Chapter 7 Flashcards
(27 cards)
What are the four general principles for protein synthesis?
- Ribosomes are located in cytosol (they can be free or located on membrane bound organelles) slide 6 picture
- Synthesis of all proteins start on free ribosomes, but some will finish up translation while the ribosomes become membrane bound slide 7
- Results in two major branches of protein sorting (cytosolic vs secretory) slide 8
- Final destinations of protein are associated with which pathway it came from (cytosolic or secretory) slide 8
What is the cytosolic pathway?
What are it’s targets?
Proteins are synthesized on free ribosomes in cytoplasm then released directly to the cytoplasm Then moved to final destination by recognition of target amino acid sequences (signal seqeunces) Targets of cytosolic pathways include: Non membrane bound cytosolic proteins Nucleus Mitochondria Peroxisomes Chloroplasts Slide 11
What is the secretory pathway?
What are it’s targets?
The ER, Golgi apparatus, lysosomes and vesicles form the secretory pathway
Carries out sorting of both free and membrane bound proteins to intracellular destinations and secretes proteins from cell
Targets: nuclear membrane proteins, ER proteins, lysosomes, endosomes, Golgi proteins, secretory vesicles
Slide 14
Where is the rough ER located?
What’s the differences between rough ER and smooth ER?
It is continuous with the outer nuclear membrane
Slide 17 pictures
Difference is Rough ER has ribosomes and is protein metabolism and is entry point for most proteins into secretory pathway and smooth ER doesn’t have ribosomes and is lipid metabolism
How do the majority of proteins destined for secretory pathway translocate into the ER during synthesis on membrane bound ribosomes?
The signal for ribosome attachment to the RER was demonstrated to be an amino acid sequence (signal sequence) near amino terminus of growing polypeptide chain
Polypeptide structure on slide 20
Where is the C terminus, N terminus, and signal sequence located on a secretory pathway?
Carboxyl terminus (end of peptide) Amino terminus (start of peptide) Signal sequence
All on slide 21
How does a signal sequence target a protein to the endoplasmic reticulum? (5 steps)
- A signal sequence at beginning (Nterminus) of protein being synthesized
- A signal recognition particle (SRP) in cytoplasm binds to signal sequence
- SRP receptor on ER binds to SRP
- Channel called translocon runs through ER membrane and is attached to SRP receptor on cytosolic side of ER
- Signal peptidase enzyme at bottom of translocon cleave off signal sequence
Slides 23-25
What happens when a protein is translocated across the ER?
Passage into the ER lumen and ER membranes is done by the action of molecular chaperones that are in the ER
Proteins cross unfolded then once through they fold into their 3D confirmations
What are the two major classes of proteins targeted to the RER?
Proteins destined for secretion
Integral membrane proteins- once protein is in membrane, it’s orientation is fixed (this is why it’s important for proteins to get inserted in the correct way in the ER during translation)
Slide 30
VERY FEW PROTEINS ARE EMBEDDED IN THE OUTERMEMBRANE, MOST ARE IN ER
What is the transmembrane sequence in the poly peptide being synthesized?
- It stops the polypeptide from entering the lumen of the ER
- it changes the confirmation of the translocon channel (Releasing the polypeptide chain to the ER membrane)
What is the secretory pathway of proteins from lumen to plasma membrane?
Study picture on slide 32 and 33
How are membranes created?
Membranes always arise from pre existing membranes!!
They are not generated spontaneously
New phospholipids are synthesized from the precursor glycerol by enzymes bound to the membrane on the cytoplasmic facing side of the phospholipid bilayer of the ER membrane
What are flippases?
Enzymes that facilitate the translocation of newly synthesized phospholipids to the opposite side of the bilayer
Maintains stable membrane making sure the growth of both sides of phospholipid bilayer is even
Slide 35
What is the cis face of Golgi and trans face of Golgi?
Cis- closest to ER (where proteins enter)
Trans- furthest from ER (where proteins exit)
Slide 38
How are proteins and lipids exported from the endoplasmic reticulum?
Proteins free in the ER and membrane proteins and membrane phospholipids travel along the secretory pathway in transport vesicles which bud from the membrane and fuse with the membrane of another membrane
Vesicles leave via ERGIC and move to Golgi via these vesicles
Picture on slide 40
Where does real sorting of protein start?
In the Golgi!!
Proteins can be exported out of ER, sorted in Golgi and sent back into the ER
What is protein glycosylation?
Mannose 6 phosphate residues target proteins for lysosomes (all proteins going to lysosomes should have this glycosylation)
It is protein processing within Golgi with synthesis/extensive modification of carbs
What are the 2 key steps of vesicular transport?
VT is responsible for molecular traffic between a variety of membrane enclosed compartments
1. Get the correct protein into the correct vesicle
2. Get the vesicle to its correct final destination within the cell
Picture on slide 46
What are coated vesicles?
Transport vesicles costed with cytosolic cost proteins that carry secretory proteins from ER to Golgi and from Golgi to other targets
Make sure everything gets where they need to go
What are lysosomes?
Membrane enclosed organelles that contain an array of enzymes capable of breaking down all types of biological polymers (proteins, nucleus acids, carbs and lipids)
How are lysosomal storage diseases caused?
Deficiency or absence of any one of a number of lysosomal enzymes
Results in failure of lysosome to degrade contents
How are vesicles docked and fused?
GTP bound Rab proteins recognize and bind tethering factors on target which makes first contact with vesicle and target membrane
These tethering factors stimulate formation of SNARE complexes between vesicle and membrane which begins fusion
Tethering is like hanging on to boat from dock to make sure it’s the right dock, if it’s the right dock you’ll tie it off with SNARE complexes
What is a nuclear pore complex?
Consists of a structure with eight-fold symmetry organized around a large central channel
Composed of 30-50 different nucleoporins
Selective transport
Picture on slide 62
What are the two mechanisms of transport through the nuclear pore complex?
- Passive- molecules less than 20-40 kDa
2. Energy dependant- larger molecules (allows for selectivity of transport)
