OUTLINE
    To understand how and why plants grow and behave the way they do, let's focus on how the units (cells) carry out their functions.  What are the subcellular parts and how are they formed?  What chemical molecules make up the structures?  What are the key functions of each?  How do subcellular structures work together in a cell?

1.  Review of Membrane Structure and function

•  permeable to water and nonelectrolytes,
• not permeable to electrolytes (ions, sugars, aa) :. Provides a high electrical resistance
• primary structure – lipid bilayer with proteins (integral, peripheral)

2. Plant cells are eukaryotic cells. The general function of cells is similar, but specific functions and molecules required by plants cells for their growth and development can vary.

A. Organelles that contain information of life

Nucleus :

• Store of genetic material; Contains DNA/RNA, protein
• Has nuclear pores for macromolecule entry/exit
• Site of transcription

Mitochondria

Plastid:
e.g. chloroplast (photosynthesis), amyloplast (starch), chromoplast ( pigments) (Unique to plants)

B. Endomembrane System.

Endoplasmic Reticulum (ER)

• Network of tubules and flattened sacs in the cytoplasm
• Smooth-  synthesis of p-lipids for all other membranes and itself
• Rough – synthesis of proteins for secretion (lumen) or membrane proteins (integral)
• Source of membranes and proteins for the cell (FACTORY)

• Flat disks on one another
• Functions:  1. Process/modify proteins from the ER
•                      2. sort to according to cellular location
•                      3. synthesizes cell wall components in plants
• MODIFY AND DELIVER

Vacuoles

Plasma membrane

C. Other

Cytoplasm

Cytoskeleton: with some special features in plant cells

3.  Highlight unique structures of plant cells

Plastid: e.g. chloroplast (photosynthesis), amyloplast (starch), chromoplast ( pigments)

Vacuole: multi-functional organelle

• Osmotically active compartment needed for growth
• Hydrolytic enzymes (degradation) and recycling center (similar to lysosomes)
• Storage compartment:  sucrose, proteins, secondary products (ie. Nicotinic acid)

Plasmadesmata: structure that connects cytoplasm between two adjacent cells

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Cell Wall (Taiz ch. 15, summarized by DB Poli 9/2000):

I. Plant Cell Walls – mix of polysaccharides and other polymers linked by covalent and non-covalent bonds, also structural proteins, enzymes, phenolic polymers and other chemicals to help change shape

A. Functions
1. regulate cell volume (normal water relations)
2. determine cell shape
3. strength
4. protection from environment
5. Human importance – health and nutrition
Economics

B. Plant morphogenesis – depends on the control of cell wall properties
*glues cells together so they don’t slide past each other (vs. animal development)

C. Cell wall players
1. cellulose
a. linear chain of 1? 4 linked ?-D-glucose
b. cellulose + cellulose + celllulose = cellobiose
c. non-covalent between adjacent glucans =
    1. strong (high tensile strength = steel!)
    2. immune to chemical and enzymatic shock
d. synthesized by particle rosette (AKA terminal complex) embedded in PM

2.  matrix polymers
a. highly hydrated, less ordered
b. synthesized in the golgi by sugar-nucleotide polysaccharide glycosyltransferases
c. exocytosis delivery to CW
d. hemicellulose –bind to cellulose (aka cellulose-linking glycans)
e. pectins – gel-forming, contain acid sugars

      3.  structural proteins
a. crosslink
b. function? Strength?
c. Classified by aa composition

D. Main Types of CWs – plant cells have varied architecture depending on where in the plant they are (cortical parenchyma is thin, epidermis is thick, cutin, wax) :. Wall arch = function of the cell

1. primary walls
a. formed during growth, originate at final stages of cell division, when the cell plate can withstand Turgor pressure (cell plate forms at phragmoplast when Golgi and ER pieces come together)
b. similar in all cell types
c. relatively unspecialized
d. 25% cellulose microfibrils in  matrix of 25% hemicellulose and 35% pectins and 1-8% structural proteins.  70-80% water (decrease water Increase stiffness)  %vary in genus

2. secondary walls
a. formed once growth stops
b. specialized in structure and composition  ie. Xylem is strengthened by lignin
c. lignin found here
d. 60-80% cellulose :. Stiff

3. middle lamella
a. holds 2 cells together
b. high pectin content
c. breaks down when fruit ripen

Summary
Synthesis --> secretion --> assembly --> expansion -->cross linking -->  secondary wall    formation
 

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Taiz and Zeiger, ch. 1

Lecture Review []

1.  What is the composition and structure of  membranes?
        Name two functions of integral proteins on the plasma membrane. 

2.  Name the principal organelles in a plant cell, and describe the distinctive features of each.
    Briefly describe one major function of each organelle. e.g. nucleus, ER, Golgi, vacuole, mitochondria, chloroplast.

3.  What is the cytoskeleton?  What are its roles in the cell?

4.  What is the chemical make-up of cell walls?  What is the functional difference between the primary cell wall and the middle lamella?

5.  The function of a root hair cell differs from that of a leaf mesophyll cell (ground tissue of leaf).  What is the major function of these cells?  How do the cells differ in their cellular organelles?

6. When cells divide, the number of mitochondria or chloroplast increase by what method? Clue: both organelles contain DNA.

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