lecture 27 - prokaryotic cells Flashcards
What proportion of the earth’s biomass are made up of bacteria?
~50%
What are the 3 distinct types of shape possible for bacteria?
Cocci, rod, spiral
What is the structure of the bacterial chromosome?
bacteria have a single, circular chromosome of DNA
Do bacteria have a nuclear membrane?
No
How is the bacterial genome contained when there is no nuclear membrane?
It is restricted to the nucleoid
What are plasmids?
Small, circular, self-replicating DNA molecule found in the cytosol of a bacterial cell
What type of nucleic acid is in a plasmid?
Circular, double stranded DNA
What are bacterial cell walls made up of?
Peptidoglycan
What is peptidoglycan?
A rigid macro molecular layer that makes up the bacterial cell wall.
What is the function of the bacterial peptidoglycan cell wall?
Provides strength, prevents osmotic lysis/rupture, confers cell shape.
What is the structure of peptidoglycan?
Polysaccharide chains - alternating NAG and NAM - cross linked by peptides that have amino acid side chains (cross linking via transpeptidase)
What enzyme is involved in the peptide cross bridges between polysaccharide chains in peptidoglycan?
Transpeptidase
What is gram staining?
A laboratory staining process that will turn certain bacterial purple, and others pink
What type of bacteria will turn purple during gram staining?
Gram positive bacteria
Why type of bacteria will turn pink during gram staining?
Gram negative bacteria
What agent is initially used in gram staining to give the purple colour?
Crystal violet
What is the structure of gram positive bacteria, and how does this determine their behaviour during gram staining?
Has a thick cell wall (peptidoglycan layer) above their cell membrane, which traps crystal violet giving them a purple colour.
What is the structure of gram negative bacteria, and how does this determine their behaviour during gram staining?
Thin layer of peptidoglycan between outer and inner membranes, meaning crystal violet cannot be effectively trapped.
What are bacterial flagella?
Appendages on motile bacteria that allow them to move through a liquid medium.
What are bacterial flagella made of?
Proteins - they are proteinacus
How many flagella are typically on each motile bacterial cell?
5-10
What acts as the ‘motor’ for movement of bacteria via flagella?
‘Motors’ embedded in the cell membranes/peptidoglycan, which use an electrochemical gradient to generate thrust.
What is chemotaxis, in terms of bacterial motility?
A tactic response by bacteria, in which they move along a concentration gradient towards a chemical attractant or away from a chemical repellant.
What are the 2 types of bacterial adherence factors?
Fimbriae and pili
What are fimbriae/adherins
Structures with adhesive properties that are founds on the surface of bacteria and allow them to adhere to surfaces.
How do fimbriae differ to flagella on bacteria?
Fimbriae are shorter, smaller in diameter and more numerous than flagella. Are adapted for sticking to surfaces (adherence) rather than motility
What are bacterial pili/sex pili?
An adherence factor that allows bacteria to attach to other bacteria and transfer genetic information in a process called conjugation.
What is the name for the transfer of genetic information between bacteria using sex pili?
Conjugation
What type of gene transfer is conjugation via sex pili?
Horizontal gene transfer
How are bacteria able to share genetics and thereby adapt to challenging conditions?
Via horizontal gene transfer, especially through conjugation using sex pili
What is glycocalyx?
A gelatinous polysaccharide covering that surrounds bacteria when produced.
What is glycocalyx made of?
Polysaccharide and/or peptides, which form a gelatinous substance
What are the two types of structure formed by glycocalyx?
Slime layer, capsule
What is a bacterial slime layer?
Disorganised glycocalyx layer that adheres loosely to bacterial cell walls.
What is a glycocalyx capsule?
A capsule of organised glycocalyx that is attached firmly and evenly to the bacterial cell wall and contains virulence factors.
What do glycocalyx capsules contain to protect the bacterial cell?
virulence factors
What are virulence factors?
Cellular structures, molecules and regulatory systems that enable microbial pathogens to colonise hosts effectively.
What does the glycocalyx capsule protect bacterial cells from?
Phagocytosis/engulfment by immune cells, desiccation (drying out)
What are bacterial endospores?
A structure formed within a bacterium that are formed during unfavourable conditions and protect bacteria from stress. They can lie dormant until triggered by environmental stressors.
What type of bacteria have bacterial endospores?
Some types of gram-positive bacteria
