Bio Lecture 7 Notes

Front 1

What is a localization signal

Back 1

signal or tag that consists of a continuous section in the peptide chain

Front 2

What is a Localization patch

Back 2

signal or tag that consists of a contiguous section in the folded protein (AAs not next to each other unfolded)

Front 3

What is Co-translational import

Back 3

• How proteins enter the ER - they enter as they are made

• Can either remain in membrane (single or multipass) or pass all the way through across the membrane and end up in lumen of ER (soluble or peripheral)

Front 4

Where do proteins w.o tags

Back 4

• free ribosomes with no tag’s default location is the soluble cytoplasm

Front 5

Post-translational import

Back 5

Proteins imported after synthesis; fate of proteins made on free ribosomes (for proteins that are NOT part of the EMS)

Front 6

Pathway for newly made proteins to be secreted

Back 6

Go → RER → Golgi → secretory vesicles → outside

Front 7

How do proteins enter the ER

Back 7

• 1. ribosome unattached to ER starts making protein. If SP(+), then ribosome + growing chain will attach to ER membrane, and co-translational import (chain enters ER as it grows)

• 2. SP binds to SRP

Front 8

How does Growing Chain enter ER

Back 8

• 3. SRP binds to SRP docking protein

• 4. SRP released + recycled, ribosome binds to pore/translocon, translocon opens and peptide enters as loop, and ribosome continues trans

Front 9

How does a new protein end up in the lumen of the ER

Back 9

• 5. Translation + movement through transloc

• 6. Trans +transloc complete; transloc closes

• 7 signal peptidase cuts off SP; protein is released into lumen of ER and ribosome + mRNA released (soluble)

Front 10

Types of proteins that can result from co-translational import

Back 10

• Soluble protein in lumen

• integral memb prot anchored in memb by SP w no cytoplasmic domain

• single pass T.M prot (amino is on lumen side)

• single pass T.M prot (carboxyl is on lumen side)

• MP T.M prot

• Lipid anchored proteins

Front 11

Where is the SP?

Back 11

USUALLY (not always) at the amino

Front 12

What is SRP

Back 12

• signal recognition particle (example of ribonucleoprotein particle)

• temporarily blocks translation, ferries baby protein to ER.

• SRP contains proteins + RNA

• helps attach ribo to ER

Front 13

What is a translocon

Back 13

• Found on ER; gated pore or channel through membrane that allows growing chain to pass through membrane as chain is made

Front 14

Stop-transfer sequences

Back 14

hydrophobic sequences can stop process of moving through transloc and anchor prot in membrane

Front 15

Start-transfer sequences

Back 15

• hydrophobic sequences in middle of peptide can RESTART looping → MP prot

• sequence that starts or REstarts passage of prot through transloc

Front 16

Where do proteins without SP go?

Back 16

cytoplasm, non EMS systems, or nucleus

Front 17

Examples of secreted proteins

Back 17

• ECM proteins (laminin, fibronectin, collagen, etc)

• signaling proteins (EGF, insulin, etc)

Front 18

• Proteins that go to plasma membrane

Back 18

• from attached ribosomes

• secreted proteins

• integral proteins