BIO130 Organelles & Endomembrane System

Cytosol

-Half of cell volume

-Protein synthesis and degradation

Rough ER

-Membrane-bound ribosomes

-Synthesis of proteins and transmembrane proteins

Smooth ER

-Phospholipid synthesis, detoxification

Organelles

a discrete structure or sub-compartment of eukaryotic cell specialized for a function

How are proteins sorted?

-Sorted by signal sequence

-Each signal sequence specifies a destination

-Signal sequence are recognized by receptors to take proteins

2 steps of Protein Sorting

1) Post-translational sorting

2) Co-translational sorting

Post-translational Sorting

-Fully synthesized in cytosol before sorting

-Folded: nucleus, peroxisomes

-Unfolded: mitochondria, plastids

Co-translational sorting

-Proteins have an ER Signal Sequences

-Associated with ER during protein synthesis in the cytosol

Transcription activators are required in...

the nucleus fro eukaryotic transcription

Peroxisomes (folded)

contain complex enzymes fro oxidative reactions (break down fatty acids)

Mitochondria and Chloroplasts

-have their own genomes

-Unfolded proteins are imported by chaperone proteins

Proteins that enter the ER

-Soluble proteins

-Transmembrane proteins

ER Signal Sequences

-At N-terminal of protein (Removed by signal peptidase)

-Internal ER signal sequence (not removed, remains part of protein)

Secretory Pathway

-Proteins + Lipids made in ER to deliver compartments

Endocytic Pathway

Contents move into cell (Endocytosis)

Retrieval Pathway

Retrieval of lipids, selected proteins for reuse

Exocytosis

-Vesicle expels into the extracellular space

Endocytosis

-Vesicle comes from the space into the plasma membrane

Vesicles

Transport from ER to Gogli

Pathway of Secretory/Transmembrane Protein

ER → Golgi Apparatus → Plasma Membrane

Specifically Secretory Protein

released to extracellular space

Specifically Transmembrane Protein

transferred to plasma membrane

Maintenance of membrane protein asymmetry

vesicular transport

Golgi Apparatus

-Receives proteins and lipids from ER, modifies them, then distribute

Protein Glycosylation

Starts in ER, a single complex oligosaccharide occurs in golgi apparatus

Endosomes

-Membrane-bound organelles

-Contain material ingested by endocytosis

Lysosomes

-Membrane-bound organelles

-contain hydrolytic enzymes to digest worn-out proteins, organelles, other waste

-Acidified by low pH (H pump)

Proteins in Lysosomal Membrane

-Amino acids

-Sugars

-Nucleotides

Major Functions of Cytoskeleton

1) Structural Support

2) Internal Organization of Cell

3) Cell divison

4) Large Scale Movements

Immunofluorescence Microscopy

-Used to determine location of proteins within cell

-

3 types of filament form the cytoskeleton

-Actin Filament

-Intermediate Filaments

-Microtubules

Keratin Filaments in Epithelial Cells

-Form networks in cytoplasm

-Anchored by cell junctions

-Provides mechanical strength

Microtubules

-Organizing function

-involved in mitosis, structural support, cell transport, tubulin

Microtubule Organizing Centers

Microtube grow out from here

-Centrosome

Dynamic Instability: growing

-Free tublulin dimers (bound to GTP)

-hydrolyzes GTP to GDP

-Rapid addition of dimers

Dynamic Instability: shrinking

-Free tublulin dimers (bound to GTP)

-hydrolyzes GTP to GDP

-Slower addition of dimers

Dynamic Instability: Mechanism

-B-tubulin GTP --> hydrolyzed to GDP

-Tightly-bound GTP to a-tubulin

GTP cap

straight filaments (stronger binding, favours growth

GTP hydrolysis (GDP dimers)

small confomational change, weaker binding, curved filaments and disassembly

y-tubulin ring complex

-Protein complex

-acts as an attachment site for dimers

How does neurotransmitters to be synthesized in the ER to the axon terminals?

it uses motor proteins on the microtubules

Kinesins

-Generally move towards + end of tubules

-cargo of vesicles macromolecules

Dyneins

-move towards minus end of tubules

-worn out mitochondria

Microtubule positioning

-ER From nuclear envelope to cell periphery (kine)

-golgi near centrosome (dyne)

Actin Filaments (microfilaments)

-Made of actin monomers

-Flexible

-Myosins (motor)

Actin filaments functions

-Stiff, stability structures

-Contractile activity

-Cell motility

-Cytokinesis

Helical filament

-Composed of single glob protein

-twisted in helix

Actin monomers

-Bound to ATP

-Hydrolyzes ATP to ADP

-Rapid addition leads to ATP cap

Treadmilling

A) Actin filament growth

Regulated by actin binding proteins

- Severe filaments

-Organize bundle cross-link filaments

-stabilize filament by capping

-promote nucleation to form filaments

-prevent polymerization

Myosins

- Actin motor proteins

-generally move towards the plus end of actin

-head move along and hydrolysis fro movement

Myosin 1

tail domain, binds to cargo (vesicles, plasma membrane)

Myosin 11

-Dimers assemble into myosin 11 using tail

-tails organized in coiled-coil

-ie. bipolar myosin filament - generates contractile force