Prokaryote Cell Structure Flashcards
(21 cards)
Why is studying prokaryotic cell structure important?
- Developing antibiotics
- Agriculture
- Biotechnology
- Understanding basic life processes
What are prokaryotes ?
Cells without a nucleus and membrane-bound organelles
Bacteria and archaea
What is the difference between bacteria and archaea ?
- Bacteria have a peptidoglycan cell wall
- Cell membrane lipids are fatty acids with ester bond in Bacteria, but are branched isoprenoids with ether bonds in archaea
How do the size and shape of prokaryotic and eukaryotic cells compare ?
Prokaryotes are between 0.1-5um
Eukaryotes are between 10-100um
Prokaryote shapes: coccus, bacillus, spirillum, vibrio
Eukaryote shapes are more variable and complex
What is the structure of the prokaryotic cell membrane ?
Phospholipid bilayer that is made of two layers of phospholipids:
Hydrophilic heads face outward
Hydrophobic tales face inward
There are integral proteins that are found within the bilayer
They do not normally contain sterols (eg. Cholesterol)
What are the purposes of the prokaryotic cell membrane?
- Controls what enters and leaves the cell
- Regulates passive and active transport
- Energy conservation site
- Contains proteins
What is a limiting factor of size in prokaryotes ?
Surface area : volume ratio
What are key structures of the prokaryotic cell wall ?
In bacteria: made of peptidoglycan. Can be gram postivive or negative
In archaea: no peptidoglycan
Helps maintain cell shape and prevent osmotic lysis.
Bacteria cell walla contain a high concentration of of dissolved solutes which cause turgor pressure to develop, so the cell walls stop the cell from ‘popping’.
How to differentiate between gram positive and gram negative cell walls ?
The gram stain identifies the 2 groups of bacteria.
1. Gram positive bacteria retain the crystal violet stain and so look purple.
2. Gram negative bacteria do not retain the stain so appear red/pink.
What structure causes Gram positive bacteria to stain using a gram stain ?
- Gram positive bacteria has a thick peptidoglycan cell wall outside of the membrane, which is very robust.
- Gram negative bacteria have a thin peptidoglycan cell wall on the inside between 2 membranes
What gives the peptidoglycan cell wall its thickness and rigidity ?
It is composed of repeating units of two sugar derivatives, N-acetylglucosamine and N-acetylmuramic acid and a small number of special amino acids.
Glycosidic bonds connecting sugars cannot provide rigidity in all directions so chains are cross-linked by amino acids.
What are teichoic acids ?
They are part of gram-positive cell walls.
They are negatively charged which helps to bind and regulate cations, which are needed for enzyme function and stability.
What is found in archaea cell walls ?
Pseudopeptidoglycan
Alternating repeats of NAG and NAT
Name some prokaryotic cell appendages
- Flagella
- Pilli
- Capsule or slime layer
What are flagella used for ?
Movement
They are helical shaped
Fli proteins cause the rotation of the flagellum
What are pilli used for ?
For attatcment to surfaces (fimriae) and DNA transfer during conjugation (pili)
What is the s layer ?
Paracrystalline surface layer
Most common cell wall type in archaea
What is a capsule or slime layer ?
It is made of polysaccharides and protein.
It is for protection and can also help with attachment to surfaces
What are gas vesicles and what are they for ?
They are hollow, protein bound structures that play a key role in buoyancy control- keeping the cell in its vertical position.
What are the differences between eukaryotic and prokaryotic genomes ?
- Prokaryotic DNA is in the cytoplasm, eukaryotic is inside a nucleus
- Prokaryotic DNA is circular, eukaryotic is linear
- Bacteria contain plasmids, eukaryotes don’t
What is the function of plasmids ?
They are small, circular, double stranded DNA molecules.
1. Many carry antibiotic resistance genes
2. They can be transferred between cells via conjugation
3. Used in biotechnology as vectors
