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Phys-Pro - Section 1 > Cytoplasmic membrane > Flashcards

Cytoplasmic membrane Flashcards

1
Q

Why is a cytoplasmic membrane considered to be “fluid”

A

There is extensive lateral mobility of bulk proteins and phospholipids

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2
Q

Selectivity of the cytoplasmic membrane

A

Can cross: water, gases, and small hydrophobic molecules

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

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3
Q

Composition of phospholipids

A

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

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4
Q

Phospholipids form ___ in a watery environment

A

Micelles

  • if there is a high enough concentration of phospholipids
  • each type of phospholipid has a different critical concentration that must be reached
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5
Q

Phospholipids are said to be ____

A

amphipathic

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6
Q

Fatty acids without any DB are?

A

Saturated

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7
Q

Fatty acids with one DB or more are?

A

Monounsaturated or polyunsaturated

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8
Q

As the # of DB increases, the melting point ____

A

Decreases

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9
Q

A membrane with lots of unsaturated FA will be very

A

Fluid

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10
Q

A membrane with lots of saturated FA will be very?

A

rigid

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11
Q

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

A

It allows them to exist over a range of temperatures

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12
Q

What is the predominant saturated fatty acid in bacteria?

A

Palmitic acid (C16)

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

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13
Q

What are the main unsaturated fatty acids in bacteria?

A 
Oleic acids (C18)
-monounsaturated
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14
Q

Are polyunsaturated fatty acids found in bacteria?

A

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

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15
Q

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

A

Lipid A of the LPS

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16
Q

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

A

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

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17
Q

_ steps of fatty acid biosynthesis

A
  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
18
Q

Which enzyme catalyzes the synthesis of fatty acids

A

Fatty acid synthase

-substrates are acetyl-CoA and malonyl-CoA

19
Q

Where is NADPH generated

A

Pentose phosphate pathway!

20
Q

Phospholipid biosynthesis - 1st step

A

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

21
Q

Phospholipid biosynthesis - 2nd step

A

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

22
Q

Phospholipid biosynthesis - 3rd step

A

Head groups are then added to CDP-diglyceride

  • if serine is added it becomes phosphatidylethanolamine
  • if glycerol-3-phosphate is added it becomes phosphatidylglycerol
23
Q

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

A

Phosphatidyl ethanolamine and phosphatidyl glycerol

24
Q

2 types of membrane proteins and how they can be removed

A
  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

25
Q

7 functions carried out by membrane proteins

A
  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
26
Q

Membrane protein export occurs by what kind of system

A

A Sec system

27
Q

4 factors involved in a Sec system

A
  1. leader peptide on the membrane protein
  2. A chaperone protein
  3. A membrane bound SecYEG complex
  4. Peripheral ATPasse: SecA
28
Q

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

A
  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
29
Q

The leader peptide directs the protein to the ?

A

Membrane

30
Q

2 requirements for thermodynamic stability of the protein within the membrane

A
  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
31
Q

What is the function of bacteriorhodopsin

A

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

32
Q

Lipid composition of the archaeal cell membrane

A

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

33
Q

Monoglycerol diethers form a lipid___

A

Bilayer

34
Q

Diglycerol tetraethers form a lipid ___

A

monolayer

35
Q

Archaea can have as many as __ different phospholipids

A

25

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

36
Q

What special compound do mycobacteria contain in their cell membrane

A

Sterols

37
Q

Where do sterols come from/what is their function

A

Acquired from the environment (usually cholesterol from the host)

Sterols are thought to hold the cell shape

38
Q

Why are beta-lactam antibiotics ineffective against mycobacteria ?

A

Because they lack a cell wall

-don’t have any peptidoglycan

39
Q

Polymixin - composition

A

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

40
Q

Polymixin - mode of action

A

Inserts itself and disrupts membranes rich in phosphatidyl ethanolamine

*topical use only

41
Q

Polymixin is one of the few antibiotics bacteriocial to ….

A

non growing cells

Phys-Pro - Section 1 (8 decks)

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