Section 4, Part B

Question 1

Are prokaryotic organisms unicellular, colonial, or multicellular? Explain your answer with examples.

Answer 1

The vast majority of prokaryotes are unicellular, yet there are some exceptions. Some prokaryotic organisms grow in colonies.

Cyanobacteria are prokaryotes that vary in organization. Some are unicellular and some can grow in colonies, often coated by a sheath. Nostoc are a type of cyanobacteria that may grow in circular colonies that may grow to be as large as 3 or 4 cm in diameters.

Question 2

What is the basic structure of prokaryotic cell? What are the parts and their functions.

Answer 2

Prokaryotic cells lacks a nucleus and any membrane bound organelles. The genetic material is found within the nucleoid.
Parts of the cell:
Plasma membrane: membrane enclosing cytoplasm
Cell Wall: rigid structure outside plasma membrane
Capsule: ( not always present) jelly like outer coating
Fimbriae: attachment structures on surface of some prokaryotes, may be used for movement
Flagella: locomotion organelles
Within cytoplasm:
Nucleoid: region where cell’s DNA is located, in the form of chromosomes
Plasmids: circular small amounts of DNA material, independent from chromosomes.

Question 3

Compare and contrast the basic genomic organization of bacteria, archaea, and eukaryotes.

Answer 3

Prokaryotic DNA is circular, smaller, supercoiled, and found in the nucleoid, while eukaryotic dna is larger, found in the nucleus and packaged with the help of histones.

Question 4

How are prokaryotic organisms diverse in shape?

Answer 4

Bacteria and archaea take on varying morphologies. Shapes rely on the construction of their cell walls. This cell wall is the main method of protection for the cell and therefore these varying shapes can be seen as adaptations. 
The three most common shapes are :
-rod (bacilli)
- spherical (cocci)
-spiral

Question 5

How does the structure of the bacterial cell wall differ from archaean, plant, fungal, and animal cell walls?

Answer 5

Bacterial cell walls are composed of peptidoglycan, which consists of peptide ( a small protein) and glycan ( a sugar). This allows the cell wall to become very rigid and to stop small particles from entering it, which is very different from other cell walls that are often (semi) permeable, allowing different molecules to enter and leave. Archaea have varying cell wall structures. There are two types of cell walls belonging to two different types of bacteria: gram postive and gram negative.

Question 6

Compare and contrast gram-positive and gram- negative bacteria. How does each react to the gram stain?

Answer 6

Gram-positive: Thick cell wall consisting of peptidoglycan surrounding the cytoplasmic membrane.
Gram-negative: Thin layer of peptidoglycan surrounded by an outer membrane which consists of phospholipids and lipopolysaccharides.

The gram stain is used to differentiate the two bacteria. The dye, crystal violet, is applied to all the bacteria, then washed away. Gram-POSITIVE bacteria retains this dye due to it’s thick cell wall. This is what gives it it’s PURPLE hue. Gram-NEGATIVE bacteria are then found by using a lighter counter stain, which is what gives it it’s PINK color.

Question 7

How do prokaryotic organisms reproduce?

Answer 7

Asexual reproduction through binary fission:

• DNA replicates
• Replicating DNA molecules attach to plasma membrane
• As cell elongates, chromosomes are pulled apart, ring of protein FtsZ forms
• When the cell is approximately twice the orignal length, the FtsZ ring constricts, the plasma membrane grows inward and a cell wall forms between the two cells.

Lateral Gene Transfer: A genetic recombination

• Transformation: bacterium picks up fragments of DNA from environment–released by dead bacteria or secreted by live bacteria.
• Transduction: virus carry portions of bacterial DNA
• Conjugation: transfer of genetic material from one prokaryote to another( plasmids may be transferred using pili)

Question 8

What factors contribute to the ability of prokaryotes to quickly evolve and adapt to new environments?

Answer 8

There are three factors which result in a rapid evolution of prokaryotes and an adaptation to a changing environment. A small genome, simple morphologies, and asexual reproduction through binary fission allows for a shorter genaration time. This allows for evolutionary changes to take place. The processes of gene transfer ( transformation, transduction, and conjugation) are also factors that allow for more genetic variation and therefore an ability to adapt to a changing environment.

Question 9

How do prokaryotes exhibit metabolic diversity with respect to nutitional mode and oxygen?

Answer 9

NUTRITION:

1. Photoautotroph: photosynthetic organisms
2. Chemoautotroph: obtain energy by oxidizing inorganic substances
3. Photoheterotoph: light energy, obtain carbon organically.
4. Chemoheterotroph: consume organic molecules for energy and carbon

OXYGEN

1. Obligate aerobes: require oxygen for growth
2. Facultative anaerobes: will use oxygen if present, but able to grow without it.
3. Obligate anaerobes: poisoned by oxygen.