Microbial Cell Structure

Question 1

Define cell envelope

Answer 1

Plasma membrane and all layers external to it

Question 2

Define protoplast

Answer 2

The whole cell excluding the cell wall

Question 3

What is the PM mainly composed of

Answer 3

Bilayer of amphipathic phospholipids

Question 4

Give 3 roles of membrane proteins

Answer 4

• Structural support
• Secretion of communication signals
• Transportation of ions

Question 5

What are the two types of membrane proteins and which is more abundant

Answer 5

Integral - 70% - 80%
Peripheral - 20% - 30%

Question 6

What is the bacterial version of cholesterol

Answer 6

Hopanoids

Question 7

What is the main difference between archaeal and bacterial PM

Answer 7

Archaea lack fatty acids and instead have isoprene which forms an ether bond with glycerol rather than an ester bond

Question 8

What is the bacterial cell wall also known as

Answer 8

Sacculus

Question 9

What is the cell wall made of - 2 names

Answer 9

Peptidoglycan or Murein

Question 10

Give 3 functions of the cell wall

Answer 10

• Structure and support
• Protection from toxic substances
• Withstand osmotic pressures

Question 11

What is PDG replaced by in archaea

Answer 11

Pseudomurein

Question 12

Which two sugars make up PDG, what bond do they form and what shape does it make

Answer 12

NAM and NAG - beta
1-4 glycosidic bond
Helical

Question 13

What can destroy PDG

Answer 13

Lysosomes

Question 14

The cell wall in gram +ve bacteria is primarily made of PDG - what colour do they stain - monoderm or diderm

Answer 14

Purple
Monoderm

Question 15

What does the cell wall of gram +ve bacteria also contain - what are their function (1)

Answer 15

Teichoic acid
Protection from environmental substances

Question 16

What does the cell wall of gram -ve bacteria consist of

Answer 16

PDG and an outer membrane made of LPS

Question 17

What colour do gram -ve cells stain - monoderm or diderm

Answer 17

Pink/red
Diderm

Question 18

Give one function of the LPS in the OM

Answer 18

Stabilises OM structure

Question 19

How is the OM and PDG linked in gram -ve bacteria

Answer 19

Braun’s lipoproteins

Question 20

Is the periplasmic space bigger in gram -ve or gram +ve bacteria

Answer 20

gram -ve bacteria

Question 21

What are the 2 barriers that a solute must cross in gram -ve bacteria and what are the channels called

Answer 21

Outer membrane into the periplasm
Plasma membrane
Porins

Question 22

Why do the pores in the cell wall of gram +ve bacteria close during staining whereas the cell wall of gram -ve bacteria doesn’t

Answer 22

The PDG is much thicker in gram +ve bacteria

Question 23

How do extra-cellular vesicles develop - what do they transfer between cells

Answer 23

Membrane buds out, pinches off and is released from the cell
Genetic information

Question 24

What makes up a gram -ve EV

Answer 24

OM surrounding periplasm

Question 25

What makes up a gram +ve EV

Answer 25

PM surrounding periplasm

Question 26

What are the 4 structures outside the cell wall and what are their functions - G(CS)S

Answer 26

Glycocalyx - aid in attachment to solid surfaces Capsules - Protective advantages Slime layers - Similar to capsules but easily removed S-layers - maintain shape and rigidity

Question 27

What are the three structures that form the cytoskeleton - give 2 bacterial examples

Answer 27

Actin filaments Microtubules Intermediate filaments FtsZ and MreB

Question 28

What are inclusions aggregated of - what is their function (2)

Answer 28

Organic and inorganic substances - Segregate cellular components - Storage of glycogen or carbon

Question 29

What are microcompartments encapsulated by

Answer 29

selectively permeable protein shell

Question 30

What are endospores and how are they advantageous (2)

Answer 30

Dormant bacterial cells Survive heat damage and dessication

Question 31

What are the 3 processes involved in an endospore becoming a vegetative cell

Answer 31

Activation Germination Outgrowth

Question 32

What are fimbriae and what is their function

Answer 32

Short, thin hair-like projections Surface attachment and motility

Question 33

What are pili and what is their function

Answer 33

Long, thick projections Surface attachment and gene transfer mechanisms (conjugation)

Question 34

What are the 3 constituents of the flagella - in order

Answer 34

basal body - hook - filament

Question 35

What are 2 functions of flagella

Answer 35

Attachment and motility

Question 36

Define chemotaxis

Answer 36

Movement to or from chemical attractants or chemical repellents

Question 37

What does CW and CCW rotation cause

Answer 37

CW - Tumble CCW - Forward run

Question 38

In the presence of an attractant what is the frequency of tumbles and runs

Answer 38

tumbling frequency is reduced and runs in a direction are longer

Question 39

How is gliding an anomaly - what is it aided by

Answer 39

Requires no appendages - aided by slime secretion