Structure And Function In Bacteria 2 Flashcards
What is the ratio of phospholipids to proteins in the cell membrane?
40% phospholipid 60% protein
What are the general features of a plasma membrane? (13)
Cytoplasmic membrane
Most dynamic structure of prokaryotic cell
Encompasses cytoplasm of all cells
Selectively permeable barrier
Allows water passage and uncharged molecules
Osmotic or permeability barrier
Location of transport systems for specific solutes
Energy generating functions
Synthesis of membrane lipids
Synthesis of PGL
assembly and secretion of extra cytoplasmic proteins
Coordination of DNA replication and segregation, septum formation and cell division
Location of specialise enzyme systems
What do bacterial membranes lack and what do they have to compensate?
Sterols
Steroid like hopanoids
What are most membrane associated lipids and which ends interact with water and without?
Amphipathic- having both hydrophobic and hydrophilic ends
Polar - hydrophilic - interacts with water
Non-polar- hydrophobic - insoluble in water, interact with one another
What are the two types of plasma membrane proteins?
Integral/transmembrane
Peripheral
What are the features of integral/transmembrane proteins?
Not easily extracted from membranes
Insoluble in aqueous solution when freed of lipids
Amphipathic -hydrophobic regions in buried in lipid hydrophilic project from membrane surface
Carbohydrates are attached to outer surface of membrane proteins
Responsible for secretion, energy conserving and interaction with the environment
What are the features of peripheral proteins?
Loosely connected to membrane
Easily removed
Soluble in aqueous solution
20/30% of total membrane protein
What are mesosomes?
An organelle of bacteria that appears I electron micrographs as an invagination of the plasma membrane and is a site of localisation of respiratory enzymes
Features of the nucleoid?
Single, circular loop of essential double stranded DNA aggregated in a dense area of the cell known as the nucleoid
Contains cells and chromosomes + numerous proteins
Some organisms have a linear chromosome while others may have more than 1
Chromosomes are much larger than the length of the cell
How many genes are in a bacterial cell and how are they packaged?
3-4000
Packaged by supercoiling
Features of plasmids?
Small, circular, 1/10th the size of chromosome
Double stranded DNA
Free in cytoplasm
Can link into chromosome
Not essential for metabolic growth or cell reproduction
Replicate independently
Can be removed by curing
What are some of the functions of plasmids?
R plasmids - resistance to antibiotics Fertility factors Virulence plasmids Metabolic plasmids Bacteriocins - destructive chemicals
Features of Fimbriae?
Prokaryotes have short, fine, hairlike appendages that are thinner than flagella
Slender tubes composed of helically arranged protein subunits and are about 3-10nm in diameter and up to several micrometers long
A cell may be covered with up to 1000 Fimbriae
Attach bacteria to solid surfaces
May be used in locomotion
Features of pilli?
Often larger than Fimbriae 9-10nm in diameter
Bacteria have about 1-10 sex pili per cell
Genetically determined by conjugation plasmids and are required for conjugation
What is the role of the flagellum and what are the three components of it?
Movement of cell
Filament, hook and basal body
Features of flagella?
Bacterial flagella are slende, rigid structures about 20nm diameter and up to 15-20 micrometers long
Threadlike loco motor appendages extending outward from the plasma membrane and cell wall
Involved in motility, movement over surfaces and attachment
Bacterial species often differ distinctively in their patterns of flagella distribution and so are useful in identification
Name 4 types of flagella?
Monotrichous - 1 flagellum
Lophotrichous - multiple at 1 side
Amphitrichous - multiple at 2 sides
Peritrichous - multiple covering whole cell
What is a periplasmic flagella?
A type of modified flagella
Found in a group of bacteria known as spirochates
Consists of a filament and a hook but the entire structure is located between the cell wall and the membrane (the periplasmic space)
The filament is wrapped around the cell and is free to contract and relax causing a twisting, flexing movement of the entire cell
What are the three parts of the flagella and what are there functions?
Filament - rotates, composed of protein flagellin
Hook - connects basal body and filament
Basal body - complex, not fully understood. Consists of a series of rings associated with layers of the bacterial cell
What is the basal body made up of?
A rod, 4 rings (C ring acts as flagellum motor) and a motor
What is the motor in the basal body of a flagellum composed of?
Rotor - M, S and C ring
Stator - MotA and MotB
How does the flagellum move?
Proton motive force - differences in charge and pH across membrane
Created by transfer of electrons down the electron transfer chain transfer releases energy
What is chemotaxis?
Movement in the cell in response to chemical signals either positive or negative
How is chemotaxis accomplished ie. In what ways do bacterium move?
Runs - movement in a linear direction created by anti clockwise flagellar rotation (sends cell moving forward)
Tumbles - when cell stops and reverses direction created by a clockwise flagellar rotation (sends cell tumbling randomly)
