1. Cell Structure
Chapter 6

2. YOU MUST KNOW
Three differences between prokaryotic and eukaryotic cells
The structure and function of organelles common to plant and animal cells
The structure and function of organelles found only in plant cells or animal cells
How different cell types show difference in subcellular components
How internal membranes or organelles contribute to cell function
How cell size and shape affect the overall rate of nutrient intake and waste elimination

3. Prokaryotes Found in the domains Bacteria and Archaea
Contain a single, circular chromosome in nucleoid region
Contain no membrane-bound organelles
Very small in comparison to eukaryotes

4. Interesting Facts Prokaryotes dominate the biosphere
Collective mass outweighs all eukaryotes combined by at least 10 fold
More prokaryotes inhabit a handful of fertile soil or in the mouth or skin of a human than the total number of people who have ever lived!
Found wherever there is life
Especially in extreme environments
There are a hundred billion prokaryotes per milliliter of fluid in the human colon.

5. Eukaryotes
Belong to domain Eukarya, includes animals, plants, fungi, protists
Membrane bound nucleus containing linear chromosomes
Membrane-bound organelles
Much larger than prokaryotes
Prokaryotes
Eukaryotes
Plasma Membrane
Yes
Ribosomes
Membrane-bound organelles No
Nucleus
Size
1-10um
10-100um

7. The Nucleus Contains DNA
Surrounded by a lipid bilayer (membrane) called the nuclear envelope which is connected to the rough endoplasmic reticulum and contains nuclear pores to allow things to enter and leave the nucleus
Nucleolus – region (not really a
structure) where rRNA combines
with proteins to form ribosomal
subunits

8. Ribosomes
Composed of rRNA and protein – one large subunit and one small
Sites of protein synthesis
Can be free-floating or bound to endoplasmic reticulum
Free-floating – produce proteins to be used in the cell
Bound – produce proteins that will be exported out of the cell

9. Endoplasmic Reticulum
Network or folded membranes and sacs – space between called cisternal space
Smooth– no ribosomes associated
Metabolism of lipids and carbs
Detoxification of drugs and poisons
Rough – covered in ribosomes
Ribosomes synthesize proteins
which are then wrapped in
vesicles made of the membrane
of the ER

10. Golgi Apparatus Stacks of flattened sacs of membrane called cisternae
Modifies, stores, and ships out
proteins
Sacs are polar with cis side
receiving incoming proteins from
the RER and shipping them out
from the trans side
Camilo Golgi

11. Release to monomers produced by their reactions back in to the cell
Lysosomes
Membrane-bound sacs of hydrolytic enzymes to digest unwanted or old molecules and organelles in the cell
Release to monomers produced by their reactions back in to the cell
Enzymes involved require a low pH to function, so if lysosome breaks open, they do not work
Peroxisomes
Membrane-bound sacs
Transfer hydrogen from compounds to oxygen, forming H2O2 (toxic to cell)
Contains enzymes to break down the H2O2
Breaks down fatty acids so that they can be used by the mitochondria
Detoxify substances (alcohol) by transferring its hydrogen to oxygen
Importance of compartmentalization

12. Vacuoles Membrane-bound sacs used for various reasons
Contractile vacuoles in protists – contracts to expel water out of the cell to prevent lysis in hypotonic environments
Central vacuole in plants – can make up as much as 80% of a cell, used for storage

13. Mitochondria
Sites of cellular respiration – energy conversion from food to ATP
2 membranes – outer and inner
Cristae – folds of the inner membrane, increase surface area
Matrix – fluid filled inner compartment
Contains its own circular DNA and its own ribosomes

14. Chloroplasts
Site of photosynthesis in plants – energy conversion from light to food
Also contains its own circular DNA and ribosomes
Double membrane structure

15. Endosymbiotic theory
Mitochondria and chloroplasts have many characteristics of prokaryotic cells – circular DNA, ribosomes
Double membrane indicates they were engulfed by another cell by endocytosis
Eukaryotes arose from one prokaryote engulfing others and the engulfed cells developing specialized functions

16. Cytoskeleton
Network of protein fibers for support, motility, and regulation
Microtubules – tubulin fibers, shape and support, tracks for molecules to travel along, separate chromosomes during mitosis and meiosis, form cilia and flagella
Flagella – long tails to propel cells
Cilia – shorter and more numerous than flagella, can be used to move the cell itself or to move things along outside the cell
Both in 9+2 pattern – 9 pairs of microtubules around a core of 2 microtubules

17. Microfilaments – composed of actin, smaller than microtubules, involved in muscle contractions
Intermediate filaments – maintain shape, fix position of oragnelles

18. Centrosomes – near nucleus, region where microtubules are formed
Centrioles – located within centrosomes, used during mitosis and meiosis

19. Extracellular components
Cell wall
In plants, composed of cellulose, for shape and support
Also in prokaryotes & fungi, composed of peptidoglycan & chitin
Plasmodesmata – channels in cell walls between cells to allow passage of materials from one cell to another

20. Extracellular Matrix (ECM)
Animal cells
Composed of glycoproteins secreted by cell, mostly collagen
Strengthens tissues, allows for transmittal of stimuli into the cell

21. Intercellular junctions (in animal cells)
Tight junctions – two neighboring cells are fused by their cell membranes
Desmosomes – proteins that link adjacent cells like rivets, making strong sheets
Gap junctions – protein channels connecting adjacent cells so small molecules can pass from one to the next