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Flashcards in Membranes and Membrane Transport Deck (50)
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1

Biological membranes are about ___% lipid and ___% protein.

Biological membranes are about 50% lipid and 50% protein.

2

Lipid classification

3

In most naturally occurring triglycerides, the ____ fatty acid molecule is ____.

In most naturally occurring triglycerides, the central fatty acid molecule is unsaturated.

4

In solution, fatty acids spontaneously form. . .

a micelle

5

In solution, glycerolipids spontaneously form. . .

a lipid bilayer

6

Cholesterol

7

Cholesterol in membranes

8

Glycerophospholipid

If there is no head group, it is phosphatidic acid.

 

If there is a head group it is phosphatidyl x.  (example: if x is a choline, it is phosphatidyl choline).

9

Types of glycerophospholipid

10

Types of sphingolipid

11

glucocerebrosides, unlike phosphatidylinositol, are ___.

glucocerebrosides, unlike phosphatidylinositol, are neutral.  They do not carry a phosphate group.

12

Different membranes have different ____.

Different membranes have different membrane lipid compositions.  Different leaflets also have different membrane lipid compositions.

13

Major Routes of Protein Trafficking

Proteins translated in the cytosol may end up in compartments 1, 2, 3, or 4.

 

Proteins translated in the ER may end up in 5, 6, 7, 8, or 9.

 

Proteins from outside the cell may end up in compartments 10 or 11.

14

Signal sequence for cytoplasm

none

15

Signal sequence for nucleus

Nuclear localization sequence

 

ex, PAAKKKKLD

 

The NLS is a short stretch of basic amino acids arginine (R) and lysine (K)

16

Signal sequence for mitochondria

Mitochondrial localization sequence

 

 

17

Basic localization flowchart

18

Signal sequence for peripheral membrane proteins

CAAX motif

 

Must be c-terminal.  example:  CCIL-Cterm

19

Signal sequence for integral membrane protein

Transmembrane domain

 

Must also contain ER signal seq, as it requires ER processing.

 

SXXS - Hydrophobic span, ~22 amino acids - R and K-rich region, ~6 amino acids

Ecto domain -        Transmembrane domain -                    cytoplasmic domain

20

Signal sequence for constitutive secretion

Just the ER localization sequence is sufficient to enter the secretory pathway.

21

Signal sequence for regulated secretion

Various sequences for targeting to specific regulated secretory granules.  Often controlled by calcium.

ex, insulin

22

Signal sequence for ER residents

ER localization sequence

 

C-terminal KDEL sequence

23

Signal sequence for lysosomal proteins

Mannose-6-phosphate

 

 

24

Architecture of nucleus

25

Nuclear transport occurs through. . .

Nuclear pores complexes

 

Attached is an image showing scanning EM of both sides of a nuclear pore.  Note the 8-fold symmetry.

26

The nuclear localization sequence is a binding site for ____.

The nuclear localization sequence is a binding site for importins.

 

The nuclear pore proteins (nucleoporins) have long tails that have repeats containing hydrophobic amino acids like phenylalanine. These hydrophobic tails stick together due to the hydrophobic effect, creating a meshwork that blocks the passage of moderate- to large-sized proteins. The importin proteins have hydrophobic amino acids on their surface that can interact with the hydrophobic tails of the nucleoporins, allowing them to “melt” the meshwork and pass through it. By binding cargo proteins with NLS’s, the importins can piggyback proteins through the meshwork.

27

Signal sequence for peroxisome

SKL = Serine-Lysine-Leucine

28

Anchoring of peripheral membrane proteins

All of these proteins are considered peripheral membrane proteins, but only the proteins on the inside of the cell would be translated by cytosolic ribosomes. The protein on the outside of the cell would be translated by a ribosome attached to the ER.

29

Cartoon of the secretory pathway

30

Translocon

Channel in the ER membrane that binds proteins by the ER localization sequence as they are being translated and facilitates their translation into the ER.