Chapter 4.5

The Endoplasmic System

AP BiologyFall 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) .