A View of the Cell

1. A View of the Cell Dr. Stafford 2016

2. A View of the Cell • Before microscopes people believed in curses and the supernatural as the cause of diseases • Microscopes opened a whole new world – Microorganisms – organisms only seen by microscope • Cells – the building blocks of all living organisms

3. A View of the Cell • Anton van Leeuwenhoek used a simple microscope with natural light in mid 1600’s • Compound light microscope – 2 or more lens magnify up to 1500X’s • Had to learn size relationships • http://www.cellsalive.com

4. A View of the Cell • The cell theory - three main ideas 1. All organisms are composed of one or more cells – unicellular or multicellular 2. The cell is the basic unit of organization 3. All cells come from preexisting cells – cells that are living

5. A View of the Cell • Cell theory (cont.) • Scientists involved in its development 1. Robert Hooke – cork cells – named cells after rooms in monastery 2. Matthias Schleiden – observed plants and determined they were cells 3. Theodore Schwann – observed animals

6. A View of the Cell • Electron microscopes – 1940’s – 500,000X 1. Used beam of electrons instead of light 2. Scanning electron microscope (SEM) – scan surface – 3-D shape 3. Transmission electron microscope (TEM) – structures inside cell

7. A View of the Cell • Two different types of cells 1. Prokaryotes – means Pro = before and Karyote = nucleus – so prokaryote means cells without a nucleus. Also has no membrane- bound organelles – example bacteria

8. A View of the Cell • Two types of cells (cont.) 2. Eukaryotes – means eu = after and karyote = nucleus so eukaryote cells have a nucleus and also membrane-bound organelles – examples are plants and animals and all organisms except bacteria

9. A View of the Cell • Two types of cells (cont.) • All cells have 1. DNA 2. Cytoplasm 3. Ribosomes 4. Cell membrane

10. A View of the Cell • Two types of cells (cont.) Eukaryotes also have a nucleus and membrane-bound organelles that allow compartmentalization – Many chemical reactions can occur in the cell at the same time. Also the nucleus protects the DNA.

11. Plasma membrane

12. Cell (Plasma) Membrane • Homeostasis –The process of maintaining the cell’s internal environment constant.

13. Cell (Plasma) Membrane • Plasma membrane – cell membrane – the boundary between the cell and its environment. The plasma membrane defines the cell and controls what goes into and out of a cell. • The plasma membrane must let nutrients into the cell and allow waste and other products to leave the cell.

14. Cell (Plasma) Membrane • Plasma membrane (cont.) • Selective permeability – allows some things to go into or out of the cell while not allowing other things to flow through it. Compare it to a screen on a window – lets air through but not bugs.

15. Cell (Plasma) Membrane • Plasma membrane (cont.) • Structure of plasma membrane 1. Phospholipids – lipids with a phosphate group attached to it. The phosphate head is polar and likes water while the fatty acid tails are nonpolar and hate water. They align themselves in a bilayer (2 layers) with the phosphate heads toward the watery environment inside and outside the cell.

16. cell membrane • Cell membranes are composed of two phospholipid layers.

17. Cell (Plasma) Membrane • Plasma membrane (cont.) • Structure of plasma membrane (cont.) 1. Phospholipids (cont.) The fatty acid tails align themselves with each other to form a nonpolar layer between the two layers of phosphate heads.

18. cell membrane • Cell membranes are composed of two phospholipid layers. • The cell membrane has two major functions. • forms a boundary between inside and outside of the cell • controls passage of materials outside cell inside cell

19. Cell (Plasma) Membrane • Plasma membrane (cont.) • Structure of plasma membrane (cont.) Fluid mosaic model – called this because it is flexible with the phospholipids move within the membrane as a water molecule moves in a lake.

20. Cell (Plasma) Membrane • Plasma Membrane (cont.) • Structure of plasma membrane (cont.) 2. Cholesterol – a lipid molecule – prevents the fatty acids in phospholipids from sticking together. 3. Transport proteins – allows substances to enter or leave the cell through the plasma membrane.

21. Cell (Plasma) Membrane • Plasma membrane (cont.) • Structure of plasma membrane (cont.) 4. Proteins and carbohydrate chains stick out from the outer surface of the cell membrane for identification and communication with other cells.

22. Cell (Plasma) Membrane • Receptors • A protein in the membrane that detects a signal molecule and performs an action in response.

23. Cell (Plasma) Membrane • Receptors (cont.) • Intracellular receptor – inside the membrane and responds to a molecule that can cross the membrane • Ex. hormones

24. Cell (Plasma) Membrane • Receptors (cont.) • Extracellular receptor – a receptor on the outside of the cell that responds to a signal that cannot cross the membrane

25. Chemical signals are transmitted across the cell membrane. • Receptors bind with ligands and change shape. • There are two types of receptors. • intracellular receptor

26. Cell (Plasma) Membrane • Receptors (cont.) • Membrane receptors – usually a protein in the membrane – responds to a signal from the outside of the cell • Receptor changes shape and transfers the signal to the inside of the cell.

27. Chemical signals are transmitted across the cell membrane. • Receptors bind with ligands and change shape. • There are two types of receptors. • intracellular receptor • membrane receptor