Cell Structure

Cell Structure
History of the Cell - Scientist were aware of cells only after the discovery of microscopes.
“Guys” who contributed to cell theory:

Hooke (1665) – coined term ‘cell’
Van Leeuwenhoek – viewed first living cells
Schleiden (1838) – plants are composed of cells
Schwann (1839) – animals are composed of cells
Virchow (1858) – cells come from cells

Cell theory which states:

All living things are composed of one or more cells.
In organisms, cells are the basic units of structure and function.
Cells are produced only from existing cells.
ALL cells share certain structural characteristics:

Cell or Plasma membrane
Cytoplasm
Genetic Material

1. Cell or plasma membrane –

Composed of lipid bilayer and proteins.
Separates the cell contents from materials outside the cell.
Regulates what enters and leaves the cell, maintaining homeostasis; called selectively permeable.
Cell Membrane
2. Cytoplasm – gel-like substance that suspends organelles and contains sugars, amino acids, and proteins.
Contains Organelles – membrane-bound internal compartments that carry out specific functions.
Contains free-floating ribosomes.
Site of protein synthesis (where proteins are made).
Not considered organelles because they have no membranes surrounding them.

Ribosomes: the little
black dots!
Genetic material:
Composed of DNA
Controls reproduction of cell, contains hereditary information, and carries out the day-to-day cellular activities.
In eukaryotic cells, DNA surrounded by a double membrane (nuclear membrane) is the Nucleus.
Nuclear membrane is passageway for RNA and ribosome subunits.
Nucleus contains chromosomes (DNA super- wound around histone proteins into highly condensed form)
Nucleolus – where ribosome subunits are made.

Plant nucleus
Nuclear membrane and pores
DNA: chromatin
Nucleolus
The Interior of a Cell:

Internal Membranes (double layer of lipids):
Endoplasmic reticulum (ER)
Series of channels that weave through the cell transporting substances made by the cell
Isolated spaces of ER forming sacs are called vesicles
Rough ER – ER that contains ribosomes on the outside and carry proteins.
Smooth ER – ER with no ribosomes on the outside and carry lipids.

Rough ER
Sorry, no pictures
of smooth ER.
Vesicles
Golgi apparatus (bodies) – collect, package, and distribute molecules made in the cell.

Golgi bodies
Powerhouses:

Mitochondria
Contains folded membranes called cristae (increases surface area).
Generate energy for the cell through cellular respiration.


Chloroplast:
Consist of stacks of membranes called grana surrounded by liquid called stroma.
Sites of photosynthesis (make food in form of sugar) in plants and algae.
Chloroplasts
Central Vacuole
Grana

Stroma
Biochemical factories - membrane-bound spheres

Peroxisomes:
Some contain enzymes that convert fats to carbohydrates
Some alter harmful molecules to harmless molecules

Lysosomes
Contain digestive enzymes to breakdown proteins, nucleic acids, lipids, and carbohydrates
Digest and recycle the cell’s used component

Lysosome
Internal framework

A. Microtubules - hollow protein fibers that makeup:
Cytoskeleton: support shape of cell and anchor organelles

Cytoskeleton
Flagella – long, whip-like tail used for locomotion




Cilia – shorter, more numerous hairs cell

Centrioles – associated with microtubules that move chromosomes during cell division.

B. Microfilaments – protein fibers called actin and myosin; used in muscle contraction.

Central vacuole
Found in plant cell
Contains large amounts of water along with sugars, ions, and pigments.
Provides rigidity in plant cell (acts as “skeleton”)

Central Vacuole
Cell Wall
Found in plant cell.
Made of cellulose.
Surrounds cell membrane.
Provides structure.
Contains openings called plasmodesmata.
Cell Wall

Plasmodesmata