Introduction to the Cell

Ch.3 in online textbook

Discovery of Cell

• Robert Hooke – looked at cork cells and saw tiny units of life named them cell.

• Leeuwenhoek – invented a microscope to look at cells.

The Cell Theory

• Schwann and Schleiden• Proposed:– All living things are made of cells.– Basic building blocks of life.Virchow discovered:- Cells come from other cells.

- These scientists came up with the cell theory.

Cell Theory states:

• All organisms are made of one or more cells.• All the life functions of organisms occur within

cells.• All cells come from already existing cells.

Microscopes

• Light microscopes – view organisms by shining light through them. Must be a small slice of the organism.

• Electron microscope – uses a beam of electrons to observe extremely small objects.– Allowed scientists to see

organelles.

Cell size• To carry out cell functions they must be able

to quickly pass substances into and out of cell.• Anything that enters or leaves a cell must

cross its outer surface.• This limits how large a cell can be.

Surface Area : Volume

• The larger the cube (cell) the smaller surface area to volume ratio.

• Cells can’t get too large because they need enough surface area on the cell membrane to allow substances in and out.

Cell Shape

• Cells with different functions have different shapes.

• Function determines shape.

Parts of all cells• The plasma membrane (also called the cell membrane)

is a thin coat of lipids that surrounds a cell. It forms the physical boundary between the cell and its environment, so you can think of it as the “skin” of the cell.

• Cytoplasm refers to all of the cellular material inside the plasma membrane. Cytoplasm is made up of a watery substance called cytosol and contains other cell structures such as ribosomes.

• Ribosomes are structures in the cytoplasm where proteins are made.

• DNA is a nucleic acid found in cells. It contains the genetic instructions that cells need to make proteins.

Two Types of Cell

• Prokaryotic cells are cells without a nucleus. The DNA in prokaryotic cells is in the cytoplasm rather than enclosed within a nuclear membrane.

• Eukaryotic cells are cells that contain a nucleus.

Organelle

• Structure within the cytoplasm that performs a specific job in the cell.

Organelles:Mitochondria ChloroplastNucleus LysosomeVacuole Cell membraneSmooth Endoplasmic ReticulumRough Endoplasmic Reticulum Golgi Apparatus

Viruses

• Contain DNA• Lack the other parts

shared by all cells like, plasma membrane, cytoplasm, and ribosomes.

• Viruses are not cells.• They are not considered

living, but its debatable in the science community.

Cell Structures

Plasma Membrane

• Forms a barrier between the cytoplasm inside the cell and the outside.

• Protects and supports the cell and controls everything that enters and leaves the cell.

• Allows only certain substances to pass through, while keeping others in or out.

Phospholipid bilayer

• Molecule with a head and two tails.• Head “loves” water, hydrophilic.• Tails “hate” water, hydrophobic.

Crash course – the cell

• https://www.youtube.com/watch?v=cj8dDTHGJBY