Cell Structure and Function

The Cell Theory

• All living things are made of one or more cells

• All cells come from pre-existing cells

• Cells are the basic unit for structure and function of all organisms

Cell structure

• All cells are surrounded by a plasma (cell) membrane

• Cells contain organelles - small structures inside cells that perform various jobs

• All cells can be divided into two main categories:

Prokaryotic vs. Eukaryotic Cells

Prokaryotic- no nucleus

- Very small (1-10 um)

- Have very few organelles

Eukaryotic- have a nucleus

- Larger 10-100um (some larger)

- Have many organelles

Eukaryotic Cells

• Plant and animal cells are eukaryotic as well fungi and protists (amoeba, paramecium, etc)

• Plant and animal cells have important differences (see diagrams)

Eukaryotic Cellular Organization

• Single celled organisms (unicellular)

• Multiple celled organisms (multicellular)

- in multicellular organisms, cells

become specialized (do a particular

job)

Plasma (cell) membrane

• Consists of a double layer of lipids

• The outside and inside of the membrane is hydrophilic (“water-loving”)

• The interior of the membrane is hydrophobic (“water-fearing”)

• Substances must cross the membrane to enter and exit the cell

Types of Membrane Transport

Passive Transport (requires NO energy)• Moves substances from a high to a low concentration • Diffusion & osmosis, facilitated diffusion

Active Transport (requires energy)• Substances move from a low to a high concentration• Endocytosis & exocytosis

Concentration gradient

• Passive transport moves substances WITH (or DOWN) their concentration gradient

• Active Transport moves substances AGAINST their concentration gradients

HIGH LOW

ACTIVE TRANSPORT

PASSIVE TRANSPORT

Diffusion

• Movement of a substance from a high concentration to a low concentration

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Osmosis

• Movement of water from a high water concentration to a low water concentration

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Osmosis in Different Cellular Environments

• Hypotonic - solution with a lower solute concentration than the cytoplasm of the cell

• Hypertonic - solution with a higher solute concentration than the cytoplasm of the cell

• Isotonic - has same solute concentration as the cytoplasm of the cell

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

• Turgor pressure - pressure (from water) pushing against the cell wall of a plant (makes plant cells firm)

• Plasmolysis - shrinking of the cytoplasm of a cell caused by the loss of water (causes plants to wilt)

Facilitated Diffusion

• Diffusion using membrane protein channels

• Some substance must use protein channels since they cannot pass through the lipid layer of the membrane

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Active Transport

• Requires the input of energy to move a substance against its concentration gradient (low to high)

• Energy is used in the form of ATP (energy molecule produced in mitochondria)

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Types of Active Transport: Endocytosis, Exocytosis and Ion Pumps

• Endocytosis - cell takes in substances too large to pass through the membrane

• Exocytosis - cell gets rid of large substances

• Ion pumps - pump ions against their concentration gradient

See endocytosis and exocytosis in action