CELL STRUCTURE &

FUNCTION

CHAPTER 4

CELLS• ALL LIVING THINGS ARE MADE UP OF ONE

OR MORE CELLS

• A CELL IS THE SMALLEST UNIT THAT CAN CARRY ON ALL OF THE PROCESSES OF LIFE.

DISCOVERY OF CELLS

*Robert Hooke (mid-1600s)– Observed sliver of cork from the bark of a cork oak tree.– Saw “row of empty boxes”– Coined the term cell (reminded him of the cubicles or

“cells” where monks live.)

• Anton van Leewenhoek (1673) – First person to observe living cells.– Able to observe cells with green stripes from an alga of

the genus spirogyra and bell shaped cells on stalks of a protist of the genus vorticella

CELL THEORY• (1839)Theodor Schwann &

Matthias Schleiden“ all plants are made

up of cells”“ all animals are made

up of cells”

• (50 yrs. later) Rudolf Virchow“all cells come from cells”

• These three observationsWere combined to form a basic Theory about the cellular nature of Life.

CELL THEORY:

• All living things are made of cells

• Smallest living unit of structure and function of all organisms is the cell

• All cells arise from preexisting cells

CELL DIVERSITYCell Shape:• The diversity in cell shapes reflects the different functions of cells.• Each cell has a shape designed to allow the cell to perform its function effectively.

Cell Size:• The size of a cell is limited by the relationship of the

cell’s outer surface area to its volume..

Characteristics of All Cells• ALL CELLS HAVE THREE BASIC FEATURES IN COMMON:

Plasma membrane (cell membrane) – cell’s outer boundary, acts as a barrier between the inside and the outside of a cell

Cytoplasm- region of the cell within plasma membrane that includes fluid, cytoskeleton, and all organelles except nucleus.

Control center (nucleus)- contains DNA

TWO BASIC TYPES OF CELLS

Prokaryotic• First cell type on earth• Cell type of Bacteria and

Archaea• No membrane bound nucleus• Nucleoid = region of DNA

concentration• Organelles not bound by

membranes

Eukaryotic• Nucleus bound by

membrane• Include fungi, protists,

plant, and animal cells• Possess many organelles

that perform specific functions in the cell

• Usually much larger than prokaryotic cells

http://www.youtube.com/watch?v=yWy4o_UfZ4A&feature=related

ORGANELLES &

THEIR FUNCTION

Plasma Membrane• Functions: 1) allows only certain molecules in or

out of a cell 2) separates internal metabolic reactions from external environment 3) allows cell to excrete wastes and interact with its environment.

• Made primarily of phospholipids: Phospholipid B-Layer

• Membrane Proteins: Plasma membranes contain specific proteins embedded within the lipid bi-layer called integral proteins.

• Integral proteins play important roles in actively transporting molecules into the cell.

Nucleus

• Most of the functions of a eukaryotic cell are controlled by the nucleus, and houses/protects the cells genetic information.

• Nucleoplasm- jellylike liquid which holds the contents of the nucleus.

• Nuclear envelope – double membrane that surrounds nucleus. Made up of two phospholipid b-layers.

• Nucleolus – Dense area where DNA is concentrated.

Mitochondria• Tiny organelles that transfer energy from organic

molecules to adenosine triphosphate (ATP), which powers the cell.

• Mitochondrial DNA –mitochondria have their own DNA and can reproduce only by the division of preexisting mitochondria.

Ribosomes• Small roughly spherical organelles that are

responsible for building protein. Ribosomes do not have a membrane, they are made of protein and RNA molecules.

Endoplasmic Reticulum• System of membranous tubes and sacs, called

cisternae. • Functions: intracellular highway, a path along which

molecules move from one part of the cell to another.

• Two types of ER: - Rough endoplasmic reticulum – system of

interconnected flattened sacs covered with ribosomes, which produces proteins.

- Smooth endoplasmic reticulum- lacks ribosomes which has a smooth appearance and builds lipids.

Golgi Apparatus• system of flattened sacs that receive vesicles

from the ER containing newly made proteins or lipids. The Golgi apparatus labels and packs cellular products and prepares them for export.

• The “mail man” of the cell

Vesicles• Lysosomes- vesicles that bud from the Golgi

apparatus and contain digestive enzymes that break down large molecules. Lysosomes also digest worn-out organelles (autophagy), and break down cells (autolysis).

• Peroxisomes- abundant in liver and kidney cells where they detoxify alcohol and other drugs.

Cytoskeleton• Network of thin tubes and filaments that

crisscross the cytosol, which give shape to the cell.

CILIA & FLAGELLA

• CILIA & FLAGELLA: hair like structures that extend from the surface of the cell, where they assist in movement.

• Cilia are short and a re present in large numbers on certain cells whereas flagella are longer and far less numerous.

PLANT CELLS• Cell wall – rigid layer that lies outside the cell’s

plasma membrane, which contain a carbohydrate called cellulose.

• Central vacuole – A large, fluid-filled organelle that stores water, enzymes, metabolic wastes, and other materials.

• Chloroplasts – use light energy to make carbohydrates from carbon dioxide and water. Contains chlorophyll ( molecules that absorbs light and captures light energy for the cell)