Microbial Cell Structure and Function

Question 1

Cocci

Answer 1

spheres

Question 2

Diplococci

Answer 2

pairs of spheres

Question 3

Streptococci

Answer 3

chains of spheres

Question 4

Staphylococci

Answer 4

grape-like clusters of spheres

Question 5

Tetrads

Answer 5

4 cocci in a square

Question 6

Sarcinae

Answer 6

cubic configuration of 8 cocci

Question 7

Bacilli

Answer 7

rods

Question 8

Coccobacilli

Answer 8

very short rods

Question 9

Vibrios

Answer 9

resemble rods, comma shaped

Question 10

Spirilla

Answer 10

rigid helices

Question 11

Spirochetes

Answer 11

flexible helices

Question 12

Filamentous

Answer 12

• mycelium (mat)

- network of long, multicellular filaments

Question 13

Pleomorphic

Answer 13

• variable in shape
• may not have cell wall so their shape can depend on what they are against
• default shape is round

Question 14

Unique shapes

Answer 14

star

Question 15

Unique arrangements

Answer 15

palisades (picket-fence)

Question 16

What is the size range for eukaryotes?

Answer 16

0.8 micrometers-hundreds of mircometers

Question 17

What is the size range for bacteria/archaea?

Answer 17

0.2 micrometers-750 micrometers

Question 18

What is the size range for viruses?

Answer 18

0.01 micrometers-2.3 micrometers

Question 19

How does surface to volume ratio change with size?

Answer 19

smaller organisms have a larger surface to volume ratio

Question 20

Why is being small an advantage?

Answer 20

• large surface to volume ratio
• faster binary fission
• more room for diffusion
• get nutrients in and wastes out faster
• get mutations faster which leads to natural selection

Question 21

What is the cytoplasmic membrane?

Answer 21

a thin structure that separates the cytoplasm from the environment

Question 22

What are the major functions of the cytoplasmic membrane?

Answer 22

• permeability barrier
• site of many proteins: transport systems, bioenergetics, chemotaxis
• energy conservation: proton motive force

Question 23

What is the cytoplasmic membrane composed of?

Answer 23

• lipid bilayer composed of amphipathic phospholipids (polar heads and nonpolar tails)
• phospholipids can be saturated or unsaturated depending on the environment
• have hopanoids to add structural stability
• have integral and peripheral proteins

Question 24

What are the saturation levels reflected by?

Answer 24

• the environment
• cold environment: unsaturated (to increase membrane fluidity)
• warm environment: saturated (to decrease membrane fluidity)

Question 25

What are peripheral proteins?

Answer 25

- loosely connected to the membrane | - comprise 20-30% of the membrane proteins

Question 26

What are integral proteins?

Answer 26

- embedded within the membrane (amphipathic) - comprise 70-80% of the membrane proteins - carry out important functions: transport, excretion and secretion, energy conservation

Question 27

What is the difference between secretion and excretion?

Answer 27

- secretion is releasing for a purpose | - excretion is getting rid of waste

Question 28

What is the bacterial cell wall?

Answer 28

- rigid structure that lies just outside the plasma membrane - contains peptidoglycan (only in domain bacteria) - component of most bacterial cells

Question 29

What are the functions of the bacterial cell wall?

Answer 29

- provides shape to the cell (default shape is spherical without the cell wall) - protects from osmotic lysis - may contribute to pathogenicity (helps it cause disease by attaching to surfaces or keeping toxins or medicines out) - protects from toxic substances

Question 30

What does the gram-positive cell wall look like?

Answer 30

- thick layer of peptidoglycan over the plasma membrane | - no outer membrane

Question 31

What does the gram-negative cell wall look like?

Answer 31

- thin layer of peptidoglycan over the plasma membrane | - has an outer membrane

Question 32

What is the structure of peptidoglycan?

Answer 32

- mesh-like polymer - two alternating sugars form the backbone: - N-acetylglucosamine (NAG) - N-acetylmuramic acid (NAM) - alternating D- and L- amino acids

Question 33

What kind of linkage connects NAG and NAM?

Answer 33

Beta 1,4 bond

Question 34

What is the structure of NAG and NAM?

Answer 34

- NAG has a shorter chain | - NAM has a longer chain with amino acids

Question 35

What breaks the Beta 1,4 bond?

Answer 35

- lysozymes | - works well on gram positive, but not gram negative

Question 36

What does penicillin do to peptidoglycan?

Answer 36

- causes a problem with the linking of amino acids (transpeptidation) - if a bacterium is actively growing, it has to elongate and divide and it purposely puts holes in its cell membrane - peptidoglycan precursors are put in the cytoplasm - precursors are translocated to fill the holes - normally, the amino acids would link, but penicillin prevents this - then the precursor pieces to fill in the holes fall out, which causes lysing

Question 37

What kind of linkage does E. coli have?

Answer 37

direct

Question 38

What kind of linkage does S. aureus have?

Answer 38

indirect (has an interbridge)

Question 39

What is the composition of gram-positive cell walls?

Answer 39

- composed primarily of peptidoglycan (90%) - may also contain teichoic acids (negatively charged, reason why bacteria have a negative charge) - lipetechoic acids - some have a layer of proteins on surface of peptidoglycan

Question 40

What do teichoic acids do?

Answer 40

- bind Ca2+ and Mg2+ - help maintain structure of cell wall - protect from harmful substances - role in pathogenesis

Question 41

What is the composition of gram-negative cell walls?

Answer 41

- consist of a thin layer of peptidoglycan (10%) surrounded by an outer membrane - periplasm (20-40%): contains hydrolytic enzymes, binding proteins, and chemoreceptors) - outer membrane is composed of lipids, lipoproteins, and lipopolysaccharide (LPS) - porins: channels that hydrophilic molecules can pass through - does not have teichoic acids

Question 42

What is LPS?

Answer 42

- made up of lipid A, core polysaccharide, and O-specific polysaccharide (O antigen) - lipid embedded in the outer membrane

Question 43

What is the role of LPS?

Answer 43

- contributes to negative charge on cell surface (core polysaccharide) - helps stabilize outer membrane structure and can act as an endotoxin (lipid A) - may mutate to protect from host defenses (O antigen) - may contribute to attachment to surfaces and biofilm formation - creates a permeability barrier

Question 44

How does the cell wall protect from cell lysis?

Answer 44

- in hypotonic environments, the solute concentration outside of the cell is lower, so water rushes in - the cell wall acts as a barrier to keep the cell from bursting

Question 45

What is plasmolysis?

Answer 45

- happens in hypertonic environments (solute concentration outside the cell is higher) - water rushes out of the cell - cell shrivels up inside the cell wall - hypertonic environments used for food preservation

Question 46

What conditions do bacteria prefer to live in?

Answer 46

hypotonic environments

Question 47

What evidence is there of the protective nature of the cell wall?

Answer 47

- lysozyme breaks bond between NAG and NAM in gram positive cells - penicillin inhibits peptidoglycan synthesis (in actively growing cells) - when cells are treated with either of these, they will lyse if put into a hypotonic solution

Question 48

How do mycoplasma survive without a cell wall?

Answer 48

- don't have peptidoglycan - have hopanoids and sterols (like eukaryotes) - plasma membrane is more resistant to osmotic pressure - live in isotonic environments without a steep concentration gradient

Question 49

What are gram positive cells without peptidoglycan called?

Answer 49

protoplasts

Question 50

What are gram negative cells without peptidoglycan called?

Answer 50

spheroplasts