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CBNS101 Lecture 5: Transmembrane transport into the ER and mitochondria

front 1

Describe the structure of the Endoplasmic Reticulum

back 1

It is the connected to the outer nuclear membrane. With a rough side facing the cytoplasm and a smooth side

front 2

Describe the functions of the Endoplasmic Reticulum

back 2

  • The rough ER is embedded with ribosomes which aid in making proteins and translocation
  • The smooth ER is in charge of sending vesicles to the plasma membrane using the railway of microtubules

front 3

Describe co-translational transfer

back 3

Ribosomes reading the mRNA read the signal sequence of amino acids, once it know where they need to send it, they cleave off the signal and transport the protein

front 4

What is the role of a SRP (signal recognition particle) and and SRP receptor in the ER.

back 4

The SRP receptor is in the ER right next to the embedded ribosomes. The tRNA and rRNA subunits that are starting to grow a signal sequence is recognized by the SRP. The SRP binds to the signal sequence and the elongation site (stopping the tRNA from connecting any more amino acids to the sequence). In doing so, a space opens up in on the another side of the SRP allowing it to bind to the SRP receptor. It is now docked and ready to elongate the rest of the protein sequence. Once the signal is read in the protein translocator, it is cleaved off by a signal peptidase and the protein is sent off to where it needs to go. The tRNA/rRNA units are released, then the SRP to both be reused in the cycle again.

front 5

What does a signal peptidase protein do?

back 5

It cleaves off the signaling sequence

front 6

What is sec61?

back 6

It's the name of the protein translocator that the SRP receptor is next to

front 7

Since it cannot translocate folded proteins, they use ____ to keep it unfolded. Also what is its role?

back 7

chaperone proteins (round grape like proteins). They are in charge of ensuring proteins are folded (ER lumen) or prevent them from getting folded (cytosol) depending on where they are

front 8

Describe a single-pass transmembrane protein

back 8

The transmembrane segment is recognized by the SRP and brought to the SRP receptor next to sec61.

  • If N terminal is long, folded and can't cross the membrane or N side has a (+) charge, the C terminus will pass through to the other side
  • If the N terminal is short, unfolded and the C side has a (+) charge, the N terminus will pass through to the other side
  • Only a (-) charge will pass through

front 9

What needs to happen is a long N terminus needs to pass through to the ER lumen?

back 9

The signal sequence would need to be placed in sec61 first thing. Then it will elongate in a folded u-shape already on the outside. The transmembrane segment will then come by, stopping protein synthesis and releasing the protein into the ER lumen

front 10

Describe a multi-pass transmembrane protein

back 10

The same N terminus law as single pass. However, he next protein that gets embedded is in the opposite orientation as the previous one and the protein is not cleaved by signal peptidase

front 11

Describe what happens when proteins are improperly folded in the ER lumen

back 11

The lectin proteins that do quality checks send it back in the direction of the translocator complexes, which adds a (poly)-ubiquitin protein tag to it which marks it for degradation. The tags lead them to a proteasome in the cytosol which breaks it down

front 12

What is UPR

back 12

It is the unfolded protein response. Basically calls for quality control and demands the ER to produce better properly made proteins

front 13

What are scramblases?

back 13

Enzymes that catalyze the random flip flopping of lipids in the lipid bilayer in the ER membrane

front 14

What are flippases?

back 14

Enzymes that catalyze the random flip flopping of lipids in the lipid bilayer in the golgi and other membranes

front 15

T/F Mitochondrial transport also depends on signal sequences of translocators

back 15

True

front 16

T/F Other proteins have internal signal sequences that are not removed

back 16

True

front 17

Describe the Mitochondrial protein transport process

back 17

(TOM) recognizes the signal sequence and inserts the unfolded proteins through the mitochondrial membrane. If it reaches SAM, they get turned into Beta-barrel proteins that stay in the outer membrane. If they reach TIM22, TIM23 or OXA, they are further inserted into the inner membrane of the mitochondria

front 18

What are the layers with the translocators of the mitochondria?

back 18

Cytosol

----Outer membrane-------MIM1---------TOM--------SAM------

Intermembrane space

----Inner membrane----TIM22-----TIM23-----OXA--------------

front 19

What trans-locational complexes are in chloroplasts? What are they called?

back 19

TIC/TOC