Cell Bio 406 Lecture 5

The interior hydrophobic layer

channels and carriers, depending on the mode of transportation.

catalyze the rapid and selective transport of ions down their electrochemical gradient

transporters and pumps.

They transport against the electrochemical gradient.

channels

gating mechanisms

channel pore

Channel proteins.

Gating

• ligand-activated
• voltage-activated
• stretch-activated
• temperature-activated

transporters and pumps

• uniporters
• symporters
• antiporters

couple with energy stores in electrochemical membrane gradients to facilitate movement

Use ATP hydrolysis to drive energetically less favorable substrate accumulation

active

ATP

electrochemical potential difference

inside the cell is slightly more negative than outside

ion movement across the membrane

a voltage difference

membrane potential

millisecond

very small

electrical signals that depend on several types of ion channels.

enable rapid communication between cells.

• Na+
• K+
• Ca2+ currents

by the flow of Na+ ions into the cell through voltage dependent Na+ channels.

transport of K+ ions through several different types of K+ channels.

a predisposition for arrhythmias or epilepsy.

cells localizing proteins to specific organelles and membranes.

ER

targeting/sorting signals (amino acid sequences in polypeptide)

ER

post-translational and co-translational

protein tag

It remains in the cytoplasm.

By small vesicles that bud off the membrane of the source organelle and fuse with the membrane of the distention organelle, releasing the enclosed protein within.

ER for translocation

they translocate completely

They are integrated into the ER membrane

Fold and modify proteins

enzymes and chaperones

SRP binds to the new sequence as it emerges from the ribosome and docks it to the ER membrane

energy

• 1. Signal sequence translated at 5' end of mRNA.
• 2. Sequence recognized by SRP and translation halted.
• 3. SRP recognizes docking protein and brings ribosome to rough ER and signal sequence is inserted.
• 4. SRP is released. 
• 5. Preotein synthesis restarts and polypeptide chain is pulled through membrane. Signal sequence is cleaved off.
• 6. Protein in lumen of RER. Ribosome is recycled.

Chaperones

Hsp-70 and Hsp-90

a chaperone

In the ER lumen

with cochaperones

They are targeted for degradation

proteosome?

ubiquitin attachment

• unfolded protein response activates ATF6 an d Xbp1.
• UPR inhibits protein synthesis.
• Triggers cell protective and cell death responses.

secretion

steriod synthesis and drug detox

calcium storage and release

in contractile cells

in response to the needs of the cell

Reticulons (proteins in ER that change its curvature) form tubules

associate physically and the protein being imported passes directly from one to the other.

Hsp70 (ATPase chaperone)

before they are imported into the peroxisomes

catabolism of fatty acids and other metabolic pathways

in the cytosol

To a translocation channel

2

bringing in of material from outside cell

• phagocytosis
• pinocytosis
• receptor-mediated endocytosis

discharge of material from vesicles at the cell surface to outside

ER and golgi

• early and late endosomes
• and lysosomes

a membrane bound vesicle buds from one compartment and fuses with another

constitutive or regulated

low pH and degradative enzymes in endosomes

used to internalize nutrients and regulate the cell surface expression of proteins

they are recycles or degraded

• 6.5- early endosome
• pH of organelle0 late endosome
• 4.5- lysosome

engulfing a solid particle by a phagocyte or a protist to form an internal phagosome

small particles are brought into the cell forming an invagination (liquids)

clathrin-mediated or caveolin-mediated

• 1.budding
• 2. fission
• 3. uncoating
• 4. tethering
• 5. docking
• 6. fusion
• (recycle)

small GTPases that localize to particular organelles.

cytosolic

membrane associated

some are recycles to the cell surface. Others are degraded in lysosomes.

cell polarity.