lecture 2 - prokaryote taxonomy structure and function

Question 1

What two domains are prokaryotes divided into?

Answer 1

Archaea and bacteria

Question 2

What are the main differences between different phyla of bacteria?

Answer 2

Cell envelope structure

Question 3

What is important to remember in relation to taxonomy?

Answer 3

lots of different phyla - complicated and in flux

Question 4

How small are prokaryotes?

Answer 4

Most are 1-3 μm

Question 5

What are the different prokaryotic cell shapes?

Answer 5

Coccus - round
Rod/Bacillus - rod-shaped
Spirillum/Spirochete - curved

Question 6

What are the key differences between prokaryotes and eukaryotes?

Answer 6

prokaryotes’ lack of membrane bound organelles (unlike eukaryotes), the structure of cell envelope and absence of nucleus / ER

Question 7

What is the importance of the cell envelope?

Answer 7

boundary between the internal part of the microbe and external environment

Question 8

What are the major functions of prokaryotic cytoplasmic membranes?

Answer 8

Selective permeability and transport of solutes -is a permeability barrier so prevents leakage and functions as a gateway for transport of nutrients into and out of the cell

Protein anchor - site of many proteins involved in transport, bioenergetics and chemotaxis

Energy conservation - site of generation and use of the proton motive force
Electron transport and oxidative phosphorylation

Excretion of hydrolytic enzymes

Bearing the enzymes and carrier molecules involved in the synthesis of DNA cell wall polymers and membrane lipids

Bearing the receptors and other proteins of the chemotactic systems

Question 9

What does the cell wall consist of?

Answer 9

Almost all bacteria are contained by a wall comprising of a mucopeptide (or peptidoglycan/muerin) complex.

Made up of alternating links of two amino sugars:
N-acetylglucosamine (NAG)
N-acetylmuramic acid (NAM).

The chains of amino sugars are cross-linked by pentapeptide bridges. (Pentapeptides cross linked by transpeptidation reaction)

Question 10

What is the cell envelope?

Answer 10

Combination of cell wall and cytoplasmic membrane referred to as “cell envelope”

Almost all prokaryotic cells have a cell envelope

Structure and chemistry differs amongst different groups of prokaryotes

Can be a single homogenous layer or complex multilayer structure.

Question 11

What is the difference between a gram positive and gram negative bacterial cell envelope?

Answer 11

Gram positive: cell membrane surrounded by a thick layer of peptidoglycan
Gram negative: cell membrane surrounded by periplasm which contains peptidoglycan and an outer membrane of phoshoplipid bilayer with lipopolysaccharide and protein

Question 12

What is the role of the nucleoid?

Answer 12

Most prokaryotes have a single, circular chromosome.

Many prokaryotes have plasmids in addition to their chromosome.
Plasmids are small circular DNA molecules carrying genes that are not necessary for cell growth. For example, a plasmid-encoded function is antibiotic resistance.

The genome is the total complement of genes in a cell.

Chromosome and plasmids are supercoiled. Many proteins condense the chromosome into an highly packed and ordered structure containing ~ 500 loops.

Question 13

What is the difference between prokaryotic and eukaryotic ribosomes?

Answer 13

Prokaryotic ribosomes differ from those found in Eukaryotes in that they are smaller an made up of different subcomponents.

Prokaryotic			Eukaryotic	
70S (30S+50S)		80S (40S+50S)

Question 14

What role do ribosomes play?

Answer 14

Ribosomes are the site of protein synthesis.
Tens of thousands of ribosomes per cell all making proteins
Transcription and translation are coupled in prokaryotic cells

Question 15

What is the structure of the prokaryotic cytoskeleton?

Answer 15

Cytoskeleton is formed by polymeric proteins that assembles into filamentous structures,

Involved in maintaining the cell shape, cell motility, molecules trafficking within the cell, chromosome segregation…

The two principal proteins of the eukaryotic cytoskeleton are actin and tubulin.

Prokaryotic cells were thought to lack cytoskeletal proteins.

Proteins homologous to actin and tubulin have been discovered in bacterial and archaeal cells.

MreB and ParM Actin-like proteins

Question 16

What is the importance of FtsZ?

Answer 16

FtsZ is a tubulin-like protein.
It is involved in cell division in
bacteria and some archaea. It
forms a ring at micell and
recruits all the other cell
division proteins at that site.

Question 17

Why are intracellular granules important?

Answer 17

Storage granules are polymeric reserves of nutrients. 
Most common are polymers
of glucose, forming glycogen,
and polymers of β-hydroxybutyric acid,
Forming poly-β-hydroxybutyrate (PHB).

Magnetosomes are granules of a magnetic mineral
(usually magnetite, Fe3O4) enclosed in a membranous
invagination of the cell membrane. Act like a compass and allow bacteria to distinguish north from south.

Sulphur, phosphate (called Volutin granules) and starch granules are also found in some species.

Question 18

What are spores?

Answer 18

Survival structures
Resistant to adverse conditions that would normally kill vegetative bacteria e.g. disinfectants, desiccation and sunlight
Can survive in the environment for a long time
Under favourable conditions the spore can germinate and new bacterial growth occur.

Question 19

What is the only effective way to kill spores?

Answer 19

autoclave them at 120˚C or higher for 10 or more minutes.

Question 20

Why are spores so resistant?

Answer 20

due to the hard spore case, low metabolic activity, and low water content

Question 21

What is the glycocalix?

Answer 21

loose meshwork of fibrils that extend outwards from the cell - “the slime layer” that surrounds some bacteria

Made up of glycoprotein

Plays a major role in the adherence of bacteria to surfaces in their environment.

Normally only found on gram negative bacteria

Question 22

What are capsules?

Answer 22

Bacteria that possess a thick gelatinous layer outside the cell wall are referred to as Capsulate.

Generally made up of a polysaccharide material.

Helps pathogenic (disease causing) bacteria to invade the host by preventing phagocytosis.

Found only in Gram negative bacteria

Question 23

What are pili and fimbriae

Answer 23

Terms Pili and Fimbriae are sometimes interchanged

Ordinary fimbriae play a role in the adherence of bacteria to host cells in either symbiotic or pathogenic situations.

Sex pili, are responsible for the attachment of donor and recipient cells in bacterial conjugation

Used to transfer genetic material from one bacterium to another

The closest bacteria get to sex!

Question 24

What are flagella?

Answer 24

Used for locomotion

Hollow tube like appendages composed entirely of a protein called flagellin.

12-30 nm in diameter

Connected to the bacterial cell body by a complex structure consisting of a hook and basal body.