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Endomembrane system

interconnected organelles (ER, Golgi, vesicles, lysosome)

Protein trafficking

movement of proteins between compartments

Signal sequence

amino acid tag directing protein location

Sec61 translocon

channel that inserts proteins into ER

Signal peptide

directs ribosome to ER

BiP (chaperone)

helps protein folding

PDI (protein disulfide isomerase)

forms disulfide bonds

Glycosylation

addition of sugars to proteins

Protein Targeting to ER

• Ribosome starts translating protein 1

• Signal sequence appears 2

• SRP binds → pauses translation 3

• Ribosome docks to ER 4

• Protein goes through Sec61 5

• Translation resumes into ER lumen 6

Protein Folding in ER

1. Chaperones (BiP) bind

2. Disulfide bonds form (PDI)

3. Glycosylation added

4. Misfolded proteins → degraded

If folding fails → ER stress

Golgi apparatus

organelle that modifies, sorts, and ships proteins/lipids received from the ER

Cis-Golgi network (CGN)

entry face of Golgi (closest to ER); receives vesicle

Medial Golgi

middle region where proteins are chemically modified

Trans-Golgi network (TGN

exit/sorting station; decides final destination of proteins

Glycosylation

addition or modification of sugar groups on proteins (important for stability + targeting)

N-linked glycosylation

sugars added to asparagine

O-linked glycosylation

sugars added to serine/threonine

Mannose-6-phosphate (M6P)

lysosome targeting tag

Golgi Trafficking

• Entry at cis

• Modification across stacks

• Sorting at trans

cis = in trans = out

Vesicular model

cargo moves

Cisternal model

compartments move

COPII

ER → Golgi transport, forward

COPI

Golgi → ER transport, backward

Clathrin

Golgi → lysosome / endocytosis

ARF GTPase

initiates vesicle formation

Rab GTPase

vesicle targeting

v-SNARE

on vesicle

t-SNARE

on target membrane

Vesicle Transport

1. Coat assembles

2. Vesicle buds

3. Rab targets vesicle

4. SNAREs fuse membranes

Constitutive secretion

continuous release

Regulated secretion

stored, released when signaled

Clathrin + AP1

Golgi → lysosome

Clathrin + AP2

endocytosis

Dynamin

pinches off vesicle

LDL receptor

brings cholesterol into cells

Lysosome Targeting

• M6P tag added

• Recognized in Golgi

• Packaged into vesicle

• Sent to lysosome

M6P

lysosome signal

Autophagy

degradation of cell components

Autophagosome

double-membrane vesicle

Lysosome

degradation organelle

ATG proteins

regulate autophagy

Autophagy

• Isolation membrane forms

• Engulfs material

• Fuses with lysosome

• Degrades contents

happens during stress/starvation

• Endocrine

• Paracrine

• Autocrine

• → long distance

• → local

• → self

short vs long term signaling

short = speed long = decision gene expression

Actin filament

cytoskeleton component

Plus (+) end

fast growth

Minus (-) end

slow growth

Arp2/3 complex

creates branches

WASp

activates Arp2/3

Lamellipodia

branched network (movement)

Stress fibers

contractile bundles

Microvilli

stable bundles = structure

Actin Polymerization

1. ATP-actin added to + end

2. ATP → ADP

3. Filament treadmills

Myosin

motor protein atp needed to detach it

Actin

filament track

Sarcomere

contractile unit

Contraction Cycle

1. Myosin binds actin

2. Power stroke

3. ATP binds → release

4. ATP hydrolysis → reset

Tubulin (α/β)

building blocks

Protofilament

chain of tubulin

Microtubule

hollow tube

Plus end minus end

grows fast grows slow

DYNAMIC INSTABILITY

• GTP cap → stabilizes

• Catastrophe → shrink

• Rescue → regrow

MOTOR PROTEINS

• Kinesin → + end (outward)

• Dynein → - end (inward)

Cyclin

regulatory protein (timer

Cdk

kinase enzyme engine

Cyclin-Cdk

active complex

Wee1

inhibits Cdk

Cdc25

activates Cdk

Checkpoint

control point

cell cycle progression controlled by cyclin cdk

1. Cyclin builds up

2. Binds Cdk

3. Phosphorylates targets mechanism of control

4. Cell progresses

5. Cyclin degraded

Kinetochore

• attachment site

PHASES

1. Prophase → chromosomes condense

2. Prometaphase → nuclear envelope breaks

3. Metaphase → align

4. Anaphase → separate

5. Telophase → nuclei reform

6. Cytokinesis → split cell

adhesion complex

protein complex for cell movement steps are:

1 extension with the lameillipodium

2 adhesion

3 translocation cell body movement

4 de adhesion and endocytic recycling

acts like how youd think a octopus would move

focal adhesions

theyre the feet that cells use to pull around the enviorment

IPALM experiment

5 distinct layers

1 membrane apposed integrin signalling layer containing integrin cytoplasmic tails, focal adhesion kinase and paxillin

2 intermediate force transduction layer containing talin and vinculin

3 upper most actin regulatory layer with zyxin vasodilator stimulated phosphoprotein and a actinin

4 integrin/ecm layer

5 actin layer

Forster resonance energy transfter FRET

determines if two molecules are within nanometers

receptor tyrosine kinases RTKS

receive signals from growth factors. activation of tyrosine kinases leads to abundant phosphorylation

Ras Rat Sarcoma

small GTPase G protein most common mutation in cancer active Ras triggers a kinase cascade RTK to GRB2 to Sos to Ras then from Ras to Raf then to MEK to MAPK