Protein control: (Vuister) membranes and transport 1

Question 1

Types of membrane proteins

Answer 1

transport proteins (porins, ion channel, ionic
pump and specific carriers)
receptors
enzymes with regulatory function
adhesion/structural proteins

Question 2

What is Bacteriorhodopsin?

Answer 2

protein used by Archaea

- acts as a proton pump

Question 3

Characteristics of TM helices?

Answer 3

Typical length of 20aa residues
~ 6 turns throughout a membrane

Spans the membrane completely

Charged aa at ends

Question 4

Purpose of hydrophobicity plot?

Answer 4

Used to identify a region of
hydrophobic residues in a
sequence

• Based on a hydrophobic
index

• A TM helix has a region of
high consecutive
hydrophobic scores

scored via algorithm e.g. Kyte-Doolite

Question 5

What is the (Von Heijne) Positive inside rule?

Answer 5

cytoslic loops near the lipid bilayer contain more positively charged amino acids

• 2-4 times more positive Arg/Lys
in cytoplasmic loops

• allows prediction of orientation
of TM helices

Question 6

What are Porins? Defining characteristics of Porins?

Answer 6

Porins = class of proteins whose molecules can form channels (allow passage of small molecules) through cellular membrane

Hydrophobic exterior
Hydrophilic core
Usually involved in transport
Located in membrane

Question 7

What is a beta barrel?

Answer 7

beta barrel is a beta-sheet composed of tandem repeats that twists and coils to form a closed toroidal structure in which the first strand is bonded to the last strand

(cylinder like channel structure)

Question 8

Characteristics of membrane anchors?

Answer 8

• Covalent modifications
• Hydrophobic
• Tether proteins to
membrane