Chapter 7

The Cell

• Cells Were discovered by Robert Hooke. He observed the slices of cork from the bark of an oak tree-dead plant cells. Van Leewenhoek observed pond water & saw it was full of living things.

• Observations and conclusions of scientists from the late 17th century to the time of scientists, Schwann, Schleiden, and Virchow are summarized into the Cell Theory.

Three parts of the cell theory:1. All living things are made of one or more cells.2. The cell is the basic unit of structure and function in organisms.3. All cells come from pre-existing cells.

= Life

1. There are two cell types:1.) Prokaryote-the simplest cells

* Small, simple and lack membrane-bound organelles.

*They have no nucleus. *DNA is found floating in the cytoplasm.

Prokaryotic cells contain:*cell wall*cell or plasma membrane*cytoplasm*ribosomes

Examples: BACTERIA* Flagella-Many bacteria have flagella, which are long, threadlike structures that protrude from the cell’s surface and enable movement.* Bacteria flagella rotate, propelling a bacterium through its environment.

2.)Eukaryote*Large, complex and contain membrane bound organelles such

as a nucleus.* Example: Plants, Fungi, and Animals

* Eukaryotic cells have a nucleus which is an internal compartment that houses the cell’s DNA. Other internal compartments, called organelles, enable eukaryotic cells to function in ways different from bacteria.

* An organelle is a structure that carries out specific activities in the cell.

– Many single-celled eukaryotes use flagella for movement. Short hair like structures packed in tight rows, called cilia protrude from the surface of some eukaryotic cells. Flagella or cilia propel some cells through their environment.

– In other cells, cilia and flagella move substances across the cell’s surface. Example: Cilia on cells of the human respiratory system sweep mucus and other debris out of the lungs.

CiliaFlagella

2. Cell Size:

The symbol “μ” stands for the prefix micro. A micrometer (μm) is a unit of linear measurement equal to one-millionth of a meter, or one-thousandth of a millimeter. Cell size and organelle size is measured in micrometers (μm). This means that they are microscopic.

Both Animal and Plant Cells Contain These Organelles

• 1. Cell Membrane– The cell membrane is primarily composed of

phospholipids. Various proteins are located in the lipid bilayer of a cell membrane. A phospholipid is a lipid made of a phosphate group (head) and two fatty acids (tails).

A phospholipid “head” is polar and its two fatty acid “tails” are nonpolar. Transport proteins aid in the movement of substances into and out of the cell.

– It surrounds and protects the cell and allows only certain substances to pass in and out of the cell. The cell membrane allows the cell to remain separate from the environment.

Both Animal and Plant Cells Contain These Organelles

• Cell Membrane Cont.– It is a Selectively permeable membrane, which

means it keeps out some molecules but allows others to pass through.

Small molecules like H2O, CO2,O2 and soluble end products of digestion pass through easily.

Large molecules like glucose and ions do not pass through easily.

The cell membrane regulates or controls what comes into and out of the cell. Like gases, nutrients and wastes. This control keeps the cell alive and well. If it wasn’t selectively permeable everything on the outside would come into the inside.

Both Animal and Plant Cells Contain These Organelles

• 2. Cytoplasm– A fluid-like material that fills the space

between the cell membrane and the nucleus.– Contains the organelles

• **The cytoskeleton (in the cytoplasm) is a web of protein fibers that holds the cell together and keeps the cell membrane from collapsing or folding.

Both Animal and Plant Cells Contain These Organelles

• 3. Nucleus– The control center of “brain” of the cell (Most functions of a

eukaryotic cell are controlled by the cell’s nucleus).– The nucleus directs cell activities and stores DNA.– Stores DNA which forms long strands called chromatin.

(Chromatin is made of DNA and proteins that become chromosomes during cell division.” **Chromosomes carry the genes (DNA and are in the nucleus of eukaryotic cells**

– The nucelus is surrounded by a double membrane called the nuclear envelope or membrane. The nuclear envelope is made of two bilayers that separate the nucleus form the cytoplasm.

– Substances that are made in the nucleus include ribosomal proteins and RNA, which move into the cytoplasm through nuclear pores.

Both Animal and Plant Cells Contain These Organelles

• 4. Nucleolus– Dense struc-

tures inside the

nucleus.– Stores RNA

that forms

ribosomes.

Both Animal and Plant Cells Contain These Organelles

• 5. Ribosomes–Tiny “dot” organelles located on the

rough ER and throughout the cytoplasm.

–They are the site of protein synthesis.–A cell makes proteins on ribosomes.

The building of proteins from amino acids occurs on the cell’s ribosomes.

–Some ribosomes float freely in the cytoplasm, while others are attached to the endoplasmic reticulum.

Both Animal And Plant Cells Have These Organelles

• 6. Endoplasmic Reticulum– Materials can be moved around within a cell by using

the endoplasmic reticulum. The rough ER helps transport the proteins that are made by its attached ribosomes. As each protein is made, it crosses the ER membrane and enters the ER. The portion of the ER that contains the completed protein then pinches off to form a vesicle. A vesicle is a small, membrane-bound sac that transports substances in cells. By enclosing certain proteins inside vesicles, the eukaryotic cell keeps these proteins separate from proteins that are produced by free ribosomes in the cytoplasm. Proteins must enter the endoplasmic reticulum to be transported to other parts of the cell.

Both Animal And Plant Cells Have These Organelles

• 6 Endoplasmic Reticulum Cont.– A network of tunnels, channels or canals that transports proteins

and other substances throughout the cell. The canals of the ER connect the cell membrane with the nuclear membrane.

– Two Types of ER:– 1. Rough ER

» Has ribosomes on the membrane and helps transport the proteins that are made by its attached ribosomes.

» A vesicle is a small, membrane-bound sac that transports substances in cells. By enclosing certain proteins inside the vesicles, the eukaryotic cell keeps these proteins separate from proteins that are produced by free ribosomes in the cytoplasm.

– 2. Smooth ER

» It lacks ribosomes (appearing smooth) and produces certain lipids.

Both Animal And Plant Cells Have These Organelles

• 7. Golgi Apparatus– Vesicles that contain newly made proteins move

through the cytoplasm from the ER to an organelle called the golgi apparatus.

– It is stacks of flattened membranes with vesicles that packages and assembles many cell products. The Golgi Apparatus serves as the packaging and distribution center. It receives, chemically modifies, and repackages proteins into forms the cell can use, expel, or keep stored. The modified proteins are then enclosed in new vesicles that bud from the surface of the golgi apparatus. Some of these vesicles include lysosomes.

Both Animal And Plant Cells Have These Organelles

• 8. Lysosomes– Small spherical or- ganelles that contain digestive enzymes.– They take care of foreign particles entering the cell and “digest” worn out cell parts.

Both Animal And Plant Cells Have These Organelles

• 9. Mitochondria – They are called the “powerhouse” of the cell

because it produces energy (ATP). – They are the site of aerobic cellular

respiration.– A cell that requires a lot of energy, like a

muscle cell, would contain large numbers of mitochondria.

=

Mitochondria Power

Both Animal And Plant Cells Have These Organelles

• 10. Vacuole– Small, fluid-filled structures that store

materials like food, enzymes, and other materials needed by the cell.

– **Plant Cell have a single large vacuole.**

Found In Animal cells Only

• Centrioles– Tiny, cylindrical structures that are found in

pairs near the nucleus.– They are involved in cell division.

Found In Plant Cells Only• 1. Chloroplasts

– Small green pigmented structures that contain chlorophyll.

– It is the site of photosynthesis.

Found in Plant Cells Only

• 2. Cell Wall– The cell wall consists of a mixture of proteins

and carbohydrates, including the polysaccharide cellulose. A polysaccharide is also known as a sugar.

– Structure found outside of the cell membrane in plants that provides strength and rigidity, but does not affect passages of materials in and out of the cell

**Plant cells have a LARGE vacuole that stores water which can occupy most of the space in a plant cell.**