Lecture 27

Question 1

Prokaryotic cell structure

Answer 1

Question 2

Chromosomes

Answer 2

Single circular chromosome
1 - 2 micrometer long

Question 3

Three types of prokaryotic cells

Answer 3

Cocci
Rods
Spirals

Question 4

Circular Chromosome nuclear membrane?

Answer 4

No nuclear membrane

Question 5

Answer 5

Question 6

Region of the chromosome within the cell

Answer 6

Defined region known as nucleoid

Question 7

What can be found in the cytosol of the bacteria?

Answer 7

Other small self-replicating DNA moleculecules (seperate to the main chromosome)
- these are known as plasmids

Question 8

Average bacteria genome compared to human

Answer 8

Bacteria: 5000 genes / 5 million base pairs

Human: 20-25000 genes / 3 billion base pairs

Greater then 90% of the genome is giving rise to functional proteins

Question 9

Major structural component of the cell wall of bacteria

Answer 9

Peptidoglycan

Question 10

Cell wall, peptidoglycan function:

Answer 10

• rigid macromolecular layer that provided strength to cell
• protect cells from osmotic lysis and confers cell shape

Question 11

Structure that betalactin targets and how they target them

Answer 11

Peptidoglycan

They target the enzymes that are involved in assembling peptidoglycan

Question 12

Prokaryotes that lack cell walls

Answer 12

Mycoplasmas - group of pathogenic bacteria

Question 13

Physical structure of the cell wall - mesh like structure

Answer 13

Question 14

Structure of petioglycan

Answer 14

Question 15

Answer 15

Question 16

Petdiglycan stucture and how its made kinda

Answer 16

• consists of a network of fibres
• chain of sugars called NAM and NAG all linked together and repeating
• on NAM molecules there is a sort stretch of amino acids - a tetrapeptide - 4 amino acids are assembled onto NAM
• all chains stack together to create macromolecular molecule
• glycan chains are being wrapped around the cell
• cell is synthesising them inside cytoplasm and exports them to outside of cell and get assembled into larger network
• nag nams held together by strong bonds
• glycan chains are linked by tetrapeptides (a cross bridge)

Therefore strong

Question 17

What enzyme catalyses the cross linking of the peptidoglycan chains to form rigid cell walls ?

Answer 17

Trandpeptidate (penacilin targets this enzyme)

Question 18

Gram stain

Answer 18

A gram stain of mixed:
- staphylococcus aureus, gram-positive cocci (purple)
- Escherichia, gram negative bacilli (red)

Most common bacteria in reference bacteria

Question 19

Gram stain proceedure

Answer 19

1. Application of crystal violet (purple die)
2. Application of iodine (mordant - fixes cell into cell wall)
3. Alcohols wash (decolourization)
4. Application of safranin (counterstain

Question 20

Structure of gram- positive bacterial cell wall

Answer 20

• peptidoglycan traps crystal violet, which masks the red safranin dye - when washed away - too thick to leave.
• they will stain a darker colour and have a thicker cell wall of peptidoglycan (20-80nm)

Question 21

What is the reason for the difference in the Gram stain reaction?

Answer 21

Structural differences between cell walls of gram-positive and gram-negative bacteria

Question 22

Structure of gram negative bacterial cell wall

Answer 22

• crystal violets is easily rinsed away, revealing the red safranin dye
• there is a thinner layer (5-10mm) of peptidoglycan between plasma and outer membranes

Question 23

Function of bacterial flagella

Answer 23

Some bacteria are capable of movement in liquid medium

Question 24

How are bacterial flagella capable of movement in a liquid medium

Answer 24

• motile bacteria produce flagella
• long flexible appendage resembling “tails”
• proteinaceous 10-20nm in diameter, 5-10 per cell
• number of flagella and location on cell surface varies
• act like a propellant; cell rotates them to move through a liquid medium

Question 25

Tactic responses: chemotaxis

Answer 25

Bacteria move along a concentration gradient towards a chemical attractant (positive) or away form a chemical repellent From lecture voice - too small to sense glucose difference at each end of cell - thus it senses the tempal gradient (swims along, senses conc outside the cell, swims off again, senses concentration again, senses whether that concentration was either higher or lower)

Question 26

Fimbiae - bacterial adherence factors

Answer 26

Function: structures with adhesive properties that cause bacteria to stick/adhere to surfaces - not all bacteria possess fimbriae: it is an inherited trait - can be mistaken for flagella but are not involved in motitily - much shorter and more numerous then flagella “hair-like” - 100-1000 per cell and 2-8 nm in diameter - 1 micrometer in length - receptors that recognise the cells they’re colonises - they are specific

Question 27

Pili (sex conjugation pili or F pili)

Answer 27

- attachment to other bacteria - transfer genetic material from one cell to another - the genetic transfer is called conjugation - conjugation is a form of horizontal gene transfer

Question 28

Glycocalyx

Answer 28

A gelatinous polysaccharide and / or polypeptide outer covering Forms a sticky mesh work of fibres

Question 29

Another structure bacteria can use to attach to surfaces

Answer 29

Glycocalyx - capsules and slime layers

Question 30

Two arrangements of Glycocalyx - capsules and slime layers

Answer 30

Organised into a friended structure attached firmly to a cell wall: CAPSULE Disorganised without cell shape, attached loosely to cell wall = slime layer

Question 31

Functions of capsules

Answer 31

- Virulence factors - protecting bacteria from phagocytosis and engulfment by immune cellls - bacterial that make capsules are difficult to eradicate - prevent cell from drying out (desiccation)

Question 32

When are Bacterial Endo spores formed

Answer 32

- during unfavourable growth conditions and germinate under favourable conditions

Question 33

What do bacterial Endo spores do

Answer 33

- protect cells from stress

Question 34

Only two gram-positive bacteria that contain bacterial Endo spores

Answer 34

- genus bacillus (anthrax caused by the bacterium bacillus anthracis) - clostridium (e.g clostridium difficle)

Question 35

Stresses that trigger endospore formation

Answer 35

- nutrient starvation - high cell density - mother cell produces endospore via asymmetric cell division and dies

Question 36

Endospore definition

Answer 36

- highly defines differentiated cells resistant to heat, harsh chemicals, antibiotics, disinfectants and radiation. - dormant stage of bacterial life cycle - can stay dormant for a very long time - all machinery for life is preserved on the inside of the endospore so when conditions become right they can germinate and goes back to normal life cycle - survival strategy