1. Cells: The Living Units Intro and Membrane
Chapter 3
Cells: The Living Units
Intro and Membrane

2. Cell
The basic structural and functional unit of all living things

3. 4 Concepts of Cell Theory
Cell is the basic structural and functional unit of life
The activity of an organism depends on the individual and collective activities of cells
The function of the cell depends on its organelles (principle of complementarity)
Continuity of life has a cellular basis

4. Characteristics of Cells
Cells vary greatly in their size, shape, and function
A cells shape reflects its function
All cells are composed of carbon, hydrogen, nitrogen, oxygen and trace amounts of other elements
A generalized human cell contains the plasma membrane, cytoplasm, and nucleus

5. 3 Main Parts of Human Cells
Plasma membrane
Cytoplasm
Nucleus

6. Plasma Membrane
Membrane, composed of phospholipids, cholesterol, and proteins, that encloses cell contents; outer limiting cell membrane

7. Plasma Membrane Intracellular fluid Extracellular fluid
Fluid inside the cell
Extracellular fluid
Fluid outside of the cell

8. Plasma Membrane Fluid Mosaic Model
Because the proteins that float in the lipid bilayer form a constantly changing mosaic pattern

9. Plasma Membrane Composition Phospholipids – most Cholesterol – small
Glycolipids – small

10. Plasma Membrane Phospholipids
Head – polar  hydrophilic (water loving) – faces the intra/extracellular fluid
Tail – nonpolar  hydrophobic (water fearing) – tails are facing towards the inside

11. Plasma Membrane Glycolipids Phospholipids with attached sugar groups
Only found on the outer surface of the plasma membrane

12. Plasma Membrane Lipid Rafts
Groups of saturated phospholipids that are packed tightly together. Associated with shphingolipids and cholesterol.
More stable and less fluid that the rest of the membrane
Assumed that they are needed for cell signaling

13. Plasma Membrane Integral Protein
Protein that is inserted into the lipid bilayer.
They have both hydrophobic and hydrophilic regions so that they can interact with the different regions of the lipid bilayer.

14. Plasma Membrane Integral Protein
Can protrude from one surface, but most are transmembrane which means that they go through the entire membrane.

15. Plasma Membrane Integral Protein
Transmembrane proteins are mainly involved with transport – when many cluster together they form channels or pores so “stuff” can flow into and out of the membrane (water soluble ions or molecules)
Also act as carries that bind a substance and then move it through the membrane

16. Plasma Membrane Peripheral Protein
Proteins that aren’t embedded in the lipid bilayer; attached loosely to integral proteins or membrane lipids. Removed easily without disrupting the plasma membrane

17. Plasma Membrane Peripheral Protein
Some are enzymes and others are involved in mechanical functions (changing cell shape during mitosis, muscle cell contraction, or linking cells together).

18. Plasma Membrane Glycocalax “sugar covering”
Fuzzy sticky carbohydrate rich area surrounding the cell

19. Plasma Membrane Microvilli “little shaggy hairs”
Small fingerlike projections of the plasma membrane.
Increase the surface area.
Found in areas where lots of absorption take place (intestine and kidneys)

20. Factors that Join Cells
Glycoproteins act as an adhesive
Wavy contours of the membranes of adjacent cells fit together in a tongue and groove fashion
Special membrane junctions (tight junction, desmosomes, gap junctions)

21. Special Membrane Junctions
Tight Junction
Integral proteins of adjacent cells fuse together to form an impermeable junction that encircles the cell.
Help to prevent molecules from passing through the extracellular space between cells.
Found in lining of the digestive tract.

22. Special Membrane Junctions
Desmosomes
“binding bodies” or anchoring junctions
Like rivets to prevent cells from separating and distributes tension throughout a cellular sheet to reduce the chance of tearing.
Present in skin and heart muscle

23. Special Membrane Junctions
Gap Junction
“bond” or nexus
Communicating junction between adjacent cells
Cells are connected by hollow cylinders called connexons.
Small molecules pass through the water filled channels from one cell to the next.
Present in electrically excitable tissues like heart and smooth muscle

24. Functions of the Plasma Membrane
Cells are bathed in an extracellular fluid called interstitial fluid.
Derived from the blood.
Contains thousands of ingredients
Amino acids, sugars, fatty acids, vitamins, hormones, neurotransmitters, salts, waste products, etc.
Cells “take” from the interstitial fluid what they need when they need it.