Lecture 1- Prokaryotic Function Flashcards
1.) Structure of plasma membrane
The plasma membrane contains lipids and proteins. It is highly organised, asymmetrical, flexible and dynamic. It has a lipid bilayer with hydrophilic heads (polar). Within the lipid there are proteins embedded.
2.) Structure of peptidoglycan
This structure is made up of nam and nag joined together at the beta-1,4-glycosidic bond. They have peptide side chains and a polysaccharide backbone. The peptide side chains are joined together by pentaglycine. Lysozyme works by breaking down the beta-1,4-glycosidic bond to create holes in the cell wall. Penicillin work by breaking down the peptide interbridge causing defects in the structural integraty.
3.) Difference between gram positive and negative cell walls
Gram positive has thick outer peptidoglycan cell wall with an inner plasma membrane. Gram negative have an outer membrane with a thin peptidoglycan wall behind, with a periplasmic space inbetween the peptidoglycan and the plasma membrane.
5.) Attachment of flagella hook to cell surface in gram neg
The hook of flagella in a gram neg is embbedded in the cell wall through the basal body with a series of rings. The L ring is connected to the outer membrane with the p ring being bound to the peptidoglycan and the c & ms attaches to plasma membrane.
6.) Why is peptidoglycan structure rigid
This is because they are multilayered attached to a peptide interbridge, these multiple layer are what gives it strengths and adds to the rigidity.
7.) Functions of outer membrane in gram neg
The functions are to prevent from host defences, contributes to negative charge on cell surface, helps stabilise cell wall , serves as a protective barrier and is more permeable than plasma membrane so allows certain substance to cross the membrane.
8.) Purpose of nucliod in bacterial cells
The purpose of the nucliod is to contain and store dna
10.) Structure and function of capsule and slime
Capsules and slime are layers of material lying outside the cell wall. They are usually composed of polysaccrides. Capsule are well organised and not easily removed. Where as capsules diffuse, unorganised and are easily removed. There functions are attachment to surfaces, motility of gliding bacteria, protection and to survive unrecognised in host and avoid detection.
11.) How is movement of flagella powered
Flagelumm move by rotating like a propeller. Counterclockwise rotation cause forward movement and clockwise rotation disrupts causing a tumble allowing it to turn
12.) How is motile bacteria able to sense an attractant and move toward it
They are able to sense chemical attractants and chemorepellants by chemoreceptors on the surface of cells
14.) Define plasmids
plasmids are usually small, closed circular dna molecules that exsist and replicate independently of chromosomes. Not required for the growth and reproduction and may carry genes that confer selective advantage.
Prokaryote Vs Eukaryote?
The Three architectural regions of Prokariotic cells
Cytoplasmic region
Cell Envelope
Cell surface Attachments
Whats is inside the cytoplasmic region of a cell?
nucleoid (DNA)
ribosomes
inclusion bodies
cytoplasmic matrix
Three cytoskeletal elements of bacteria?
Actin filament- made from actin
Microtubules- made from tubulin
Intermediate filaments- a mixture of different classes of proteins
Define Inclusion bodies?
Granules of organic or inorganic material that are stockpiled by the cell for future use
Example of organic inclusion bodies?
o Glycogen
o Poly-β-hydroxybutyrate (PHB) o Gas vacuoles
o Cyanophycin granules
o Carboxysomes
Examples of inorganic inclusion bodies
o Polyphosphate granules
o Sulphur granules
o Magnetosomes
Define Ribosomes
complex structures consisting of protein and RNA, that are site of protien synthesis
Define Sporogenesis?
the process of spore formation
What are the main components of the cell enevelope?
o Cytoplasmic or plasma membrane
o Cell Wall
o Capsules and slime layers
What is the plasma membrane?
o Encompasses the cytoplasm
o Contains lipids and proteins
o Highly organised, asymmetric, flexible and dynamic
Describe the asymmetry of most membrane lipids?
Usually form a bilayer
• Polar ends
interact with water hydrophilic
• Nonpolar ends
insoluble in water hydrophobic
What is a membrane protien
Proteins that are embedded in or associated with lipid membrane
What is a membrane protien?
loosely associated with the membrane and easily removed
Integral proteins?
embedded within the membrane and not easily removed
Functions of the plasma membrane?
o Separation of cell from its environment
o Selectively permeable barrier
o Location of crucial metabolic processes
o Sensory
Decribe a prokaryotic cell wall?
Rigid structure that lies just outside the plasma membrane
Decribe the typical gram positive membrane?
Decribe the typical gram negative membrane
Decribe typical structure of gram negative membrane?
Decribe Peptidoglycan synthesis?
o Autolysins, cleaves β-1,4 glycosidic bond linking NAM
& NAG in small areas of pre-existing PG
o Newly synthesised PG inserted until cross-wall forms and cell divides
o 2 carriers involved :
o uridine diphosphate (UDP)
o bactoprenol
Decribe process of TRANSPEPTIDATION?
What are Teichoic acids?
Polymers of glycerol and ribitol joined byphosphate groups
Only present in Gram positive bacteria
Extend beyond the surface of peptidoglycan
Basic structure of polysaccrides
o Consist of three parts
o lipid A
o core
o polysaccharide o O side chain
o (O antigen)
Importance of the LPS?
o Protection from host defenses (O antigen)
o Contributes to negative charge on cell surface (core polysaccharide)
o Helps stabilize outer membrane structure (lipid A) o Can act as an endotoxin (lipid A)
Effect of β-lactam antibiotics?
o Enzymes that catalyse transpeptidation of peptidoglycan also called penicillin binding proteins
o Lysozyme cleaves β-1,4 glycosidic bond
Osmosis?
movement of water across selectively permeable membrane from dilute solutions to more concentrated solutions
hypotonic solutions
[solute]outside cell < [solute]inside cell
What is Osmotic lysis?
occur when cells are in hypotonic solutions , movement of water into cell causes swelling and lysis due to osmotic pressure
Plasmolysis
occurs when cells are in hypertonic solutions, water moves out of cell causing cytoplasm to shrivel and pull away from cell wall
hypertonic solutions?
[solute]outside cell > [solute]inside cell
Importance of Plasmolysis
useful in food preservation
Importance of Osmotic lysis?
basis of lysozyme and penicillin action
What is Protoplast
cell completely lacking cell wall
What is a Spheroplast
cell with some cell wall remaining
Decribe the action of penecilin?
Layer of material lying outside the cell wall, usually composed of polysaccharides, well organized and not easily removed from cell
What is a capsule
slime layers?
similar to capsules except diffuse, unorganized and easily removed
Glycocalyx?
network of polysaccharides extending from the surface of the cell ( a capsule or slime layer composed of polysaccharides can also be referred to as a glycocalyx)
Functions of capsules and slime layers?
o Attachment to surfaces
o Motility of gliding bacteria
o Protection
How do capsule aviod host defenses?
by Surviving unrecognised in host and avoid detection this is done by;
o Prevent complement activation by masking activatingc molecules
o Avoid phagocytosis by preventing effective contact (e.g. Streptococcus pneumoniae)
o Capsules that are not antigenic as resemble host tissue (e.g. S. pyogenes)
Cell surface attachments?
o Pili
o Fimbriae
o Flagella
Fimbriae (s., fimbria)?
short, thin, hairlike, proteinaceous appendages, that mediate attachment to surfaces
Sex pili
similar to fimbriae except longer, thicker, and less numerous
Flaggela’s primary responsiblity?
motility
Type of bacteria that has flagella
o Half of all bacilli and all spiral and curved bacteria are motile o Very few cocci are motile
Type of flagella arrangements?
o Monotrichous – one flagellum
o Polar flagellum – flagellum at end of cell
o Amphitrichous – one flagellum at each end of cell
o Lophotrichous – cluster of flagella at one or both ends
o Peritrichous – spread over entire surface of cell
What are the three parts that make up a flaggela?
filament
basal body
hook
Flagella structure in gram neg bact?
Decribe filament on flagella
o Hollow, rigid cylinder
o Composed of the protein flagellin
o Some prokaryotes have a sheath around filament
Decribe role of hook on flagella
links filament to basal body
Basal body
series that drive the flagella motor
Descibe Flagellar synthesis?
o An example of self-assembly
o Complex process involving many genes and gene products
o New molecules of flagellin are transported through the hollow filament
o Growth is from tip, not base
How does a flagella move
Flagellum rotates like a propeller
o in general, counterclockwise rotation causes forward motion
(run)
o in general, clockwise rotation disrupts run causing a tumble (twiddle)
Other examples of motility in a prokaryiotic cell?
o Spirochetes
o axial filaments cause flexing and spinning
movement
o Gliding motility
o cells coast along solid surfaces
o no visible motility structure has been identified
What is chemotaxis
o Movement towards a chemical attractant or away from a chemical repellant, detected by chemoreceptors on surfaces of cells
What are the mechanism of chemotaxis?
Complex but rapid which involves conformational changes in proteins and also methylation or phosphorylation of proteins
What are the main cytoplasmic regions?
Nucleoid (DNA)
Ribosomes
Inclusion bodies
Cytoplasmic matrix
What are the main cell wall regions?
Capsules and slime layers
Cell wall
Cytoplasmic or plasma membrane
What are the cell surface attachments?
Flagella
Pili
