1. CHAPTER 4
A TOUR OF THE CELL

2. Most cells are between 1 & 100um in diameter (Fig. 4.2A p. 54)
Sect. 4.2
Cell Size
Most cells are between 1 & 100um in diameter (Fig. 4.2A p. 54)
Plasma membrane (PM): selective barrier that consists of proteins & lipids (phospholipid bilayer)

3. Cell size is limited due to:
-a single nucleus controlling the entire cell
-enough surface area in relation to volume to obtain nutrients and dispose of wastes

4. Two Types of Cells Prokaryotic Sect. 4.3 Eukaryotic
No membrane bound organelles, only nucleoid region
Has ribosomes & DNA
Cell wall, capsule & pili help attach, flagella
Found in the Domains Bacteria & Archaea
Eukaryotic
Have cytoplasm – region between the nucleus and the cell membrane (consists of a semifluid medium called cytosol)
Contain organelles – structures w/special functions
Found in protists, plants, fungi, and animals

5. The Nucleus (genetic control center of a eukaryotic cell)
Sect. 4.5
The Nucleus (genetic control center of a eukaryotic cell)
Nuclear Envelope
boundary around nucleus, separating it from the contents of the cytoplasm
Double membrane – each with a phospholipid bilayer

6. Contents of the Nucleus
- nearly all of the cell’s DNA is here (organized along w/proteins into chromosomes)
- unless the cells are dividing, chromosomes are seen as a tangled up mess called chromatin
- nucleolus functions in the synthesis of ribosomes

7. Sect. 4.4
Ribosomes
Function
assemble enzymes and the entire cell’s other proteins
there are genetic instructions for this to occur
not membrane bound

8. exist in 2 places w/in cytoplasm
Location
exist in 2 places w/in cytoplasm
1) free ribosomes - suspended in cytosol (make proteins for cell use)
2) bound ribosomes – attached to endoplasmic reticulum (make proteins for export outside cell)

9. ribosomes usually occur in clusters called polysomes

10. Endoplasmic Reticulum (ER)
Sect. 4.6
Endomembrane System
Endoplasmic Reticulum (ER)
a network of interconnected compartments, continuous w/the outer membrane on the nuclear envelope p. 58
W/in the ER is a space known as the lumen

11. 2 distinct regions of the ER (interconnected flattened sacs)
Sect. 4.8
2 distinct regions of the ER (interconnected flattened sacs)
Rough ER - has ribosomes on surface
- makes proteins destined to be secreted
- makes membranes

12. Smooth ER - lack ribosomes (p. 59), membrane is continuous w/rough ER
Sect. 4.7
Smooth ER - lack ribosomes (p. 59), membrane is continuous w/rough ER
- serves as a transition area for ER products
- makes steroids and sex hormones
- tolerance to drugs
- calcium for muscles

13. after leaving the ER, most transport vesicles travel to this organelle
Sect. 4.9
Golgi Complex (p. 60)
after leaving the ER, most transport vesicles travel to this organelle
manufactures, warehouses, and ships (products of the ER are modified, stored, and shipped to other locations in transport vesicles)
- consists of flattened sacs stacked up like pancakes (not connected)
- molecules move from sac to sac

14. membrane-bound bag of hydrolytic (digestive) enzymes
Sect. 4.10
Lysosomes
membrane-bound bag of hydrolytic (digestive) enzymes
- cell uses these enzymes to digest macromolecules
- these enzymes work best at pH 5

15. made by the rough ER, processed, and released by the Golgi
function by using phagocytosis (engulfs particles) then digests them

16. also function in recycling cell’s own organic material (recycling centers for damaged organelles)
ex: webbing between fingers in embryonic development

17. lysosomal storage diseases (missing one of the hydrolytic enzymes):
Sect. 4.11
lysosomal storage diseases (missing one of the hydrolytic enzymes):
Pompe’s disease (liver can’t break down polysaccharide glycogen)
Tay-Sachs (overload of lipids on nervous system)

18. Microbodies bounded by a single membrane
compartments specialized for specific metabolic pathways (each has a particular kind of enzymes)

19. 2 kinds of microbodies:
Peroxisomes - have enzymes which transfer H from various substrates to O (produce H2O2 as a byproduct)
Glyoxysomes - contain enzymes to convert fats to sugar (in plants)

20. Vacuole a large membrane sac various functions:
Sect. 4.12
Vacuole
a large membrane sac
various functions:
food vacuole - formed by phagocytosis
contractile vacuole - found in freshwater protists (pumps out excess water from the cell)

21. Central vacuole - found in mature plant cells - bounded by a tonoplast (membrane)
- stores organic compounds

22. Energy Transducers (have their own DNA)
Sect. 4.14
Energy Transducers (have their own DNA)
Chloroplasts
formed only in plants
functions in photosynthesis
chloroplast – contains a green pigment (chlorophyll)
p. 63

23. chloroplast’s elaborative structure:
-consists of flattened green sacs which are stacked up
-sacs called thylakoids
-stack of thylakoids called a granum (if more than one granum, it’s called grana)
-stroma: thick fluid surrounding thylakoids

24. site for cellular respiration
Sect. 4.15
Mitochondria (p. 63)
site for cellular respiration
found in plants and animals

25. these foldings divide inner region of mitochondria
- intermembrane space – region between inner and outer membranes
- has inner membrane that’s convoluted within foldings called cristae (this greatly increases surface area to enhance ATP production)
- mitochondrial matrix – is enclosed by the inner membrane (most of the respiration takes place here)

26. Sect. 4.16
Cytoskeleton – supportive meshwork of fine fibers for structural support
Microfilaments
(thinnest type of fiber)
solid rods of globular proteins called actin – linked in chains
best known for role in muscle contraction

27. protein called myosin is imbedded in the actin molecule
in plants, microfilaments are involved in cytoplasmic streaming (cytoplasm flows in a particular direction ex: moving chloroplasts)

28. Intermediate Filaments
- ropelike
- reinforces cell shape
- anchors certain organelles (nucleus is caged by these to keep in place)

29. hollow rods of globular proteins called tubulins
Microtubules
p. 64
hollow rods of globular proteins called tubulins
found in cytoplasm of all eukaryotic cells
radiate out from cell centers
give cell shape and reinforce it
help w/animal cell division

30. also help other organelles navigate through cytoplasm
w/in cell center are 2 centrioles – consist of 9 sets of triplet microtubules and must be 2 centrioles (a pair) in the center
9 sets
p. 65 Fig. 4.17C

31. both have a core of microtubules and protrude from the cell
Sect. 4.17
Cilia and Flagella
Cilia – short fingerlike projections used for locomotion
Flagellum – a whip-like tail
both have a core of microtubules and protrude from the cell

32. wrapped in plasma membrane
anchored to the cell by a basal body – similar to a centriole
Ex: cilia on cells in wind pipe
flagellum on sperm

33. Cell Wall Cell Surface plants only - thicker than PM
Sect. 4.18
Cell Surface
Cell Wall
plants only - thicker than PM
there is a thin, flexible primary cell wall (between the 2 cell walls is the middle lamella - like glue) (pectin)

34. cell wall strengthens as the cell matures
some plants add a secondary cell wall between the PM and the primary cell wall
plants use the plasmodesmata
- channels in the cell wall
- strands of cytoplasm connect one cell to another

35. no cell wall in animals Extracellular Matrix glycocalyx - fuzzy coat
made of carbohydrates and helps cells stick together - strong surfaces

36. Intercellular Junctions
provides a means by which many cells can be integrated into one functional organism
cell to cell contact in animals provided by 3 junctions:
1. Tight junctions - binds cells together ex: digestive tract

37. 2. Anchoring junctions - attach adjacent cells to each other to stretch ex: skin
3. Gap junctions - allow water and other small molecules to flow between neighboring cells (similar to plasmodesmata in plants)