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Chapter 4.5
The Endoplasmic System
AP Biology
Fall 2010
Endoplasmic Reticulum
• Endoplasmic Retculum (ER): collection of
interconnected tubes and flattened sacs that
begin at the nucleus and ramble throughout
the cytoplasm
• Flattened channel, starts at nuclear envelope
and folds back on itself repeatedly in
cytoplasm
Endoplasmic Reticulum
Endoplasmic Reticulum
• Inside the channel polypeptide chains become
modified into final proteins and lipids are
assembled
• Two types distinguished by presence or
absence of ribosomes:
– Smooth ER
– Rough ER
Endoplasmic Reticulum
• Rough ER
– Consists of stacked, flattened sacs with many
ribosomes attached
– Oligosaccharide groups are attached to
polypeptides as they pass through on their way to
other organelles or to secretary vesicles
• Cells that make, store and secrete proteins
have a lot of rough ER
– Ex. Pancreas
Rough Endoplasmic Reticulum
Endoplasmic Reticulum
• Smooth ER
– Has no ribosomes
– Is the area from which vesicles carrying proteins
and lipids are budded
– Inactivates harmful chemicals and breaks down
fatty acids
– Makes lipid molecules that become part of cell
membrane
Smooth Endoplasmic Reticulum
Golgi Bodies
• Golgi Bodies: proteins and lipids undergo final
processing, sorting, and packaging
• Attach sugar side chains to proteins and lipids
they received from the ER
• Finished products are packaged in vesicles
Golgi Bodies
• Membranes of Golgi are arranged in flattened
sacs whose edges break away as vesicles
Vesicles
• Vesicles: commonly used by the cell as
transporters to and from plasma membrane
– Tiny sacs that form as buds from ER, Golgi bodies,
and plasma membrane
– Some transport substances to or from other
organelles
– Fuse and form larger membranous sac, or
vacuoles
Lysosomes
• Lysosomes: vesicles that bud from Golgi
– Carry powerful enzymes that can digest contents
of other vesicles, worn out cell part, or bacteria
and foreign particles
– Enzymes activated when another vesicle moves
through the cytoplasm and fuses with the
lysosomes
– Contents are digested into bits
Lysosomes
Peroxisomes
• Peroxisomes: hold enzymes that digest fatty
acids, amino acids, and hydrogen peroxide (a
toxic metabolic product)
– Convert H2O2 to water and oxygen or use it in
reactions that degrade alcohol and other toxins
Review
1. What are the main differences between the
rough and smooth ER?
2. What is the function of the golgi body?
3. Distinguish between a lysosome, peroxisome,
and vesicle.
Answers
1. Rough ER has ribosomes and smooth ER does not. Rough
ER is where oligosaccharide groups are attached to
polypeptides. Smooth ER is the area from which vesicles
carrying proteins and lipids are budded, inactivates harmful
chemicals and breaks down fatty acids.
2. The golgi bodies are where proteins and lipids undergo final
processing, sorting, and packaging, they attach sugar side
chains to proteins and lipids they received from the ER.
3. Vesicles are commonly used by the cell as transporters to
and from plasma membrane. Lysosomes are vesicles that
bud from Golgi, contain digestive enzymes. Peroxisomes
hold enzymes that digest fatty acids, amino acids, and
hydrogen peroxide (a toxic metabolic product) .