Roles of ER Rough

Ribosomes synthesize excreted proteins Stored in cisternae or

vesicle

Modify proteins Glycosylation of proteins

Delivery of membrane associated proteins

Often interacts with the Golgi

Smooth Tissue-specific uses Storage of

carbohydrates Detoxification reactions

in liver Synthesizes much of the

new membrane material Modification of existing

molecules

ER and Golgi Often adjacent in cytoplasm of

cell Both are membrane producers

Membrane has sides Vesicles are produced inside out Vesicle fuses with surface and

excreted proteins are released and integral proteins are added along with membrane

ER often performs first steps of modification that is later finished in Golgi

Golgi apparatus

Complex collection of membrane Has polarity

Cis and trans surfaces

Responsible for secretion Very prominent in cells that serve secretory functions-

such as epithelial cells

Modifies structures previously synthesized in the ER

Golgi Function

Cis face is nearer the center of cell Cis face is often adjacent to ER

Trans face is nearer the cell membrane Activity is directional

Starts at cis face and moves to trans

Fig. 6-13

cis face(“receiving” side of Golgi apparatus) Cisternae

trans face(“shipping” side of Golgi apparatus)

TEM of Golgi apparatus

0.1 µm

ER and Golgi Synthesis in ER but

modification in Golgi Similar to an assembly

line Options packages are

added in Golgi

Sequential passage through cisternae (cis to trans)

Each cisternae contains different enzymes

Examples of Golgi Function

Replace sugars placed on glycoproteins Modification of phospholipid acylgroups and

head groups Molecule targeting and assembly Production of vesicles to delivery membrane

associated molecules and excreted molecules to cell surface

Cell Renewal

Cells and their molecules age and become less effective

An important cellular function is renewal Old molecules and organelles are recycled New phospholipids are produced for the membrane Toxic molecules need to be collected and detoxified

Sometimes a cell needs to commit suicide Called autolysis or apoptosis

Vesicle Organelles

Perform many of the renewal functions Lysosome Peroxisome Glyoxisome

Lysosome Contains digestive enzymes used to degrade

macromolecules or organelles Originates in ER but enzymes are activated in

Golgi Important in macrophages for degradation of

particles acquired via phagocytosis Used to degrade organelles-autophagy

Fig. 6-14a

Nucleus 1 µm

Lysosome

Lysosome

Digestive enzymes

Plasma membrane

Food vacuole

Digestion

(a) Phagocytosis

Fig. 6-14b

Vesicle containingtwo damaged organelles

Mitochondrion fragment

Peroxisome fragment

Peroxisome

Lysosome

DigestionMitochondrionVesicle

(b) Autophagy

1 µm

Cell Death

Sometimes used in development of organism Hand development Certain cells are programmed to die at appropriate times

Defense against viral or intracellular bacterial infections Self-destruct Program is started by T cells

Apoptosis is often accomplished by leaky or popping lysosomes

Peroxisomes

Contain enzymes to collect free hydrogen and oxygen and combine into H2O2 (peroxide)

Peroxide is also toxic so they contain enzymes to degrade into water and oxygen molecules Catalase experiment in lab

Peroxisomes are formed by aggregation of lipids and proteins (not formed in ER)

Many are found in liver cells Degrade alcohols into peroxide then into water and

oxygen

Peroxisome pt 2

Also responsible for degradation of fatty acids in cytosol

Modify fatty acids and phospholipids and incorporate into peroxisome membrane

Divide by binary fission

Glyoxysomes

Specialized peroxisomes found in plant seeds Recognize appropriate signals and begin to

degrade stored fat in seed Fat is converted to sugars which allows

seedling to sprout Once photosynthesis starts, glyoxysomes

degrade