Lecture 5: Cytoplasmic Membrane Flashcards Preview

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Flashcards in Lecture 5: Cytoplasmic Membrane Deck (36)
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1
Q

Prokaryotic cytoplasmic membrane consists of

A

A phospholipid bilayer composed of phospholipids and proteins

2
Q

Fluid mosaic model

A

The membrane is fluid because there is extensive lateral mobility of bulk proteins and phospholipids

3
Q

What can cross the selectively permeable cytoplasmic membrane?

A

Water, gases, and small hydrophobic molecules

4
Q

What cannot cross the selectively permeable cytoplasmic membrane?

A

Most polar compounds such as amino acids, organic acids, and inorganic salts.

5
Q

What is a phospholipid made of?

A

2 fatty acid chains attached to the 2 carbon atoms of glycerol by ester bonds
A phosphate is attached to the third carbon atom of glycerol
Small organic groups linked to the phosphate group give additional variety of phospholipids

6
Q

What fatty acid feature makes membranes more fluid?

A

Unsaturated fatty acids (i.e. double bonds within the fatty acid chain) and branched fatty acids make membranes more fluid.

7
Q

Palmitic Acid (C16)

A

The predominant saturated fatty acid in bacteria

8
Q

4 fatty acids present in bacteria

A

Palmitic acid (C16, most common), myristic (C14), stearic (C18), and lauric (C12)

9
Q

Main unsaturated fatty acids in bacteria

A

Oleic acids (C18 monounsaturated)

10
Q

(T/F) Polyunsaturated fats are not found in bacteria

A

True

11
Q

Fatty acid features common in bacteria

A

Branched, hydroxylated, methylated, or cyclopropane ring-containing

12
Q

What catalyzes fatty acid biosynthesis and what substrates are needed?

A

Fatty acid synthetase uses acetyl-CoA and malonyl-CoA as substrates

13
Q

How is malonyl-CoA made?

A

From the carboxylation of acetyl-CoA using ATP as the energy source

14
Q

Acyl carrier protein (ACP)

A

Serves as the carrier for the growing fatty acid chain

15
Q

What is required as the reductant in fatty acid biosynthesis?

A

NADPH

16
Q

Why do fatty acids always have an even number of carbons?

A

Because fatty acid synthetase adds two carbons at a timeto the carboxy end of the growing fatty acid chain

17
Q

What happens to the inital carbon added to form malonyl-CoA at the end of fatty acid biosynthesis?

A

It is lost as CO2.

18
Q

Pentose phosphate pathway

A

the source of reduced NADP (NADPH) used in fatty acid biosynthesis

19
Q

What are the steps of phospholipid biosynthesis?

A
  1. FA CHAINS ADDED: ACP-fatty acid chains are added onto glycerol-3-phosphate, forming phosphatidic acid.
  2. COUPLING TO CDP: Phosphatidic acid is coupled to CDP -> CDP-diglyceride (CDP is the carrier)
  3. Head groups are added to CDP-diglyceride
  4. Serine is added to make phosphatidylethanolamine
  5. Glycerol-3-phosphate is added, making phosphatidylglycerol
20
Q

The two most common phospholipids found in the bacterial membrane:

A

Phosphatidyl ethanolamine and phosphatidyl glycerol

21
Q

Functions carried out by membrane proteins (7)

A
  • Solute transport (e.g. ABC transporter for nutrient uptake)
  • Electron transport (e.g. cytochromes)
  • ATP synthesis (ATPase_
  • Protein secretion (e.g. Sec translocase)
  • Motility (flagella motor)
  • Sensing environmental signals (sensor histidine kinase of a two component regulatory system)
  • Biosynthesis of cell wall polymers and lipids
22
Q

Function/ components of the Sec system

A

Involved in translocation of membrane-bound proteins

  • Leader peptide (on membrane protein)
  • Chaperon protein (SecB)
  • Membrane bound SecYEG complex
  • Peripheral ATPase (SecA)
23
Q

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

A
  1. Leader peptide is not recognized and therefore not cleaved by the signal peptidase
  2. An internal hydrophobic region of amino acids called the “stop transfer sequence”
  3. Both the leader peptide and stop-transfer sequence
24
Q

Once proteins are at the membrane, they will fold into a _________, which requires:

A

Conformation that is most stable thermodynamically.

  • Most of the AA side chains must be non-polar (Ala, Val, Leu, Ile, Phe) to allow interactions with phospholipids
  • Polar part of the protein backbone of transmembrane segments must hydrogen bond, which is accomplished via alpha-helices or beta-barrels
25
Q

How is H bonding achieved in membrane proteins?

A
  • When all peptide bons are H-bonded internally, an alpha-helix forms
  • Beta sheets can also achieve H-bonding, provided that the beta-strands form closed beta-barrels
26
Q

Bacteriorhodopsin

A

A proton pump produced by some archae to capture light energy for pumping out protons (to generate a proton motor force)

27
Q

Lipids in archaeal cell membranes consist of either:

A
  • C20 isopranoid alcohols ether-linked to a glycerol to form monoglycerol diethers
  • C40 isopranoid alcohols ether-linked to 2 glycerols to form diglycerol tetraethers
28
Q

Monoglycerol diethers form a

A

Lipid bilayer

29
Q

Diglycerol tetraethers form a

A

Monolayer, because they are long enough to span the entire membrane

30
Q

(T/F): Archaeal cell membranes can only contain either diethers or tetraethers

A

False. The ratio of diethers and tetraethers varies depending upon the bacterium

31
Q

Two key differences between archaeal and bacterial membrane lipids

A
  • Bacterial lipids are ester bonded ad are made of fatty acids
  • Archaeal lipids are ether bonded and are made of isoprene (isopranoid alcohols)
32
Q

Mycoplasma

A

Bacteria that lack a cell wall (just have a membrane, no PG).
The membrane contains sterols that hold the cell shape in addition to phospholipids

33
Q

Sterols (where are they found and how are they acquired?)

A

In mycoplasma cytoplasmic membrane. Hold the cell shape.

Sterols are acquired from the environment, usually as cholesterol from the host.

34
Q

Why are beta-lactam antibiotics ineffective against mycoplasma?

A

Beta-lactam antibiotics cannot attack mycoplasma because they dont have a cell wall

35
Q

Mycoplasma human pathogens

A

M. pneumoniae and M. gentalium

36
Q

Polymyxin

A

An antibiotic that affects membrane function

  • Cationic antimicrobial peptide (cyclic peptide, long FA tail)
  • Inserts into and disrupts membranes rich in phosphatidyl ethanolamine
  • Can kill bacteria that is not growing
  • Topical use only (e.g. Polysporin)