The Cell Envelope

Question 1

What is the cell envelope?

Answer 1

The cell envelope is the outermost layer of a cell that provides structure and protection.

Question 2

What two structures make up the cell envelope?

Answer 2

The cell envelope is made up of the cell membrane and the cell wall.

Question 3

What are six general functions of the cell envelope?

Answer 3

1. Protection from environmental hazards
2. Structural support
3. Selective permeability
4. Communication with the environment
5. Transport of substances
6. Energy generation.

Question 4

What is selective permeability?

Answer 4

Selective permeability is the ability of a membrane to allow certain substances to pass while blocking others.

Question 5

What are the basic structural components of all cell (cytoplasmic) membranes?

Answer 5

The basic structural components are a phospholipid bilayer, proteins, and carbohydrates.

Question 6

How are archaeal cytoplasmic membranes chemically and structurally different from the membranes of Bacteria and Eukarya?

Answer 6

Archaeal membranes contain ether-linked lipids and can have a monolayer structure, unlike the ester-linked lipids of Bacteria and Eukarya.

Question 7

How are archaeal cytoplasmic membranes similar to the membranes of Bacteria and Eukarya?

Answer 7

permeability barrier and protein anchor

Question 8

What are the three major functions of the prokaryotic cytoplasmic membrane?

Answer 8

1. Selective permeability
2. Energy generation
3. Communication with the environment.

Question 9

What is the proton motive force? How is it used?

Answer 9

The proton motive force is the gradient of protons across a membrane used to generate ATP and drive transport processes.

Question 10

What is the major functional difference between eukaryotic and prokaryotic cytoplasmic membranes?

Answer 10

In eukaryotes, the cell membrane plays a role in compartmentalizing various cellular functions within membrane-bound organelles, while in prokaryotes, where organelles are absent, the cell membrane is responsible for a wider range of cellular processes due to its direct exposure to the cytoplasm

Question 11

What are the major functions of the prokaryotic cell wall?

Answer 11

Maintains the cell’s shape, protects the cell interior, and prevents the cell from bursting when it takes up water (osmotic pressure)

Question 12

Why is an understanding of cell wall structure and function important?

Answer 12

Understanding cell wall structure and function is crucial for developing antibiotics and understanding bacterial resistance.

Question 13

What is the major structural difference between the gram-positive and gram-negative cell envelopes of Bacteria?

Answer 13

Gram-positive bacteria have a thick peptidoglycan layer, while gram-negative bacteria have a thin peptidoglycan layer and an outer membrane.

Question 14

What are the major chemical constituents of the glycan tetrapeptide of peptidoglycan? How are these constituents arranged?

Answer 14

The major constituents are N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) arranged in alternating chains.

Question 15

What is the major difference in how strands of peptidoglycan are cross-linked in typical gram-positive and gram-negative cell walls?

Answer 15

In gram-positive walls, cross-linking is extensive, while in gram-negative walls, it is less extensive.

Question 16

What are the major chemical constituents of teichoic acids? How are these constituents arranged?

Answer 16

Teichoic acids are composed of glycerol or ribitol phosphate and are arranged in a linear fashion.

Question 17

What is the difference between teichoic acids and lipoteichoic acids?

Answer 17

Teichoic acids are anchored to the peptidoglycan, while lipoteichoic acids are anchored to the cytoplasmic membrane.

Question 18

How does lysozyme damage bacterial cell walls?

Answer 18

Lysozyme breaks down the glycan chains in peptidoglycan, leading to cell lysis.

Question 19

How does penicillin damage bacterial cell walls?

Answer 19

Penicillin inhibits the enzymes involved in peptidoglycan cross-linking, weakening the cell wall.

Question 20

How are archaeal cell walls different from bacterial cell walls?

Answer 20

Archaeal cell walls do not contain peptidoglycan and may be composed of proteins or polysaccharides.

Question 21

What are the structural similarities and differences between pseudomurein and peptidoglycan?

Answer 21

Both have a similar structure, but pseudomurein contains N-acetylglucosamine and N-acetyltalosaminuronic acid instead of NAM.

Question 22

What effect do lysozyme and penicillin have on pseudomurein?

Answer 22

Lysozyme has little effect on pseudomurein, while penicillin is ineffective due to the lack of peptidoglycan.

Question 23

How is the outer membrane of gram-negative cells different from the cytoplasmic membrane?

Answer 23

The outer membrane contains lipopolysaccharides and is less permeable than the cytoplasmic membrane.

Question 24

What are 3 unique functions of the outer membrane?

Answer 24

1. Protection against antibiotics
2. Barrier to large molecules
3. Host interaction.

Question 25

What are the 3 major components of lipopolysaccharide (LPS)? How are these constituents arranged?

Answer 25

1. Lipid A 2. Core oligosaccharide 3. O-antigen; arranged in a complex structure.

Question 26

What is the function of the Braun lipoprotein?

Answer 26

The Braun lipoprotein anchors the outer membrane to the peptidoglycan layer.

Question 27

What portion of LPS is toxic to animals? What is this portion called?

Answer 27

The lipid A portion of LPS is toxic and is known as an endotoxin.

Question 28

What is another major function of the outer membrane?

Answer 28

The outer membrane acts as a barrier to protect the cell from harmful substances.

Question 29

What is the periplasm?

Answer 29

The periplasm is the space between the inner and outer membranes in gram-negative bacteria.

Question 30

What are four types of proteins (& their functions) often found in the periplasm?

Answer 30

1. Enzymes (break down nutrients) 2. Binding proteins (transport molecules) 3. Chaperones (assist protein folding) 4. Signal transduction proteins (relay signals).

Question 31

What are porins? Where are they located? What is their function?

Answer 31

Porins are proteins located in the outer membrane that allow the passage of small molecules.

Question 32

What are the major structural components of a porin?

Answer 32

Porins are typically composed of beta-barrels that form a channel through the membrane.

Question 33

What is an S-layer?

Answer 33

An S-layer is a crystalline layer of protein that forms a protective coat around the cell wall of some bacteria and archaea.

Question 34

What is the general structure of an S-layer?

Answer 34

The general structure of an S-layer consists of a two-dimensional array of proteins or glycoproteins.

Question 35

What are several functions of the S-layer in Archaea?

Answer 35

The S-layer in Archaea serves multiple functions including protection from environmental stress, maintaining cell shape, and acting as a selective barrier.

Question 36

How do S-layers increase the pathogenicity of some bacteria?

Answer 36

S-layers can increase the pathogenicity of some bacteria by enhancing their ability to evade the host immune system and adhere to host tissues.

Question 37

What is an example of a Bacteria that lacks a cell wall?

Answer 37

An example of a Bacteria that lacks a cell wall is Mycoplasma pneumoniae. ## Footnote Mycoplasma pneumoniae has a unique cell membrane that contains sterols, which provide stability.

Question 38

What is an example of an Archaea that lacks a cell wall?

Answer 38

An example of an Archaea that lacks a cell wall is Methanosoma.