Rider Biology 1.6–1.7 — Golgi, Vesicles & Cell Recycling

What is the Golgi apparatus?

A series of membrane-enclosed compartments that further processes, modifies, sorts, and ships proteins.

What is one Golgi compartment called?

A cisterna.

What is the plural of cisterna?

Cisternae.

Are Golgi cisternae directly connected to each other?

No.

How do proteins move from the ER to the Golgi?

In transport vesicles.

What is the first Golgi region called?

The cis Golgi.

What is the middle Golgi region called?

The medial Golgi.

What is the final Golgi region called?

The trans Golgi.

What is the normal order through the Golgi?

Cis → medial → trans.

What does anterograde mean?

Movement in the forward or outward direction through the Golgi toward final destinations.

What does retrograde mean?

Movement backward toward the ER.

Which direction is ER → Golgi → final destination?

Anterograde.

Which direction is Golgi → ER?

Retrograde.

Why can proteins move backward toward the ER?

Incoming, defective, rejected, or lost proteins may be returned.

What happens to Golgi compartments as proteins mature?

Golgi compartments can slowly move in the anterograde direction.

What happens to new cis Golgi compartments?

New cis compartments form as older compartments move outward.

What happens to old trans Golgi compartments?

They break up into delivery vesicles.

What is glycosylation?

The addition and modification of sugar or glycan groups on proteins.

Where does Golgi protein modification begin?

In the cis Golgi compartments.

Why does the Golgi modify proteins?

To help prepare them for their ultimate jobs.

What does the Golgi add to help identify a protein's destination?

Targeting signals.

Where does most final sorting occur in the Golgi?

In the trans Golgi.

What are four major destinations for Golgi-sorted proteins?

Lysosomes, outside the cell, plasma membrane, or back toward the ER.

What type of proteins can the Golgi send to lysosomes?

Digestive enzymes, lysosomal components, and proteins to be destroyed.

What type of protein might be secreted outside the cell?

A hormone.

What type of proteins may be sent to the plasma membrane?

Ion channels and receptors.

What carries proteins away from the trans Golgi?

Vesicles.

Why do vesicles have different coats and delivery tags?

To help direct them to the correct destination.

What is an endosome?

A membrane compartment that brings material into the cell from outside.

What process brings material into the cell?

Endocytosis.

What are examples of things endosomes may bring into cells?

Nutrients and sometimes viruses.

What is endocytosis?

The process of hauling something into the cell.

What is exocytosis?

The process of hauling something out of the cell.

What do vesicles do inside cells?

Transport materials from one location to another.

What is an example of internal vesicle transport?

Moving proteins from the ER to the Golgi.

What is an example of vesicle transport to the outside?

Carrying proteins that will be secreted or added to the plasma membrane.

What is a vacuole?

A membrane compartment used mainly for storage.

What may plant cells store in vacuoles?

Nutrients.

What else can cells store in vacuoles or similar compartments?

Toxic substances they cannot easily get rid of.

What is an autophagosome?

A double-membraned compartment that engulfs cellular material to be destroyed.

How many membranes does an autophagosome have?

A double membrane.

Where does an autophagosome send its contents?

To lysosomes.

What is the main job of a lysosome?

Destroy material using acid and digestive enzymes.

What powers proton pumps in lysosomal membranes?

ATP.

What ion is pumped into lysosomes?

H⁺.

Why does H⁺ build up inside a lysosome?

ATP-powered proton pumps move H⁺ from the cytosol into the lysosome.

What negatively charged ion enters lysosomes?

Chloride, Cl⁻.

Why does chloride enter the lysosome?

It is attracted by the positively charged H⁺ ions.

What acid is formed in lysosomes according to Rider?

Hydrochloric acid, HCl.

What pH does Rider give for lysosomes?

About 4.8.

Why is the inside of a lysosome acidic?

It contains many H⁺ ions and chloride ions.

Where do lysosomal digestive enzymes come from?

The Golgi apparatus ships them to lysosomes.

Why do lysosomal enzymes work well in lysosomes?

They are adapted to acidic conditions.

What happens to molecules after lysosomes digest them?

The pieces can be reused by the cell.

What is the main job of a peroxisome?

Destroy molecules by oxidation and enzymatic digestion.

How is a peroxisome different from a lysosome?

A lysosome uses acid; a peroxisome uses oxidation.

What oxygen-rich molecule is associated with peroxisomes?

Hydrogen peroxide, H₂O₂.

What organelle sends enzymes to peroxisomes?

The endoplasmic reticulum.

What type of enzymes does the ER send to peroxisomes?

Enzymes that work under highly oxidizing conditions.

What are the three major cellular destruction systems discussed so far?

Proteasomes, lysosomes, and peroxisomes.

What does a proteasome mainly destroy?

Ubiquitin-tagged proteins.

What does a lysosome mainly use to destroy material?

Acid and digestive enzymes.

What does a peroxisome mainly use to destroy material?

Oxidation and enzymes.

What is a donor membrane?

The membrane from which a vesicle buds.

What is a target membrane?

The membrane where a vesicle delivers its cargo.

What happens during membrane budding?

A section of donor membrane bulges outward, pinches off, and traps cargo inside a vesicle.

What helps vesicle budding occur?

Coat proteins and other proteins.

What coat is used for ER → Golgi vesicles?

COPII.

What coat is used for Golgi → ER vesicles?

COPI.

What coat is used for outgoing exocytic vesicles?

Clathrin plus AP1.

What coat is used for incoming endosomes?

Clathrin plus AP2.

What is the direction of a COPII-coated vesicle?

ER → Golgi.

What is the direction of a COPI-coated vesicle?

Golgi → ER.

What does clathrin + AP1 usually mark?

An outgoing exocytic vesicle.

What does clathrin + AP2 usually mark?

An incoming endosome.

What happens to the vesicle coat after budding?

The coat proteins come off.

What is uncoating?

Removal of coat proteins from a vesicle after it buds.

What targeting proteins remain on a vesicle after uncoating?

Rab proteins.

What do Rab proteins do?

Help direct vesicles to the correct target membrane.

How does Rider compare Rab proteins to a familiar system?

They act like zip codes.

What recognizes a Rab protein at the target membrane?

A specific Rab effector protein.

What happens after Rab recognition?

The vesicle is pulled close to the target membrane.

What is a v-SNARE?

A SNARE tethering protein on the vesicle.

What is a t-SNARE?

A SNARE tethering protein on the target membrane.

What happens when v-SNAREs and t-SNAREs interact?

They pull the vesicle and target membrane close together.

How does Rider describe SNARE interaction?

Like Velcro.

What is membrane fusion?

The joining of the vesicle membrane with the target membrane.

What happens after membrane fusion?

The vesicle delivers its cargo.

What is the sequence of vesicle delivery?

Budding → coated vesicle → uncoating → Rab recognition → SNARE tethering → membrane fusion → cargo delivery.

What is the role of coat proteins in vesicle traffic?

They help vesicles bud from donor membranes.

What is the role of Rab proteins in vesicle traffic?

They help identify the correct target membrane.

What is the role of SNARE proteins in vesicle traffic?

They tether the vesicle to the target membrane and help bring the membranes together.

A protein leaves the ER for the Golgi. Which coat should its vesicle have?

COPII.

A protein is being returned from the Golgi to the ER. Which coat should its vesicle have?

COPI.

A vesicle is carrying material out of the cell. Which coat system is associated with it?

Clathrin plus AP1.

A vesicle is bringing material into the cell. Which coat system is associated with it?

Clathrin plus AP2.

A cell needs to digest damaged cellular material using acid. Which organelle should receive it?

Lysosome.

A cell needs to destroy a molecule by oxidation. Which organelle is best suited?

Peroxisome.

A cell needs to store nutrients for later. Which compartment is appropriate?

Vacuole.

A cell wants to engulf and send damaged internal material for destruction. Which compartment starts this process?

Autophagosome.