Cytoplasmic membrane

Question 1

Why is a cytoplasmic membrane considered to be “fluid”

Answer 1

There is extensive lateral mobility of bulk proteins and phospholipids

Question 2

Selectivity of the cytoplasmic membrane

Answer 2

Can cross: water, gases, and small hydrophobic molecules

Cannot cross: most polar compounds (AA, organic acids, inorganic salts)

Question 3

Composition of phospholipids

Answer 3

2 fatty acid chains esterified to the 2 carbon atoms of glycerol

Phosphate is attached to the third carbon of glycerol

Small organic groups linked to the phosphate give it additional variety

Question 4

Phospholipids form ___ in a watery environment

Answer 4

Micelles

• if there is a high enough concentration of phospholipids
• each type of phospholipid has a different critical concentration that must be reached

Question 5

Phospholipids are said to be ____

Answer 5

amphipathic

Question 6

Fatty acids without any DB are?

Answer 6

Saturated

Question 7

Fatty acids with one DB or more are?

Answer 7

Monounsaturated or polyunsaturated

Question 8

As the # of DB increases, the melting point ____

Answer 8

Decreases

Question 9

A membrane with lots of unsaturated FA will be very

Answer 9

Fluid

Question 10

A membrane with lots of saturated FA will be very?

Answer 10

rigid

Question 11

being able to change the composition of FA is important for bacteria because?

Answer 11

It allows them to exist over a range of temperatures

Question 12

What is the predominant saturated fatty acid in bacteria?

Answer 12

Palmitic acid (C16)

Stearic (C18), myristic (C14) and lauric (C12) also present but in lesser quantities.

Question 13

What are the main unsaturated fatty acids in bacteria?

Answer 13

Oleic acids (C18)
-monounsaturated

Question 14

Are polyunsaturated fatty acids found in bacteria?

Answer 14

No, they don’t have the enzyme to make it

Question 15

Myristic acid (c14) is found in what structure of gram negative bacteria

Answer 15

Lipid A of the LPS

Question 16

How do bacteria compensate for the fluidity lost by not having polyunsaturated fatty acids?

Answer 16

They make branched-, hydroxylated-, methylated-, or cyclopropane ring-containing fatty acids

Question 17

_ steps of fatty acid biosynthesis

Answer 17

1. Formation of malonyl-CoA from the CARBOXYLATION of acetyl CoA using ATP
2. Acyl carrier protein (ACP) is a small protein that carries the growing FA chain
3. NADPH is required for REDUCTION
4. Fatty acid synthase adds 2 carbons at a time to the carboxyl end of the chain
5. Initial carbon added to form malonyl-CoA is lost as CO2

Question 18

Which enzyme catalyzes the synthesis of fatty acids

Answer 18

Fatty acid synthase

-substrates are acetyl-CoA and malonyl-CoA

Question 19

Where is NADPH generated

Answer 19

Pentose phosphate pathway!

Question 20

Phospholipid biosynthesis - 1st step

Answer 20

Adding the ACP-fatty acid chains on to glycerol-3-phosphate forming phosphatidic acid

Question 21

Phospholipid biosynthesis - 2nd step

Answer 21

Phosphatidic acid is then coupled to CDP forming CDP-diglyceride. Cystidine diphosphate (CDP) is used as the carrier.

Question 22

Phospholipid biosynthesis - 3rd step

Answer 22

Head groups are then added to CDP-diglyceride

• if serine is added it becomes phosphatidylethanolamine
• if glycerol-3-phosphate is added it becomes phosphatidylglycerol

Question 23

What are the 2 most common phospholipids found in the bacterial membrane

Answer 23

Phosphatidyl ethanolamine and phosphatidyl glycerol

Question 24

2 types of membrane proteins and how they can be removed

Answer 24

1. Integral: embedded in the membrane, can only be removed by solubilizing the membrane with detergents or solvents

Peripheral: attached to the membrane surface, can be removed with salt solutions

Question 25

7 functions carried out by membrane proteins

Answer 25

1. Solute transport 2. Electron transport 3. ATP synthesis 4. Protein secretion 5. Motility 6. Sensing environmental signals 7. Biosynthesis of cell wall polymers and lipids

Question 26

Membrane protein export occurs by what kind of system

Answer 26

A Sec system

Question 27

4 factors involved in a Sec system

Answer 27

1. leader peptide on the membrane protein 2. A chaperone protein 3. A membrane bound SecYEG complex 4. Peripheral ATPasse: SecA

Question 28

3 ways the membrane proteins can be retained on the cytoplasmic membrane

Answer 28

1. The presence of the leader peptide - it is not recognized or cleaved by the signal peptidase - 20 AA in length on the N terminus 2. An internal hydrophobic region called the "stop transfer sequence" 3. Both the leader peptide and the stop transfer sequence

Question 29

The leader peptide directs the protein to the ?

Answer 29

Membrane

Question 30

2 requirements for thermodynamic stability of the protein within the membrane

Answer 30

1. The transmembrane segments of the protein need to be non polar to interact with phospholipids 2. The polar part of the transmembrane segments need to participate in H bonds - easily accomplished with alpha helices - can use beta sheets as long as they form closed structures like a beta barrel

Question 31

What is the function of bacteriorhodopsin

Answer 31

a proton pump with pigment in it that gets excited and causes the sequential passage of protons throughout the structure -allows archae to capture light energy and generate a PMF

Question 32

Lipid composition of the archaeal cell membrane

Answer 32

Lipids are either C20 isopranoid alcohols ether-linked to a glycerol to form monoglycerol diethers. or C40 isopranoid alcohols ether-linked to 2 glycerols to form diglycerol tetraethers **occur in varying ratios depending on the bacterium

Question 33

Monoglycerol diethers form a lipid___

Answer 33

Bilayer

Question 34

Diglycerol tetraethers form a lipid ___

Answer 34

monolayer

Question 35

Archaea can have as many as __ different phospholipids

Answer 35

25 | -the head groups attached to the di or tetra ethers can be quite diverse

Question 36

What special compound do mycobacteria contain in their cell membrane

Answer 36

Sterols

Question 37

Where do sterols come from/what is their function

Answer 37

Acquired from the environment (usually cholesterol from the host) Sterols are thought to hold the cell shape

Question 38

Why are beta-lactam antibiotics ineffective against mycobacteria ?

Answer 38

Because they lack a cell wall | -don't have any peptidoglycan

Question 39

Polymixin - composition

Answer 39

Cationic anti-microbial peptide (consists of a cyclic peptide with a long fatty acid tail)

Question 40

Polymixin - mode of action

Answer 40

Inserts itself and disrupts membranes rich in phosphatidyl ethanolamine *topical use only

Question 41

Polymixin is one of the few antibiotics bacteriocial to ....

Answer 41

non growing cells