1. The Cell
Chapter 6

2. Cell Size Why are cells small?
Most cells are relatively small because as size increases volume increases much more rapidly than surface area.

3. As cells get bigger they need more O2 and raw materials and need to export more waste products.
The actual amount of cell membrane needed this exchange is less relatively speaking as the cell gets bigger.
This is why most cells are microscopic. This is the optimal size for exchange with the environment.
RLE (Real life example) Think how long it takes to exit the Foxboro High School parking lot after school versus exiting Gillette Stadium after a football game.

4. Examples
Some cells increase surface area relative to volume because their main job is exchange with the surrounding environment
Root hairs
Villi of small intestine

5. Prokaryotic cells vs Eukaryotic cells
Eukaryotes
Have nucleus
Have all organelles that prokaryotes plus membraneous organelles
Prokaryotes
No nucleus
No membraneous organelles
Do have flagella, cell wall, DNA, and ribosomes
Membraneous bound organelles

6. Compartmentalization
Eukaryotic cells are full of membrane-enclosed compartments (organelles)
These separate incompatible chemical and physical conditions
Organelles also increase surface area for these reactions to occur.

7. Major Eukaryotic Compartments

8. Examples
The stomach in the human body separates the HCl from other organs. What would happen if stomach acid was not contained in the stomach?
The lysosome in the cell also contains enzymes that break down molecules. What would happen if these were not contained in the lysosome?

9. Organelles Crowd the Cell
A rat liver cell.
Organelles Crowd the Cell

10. Cell Organelles Ribosomes Endoplasmic reticulum Golgi apparatus
Vacuoles
Lysosomes
Chloroplasts
Mitochondria

11. Ribosomes Great numbers of ribosomes are found in the cell
Found on Rough ER and floating freely in cytoplasm
Make proteins as directed by the nucleus
Ribosomes have no membrane
Found in all cells
They are made up of ribosomal RNA (rRNA) and protein
Amino acids are bonded together to form polypeptides and proteins

12. Ribosome Image
Click here to see a quick clip of the ribosome in action

13. Endoplasmic Reticulum
Highly folded membrane that acts as a workspace (folding increases the surface area)
There are two types of ER, rough and smooth.
Rough ER has ribosomes attached to it, and smooth ER does not.

14. Smooth ER: Lipid synthesis
Rough ER: Along with ribosomes involved in protein assembly & transport within the cell
Transports things between nucleus and cytoplasm

15. Golgi Apparatus Made up of flattened sacs call cisternae
This organelle modifies molecules and packages them into small membrane bound sacs called vesicles
These sacs can be targetted at various locations in the cell and even to its exterior
Produces lysosomes

16. Lysosomes
Membrane organelles that contain hydrolytic (digestive) enzymes and are important in intracellular digestion
Digest food or old and unwanted organelles
Also involved in apoptosis (programmed cell death)

17. Vacuoles Temporary storage of materials
Fat cells with large vacuole storing lipids
Vacuoles
Temporary storage of materials
Involved in intracellular digestion: can fuse with lysosomes
Plant cells have large one and animal cells have many smaller ones
Can store food, water, waste products, and enzymes
Plant cell with large central vacuole

18. THE SECRETORY PATHWAY: A MODEL
RNA
cis face of Golgi apparatus
trans face of Golgi apparatus
Rough ER
Golgi apparatus
Plasma membrane
1. Secreted proteins enter ER as they are being synthesized by ribosome.
2. Protein exits ER in vesicle.
3. Protein travels through the cisternae of the Golgi apparatus.
4. Protein enters a secretory vesicle that fuses with cell membrane.
5. Protein is secreted from cell.
Various glycosylation reactions
The major organelles of the endomembrane system are: the endoplasmic reticulum (ER), with its rough (RER) and smooth (SER) components; the Golgi apparatus (GA); endosomes (endo); lysosomes (lys); secretory vesicles (sec ves) and granules (SG) and the plasma membrane (PM). The outer membrane of the nuclear envelope (NE) is studded with ribosomes and is continuous with the rough ER. Transitional elements (TE) are specialized ER cisternae from which membrane vesicles (MV) bud off that deliver materials from the ER to the cis region of the Golgi apparatus, possibly by first fusing with each other to form structures that together with the first (cis) Golgi cisterna, constitute the cis Golgi network (CGN). Transport across the Golgi apparatus, from the cis to the trans face is also mediated by membrane vesicles (MV). The trans Golgi network (TGN) is a region in the trans most side of the Golgi apparatus where sorting of proteins destined to distal portions of the endomembrane system takes place. In the TGN, some secretory proteins and plasma membrane proteins are incorporated into secretory vesicles (sec ves). Other secretory proteins are packaged into immature secretory granules or condensing vacuoles (CV), that mature into secretory granules (SG). Secretory vesicles and granules release their contents into the extracellular space by exocytosis, a process that involves the fusion of their membranes with the plasma membrane. Secretory vesicles undergo constitutive exocytosis whereas secretory granules undergo regulated exocytosis in response to signals received at the plasma membrane. Proteins of the membranes of secretory vesicles or granules are incorporated into the plasma membrane during these exocytic events. In polarized epithelial cells in which the plasma membrane has distinct apical and basolateral domains, two populations of secretory vesicles destined to the two aspects of the cell surface emerge from the TGN.
Materials taken into the cell by endocytosis are incorporated into membrane vesicles derived from the plasma membrane and transported to early endosomes (e. endo). The endosomal compartment is polymorphic and includes several classes of endosomes that represent stages in their development and their conversion into lysosomes. These include the CURL (Compartment for Uncoupling of Receptors from Ligands), or sorting endosome, from which membrane vesicles bud to return interiorized receptors to the cell surface, late endosomes (l. endo) and multivesicular bodies (MVB), which receive lysosomal hydrolases brought by vesicles derived from the TGN and are converted to lysosomes (lys). To maintain the characteristic structure and composition of all the organelles of the endomembrane system that communicate with each other by a forward vesicular flow, a retrograde vesicular flow must also take place.

19. Mitochondria Mitochondria convert food into energy (ATP)
The major energy production center in eukaryotes
Mitochondria have a double membranes, an inner and an outer
The outer membrane is smooth and the inner is highly folded to produce many folds called cristae
Cristae increase surface area for ATP production and the enzymes that are responsible for it

20. A sperm cell containing many mitochondria near the tail
Figure 3-9: Mitochondria

21. Chloroplasts
These organelles are the site of photosynthesis in plants and other photosythesizing organismslike algae Capture and convert it to food.
Chlorophyll is the pigment stored in chloroplasts that capture the energy in sunlight to convert to ATP. Chlorophyll a is the most important pigment in plants and give them their green color.
They also have a

22. Chloroplasts also have a double outer membrane and membrane structure inside called thylakoids.
Inside the thylakoids they are further organized into stacks called grana.
This is where the energy in sunlight is converted to energy rich molecules like ATP and NADPH2
Carbon fixation occurs in the stroma which is the liquid that surrounds the thylakoids. This is where carbon fixation takes place.
In carbon fixation CO2 is made into sugars.