Structure of Bacterial cells

Question 1

Bacteria have three shapes

Answer 1

Cocci(spheres)
Bacilli(rods)
Spirochetes(spirals)

Question 2

Cocci are arranged in three pattern

Answer 2

Pairs(diplococci)
Chains(streptococci)
Clusters(stapthylococci)

Question 3

The size of most bacteria ranges

Answer 3

From 1 to 3 مايكرومول

Question 4

What are the smallest bacteria

Answer 4

Mycoplasma

Question 5

All bacteria have a cell wall composed of peptidoglycan except

Answer 5

Mycoplasma (which are surrounded only by a cell membrane.

Question 6

All bacteria have a cell wall composed of peptidoglycan except

Answer 6

Mycoplasma (which are surrounded only by a cell membrane.

Question 7

Gram positive bacteria have a thick peptidoglycan and no outer membrane

Answer 7

True

Question 8

Why gram negative bacteria lose the stain when exposed to a lipid solvent in the gram stain process, whereas gram positive bacteria retain the stain and remain purple

Answer 8

Because gram negative bacteria have a thin peptidoglycan covered by an outer lipid containing membrane, whereas gram positive bacteria have a thick peptidoglycan and no outer membrane

Question 9

The outer membrane of ram negative bacteria contains endotoxin (lipopolysaccharide, LPS) the main inducer of septic shock.

Answer 9

True

Question 10

Endotoxin consists of…………….., which causes the fever and hypotension seen in septic shock, and a polysaccharide called……………., which is useful in laboratory identification.

Answer 10

1. lipid A

2. O antigen

Question 11

Between the inner cell membrane and the outer membrane of
gram-negative bacteria lies the…………… , which is the
location of…………….. —the enzymes that degrade β-lactam
antibiotics, such as penicillins and cephalosporins.

Answer 11

1. periplasmic space

2. β-lactamases

Question 12

Peptidoglycan is found only in bacterial cells, It is a network that
covers the entire bacterium and gives the organism its shape.

Answer 12

True

Question 13

Peptidoglycan

composed of………………… and………………. .

Answer 13

1. A sugar backbone(glycan)

2. peptide side chains (peptido)

Question 14

The side chains are cross-linked by………………

the enzyme that is inhibited by penicillins and cephalosporins.

Answer 14

Transpeptidase

Question 15

The cell wall of mycobacteria (e.g., M. tuberculosis) has more
lipid than either the gram-positive or gram-negative bacteria. As a
result, the dyes used in the Gram stain do not penetrate into (do
not stain) mycobacteria.

Answer 15

True

Question 16

What is the stain used in mycobacteria stain?

Answer 16

Acid-fast stain

Question 17

Lysozymes kill bacteria by cleaving the glycan backbone of

peptidoglycan.

Answer 17

True

Question 18

The cytoplasmic membrane of bacteria consists of……………… located just inside the peptidoglycan, It
regulates active transport of nutrients into the cell and the
secretion of toxins out of the cell.

Answer 18

Phospholipid bilayer (without sterols)

Question 19

Gram stain is the most important staining procedure, Gram positive bacteria stain………….. , whereas gram-negative bacteria
stain………….. .

Answer 19

1. purple

2. pink

Question 20

Why gram positive bacteria stain purple?

Answer 20

is due to the ability of gram-positive
bacteria to retain the crystal violet–iodine complex in the
presence of a lipid solvent, usually acetone–alcohol.

Question 21

Why gram negative bacteria lose the purple dye when treated with acetone alcohol.

Answer 21

because they have an outer lipid-containing

membrane and thin peptidoglycan

Question 22

gram negative bacteria become colorless when exposure to acetone alcohol and then stain pink when exposed to a red dye such as safranin.

Answer 22

True

Question 23

some important human pathogen cannot be seen using gram stain. Mention this pathogens.

Answer 23

tuberculosis and syphilis

Question 24

the Bacterial genome consists of a single chromosome of circular DNA located in the nucleoid.

Answer 24

True

Question 25

define (Plasmids)?

Answer 25

are extrachromosomal pieces of circular DNA that encode both exotoxins and many enzymes that cause antibiotic resistance.

Question 26

define (transposons)?

Answer 26

are small pieces of DNA that move frequently between chromosomal DNA and plasmid DNA, They carry antibiotic-resistant genes.

Question 27

define (capsules)?

Answer 27

are antiphagocytic; that is, they limit the ability of | neutrophils to engulf the bacteria.

Question 28

all capsules are | composed of polysaccharide; the polypeptide capsule of................ is the only exception.

Answer 28

anthrax bacillus

Question 29

Capsules are also the antigens in | several vaccines, such as the pneumococcal vaccine.

Answer 29

True

Question 30

Antibodies against the capsule neutralize the antiphagocytic effect and allow the bacteria to be engulfed by neutrophils.

Answer 30

True

Question 31

define (opsonization)?

Answer 31

is the | process by which antibodies enhance the phagocytosis of bacteria.

Question 32

define (pili)?

Answer 32

are filaments of protein that extend from the bacterial surface and mediate attachment of bacteria to the surface of human cells.

Question 33

define (glycocalyx)?

Answer 33

is a polysaccharide “slime layer” secreted by certain bacteria. It attaches bacteria firmly to the surface of human cells and to the surface of catheters, prosthetic heart valves, and prosthetic hip joints.

Question 34

define (spores)?

Answer 34

are medically important because they are highly heat resistant and are not killed by many disinfectants. Boiling will not kill spores.

Question 35

spores formed by certain gram positive rods, especially.............. and.............. species

Answer 35

bacillus and clostridium

Question 36

Spores have.................. that allows them to survive | for many years, especially in the soil

Answer 36

a thick, keratinlike coat

Question 37

Spores are formed when nutrients are ................ , but when nutrients are............... , spores germinate to form bacteria that can cause disease.

Answer 37

1. in short supply | 2. restored

Question 38

Spores are metabolically inactive but contain DNA, ribosomes, and other essential components.

Answer 38

True

Question 39

The initial step in the process of many bacterial infections is adherence of the organism to mucous membranes. The bacterial component that mediates adherence is the....................

Answer 39

Pilus

Question 40

In the Gram stain procedure, bacteria are exposed to 95% alcohol or to an acetone/alcohol mixture. The purpose of this step is:

Answer 40

To disrupt the outer cell membrane so the purple dye can leave the bacteria

Question 41

In the process of studying how bacteria cause disease, it was found that a rare mutant of a pathogenic strain failed to form a capsule. Which one of the following statements is the most accurate in regard to this unencapsulated mutant strain?

Answer 41

It was nonpathogenic primarily because it was easily phagocytized

Question 42

Mycobacterium tuberculosis stains well with the acid-fast stain, but not with the Gram stain. Which one of the following is the most likely reason for this observation?

Answer 42

It has a large amount of lipid that prevents entry of the purple dye.

Question 43

Of the following bacterial components, which one exhibits the most antigenic variation?

Answer 43

Capsule

Question 44

β-Lactamases are an important cause of antibiotic resistance. Which one of the following is the most common site where β-lactamases are located?

Answer 44

Within the periplasmic space

Question 45

Which one of the following is the most accurate description of the structural differences between gram-positive bacteria and gram-negative bacteria?

Answer 45

Gram-positive bacteria have a thick peptidoglycan layer, whereas gramnegative bacteria have a thin layer.

Question 46

Bacteria that cause nosocomial (hospital-acquired) infections often produce extracellular substances that allow them to stick firmly to medical devices, such as intravenous catheters. Which one of the following is the name of this extracellular substance?

Answer 46

Glycocalyx

Question 47

Lysozyme in tears is an effective mechanism for preventing bacterial conjunctivitis. Which one of the following bacterial structures does lysozyme degrade?

Answer 47

Peptidoglycan

Question 48

Several bacteria that form spores are important human pathogens. Which one of the following is the most accurate statement about bacterial spores?

Answer 48

They are metabolically inactive yet can survive for years in that inactive state