Prokaryotes Flashcards
Prokaryotes are _____ organisms. Members of this group belong to the domains _____ and
_____.
microscopic
Archaea
Bacteria
______ were the earliest forms of life on Earth, and they have been evolving on Earth
for over 3 _____ years, and as they continue to live and flourish on Earth, they assist in changing
Earth as well.
Prokaryotes
billions
What are bacteria?
Bacteria are small, single-celled organisms (i.e. they are unicellular). As much as the
prokaryotes are such diverse organisms they do share unique unifying molecular and cellular
features.
DEFINE what a prokaryote is?
A microscopic single-celled organism which has neither a distinct nucleus with a membrane nor other specialised organelles, including the bacteria and cyanobacteria.
What are the general characteristics of prokaryotes? (3)
- Fall under Monera—>Archaea and Eubacteria
- First forms of life that assisted in the changes that allowed for more complex forms of life to occur
- Can adapt to live in almost any environment and therefore are the most abundant organisms on earth
What are the features of archaea? (5)
- Unicellular, cell wall of polysaccharides and proteins
- Live in an extreme environment
- Some are methanogens.
- Found in swamps and marshes.
- Produce methane as a waste
What are the features of bacteria? (5)
- Thrive almost everywhere
- Unicellular
- Microscopic, 0.8-8μm
- Astonishing diversity
- Many are covered in capsule (polysaccharide or protein layer)
What are the 3 shapes of bacteria?
- Cocci (sphere)
- Diplo-,
- strepto-,
- staphylo-
- Bacilli (rods)
- Spirilla (spirals)
The 1st layer of a bacterium is the slime layer/capsule, what is the structure of this? (4)
- Not always present
- Made of polysaccharides or proteins
- Dense—> capsule
- Not well organized—> slime layer
The 1st layer of a bacterium is the slime layer/capsule, what is the function of this? (2)
- Sticky to allow adherence to substrates or other individuals in a colony
- Prevent dehydration or attack from host’s immune system
True or false
The 2nd layer which is the outer polysaccharide layer/membrane is ALWAYS present.
FAlse, it is not always present.
The third layer is the cell wall, what is its structure?
Made from peptidoglycan (modified sugars & polypeptides).
What is the function of the cell wall? (4)
- Gives bacterium shape
- Provides protection
- Prevents from bursting in hypotonic (low-salt) environment
- Encloses bacterium and anchors molecules extending from surface
What is the function of the 4th layer which is the cell membrane?
Encloses cytoplasm
What are pilli?
Appendages that pull two cells together prior to DNA transfer from one cell to another.
What is a plasmid? (2)
- Circular DNA
- Released into environment upon cell death
What is the function of a flagella (flagellum singular) ? (4)
- Aids in motility of cell
- Differs entirely from flagella of eukaryotes
- Can be many or isolated on one end
- Move in response to stimulus
What are ribsomes? (3)
- Smaller than eukaryotes
- 2 sub units
- Aids in protein synthesis
DNA
- Not enclosed or ______ by membrane
- Circular chromosomes, located in _____.
compartmentalized
nucleoid
What are photosynthetic lamellae? (2)
- Not present always
- Can produce food
What is the gram stain technique, and who came up with it?
It was a technique curated by Hans Christian Gram, 19th-century Danish Physician. Staining technique used to classify two different groups of bacteria based on their cell wall composition.
Describe the gram staining technique method? (5)
- Prepare slide from culture
- Stain cells with crystal violet (primary stain)
- Subsequently, Gram’s iodine (iodine and potassium iodide) is added – the specimen will look blue/violet
- Rinse with a decolouriser (ethyl alcohol or acetone)
- Counterstain with safranin (secondary stain)
What can you deduce from the fact that it retains blue/violet colour?
It is a gram positive bacterium.
What are the feautures of gram positive bacteria? (3)
- Thick peptidoglycan
- Produce exotoxin (toxin outside their cell). The toxin is the protein secreted during life
- Can be immunised against GP bact. with toxoids (Penicillin)
How can gram positive bacteria be immunised? (3)
Gram positive:
• Only produces exotoxins—>proteins excreted during lifespan
• Antibiotics such as penicillin prevents peptidoglycan cross-linking
• This results in cell wall losing functionality
What are the medical implications of staining?
Medicinal/treatment implications: Staining can determine whether infection is gram positive
or gram negative and therefore the type of treatment required.
What can you deduce from the fact that it retains a red colour?
It is a gram negative bacteria.
What are the features of gram negative bacteria? (4)
- Thin peptidoglycan and LPS
- Produce endotoxin (wall/LPS layer).
- The structural part of the cell
- Streptomycin can be used to treat the cell
How can gram negative bacteria be immunised? (3)
Lipids of the lipopolysaccharides in the wall are toxic, causing fever or shock. Outer membrane helps protect it from body’s defences. Membrane also makes it difficult to detect.
• More resistant to antibiotic than gram positive due to membrane impeding entry of drugs
• Produces both endo and exotoxins
• Enter body through wound, Treatment—> Antibiotic: streptomycin
What are the sources of antibiotics? (3)
o Actinomycetes
o Bacillus
o Moulds
What does penicillin do?
• Penicillin—>inhibits cell wall synthesis by activating
‘transpeptidase’
Explain penicillin resistance.
o Resistance—>peniciltase: bond to penicillin molecule active sight.
What do fluoroquinolones do?
Fluoroquinolones—>inhibits DNA replication by bonding to enzyme to prevent division
Explain fluoroquinolones resistance.
o Resistance—>cell blocks bonding of enzyme
What does tetracycline do?
Tetracycline—>binds to ribosome, thereby blocking protein synthesis.
Explain tetracycline resistance.
o Resistance—>bacteria pumps compound out of cell
What is the ecological importance of prokaryotes? (5)
- Nitrogen fixers
o Fix nitrogen into a form that can be used by other organisms for protein synthesis - Nutrient recyclers + decomposers
o Recycle chemical elements between living and non-living components (unblock carbon, nitrogen and other elements) - Bioremediation
o Remove pollution and pollutants from environment (oil spills, metal rusting) - Disease
o Maintain strength of gene pool, maintain population - Natural antibiotics
What is the endosymbiotic theory? (4)
• Theory stating that chloroplasts and mitochondria were integrated into eukaryotic cells
- Larger cell took in smaller cell
either as prey or entered as a parasite
• Chloroplasts and mitochondria are known as endosymbionts
• This indicates organelles in eukaryote descended from ancestral prokaryote that was engulfed by another cell (eukaryote or prokaryote)
• The engulfed cell specialized into chloroplasts and mitochondria
Provide evidence for the endosymbiotic theory. (7)
- Two different membranes: The chloroplast is surrounded by two or more membranes, while the mitochondria are bounded by a double membrane. The inner membrane is similar to that found in prokaryotes whereas the outer membrane is similar in structure and composition to eukaryotes.
- Size: The mitochondria and chloroplasts are similar in size to free-living prokaryotes.
- Structure of cristae: The inner membrane of the chloroplasts and mitochondria perhaps derived from the members of the endosymbiotic prokaryotes have several enzymes and transport systems that resemble those found in the plasma membranes of prokaryotes.
- Ribosomes: The ribosomes of the chloroplasts are more similar in size in biochemical characteristics to prokaryotic ribosomes than to the ribosomes outside the chloroplasts in the cytoplasm of the eukaryotic cell.
- DNA: The chloroplast and mitochondria contain transferred TRNA, ribosome and other equipment needed to translate and transcribe DNA into proteins.
- Division: The mitochondria and chloroplast reproduce by a splitting process similar to binary fission in bacteria.
- DNA replication: The chloroplast and mitochondria contain DNA in the form of circular molecules not associated with histones or other proteins as in prokaryotes.
