6.3.1 Bacteria structure

Question 1

Differences between prokaryotic and eukaryotic cells

Answer 1

Both: cell membrane, cytoplasm, DNA

Eukaryotic: large, complex, nucleus, membrane-bound organelles, ribosomes (80s)

Prokaryotic: smaller, simpler, no nuclues, no membrane-bound organelles, simple free floating ribosomes

Question 2

bacteria size variation, how can we see them?

Answer 2

0.4 - 10µm

light microscope

Question 3

Describe the process of gram staining
(5 stages + results)

Answer 3

1. apply some sterile water and bacteria culture on the microscope slide with a sterile loop
2. apply crystal violet
3. apply iodine (crystal violet trapped in cells)
4. alcohol wash (decolorisation)
5. apply safranin

results: gram positive bacteria purple, gram negative ones pink

Question 4

What’s the name of round bacteria?

Types of arrangement?

Majority gram + or - ?

Answer 4

cocci

pairs - diplococci

chains - streptococci

clusters - staphylococci

Majority gram +

Question 5

What’s the name for rod shaped bacteria?

Arrangements?

Majority gram + or - ?

Answer 5

bacilli

short/long/filamenous
coccobacilli
spiral (spirochaetes)

Majority gram -

Question 6

Function of flagella

Answer 6

motility and chemotaxis

flagellar protein (H antigen) used for antigenic tying (serovars) (to recognise particular types of bacteria)

Question 7

Function of fimbriae and pili

Answer 7

shorter, straighter, thinner than flagella

predominantly found in gram negative bacteria

fimbriae - attachment to surfaces (incl. other cells)

pili - join bacterial cells for conjugation (DNA transfer)

Question 8

What is a capsule (glycocalyx)?

Answer 8

polysaccharide(s)

microcapsule - thin layer

slime layer - thick, loose layer

confers mucoid appearance to the colonies

protection from phagocytosis and antimicrobials

enhances adherence to anything

Question 9

Function of cell wall

Answer 9

maintain bacterial shape

different for gram positive and negative bacteria

target for antimicrobials

Question 10

Structure of cell wall

Answer 10

made of peptidoglycans and polypeptide chains

adjacent rows linked by peptide cross-linking

Question 11

describe the becteria envelope in gram negative and positive bacteria

Answer 11

poitive - many layers of peptidoglycan, techoic acid

negative - thin peptidoglycan layer, outer membrane

Question 12

Structure and function of bacterial plasma membrane

Answer 12

encloses cytoplasm

phospholipid bilayer and proteins

target for disinfectants and antimicrobials

Question 13

Structure and function of cytoplasm

Answer 13

Facilitates chemical reactions and dissolves solutes

Aqueous solution of macromolecules, small molecules, inorganic ions for enzymatic activity

contains cell organelles

Question 14

Structure of nuclear material in bacterial cells

Answer 14

circular double stranded chromosome

no nuclear membrane

plasmids

target for antimicrobials

Question 15

Describe bacterial ribosomes

Answer 15

site of protein synthesis

70s

target for antimicrobials