cut cells into slices Vacuum TEM is more powerful than SEM

SCANNIING ELECTRON MICROSCOPE MARINE DIATOM SEM SCANNIING ELECTRON MICROSCOPE pea weevil egg

White pine sheath mite on eastern white pine Scanning electron microscope image of white pine sheath mite

Sheet metal as seen with an SEM

PROKARYOTES and EUKARYOTES Cells fall into two categories, depending on whether they contain a nucleus. Eukaryotes (YOUkaryotes)- have a nucleus. Prokaryotes (Pro=NO)- no nucleus.

PROKARYOTIC CHARACTERISTICS Smaller than eukaryotic cells Genetic information is not contained by a nuclear membrane NO internal membranes Less complex compared to eukaryotic cells

Some glide and swim through liquids. Forms of locomotion are: Cilia – hair like structures Flagella – whip like structure. ------- Example of Prokaryotes: Bacteria

EUKARYOTIC CHARACTERISTICS Larger than prokaryotes They usually contain dozens of structures and internal membranes = organelles Genetic info is carried by a nucleus. Some live solitary lives while other form large multicellular organisms. Examples: plants, animals, fungi, and protist.

PARTS OF THE CELL Cell biologists divide eukaryotic cell into two parts: the nucleus and the cytoplasm. The cytoplasm is the portion of the cell that is outside the nucleus. (includes the organelles) Cytosol = is the internal fluid of the cell, and a large part of cell metabolism occurs here

THE NUCLEUS The nucleus is the control center of the cell. It contains the cell’s DNA and the code for making proteins and other important molecules. The nucleus is surrounded by a nuclear envelope composed of two membranes.

The envelope is dotted with thousands of pores, which allow materials to leave the nucleus to other parts of the cell. Inside of the nucleus is a granular material called chromatin. Chromatin consists of DNA bound to protein (histones).

Structure of DNA http://www.johnkyrk.com/chromosomestructure.html

When a cell divides, the chromatin condenses to form chromosomes. These are the distinct structures that are passed from cell to cell…generation to generation. Deep inside the nucleus is the nucleolus which is where assembly of ribosomes begins.

? QUESTION ? WHAT KIND OF INFORMATION IS CONTAINED IN CHROMOSOMES ? ANSWER: Genetic Information known as DNA

RIBOSOMES One of the most important jobs carried out in the cell is making proteins. Proteins are assembled in ribosomes.

Ribosomes are small particles of RNA and protein found throughout the cell (mostly cytoplasm). Ribosomes produce proteins by following coded instructions that come from the nucleus.

? QUESTION ? WHAT DO RIBOSOMES PRODUCE ? ANSWER: PROTEINS

ENDOPLASMIC RETICULUM The endoplasmic reticulum also known as ER. It is the site where lipid components of the cell membrane are assembled, along with proteins and other materials.

The portion of the ER involved in synthesis of proteins is called Rough ER. Rough ER = ribosomes found on the surface. Newly made proteins leave ribosomes and are inserted into the Rough ER, where they can be chemically modified.

There are other portions of the ER called Smooth ER because no ribosomes are embedded. Smooth ER contains enzymes that synthesize lipids and the detoxification of drugs. (liver cells contain a lot of Smooth ER)

? QUESTION ? WHAT IS THE ROLE OF THE Rough ER ? ANSWER: to synthesize proteins & chemically modify them

GOLGI APPARATUS The Golgi Apparatus receives proteins from the Rough ER. The job of the Golgi Apparatus is to modify, sort, and package proteins for storage or secretion outside the cell.

The Golgi Apparatus is like a customizing shop that puts on the final touches before proteins are shipped out. It is also like the UPS of the cell. It doesn’t make anything, but it sorts and packages items.

Golgi Animation http://www.johnkyrk.com/golgiAlone.html

? QUESTION ? WHAT IS THE ROLE OF THE GOLGI APPARATUS ? ANSWER: It modifies, sorts, and packages proteins, lipids, and other materials/chemicals.

VACUOLES Vacuoles are saclike structures that store materials such as water, salts, proteins, and carbohydrates in all organisms. Plant cells have vacuoles. They help each cell maintain water pressure to hold up heavy structures such as leaves and flowers.

Some single-celled organisms & plants have contractile vacuoles which regulates the water inside the cell. Contractile vacuoles help cells maintain Homeostasis or “internal balance” Central Vacuole = holds water and waste materials for plants

? QUESTION ? WHAT IS THE ROLE OF A VACUOLE ? ANSWER: They store materials and help plants maintain their structure

LYSOSOMES Lysosomes are the clean up crew of the cell. They are small organelles filled with enzymes that break down and digest lipids, carbohydrates, and proteins.

? QUESTION ? WHAT IS THE ROLE OF THE LYSOSOME ? ANSWER: clean up the cell and get rid of material & breaks down lipids, carbohydrates, and proteins

CELLS AND THEIR POWER Nearly all eukaryotic cells, including plants contain Mitochondria. Mitochondria are organelles that convert the chemical energy stored in food into compounds that are more convenient.

In humans, all or nearly all our mitochondria come from the cytoplasm of the ovum, or egg cell. In plants, chloroplasts are the organelles that capture the energy from the sunlight and convert it into chemical energy in a process called photosynthesis.

Both mitochondria and chloroplast are the only organelles that have small DNA molecules. Scientist have evidence that these two organelles may have been descendants of ancient prokaryotes at one time.

CYTOSKELETON The cytoskeleton is a network of protein filaments that help the cell maintain its shape. Microfilaments and Microtubules make up the cytoskeleton. Microfilaments are threadlike made of a protein called actin.

Microtubules are hollow structures that are made up of proteins called tubulins. In animal cells, tubulin helps in the development of centrioles. Centrioles are located near the nucleus and help in cell division.

Cell wall (plants, fungus, and some protists) = tough outer covering Cell membrane = phospholipid double layer with protein, carbohydrates, and other molecules embedded. Cell wall (plants, fungus, and some protists) = tough outer covering Plants – made of cellulose Fungus – made of chitin