Microbiology- Bacteria And Animal Cells

Question 0

By the 1940s electron microscopes allowed for what which led to more accurate microbial classification?
Who created the five kingdom classification system and what were the five kingdoms?
Who created the three domain system and what are the three domains?

Answer 0

Electron microscopes showed the differences in cell structures.
Whittaker created the five kingdom methods, them being: prokaryotae, Protista, fungi, plantae and animaliae.
Woese created the three domain system, them being: eubacteria, archaebacteria and eukaryotes.

Question 1

The three domains of life can be distinguished by their what? Describe the differences between this characteristic.

Answer 1

By their cell wall.
Bacteria possess cell walls with peptidoglycan.
Archaea possess cell walls with pseudo-peptidoglycan.
Eukaryotes do not all possess cell walls and those that do not contain peptidoglycan.

Question 2

Most bacteria have a size between what range?
What are the four basic bacterial shapes?
Give examples for each shape.

Answer 2

0.5 - 1µm x 2 - 5µm
The four shapes are:
Coccus (spherical) Streptococcus aureus
Bacillus (rod) Bacillus anthracis
Spiral Vibrio cholerae
Filamentous Streptomyces griseus

Question 3

Describe the DNA of bacteria.

Describe the ribosomes of bacteria and eukaryotes.

Answer 3

The DNA of bacteria is free floating in the cytoplasm and not surrounded by a nuclear envelope.
The ribosomes of bacteria are also free floating. They possess a sedimentation of 70s, with 50s and 30s subunits.
The ribosomes of eukaryotes are free floating and bound to the ER. They have a sedimentation of 80s, with 60s and 40s subunits.

Question 4

What does peptidoglycan confer to the bacterial cell? What bonds hold the monomers together and what two types of bacteria are there?

Answer 4

Peptidoglycan confers rigidity in the bacterial cell walls.
Glycosidic bonds and peptide bonds bind the monomers together.
The two bacterial cell types are gram positive and gram negative.

Question 5

Describe the gram positive cell wall.

Answer 5

These bacteria have a thick peptidoglycan layer (60-90%). Additionally the cell wall has interwoven techoic acids and the surface is studded with proteins. There are no lipids in this cell wall.

Question 6

Describe the gram negative cell wall.

Answer 6

These bacterial cells have a thin peptidoglycan layer (10-20%). They also possess an outer membrane. Between the cell wall and membrane is the periplasm which contains proteins necessary for the transport of material into and out of the cell.

Question 7

What is the mechanism for gram staining?

Answer 7

Crystal violet stains all bacterial cells purple.
Iodine forms an insoluble complex with crystal violet.
Ethanol dehydrates the cell wall and traps the crystal violet-iodine complex.
Ethanol dissolves the lipid outer membrane of gram negative bacteria so the complex can escape.
Counter stain with safranin stains gram negative cell walls pink.

Question 8

Define the generation time and give its equation.

Answer 8

The generation time is the time taken for the bacterial cell to divide.
The equation for this is: generation time = time/n

Question 9

Eukaryotic cells are averagely how many times larger than prokaryotic cells?

Answer 9

10 times larger

Question 10

What maintains the cytosol separate from the external environment?
What is it made from?
What grants it impermeability and what transport specific molecules across it?

Answer 10

The plasma membrane. It is made from a lipid bilayer. The bilayer is relatively impermeable due to the hydrophobic inner regions Transmembrane membrane proteins transport molecules across it.

Question 11

How many layers comprise the nuclear envelope? Describe the main envelope features.

Answer 11

Two layers. The outer layer is continuous with the endoplasmic reticulum. Lining the inner layer is the nuclear laminins. This structure maintains the mechanical integrity of the nucleus.

Question 12

What produces ribosomes?

What is occurs within the cytosol and what is made up of?

Answer 12

The nucleolus produces ribosomes.

The cell’s metabolism occurs in the cytosol and it is made up of water, protein and ions.

Question 13

Name two self-replicating organelles.

Respiration occurs in which structure in what organelle?

Answer 13

The mitochondria and chloroplasts.

Respiration occurs in the cristae of mitochondria.

Question 14

What two types or ER are there? What are the functions of both of them?

Answer 14

The smooth ER and the rough ER. The smooth ER is the site of lipid synthesis and membrane proteins. The rough ER is the site of protein synthesis due to its surface being studded with ribosomes.

Question 15

What organelle’s function is to modify and package molecules?

Answer 15

The Golgi apparatus.

Question 16

What are the functions of lysosomes, peroxisomes and secretory vesicles?

Answer 16

Lysosomes contain hydrolytic enzymes necessary for intra cellular digestion.
Peroxisomes are responsible for protecting the cell from hydrogen peroxide, they contain oxidative enzymes.
Secretory vesicles are involved in cell secretions, such as hormones and neurotransmitters.

Question 17

What are the three main filaments that make up the cytoskeleton?

Answer 17

Actin filaments,
Microtubules,
Intermediate filaments.

Question 18

What are the functions of the cytoskeleton?

Answer 18

The cytoskeleton: helps to compartmentalise the cells organelles,
Drive mitosis and cell division,
Support the fragile cell membrane,
Give motility to some cells,
Provide the machinery for muscular contraction.

Question 19

The actin filaments in the cytoskeleton are comprised of what?
What do these filaments have important roles in?

Answer 19

Two-stranded helical polymers of the protein actin.
Actin filaments have important roles in cell motility,
Contractility,
Shape changes,
Cytokinesis,
Cell polarity,
Phagocytosis.

Question 20

Describe how actin filaments are constructed.

Answer 20

Actin polymers possess a fast growing + end (barbed end) and a slow growing - end (pointed end). ATP binds to G-actin to make it assembly competent. ATP is then hydrolysed to ADP following filament addition, however this complex is less stable. This eventually results in dissociation from the polymer, allowing for rapid construction and deconstruction of polymers.

Question 21

What are lamellipodia and filopodia?

Answer 21

Lamellipodia are a meshwork of actin filaments with there + ends at the plasma membrane.
Filopodia are thin stiff finger like projections formed from a actin bundle with + ends at the plasma membrane.

Question 22

Describe how a leading edge is formed and how adhesion occurs there. Also describe how the cell moves towards this adhesion site.

Answer 22

Actin polymerisation at the leading edges results in the membrane being pushed forward. ARP complexes nucleate the actin polymers to allow for more filaments to be made.
Focal contact sites are formed to stick the membrane to the surface, integrins allow this to occur. Contraction at the rear is facilitated by actin-myosin interactions.

Question 23

List microtubule roles.

Answer 23

Cell motility,
Intra cellular transport,
Cell shape,
Cell division,
Cell polarity,
Cell organisation,
Forms stable structures such as flagella and cilia.

Question 24

Describe the characteristics of microtubules.

Answer 24

Microtubules are long hollow cylinders of the protein tubulin. They have an outer diameter of 25nm. Microtubules are more rigid than actin filaments, with each filament being a polymer of α and β heterodimers. Microtubules have a fast growing and slow growing end, the fast growing ends normally protruding from a γ-tubulin ring complex in a centrosome.

Question 25

Describe the centrioles.

Answer 25

These are barrel shaped structures composed of triplet microtubules arranged in a pin wheel fashion. They are ranged orthogonally to one another within the centrisome.

Question 26

What is the growing and shrinking nature of microtubules called?

Answer 26

Dynamic instability.

Question 27

What are the two motor proteins that transport cargo along microtubules. Which motor protein moves towards the + end and which moves towards the - end.

Answer 27

Kinesin and dynein.
Kinesin moves towards the + end, away from the centrosome.
Dynein moves towards the - end, towards the centrosome.

Question 28

Describe the characteristics of the intermediate filaments.

Answer 28

These are non polar and rope like filaments with a diameter of 10nm. They extend from the nucleus or the cell periphery. They from a meshwork called the nuclear lamina in the nucleus. In epithelial cell IFs interconnect to keep the cells intact and together.

Question 29

What can light microscopes resolve structures down to?

What can electron microscopes resolve structures down to?

Answer 29

Light microscopes can resolve structures down to 0.2µm

Electron microscopes can resolve structures down to 0.2nm.

Question 30

What is the definition of resolution?

What does resolution depend on?

Answer 30

Resolution is the smallest distance that two objects can be distinguished between. It depends on the wavelength of light and the numerical aperture of the lens.

Question 31

What is differential-interference-contrast?

Answer 31

It is a optical microscopy illumination technique used to enhance the contrast in untainted, transparent samples. It relies on the light first being split into two and then recombined by a prism which leads to interference that allows the sample to be viewed.

Question 32

What is dark field microscopy.

Answer 32

This is where light enters through the side of the sample and it scattered, only some light entering the microscope which makes the sample appear bright.