BIOL 2020 Lecture 12: Protein Sorting - The Golgi Apparatus

Transport vesicles _______ off from one compartment and fuse with another. as they do so, they carry material as cargo

bud

Endocytic pathway leads in what direction?

inward from the plasma membrane

What do most transport vesicles form from?

specialized, coated regions of membranes

Most transport vesicles form from specialized, coated regions of membranes. They bud off as ______ ________, which have a distinctive cage of proteins

coated vesicles

Coated vesicles

have a distinctive cage of proteins

Four well-characterized types of coated vesicles

clathrin-coated, COPI-coated, COPII-coated, and retromer coated

Coats

geometrical structures that assemble into vesicle cages, around 50 nm

Rab proteins

guide transport vesicles to their target membrane

SNARE proteins

mediate membrane fusion by putting the membranes in close proximity

How do proteins leave the ER?

in COPII-coated transport vesicles that form at the ER exit site (ERES)

What ensures vesicles are loaded?

cargo receptors inside vesicles

Activated receptors recruit what?

adaptor proteins that recruit the coat proteins

Why can COPII vesicles transport vesicles accommodate large cargoes?

by assembling tubes instead of vesicles

What makes up the Golgi?

collection of flattened, membrane-enclosed compartments called cisternae

Glycosylation and phosphorylations at the Golgi are what?

a destination code

Sugar coats

destination tags

True or false: all sugar coats are transient

true

Glycosylation steps are compartmentalized in what?

different cisternae

Two mechanisms by which transport through the Golgi Apparatus occurs

vesicle transport mechanism, cisternae maturation mechanism

Vesicle transport mechanism

vesicle transport molecules between cisternae

Cisternal maturation mechanism

cisternae maturate from cis to trans together with cargo molecules

Vesicular model

vesicles bud and fuse, COPI vesicles surround the Golgi (60-90 nm)

Maturation model

proto collagen is bigger than vesicles (300 nm), PC is not detected inside vesicles, it localized to enlarged Golgi cisternae

Fluorescent live imaging

make fusion proteins, track GFP through the Golgi, see processes in real time and in different colours

Are cisternae stacked in all species?

no

What does fluorescence microscopy show in a single cisternae?

maturation dynamics

What do COPI vesicles do?

bring ER proteins back from the Golgi

What sequence do ER proteins have

KDEL sequence

What in the ER initiates vesicle formation?

KDEL receptors

KDEL

lysine, aspartic acid, glutamic acid, leucine

A ________ ________ secretory pathway transports most other proteins directly to the cell surface

nonselective constitutive

No specific signal

secretes the protein (default pathway)

_______ _______ are needed to direct secretory proteins into secretory vesicles and ________ ________ into different specialized transport vesicles

specific signals, lysosomal proteins