Prokaryotic Cells Structural Components And Roles

Question 1

Outline the structure of simple/generalised prokaryotic cell

Answer 1

Nucleoide - singular circular chromosome
Ribosomes - protein synthesis
Plasma membrane - cell regulation
Cell wall - cell integrity
Glycocalyx - extracellular cell protection
Flagella - cell movement in liquid media
Rimbrae/Pili - extracellular attachment

Question 2

Outline the nuclear envolope for Bacteria, Archaea, and Eukarya

Answer 2

Bacteria: absent
Archaea: absent
Eukarya: Present

Question 3

Outline membrane bound organelles for Bacteria, Archaea, and Eukarya

Answer 3

Bacteria: Absent
Archaea: Absent
Eukarya: Present

Question 4

Outline peptidoglycan in cell wall for Bacteria, Archaea, and Eukarya

Answer 4

Bacteria: Present
Archaea: Absent
Eukarya: Absent

Question 5

Outline chromosomal DNA for Bacteria, Archaea, and Eukarya

Answer 5

Bacteria: singular circular chromosome
Archaea: singular circular chromosome
Eukarya: Multiple linear chromosomes

Question 6

Outline growth at temperatures above 100 degrees for Bacteria, Archaea, and Eukarya

Answer 6

Bacteria: No
Archaea: Some species
Eukarya: No

Question 7

Outline the bacterial genome

Answer 7

Typically a single circular chromosome
No nuclear membrane, however chromosomes is restricted to defined region of bacterial cell - nucleoid
Other small circular self replication DNA molecules can be found in cytosol (seperate to main chromosome, known as plasmids)

Question 8

Outline the difference between the humane and bacteria genome

Answer 8

Human genome very large, contains a lot of “junk”, only small portion codes for functional proteins
Most of bacteria genome is functional, less “junk”

Question 9

What is the function of the cell wall of bacteria

Answer 9

Rigid macromolecular layer that provides strength to cell
Protects cells from osmotic lysis and confers cell shape

Question 10

What class of prokaryotes lack cell walls

Answer 10

Mycoplasmas - group of pathogenic bacteria

Question 11

What is peptidoglycan

Answer 11

A substance that forms a mesh like structure, forming the cell walls of bacteria

Question 12

Outline the structure of peptidoglycan

Answer 12

Peptidoglycan is a polymer composed of two alternating sugars, NAM and NAG, which are cross linked by short peptides (tetrapeptide side chain). Peptide cross bridge provides additional strength by linking the tetrapeptides of two adjacent peptidoglycan chains together

Question 13

Outline the gram stain procedure

Answer 13

Crystal violet (purple dye) added to culture - stains cells
Iodine added to culture - fuses stain on cell wall
Alcohol wash added to culture - washes away excess crystal violet from gram negative cells
Safranin applied to culture - stains gram negative a contrasting red/pink

Question 14

Outline the structure of gram positive bacterial cell wall

Answer 14

Thick external peptidoglycan layer surrounds internal plasma membrane
Thick peptidoglycan cell wall (20 - 80 nm), hence dark stain
Peptidoglycan traps crysta violet, which masks safranin dye

Question 15

What is responsible for differences in Gram stain reactions

Answer 15

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

Question 16

Outline the structure of gram negative bacteria cell wall

Answer 16

Thin layer of peptidoglycan (5 - 10nm) between an outer plasma membrane, and the inner plasma membrane
Crystal violet easily rinsed away (not retained by thin peptidoglycan), revealing red safranin dye

Question 17

What is the function of bacterial flagella

Answer 17

To allow bacterial movement in a liquid medium

Question 18

How does flagella facilitate movement

Answer 18

Long flexible appendage resembling tails
Ptoteinaceous, 10-20 nm in diameter
Number of, and location varies with cell
Act like propeller: rotating them to move through liquid medium

Question 19

How do bacteria Spence chemical gradients in environment

Answer 19

Too short to sense chemical gradient from head to base/tail
Sense chemical environment in location, move to another location, sense environment of new location and compare with old environment

Question 20

What is chemotaxis in terms of bacteria

Answer 20

Bacteria move along a concentration gradient towards a chemical attractant (positive) or away from a chemical repellent (negative)

Question 21

What are Fimbriae

Answer 21

Also called Adherence Pili
Protein structures with adhesive properties that cause bacteria to stick/adhere to surfaces
Not all bacteria possess fimbriae, is an inherited trait
Much shorter and more numberous than flagella (100-1000 per cell, 2-8nm in diameter, 1micrometer in length)

Question 22

What are pili

Answer 22

Singular large protein structure that facilitates attachment to bacteria
Transfers genetic material from one cell to another
Process called conjugation - form of horizontal gene transfer

Question 23

What is glycocalyx

Answer 23

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

Question 24

Outline a glycocalyx capsule

Answer 24

Glycocalyx organised into a defined structure attached firmly to a cell wall - capsule

Question 25

Outline a Glycocalyx slime layer

Answer 25

Glycocalyx disorganised without cell shape, attached loosely to cell wall = slime layer

Question 26

Outline 2 functions of capsules

Answer 26

Virulence factors - protecting bacteria from phagocytosis and engulfment by immune cells
Prevent cell desiccation

Question 27

Outline when bacterial endospores are formed

Answer 27

Bacterial endospores are formed during unfavourable growth conditions and germinate under favourable conditions - protect cells from stress

Question 28

What form of reproduction is used to produce endospores

Answer 28

Asymmetrical reproduction

Question 29

What are endospores

Answer 29

Highly differentiated cells resistant to heat, harsh chemicals, antibiotics, disinfectants and radiation.
Dormant stage of bacterial life cycle. Can stay dormant for very long time until conditions become favourable

Question 30

What is transpeptidase

Answer 30

The enzyme that cross links the peptidoglycan chains to form rigid cell walls