Lab 9 Gram stain

Question 1

What is a structural stain?

Answer 1

increases contrast of the specimen

reveals some aspect of cellular structure

Question 2

What is a Gram stain?

Answer 2

reveals the type of cell wall that surrounds the bacterial cell

Question 3

Describe an LPS molecules structure

Answer 3

• 3,6,8 fatty tails attached to 2 sugar phosphate groups

- attached to the core is a repeating patter called the O antigen

Question 4

What makes Lipopolysaccarides an endotonxin?

Answer 4

lipid A portion

Question 5

Describe a gram positive cell

Answer 5

• consists of a plasma membrane and a thick cell wall (20-40 layers of peptidoglycan)
• Peptidoglycan layer is held together by techoic acid molecules

Question 6

What will a gram positive cell stain during the gram stain and why?

Answer 6

purple; the thick cell wall of peptidoglycan retains the crystal violet

Question 7

Describe a gram negative cell?

Answer 7

• consists of a plasma membrane
• an outer membrane (lipid bilayer; inner leaf has phospholipids, outer leaf contains lipids called lipopolysaccharides)
• thin cell wall (1-5 layers of peptidoglycan)

Question 8

What color does a gram negative cell stain as and why?

Answer 8

• pink
• the thin cell wall does not retain the crystal violet
• appears pink after the counter stain with safranin

Question 9

What is the step by step Gram Staining process?

Answer 9

(wash with water after the time applying a stain)

1) crystal violet (30 sec)
2) iodine (30 sec)
3) ethanol; time sensitive (10 sec)

if still stained purple=Gram +
if not, continue

4)safranin; counter stain (30 sec)

stain pink=gram -

Question 10

What is the purpose of a lysozyme being present in tears, saliva, mucous?

Answer 10

• functions as a antimicrobial by eating through the cell wall of peptidoglycan
• kills gram positive bacteria

Question 11

What is the primary function of a bacterial cell wall?

Answer 11

maintain shape and integrity of a cell in the face of high osmotic pressure