Lecture 2 - Bacterial cell structure Flashcards
Describe 6 components of bacterial cell organisation and their intracellular structures
The main components of bacteria cell include:
Cell wall made of peptidoglycan, (and outer membrane when gram negative)
Ribosomes: The ribosome is important for mRNA translation and protein synthesis
Plasmid: small circular double stranded DNA that can replicate independently of chromosome and is not necessary for survival
Plasma membrane or cell membrane: Underneath the cell wall to separate intra and extracellular components made of hydrophobic and hydrophilic phospholipids
Flagella: Used for locomotion appendage, rotates clockwise or anticlockwise powered by ATP
Pilli: used to attach to surfaces and transduce genes
Describe the structure and role of the plasma membrane
The role of the plasma is to enclose the cytoplasm of the cell and separate the extracellular and intracellular contents of the cell. It is a double lipid bilayer with hydrophobic tails and hydrophilic heads that consist of carbohydrates, lipids and protein to prevent leakage. It also acts as a gateway through ion channels for transport of molecules in and out. In addition, it also acts as a site for the flagella anchor.
Permeability barrier: prevent leakage, gateway for transport molecule in and out of the cell
Energy conservation: generation of proton motive force for respiration
Protein anchor: site of many protein involved in genetic transport and chemotaxis (i.e flagella)
Describe the differences between a gram+ve and –ve bacteria cell. What colour does the gram stain produce in each of these species?
A gram +ve cell has a thick peptidoglycan layer with thin inner cell membrane, teichoic acids are also present in a gram positive cell; a gram stain would produce a pink colour. In contrast, a gram -ve cell has a thick outer cell membrane composed of lipopolysaccharide-lipoprotein-phospholipid layer with a thin layer of peptidoglycan underneath with the absence of teichoic acids; a gram stain would produce a purple colour.
List the different types of morphology shapes
Cocci, Rods, Spirochetes, vibrio
What are the biochemical components of the cell wall, what’s its role?
The cell wall is composed of NAM and NAG sugars that form the carbohydrate backbone. The rows of NAM and NAG are linked by disulphide bonds. The role of the cell wall is to provide structure and rigidity and protection i.e. to prevent the cell from bursting or shrinking from osmotic pressure.
Briefly describe peptidoglycan assembly
The assembly of peptidoglycan involves: NAM connected to amino acids, NAG is added to NAM to form a peptidoglycan precursor, the precursor is transported across membrane to cell wall acceptor, binding to cell wall acceptors that undergo cross linking of transpeptidase and D alanyl carboxyl peptidase known as PCBs
Briefly describe peptidoglycan disassembly
Disassembly occurs through autolysins that hydrolyze glycosidic bonds that link NAM and NAG and also break rows of sugar linked by disulphide bonds.
Describe the process of binary fission
Binary fission is the fundamental aspect of bacteria reproduction it is NOT mitosis. It mainly includes elongation of the cell and forms a new daughter cell. The process is as follows: FtsZ proteins form a ring around midpoint dividing it in half known as septum formation. MinC and D prevent Z ring from forming at both ends whilst MinE directs formation of FtsZ ring.
What are plasmids and their uses?
Plasmids are double stranded circular DNA that exist independently of the nucleoid and can replicate independently of chromosome. They can provide drug resistance, give additional metabolic activities and cause a bacteria → pathogenic.
Briefly describe the structure of the flagella
The structure of the flagella can be broken down to 3 main parts. The filament, hook and motor.
What are endospores?
Endospores are dormant resilient asexual structures that are responsible in aiding the survival of bacterium through environmental stress.
What is the role of ribosomes in bacteria?
Ribosome is the site of protein synthesis and mRNA translation composed of two subunits a large (30s) and small (50s) subunit.
What is the role of Pili in bacteria?
Bacteria can utilise pili for either attachment to surfaces or for sexual reproduction. Short pili (Fimbriae) are used for attachment to surfaces and motility. Long pili commonly referred as ‘sex’ pili can be responsible for DNA transfer (Conjugation). In gram-ve bacteria it is the transfer of DNA plasmid from donor to recipient bacterium.
Lecture 3 – Microbial growth
