ecture 1(Organelles and trafficking)
L
- Endocytosis is - curve and exocytosis is + curve
- When something is inserted or wrapped around the outer→ -
- When something is inserted in inner→ - curve
- If the outer is short→ - and if the inner os short→ +
- Cholesterol help maintain fluidity
- Higher temp= superfluid where cholesterol keep rigid
- Lower temp= superacked where cholesterol keep it fluidity
- Glycolipid= in cell recognize a
- Peripheral protein= only attached to one side of the membrane
- Cell signaling
- Integral protein= spans across the membrane
- Moving molecules across
- Amphipathic=having both hydrophobic and hydrophilic parts
Cytosolic (Inner) Leaflet:
- Phosphatidylserine (PS) → Negatively charged, involved in signaling (e.g., apoptosis
when flipped to the outer leaflet).
- Phosphatidylethanolamine (PE) → Helps with membrane curvature and vesicle
formation.
- Phosphatidylinositol (PI) → Involved in intracellular signaling and vesicle trafficking.
- Extracellular (Outer) Leaflet:
- Phosphatidylcholine (PC) → Major structural phospholipid that maintains membrane
stability.
- Sphingomyelin (SM) → Involved in forming lipid rafts with cholesterol.
- Glycolipids → Important for cell recognition and communication.
IPID SYNTHESIS
L
Fatty acids are brought into the cytosol by fatty acid-binding
proteins.
Enzymes attach CoA (a helper molecule) to activate fatty
acids.
These activated fatty acids are added to glycerol-3-phosphate,
forming phosphatidic acid.
A phosphatase enzyme removes a phosphate, turning it into
diacylglycerol.
A choline phosphotransferase enzyme adds CDP-choline,
forming phosphatidylcholine, a major membrane lipid.
Lecture 2(Membrane protein transport)
- Topology
- Like having two door that lead to different
way but the inside remains the same
- When a protein start in the ER, it
never go to cytoplasm but have a own pathway.
, - rotein is inside the ER lumen it will remain inside a connected pathway of
P
organelles and NEVER RE ENTER CYTOPLASM
- Protein into ER
- Ifsoluble, the protein enters the ER lumen.
- Any protein that need to go to ER has a “label” on it which is called the signal
sequences (short hydrophobic sequence at the N-terminus of the protein.)
- Recognize bySRP→ Pause translation and carry it to the ER and bring
onto theSRP receptoron the membrane
- Sec61 transloconis like a door that opens to let the protein in.--> protein
is in through this
- Inside= cut off the signal sequences bysignal peptidase (if
membrane bound=sequence could be cleavedO
- Co-translational→ assembling the package during delivery
- The protein is threaded into the ERwhileit's still being made.
- Uses theSec61 poreto pull the protein inside.
- Post-translational→ pushing a ready made package through the door
- The protein isfully made in the cytoplasm firstand then moved into
the ER.
- This processrequires energyfrom proteins calledBiP and Sec62/63/72
to pull the protein inside.
- Ifmembrane-bound, it has a stop-transfer or start-transfer sequence determining
orientation.
Single-Pass Transmembrane Proteins(One membrane crossing)
- Usesone start-transfer sequence(or signal sequence) to enter the membrane.
- Astop-transfer sequenceprevents further translocation into the lumen.
- The rest of the protein stays in thecytoplasm.
- Example:ER receptors, some enzyme-linked receptors.
Multi-Pass Transmembrane Proteins(Multiple crossings)
- Start sequence= open the Sec61 translocon.The ribosome keeps translating, and the
protein enters the ER lumen.
- Stop=Part of the protein is inside the ER lumen.Part of the protein is stuck in the
membrane.Part of the protein remains in the cytoplasm.
- Another start come= push down the same protein down.
- More (+) charges on N-terminal side → N stays in cytoplasm, C goes into ER
- More (+) charges on C-terminal side → C stays in cytoplasm, N goes into ER
- Protein modifications
- In ER=disulfide bond to stable 3 nd 4 structure
- Glycosylation
- N-linked glycosylation
(Asparagine-linked) → Starts in the ER.
- Oligosaccharyl transferase
adds a sugar chain to an asparagine (Asn) amino acid.
- O-linked glycosylation
(Serine/Threonine-linked) → Happens in the Golgi.
L
- Endocytosis is - curve and exocytosis is + curve
- When something is inserted or wrapped around the outer→ -
- When something is inserted in inner→ - curve
- If the outer is short→ - and if the inner os short→ +
- Cholesterol help maintain fluidity
- Higher temp= superfluid where cholesterol keep rigid
- Lower temp= superacked where cholesterol keep it fluidity
- Glycolipid= in cell recognize a
- Peripheral protein= only attached to one side of the membrane
- Cell signaling
- Integral protein= spans across the membrane
- Moving molecules across
- Amphipathic=having both hydrophobic and hydrophilic parts
Cytosolic (Inner) Leaflet:
- Phosphatidylserine (PS) → Negatively charged, involved in signaling (e.g., apoptosis
when flipped to the outer leaflet).
- Phosphatidylethanolamine (PE) → Helps with membrane curvature and vesicle
formation.
- Phosphatidylinositol (PI) → Involved in intracellular signaling and vesicle trafficking.
- Extracellular (Outer) Leaflet:
- Phosphatidylcholine (PC) → Major structural phospholipid that maintains membrane
stability.
- Sphingomyelin (SM) → Involved in forming lipid rafts with cholesterol.
- Glycolipids → Important for cell recognition and communication.
IPID SYNTHESIS
L
Fatty acids are brought into the cytosol by fatty acid-binding
proteins.
Enzymes attach CoA (a helper molecule) to activate fatty
acids.
These activated fatty acids are added to glycerol-3-phosphate,
forming phosphatidic acid.
A phosphatase enzyme removes a phosphate, turning it into
diacylglycerol.
A choline phosphotransferase enzyme adds CDP-choline,
forming phosphatidylcholine, a major membrane lipid.
Lecture 2(Membrane protein transport)
- Topology
- Like having two door that lead to different
way but the inside remains the same
- When a protein start in the ER, it
never go to cytoplasm but have a own pathway.
, - rotein is inside the ER lumen it will remain inside a connected pathway of
P
organelles and NEVER RE ENTER CYTOPLASM
- Protein into ER
- Ifsoluble, the protein enters the ER lumen.
- Any protein that need to go to ER has a “label” on it which is called the signal
sequences (short hydrophobic sequence at the N-terminus of the protein.)
- Recognize bySRP→ Pause translation and carry it to the ER and bring
onto theSRP receptoron the membrane
- Sec61 transloconis like a door that opens to let the protein in.--> protein
is in through this
- Inside= cut off the signal sequences bysignal peptidase (if
membrane bound=sequence could be cleavedO
- Co-translational→ assembling the package during delivery
- The protein is threaded into the ERwhileit's still being made.
- Uses theSec61 poreto pull the protein inside.
- Post-translational→ pushing a ready made package through the door
- The protein isfully made in the cytoplasm firstand then moved into
the ER.
- This processrequires energyfrom proteins calledBiP and Sec62/63/72
to pull the protein inside.
- Ifmembrane-bound, it has a stop-transfer or start-transfer sequence determining
orientation.
Single-Pass Transmembrane Proteins(One membrane crossing)
- Usesone start-transfer sequence(or signal sequence) to enter the membrane.
- Astop-transfer sequenceprevents further translocation into the lumen.
- The rest of the protein stays in thecytoplasm.
- Example:ER receptors, some enzyme-linked receptors.
Multi-Pass Transmembrane Proteins(Multiple crossings)
- Start sequence= open the Sec61 translocon.The ribosome keeps translating, and the
protein enters the ER lumen.
- Stop=Part of the protein is inside the ER lumen.Part of the protein is stuck in the
membrane.Part of the protein remains in the cytoplasm.
- Another start come= push down the same protein down.
- More (+) charges on N-terminal side → N stays in cytoplasm, C goes into ER
- More (+) charges on C-terminal side → C stays in cytoplasm, N goes into ER
- Protein modifications
- In ER=disulfide bond to stable 3 nd 4 structure
- Glycosylation
- N-linked glycosylation
(Asparagine-linked) → Starts in the ER.
- Oligosaccharyl transferase
adds a sugar chain to an asparagine (Asn) amino acid.
- O-linked glycosylation
(Serine/Threonine-linked) → Happens in the Golgi.
