Chapter 12 Study Guide: The Endomembrane System

Page 1

What are the Functions of Smooth ER:

Drug Detoxification

Carbohydrate Metabolism

Calcium Storage

Steroid Biosynthesis

Explain Drug Detoxification:

Involves the chemical process hydroxylation

- an Enzyme catalyzed reaction

- Addition of hydroxyl group to make drugs more soluble to be easier to discrete

+ Antibiotics

+ Steroids

+ Anticoagulates

+ Barbituates

The proteins that catalyze hydroxylation in drug detoxification are called

Cytochrome-P450.

- Also known as monooxygenases

- monooxygenases uses one of the molecular oxygen into the reaction product.

Explain Carbohydrate Metabolism:

-Hepatocytes break down glycogen by an enzyme knowns as Glucose-6-phosphatase

- Hydrolyzes a phosphate group from glucose-6-phosphate to form free glucose and inorganic phosphate

-Precent in liver cells (hepatocytes) to maintain constant levels of glucose.

Between meals

The role to metabolize glycogen:

1. Granules of glycogen are associated in the smooth ER

2. Glycogen degradation produces Glucose-6-phosphate

3. Hydrolyzed by Glucose-6-phosphatase to produce free glucose and inorganic phosphate

4. Free glucose is transported out of the cell in the membrane

Explain Calcium Storage:

Sarcoplasmic Reticulum: The smooth ER involved in Calcium Storage

- Typically Found in muscle cells

The calcium ions are pumped into the ER by ATP-Dependent Calcium ATPase

- Response by the release of extracellular signals involved in muscle contraction

-Normally Found in muscle cells

Steroid Synthesis:

The steroid hormones are:

Cholesterol and steroid hormones found in liver cells

- Cortisol - produced by cells in the adrenal gland

- Testosterone- produced by leydig cells in the testes

- Estrogen- produced by follicular cells in the ovaries

Various steroids have same:

- four ring structure

But have Different:

-different carbon Sidechains arrangements

-hydroxyl group arrangements

Page 2

How is SER function linked to

atherosclerosis? How do to statins work?

-SER contains an enzyme called HMG-CoA reductase which is a transmembrane protein HMG-CoA

- Excessive alcohol synthesis from food can lead to deposits of the cell wall arteries

-leads to heart attacks.

-Statins are a class of drugs that inhibits the enzyme HMG-CoA and lowers serum cholesterol.

Page 3

Describe the structure and organization of the Golgi complex and two models for how materials progress through it.

Golgi Definition:

-Flattened Disk Shape membrane cisternae in Eurkaryote cells.

- "intracisternal space"

-Part of the endomembrane system

-Contains Cisternae

Golgie function:

-Further processes/modifies glycoproteins

-Further sorts the modifies proteins and secretes them to their proper destination

Cisternae Definition:

-Membrane bound disks

-can have 1 to 100o's. Depends on the cell function and metabolism

Golgi has 3 components:

-Cis (CGN)

-Trans (TGN)

-Medial Cisternae

Cis Golgi Network (CGN):

-Cis golgi is closest to the ER.

-Proteins enter the Cis Golgi from ER and transitional elements

-The vesicles from ER fuse with the CGN membrane

-Membrane bound tubules

Trans Golgi Network (TGN)

-Membrane bounded Tubules

-The proteins/lipids leave the Golgi from this side

-This is done by transport vesicles

-Can turn into secretory vesicles, endosomes, lysosomes, the PM

Medial Cisternae:

-Flattened membrane sacs

-In between GNC and TNC

-Contains specific enzymes/receptors

-Enzymes

-Further processing of the proteins and enzymes

-Functionally distinct components

Two Golgi Models:

-Stationary Cisternae Model

-Cisternal Maturation Model

Stationay Cisternae Model:

-The cisternae components are stational

-The vesicles move from one cisternae to the other by fusing. "shuttle vesicles"

-Cis to trans sequence

-Proteins from the ER or the Golgi that are supposed to be retained will be transported back by retrograde movement.

Cisternae Maturation Model:

-The components of cisternae is constantly changing gradually from CGN to Medial Cisternae to TGN

-Cisternae are replaced by transport vesicles that fuse into tubular structures

Both Models:

-Cell uses both models

-Transport vesicles and secretory vesicles are formed in the TGN

-Cisternae mature at a constant rate

Anterograde movment:

-The forward movement of proteins and lipids from ER to golgi

Retrograde Movement:

-Transport that returns materal/ resident proteins back to the golgi to ER

Page 4

Where are phospholipids synthesized? Where does protein and lipid glycosylation begin and finish?

- Phospholipids are synthesized in the RER.

Protein and Lipid Glycosylation begin in the

Cytosolic surface of the RER and end in the TGN

Two types of Glycosylation is the:

-N-Linked

-O-linked

N-Linked Glycosylation:

- Addition of oligosaccharide to the The N terminal of amino acid of Asparagine

O-Linked Glycosylation:

-Addition of oligosaccharide to the Hydroxyl groups

-Serine or Threonine

Page 5

Name three vesicle coat proteins. Describe in detail the structure of best studied of the three and how it assembles.

The Three vesicle Coats are:

-COPII

-COPI

-Clathrin

Page 6

How are vesicles transported from the ER to the Golgi (in detail)? How are resident ER proteins that have escaped to the Golgi retrieved?

Vesicles are transported from the ER to the Golgi by proteins containing a specific Tag:

The Tag:

-Targets the protein to the vesicle

-Aheads to the specific location of the cell

The protein can be tagged by:

-Short Amino Acid Sequence

-Oligosaccharide Side Chain

-Hydrophobic domain

Lipids can be tagged by:

-The degree of saturation

Protein Trafficking overview:

-Ribosomes synthesize proteins and proteins enter the RER to become glycosylated

- Once glycosylated, Transition vesicles carry the proteins and lipids to the CGN from the ER that does not contain ribosomes

*The transition vesicles relies on protein coats

-Proteins and lipids move from the CGN to Medial Cisternae to TGN

- At the TGN some vesicles form secretory vesicles to be excreted by exocytosis

- or Vesicles can bud from the TGN to form endospores to form lysosomes

- Other proteins can come in from endocytosis

-Form vesicles that fuse with early endosomes

-If material needs to be degraded then the vesicles form early endosomes to late endosomes and then to lysosomes to be degraded

-Retrograde traffic returns compartment specific proteins to earlier components

Proteins that need to be retrieved have retrieval tags that contain short amino acid sequence:

Retrieval Tags:

- Soluble ER-specific components contain these tags that have short polypeptide sequence

-Bind to transmembrane receptors facing the golgi away from the lumen

-KDEL

* Lys-Asp-Glu-Leu

-KKXX (Mammals)

*X= any amino acid

-HDEL}

*His-Asp-Glu-Leu (YEAST)

After bind to the receptor and undergoes a conformational change

-The receptor ligand complex is placed into a transport vesicle and carried back to ER

-

Page 7

What signal is found on soluble resident ER proteins? On membrane resident ER proteins? What controls their binding and release in the Golgi and ER respectively?

The signal found on soluble resident proteins have:

-C-terminal sequences

KDEL

Lys-Asp-Glu-Leu

KKXX

Lys-Lys-aa-aa

-They will bind to COPI proteins

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