1. Structures and Functions of Eukaryotic Cells
Chapter 2.1
McGraw-Hill Ryerson
Biology 12 (2011)

2. Cell Membrane Cell membrane made out of a phospholipid bilayer
Semi-fluidity of phospholipids in this arrangement allows flexibility of the membrane
Also allows membrane to be embedded with proteins and carbohydrates
“Fluid Mosaic Model”

3. Cell Membrane Phospholipid bilayer
Lipids are held together by weak intermolecular forces
Thus molecules in membrane are able to move freely
The phospholipids are aligned like this due to the hydrophillic head and hydrophobic tails

4. Cell Membrane Phospholipid bilayer fluidity
If the bilayer is too fluid, too many molecules diffuse in and out of the cell
If the bilayer is too rigid, not enough molecules diffuse in and out of cell

5. Cell Membrane Phospholipid bilayer fluidity
Factors affect fluidity:
Temperature (higher temperature = more fluidity)
Presence of double bonds in fatty acids of phopholipid tail (more d-bonds= more fluidity)
Fatty acid length (shorter = less intermolecular attraction between nonpolar tails = more fluidity)
Presence of cholesterol in membrane but depends on temperature
- presence of cholesterol increases intermolecular forces in membrane to hold tightly together at high temperatures = less fluidity
- presence of cholesterol break up packing that occurs as phospholipid solidify into a gel at low temperatures = more fluidity

6. Cell Membrane Proteins are embedded in cell membranes
Integral proteins: embedded in the membrane
Peripheral proteins: loosely and temporarily attached to outer regions of the membrane or to integral proteins

7. Cell Membrane
Membrane proteins help stabilize membranes and link to cytoskeleton of the cell
Membrane proteins also carry out functions:
Transport: proteins allow transport of substances across the membrane
Reaction catalysis: enzymes in cell membranes carry out chemical reactions
Cell recognition: proteins on membrane act as “identity tags”
Signal reception and transduction: Receptor proteins bind to signal molecules, and react in accordance to the signal

8. Nucleus Nucleus: Labeled 2 on Diagram Contains DNA
Surrounded by nuclear envelope
Has double membrane of two phospholipid bilayers
Membrane separates nucleus from rest of cell – why is this needed?
Nuclear pores present to permit passage of RNA
Contains Nucleolus
(1 on diagram)
Contains RNA, protein, chromatin

9. Endoplasmic Reticulum
Endoplasmic Reticulum (ER)
Rough ER
(Labeled 5 on diagram)
Studded with ribosomes
Synthesizes proteins that are part of membranes or intened for export from the cell
Smooth ER
(Labeled 8 on diagram)
Synthesizes lipids and lipid-containing molecules (e.g. phospholipids)

10. Golgi apparatus Golgi apparatus: labeled 6
Packages, processes, sorts, and distributes proteins, lipids, and other substances within the cell
Acts like a “post office”
Packaged into membrane-bound sacs called vesicles
Vesicles are labeled 4 on diagram

11. Endomembrane system
System acts as the transportation and product-processing section
Consists of:
nuclear envelope
endoplasmic reticulum
Golgi apparatus
Vesicles

12. Endomembrane system Steps:
Rough ER surface’s ribosomes produce polypeptides which are kept in the lumen of ER (rather than cytosol) to go to smooth ER
Smooth ER stores and packages proteins in vesicles and sends it to cis face of Golgi apparatus membrane
Golgi apparatus membrane merges with vesicle so that it imports protein contents. Proteins are stored and modified to be ready for delivery.
When ready for delivery, proteins pinch off from trans face of golgi apparatus membrane to form vesicles. These vesicles transport the proteins to various destinations

13. Vacuole Vacuole: labeled 10
Typical animal cells contains many small vesicles
Plant cells contain a large central vesicle called vacuole
Stores water, ions, sugars, amino acids, and macromolecules
Also contains enzymes to break down materials
Water that fills it up, allows it to engorge and push up against the cell giving it rigidity
Vacuoles determine Turgor pressure
Unwatered plants wilt because not enough turgor pressure

14. Lysosomes Lysosomes: labeled 12
Membrane-enclosed sacs with digestive enzymes (more than 40)
Enzymes’ optimal pH is ~5
Cytosol pH is ~7.2
Breaks down parts that are not needed
Also break down foreign particles
E.g. white blood cells’s lysosomes destroys bacteria

15. Mitochondria Chloroplast Mitochondria: labeled 9
Break down high-energy-yielding organic molecules to convert stored energy into usable energy
(we will see this in Unit 2)
Chloroplast: Only photosynthetic organisms
Contains chlorophyll
Uses light energy to convert CO2 and H2O, through redox reactions, into energy-rich organic molecules
Chloroplast

16. Cytoskeleton Internal network of protein fibres
Provides structure and anchoring cell membrane and organelles in place
Can act like tracts for vesicles to move

17. Cilia and Flagella Located on the outside of some cells Cilia Flagella
Conducts wave-like motion for movement
Cilia are on cells that line respiratory tract to sweep dust within mucus back to throat
Flagella
Tails that whip to propel cells

18. Homework Assignment Pg 71 #4, 8, 10, 11, 12
Draw out an animal cell and draw in the organelles and components
Draw out a plant cell and draw in the organelles and components
Make a table to correspond with your drawings and list all the organelles that you’ve learned with information and facts to help you remember what they do
Due: Saturday, May 18, 2013