Chapter 4-5. Prokaryotic Cells and Membranes

Transcription

1 Chapter 4-5 Prokaryotic Cells and Membranes

2 Four Important People Anton Von Leeuwenheok Inventing microscopes and first observing unicellular living organisms Robert Hooke Discovered and coined the term cells Matthias Schleiden Established all plants are composed of cells Theodor Schwann Established all animals are composed of cells

3 Compound Light Microscopes Out of the trillions of different cells only a small handful have ever been visible to the naked eye. Thus, we need a tool to help study them Anton Von Leeuwenhoek did not invent the first microscope, but he and his colleagues first used the object as a scientific tool. He, among others, experimented with grinding glass into lenses in order to bend light and make smaller objects appear larger.

4 Compound Light Microscopes Compound light microscopes work by running beams of light through a series of lenses. These lenses continuously zoom in on a specific target. The object can be magnified up to 1500 times

5 Electron Microscope Electron microscopes fire beams of electrons at whatever you want magnified. The electrons then interact with the structures of the object. These interactions are calculated and displayed by a computer. The result is a magnification of 500,000 to 1 million times larger than normal. Electron microscopes have allowed us to study the internal structures and functions of the cell.

6

7

8

9

10

11

12

13 Cell Theory The cell is the simplest level of organization in biology that meets the definitions of living All functions of an organ/organ system/organism are collective functions of the cells that make them up In other words, the only reason you can communicate, remove waste, move, etc is because your cells can Cells have to find a unique balance between personal, cellular survival and survival of the organism as a whole The importance of cells is clearly outlined in the cell theory

14 Cell Theory #1: All organisms are composed of one or more cells #2: The cell is the basic unit of structure and function in an organism #3: All cells come from preexisting cells

15 Cell Size One of the keys to life is the fact that cells are so small Although coordinating 10 trillion tiny cells is more difficult than coordination 1000 large cells, the benefits of multiple smaller cells far outweigh the difficulties. 1: Surface area/volume ratio Cells take in nutrients and remove waste through their membrane. The more surface area the membrane has, the more nutrients/waste can pass through If the cell is too big though, it takes too long for nutrients to reach the center of the cell Smaller cells can take up the same amount of space (volume) as larger cells, but with 4 times as much surface area

16

17 Cell Size 2: Redundancy If you have multiple cells making up an organism, the death of one cell has less of an impact Instead of one cell performing millions of functions, millions of cells perform one function each You can have lots of back-ups in case a cell is tired, damaged, or is dividing into a new cell

18 Prokaryotic Cells Prokaryotic cells are distinguished by their lack of membrane-bound organelles Prokaryote is Greek for before nucleus Prokaryotic cells are much simpler in size and structure than eukaryotic cells Eukaryotic cells are on average 50x larger than prokaryotic cells Prokaryotic cells have to be small enough to infect a Eukaryotic cell by inserting themselves inside the Eukaryotic cells The two prokaryotic groups are archaea and bacteria Bacteria are simpler in design and live in more neutral environments Archaea are highly diverse and complex and live in harsher climates

19 Prokaryotic Cell Envelope Prokaryotic cells are bound by different layers of membranes Plasma Membrane: two layers of phospholipids that regulate what goes in and out of the cell Very flexible Cell Wall: rigid outer layer that maintains the shape of the cell and prevents collapsing or swelling Very rigid (Also found in plant cells)

20

21 Cytoplasm Inside cells are numerous different objects swimming in a semi-liquid solution This solution is called cytoplasm. The cytoplasm has three functions: Provide a medium to move against within the cell (imagine trying to swim in an empty pool) Internal support of the cell In Eukaryotic cells, stabilize the organelles in place

22 Other prokaryotic structures Nucleoid A general region of the cell where the DNA is stored Plasmid A circular section of DNA Fimbriae Fibers on the surface of the cell that allow cells to attach to surfaces Sex pili Tubular structures used to pass DNA from cell to cell

23

24 Membranes The reason you are able to build immunities, use your senses, keep your temperature regulated, stay hydrated, and hundreds of other functions is because of your membrane. The membrane is one of the most-studied organelles because it s easy to see with microscopes Multiple different models of the structure of the membrane have been proposed as early as In 1972, the model recognized as the most accurate depiction of the cell membrane was introduced: the fluid-mosaic model

25 Cell Membrane Structure The majority of the cell membrane is a molecule called a phospholipid A phospholipid is a long chain of lipids attached to a phosphate molecule The phosphate molecule is hydrophilic, or waterloving. It can safely and freely be in contact with water and water-soluble molecules Polar The lipid chain is highly hydrophobic. Near the presence of water or water-soluble molecules it will repel like a magnet Nonpolar

26

27 Cell Membrane Structure The membrane is actually two layers of phospholipids. The phosphate heads face outside toward the environment and inside toward the cytoplasm. The lipid chains are sandwiched in between the two phosphate heads This is called the phospholipid bilayer

28

29 Cell Membrane Structure Attached to phospholipids are various other chemicals that enhance the stability of the membrane Cholesterol: a steroid; stiffens and strengthens the membrane Glycolipid: Carbohydrate attached to the lipid, important for cell recognition and immunity Glycoprotein: Protein attached to the lipid, important for multiple different functions (performing tasks, entry/exit from the cell, connection to other cells )

30

31 Cell Membrane Structure The glycolipids and glycoproteins are located randomly within the cell membrane Think chocolate chips in a cookie What is now known is that the molecules that make up the membrane are not stationary Proteins and lipids are able to move back and forth within the membrane like bumper cars on a track This gives the membrane a fluid appearance. Hence, the fluid-mosaic model

32

33

34 Glycolipids When we get to cell immunity, we ll cover this in more detail. Every cell in our body has specific structures of glycolipids unique to us (or unique to the human species) When a foreign substance makes contact with a glycolipid, the cell immediately recognizes what it is based on the structure of the foreign substance

35 Glycolipid If the cell does not recognize the structure on the foreign substance, it will make a copy of this glycolipid Other cells will then be given a copy of this foreign glycolipid so they can recognize it as a dangerous entity BEFORE it can penetrate the cell This is an important role for the immune system, particularly white blood cells

36 Impermeability The membrane is almost 100% effective at preventing leaks Hydrophobic substances can t get past the phosphate heads Hydrophilic substances can t get past the lipid chains If the cell is going to take in nutrients, get rid of waste, or send or receive messages, it needs gaps in the membrane Glycoproteins are large enough to span the entire distance of the membrane and perform these functions Because the cell prevents leaks, but still allows substances through, it is called semi-permeable