FR2-Observing microbes, functional anatomy

Question 1

Where is bacterial genetic information localised?

Answer 1

In a discrete region called the nucleoid

Question 2

What are the functions of bacterial plasma membranes?

Answer 2

• They are a selectively permeable barrier
• mechanical boundary
• nutrient and waste transport
• Location of many metabolic processes
• Detection of environmental cues for chemotaxis

Question 3

What are the functions of a bacterial gas vacuole?

Answer 3

It is an inclusion that provides buoyancy for floating in aquatic environments

Question 4

What are the functions of bacterial inclusions?

Answer 4

• Storage of carbon, phosphate, and other substances
• Site of chemical reactions (microcompartments)
• Movement

Question 5

What is the function of the periplasmic space?

Answer 5

In typical gram-negative bacteria, contains hyddrolytic enzymes and binding proteins for nutrient processing and uptake; in typical Gram positive bacteria, may be smaller or absent

Question 6

What are the main functions of bacterial cell walls?

Answer 6

• Protetion from osmotic stress
• Helps maintain cell shape

Question 7

What are the functions of capsules and slime layers?

Answer 7

• Resistance to phagocytosis
• adherance to surfaces

Question 8

What is the function of fimbriae and pilli?

Answer 8

Attachment to surfaces, bacterial conjugation and transformation, twitching

Question 9

What is the function of flagella?

Answer 9

Swimming and swarming motility

Question 10

What is the function of endospores?

Answer 10

Survival under harsh environmental conditions

Question 11

Label this bacterial cell

Answer 11

Question 12

What do eukaryotic membranes contain that bacterial membranes don’t?

What do bacterial membranes contain instead?

Answer 12

Bacterial membranes lack sterols (steroid- containing lipids)

Bacterial memranes contain hopanoids which are syntheised from the same precursors as steroids such as cholesterol

Question 13

How would the plasma membrane of bacteria growing at lower temperatures be different than that of higher temperatures?

Answer 13

Lower temperatures have more unsaturated fatty acids in their membranes phospholipids

At higher temperatures their fatty acids have more saturated fatty acids

Question 14

Explain the compostion of the cell wall of Bacillus Subtilis and other typical gram positive bacteria

Answer 14

Gram-positive bacteria consist of a single, 20- to 80-nm-thick homogeneous layer of peptidoglycan (murein) lying outside the plasma membrane and large amounts of other polymers such as teichoic acids

Teichoic acids are polymers of glycerol or ribitol joined by phosphate groups. Some teichoic acids are covalently linked to peptidoglycan and are referred to as wall teichoic acids. Others are covalently connected to the plasma membrane; they are called lipoteichoic acids.

Wall teichoic acids extend beyond the surface of the peptidoglycan. They are negatively charged and help give the cell wall its negative charge

There are often proteins associated with its surface, some of which are covalenetly attached to the peptidoglycan. Many covalently attached proteins have roles in virulence. For example, the M protein of pathogenic streptococci aids in adhesion to host tissues and interferes with host defenses.

Question 15

Explain the composition of the cell wall of Myococcus xanthus and other gram negative bacteria

Answer 15

A typical Gram-negative cell wall consisting of a thin layer of peptidoglycan, an outer membrane, and the periplasmic space.

The peptidoglycan layer is very thin (2 to 7 nm, depending on the bacterium) and sits within the periplasmic space. Some periplasmic proteins participate in nutrient acquisition—for example, hydrolytic enzymes and transport proteins. Some periplasmic proteins are involved in energy conservation

The outer membrane lies outside the thin peptidoglycan layer. It is linked to the cell by Braun’s lipoprotein, the most abundant protein in the outer membrane. This small lipoprotein is covalently joined to the underlying peptidoglycan and is embedded in the outer membrane by its hydrophobic end

Constituents of the outer membrane include lipopolysaccharides (LPSs). of the outer membrane. It helps create a permeability barrier. The geometry of LPS and interactions between neighboring LPS molecules are thought to restrict the entry of bile salts, antibiotics, detergents, and other toxic substances that might kill or injure the bacterium

Question 16

What are inclusions formed by?

Answer 16

They are formed by the aggregation of substances that may be either organic or inorganic. Many inclusions are used for storage (e.g., of carbon compounds, inorganic substances, and energy) or to reduce osmotic pressure by tying up molecules in particulate form. The quantity of inclusions used for storage varies with the nutritional status of the cell. Some inclusions are so distinctive that they are increasingly being referred to as microcompartments

Question 17

What are plasmids?

Answer 17

In addition to the genetic material present in the nucleoid, many bacteria contain extrachromosomal DNA molecules called plasmids.

Plasmids are small, double-stranded DNA molecules that can exist independently of the chromosome. Both circular and linear plasmids have been documented, but most known plasmids are circular.

Plasmids have relatively few genes, generally less than 30.

Their genetic information is not essential to the bacterium, and cells that lack them usually function normally

Many plasmids carry genes that confer a selective advantage to the bacterium in certain environments

Question 18

Some plasmids are able to integrate into the chromosome, what are these plasmids called?

Answer 18

Such plasmids are called episomes and when integrated are replicated as part of the chromosome

Question 19

Describe Bacterial Pili and Fimbriae

Answer 19

• Many bacteria have fine, hairlike appendages that are thinner and typically shorter than flagella.
• These are usually called fimbriae (s., fimbria) or pili (s., pilus).
• The terms are synonymous, although certain structures are always called pilus (e.g., sex pilus), while others are always called fimbriae
• Pili grow by adding protein subunits to the base of the pilus. Several different types of fimbriae have been identified.
• Most function to attach cells to solid surfaces such as rocks in streams and host tissues.
• The pili of some bacteria function as nanowires that transport electrons from a cell to solid metals during their metabolic activities

Question 20

How do motile bacteria move?

Answer 20

Many motile bacteria move by use of flagella (s., flagellum), threadlike locomotor appendages extending outward from the plasma membrane and cell wall

Although the main function of flagella is motility, they can have other roles. They can be involved in attachment to surfaces, and in some bacteria, they are virulence factors

Bacterial flagella are slender, rigid structures about 20 nm across and up to 20 mm long

Monotrichous bacteria (trichous means hair) have one flagellum; if it is located at an end, it is said to be a polar flagellum

Amphitrichous bacteria (amphi means on both sides) have a single flagellum at each pole.

lophotrichous bacteria (lopho means tuft) have a cluster of flagella at one or both ends

Flagella are spread evenly over the whole surface of peritrichous (peri means around) bacteria

Question 21

The bacterial flagellum is composed of what 3 parts?

Answer 21

(1) The filament is the longest and most obvious portion. It extends from the cell surface to the tip.
(2) The basal body is embedded in the cell envelope;
(3) a short, curved segment, the hook, links the filament to its basal body and acts as a flexible coupling.