Membrane proteins 3+4

Question 1

What is meant by resolution?

Answer 1

The precision of the structure

Question 2

1-2Aº means you can see where each individual non-H atom is. 7Aº means you can just see the characteristic spiral of alpha helix.

Question 3

Under high intensity light conditions, what happens to retinal in the bacteriorhodopsin protein?

Answer 3

Light causes isomerisation from a trans shape to a cis shape (retinal is part of the Br protein)

Question 4

What does this cause?

Answer 4

This causes a cascade of events which uses this energy from the change, to allow the Br protein to pump protons from the cytoplasm into the extracellular space

Question 5

How can you get a 3D representation of 2D crystals from electron microscopy?

Answer 5

Tilt the specimen in the beam of electron microscopy

Question 6

How many angstroms of error were there when bacteriorhodopsin was determined in its structure?

Answer 6

7 angstroms which is a lot in protein structure

Question 7

Modern EM can stitch together lots of images together very well and has great stabilisation with better detectors too

Question 8

Modern EM does not require crystallisation which is useful because growth of 3D crystals is difficult

Question 9

How does the current process work in EM?

Answer 9

Place a small amount of the protein onto an electron microscopy grid which is then dropped rapidly into liquid ethane, cooled by liquid nitrogen.

Question 10

Why is this done?

Answer 10

To freeze every molecule exactly as it was. Frozen samples at -180C to minimise damage caused by electron beam.

Question 11

How is a 3D image produced from a noncrystalline specimen?

Answer 11

Each view of a different image contains unique information so different orientations are arranged. EM software can classify orientations.

Question 12

What is this process called?

Answer 12

Single particle imaging

Question 13

Can now solve structure of proteins in the membrane. Bacteriorhodopsin has been solved to 2.5 angstroms and show the amino acids interacting with the retinal and the distance between them.

Question 14

What is an example of how a membrane acts as a receptor?

Answer 14

G protein-coupled receptors (GPCRs), can act as receptors by detecting external signals, such as hormones or neurotransmitters, and transmitting them into the cell to initiate a cellular response.

Question 15

Enzyme:

Answer 15

Membrane-bound enzymes catalyze chemical reactions at the membrane interface. For instance, membrane-bound ATPases participate in energy conversion processes, such as ATP synthesis or hydrolysis.

Question 16

Marker:

Question 17

Structural:

Answer 17

Membranes provide structural support and organization to cells. Phospholipids form a bilayer that encloses the cell and compartmentalizes its contents. Membrane proteins, like integrins, can also connect the membrane to the cytoskeleton, contributing to cell shape and stability.

Question 18

Channel:

Answer 18

Ion channels form pore-like structures in the membrane that allow specific ions to pass through. For instance, sodium channels in neurons allow the flow of sodium ions, which is essential for generating electrical signals.