The University of New South Wales
MICR2011
,MICR2011
Bold (purple) – Lecture number and core focus
Italic and underlined (black) – Heading
Bold (black) – Subheading
Lecture 2: Unicellular structure and function
In this lecture, we introduce the basic structure and function of microbes. You will learn about the major cellular components
of a bacterial cell and organelles that they use to evade, stick, swim, grow and persist.
Phylogeny of life
The last universal common ancestor is ‘Luca’, at the root of the tree.
Bacterial cell structure
A bacteria consists of:
a) Cytoplasm: contained by cytoplasmic membrane
b) Cell wall: shape and rigidity
c) Chromosome(s): usually circular, NOT contained within
nuclear membrane
d) Plasmids: extrachromosomal pieces of DNA which can
be transferred between cells
e) Ribosomes: distinct from archaea and eukaryotes
Cytoplasmic membrane
Structure
The cytoplasmic membrane is a phospholipid bilayer.
, - Hydrophobic lipids “tails” and hydrophilic phosphate head groups self-organise into bilayer in aqueous
environment.
- Proteins are attached to the cytoplasmic membrane (peripheral membrane proteins) or embedded in (integral
membrane proteins) the cytoplasmic membrane.
Function
Permeability barrier
- Excludes large and charged molecules from the cell.
- Prevents leakage of solutes from inside the cell.
- Facilitates the controlled movement of molecules across
the membrane.
Passive transport
- Movement of molecules across the cell membrane along the
concentration gradient [high] →[low].
- Does NOT use cellular energy.
§ e.g. simple diffusion (small, non-charged molecules e.g.
O2, CO2)
§ e.g. facilitated diffusion through a membrane protein
(polar or charged molecules e.g. H2O)
Active transport
- Molecules moved across the cell membrane against the concentration gradient [low] → [high].
§ This requires energy (e.g. ATP) and often involves the specific enzymes and transport proteins ‒
e.g. ions, glucose.
Energy conservation
- Respiratory chain and the proton motive force.
§ H+ are pumped out of the cell by the respiratory chain.
§ The cytoplasmic membrane is impermeable to H+, which creates a high [H+] on the outside the cell
and a low [H+] inside the cell – the proton motive force.
§ H+ is taken back in through passive transporters, e.g. ATPases which generate energy in the form of
ATP.
§ Energy is NOT required as this is along the concentration gradient.
The cell wall
Function
Strength (protection against osmotic lysis)
The cytoplasmic membrane allows accumulation of solutes inside
the cell, generating up to 2 atmospheres of osmotic pressure (car
tyre). But, how does the cell not burst?
- The cytoplasmic membrane is semi-fluid and easily ruptured.
§ Peptidoglycan surrounds the cytoplasmic membrane and prevents cell lysis.
§ Peptidoglycan is composed of chains of sugars and short peptides which are crosslinked together,
creating strength.
Cell rigidity and shape
, In addition to preventing lysing, the cell wall gives rigidity and shape.
- The peptidoglycan layer can be bent by interaction with proteins, forming characteristic shapes.
Structure
Peptidoglycan is key as strings of alternating sugars.
i. N-acetylglucosamine (GlcNAc) (G)
ii. N-acetylmuramic acid (MurNAc) (M)
- These are crosslinked by short peptides to form a
lattice-like structure.
§ The long glycan chains run parallel to each other
around the circumference of the cell.
§ The short peptide crosslinks can have two
different arrangements, one for gram-negative
and one for gram-positive.
Two general organisations of the cell wall
The thick peptidoglycan layer is anchored to the cytoplasmic membrane, termed Gram positive.
The thin peptidoglycan layer is surrounded by second outer membrane, termed Gram negative.
MICR2011
,MICR2011
Bold (purple) – Lecture number and core focus
Italic and underlined (black) – Heading
Bold (black) – Subheading
Lecture 2: Unicellular structure and function
In this lecture, we introduce the basic structure and function of microbes. You will learn about the major cellular components
of a bacterial cell and organelles that they use to evade, stick, swim, grow and persist.
Phylogeny of life
The last universal common ancestor is ‘Luca’, at the root of the tree.
Bacterial cell structure
A bacteria consists of:
a) Cytoplasm: contained by cytoplasmic membrane
b) Cell wall: shape and rigidity
c) Chromosome(s): usually circular, NOT contained within
nuclear membrane
d) Plasmids: extrachromosomal pieces of DNA which can
be transferred between cells
e) Ribosomes: distinct from archaea and eukaryotes
Cytoplasmic membrane
Structure
The cytoplasmic membrane is a phospholipid bilayer.
, - Hydrophobic lipids “tails” and hydrophilic phosphate head groups self-organise into bilayer in aqueous
environment.
- Proteins are attached to the cytoplasmic membrane (peripheral membrane proteins) or embedded in (integral
membrane proteins) the cytoplasmic membrane.
Function
Permeability barrier
- Excludes large and charged molecules from the cell.
- Prevents leakage of solutes from inside the cell.
- Facilitates the controlled movement of molecules across
the membrane.
Passive transport
- Movement of molecules across the cell membrane along the
concentration gradient [high] →[low].
- Does NOT use cellular energy.
§ e.g. simple diffusion (small, non-charged molecules e.g.
O2, CO2)
§ e.g. facilitated diffusion through a membrane protein
(polar or charged molecules e.g. H2O)
Active transport
- Molecules moved across the cell membrane against the concentration gradient [low] → [high].
§ This requires energy (e.g. ATP) and often involves the specific enzymes and transport proteins ‒
e.g. ions, glucose.
Energy conservation
- Respiratory chain and the proton motive force.
§ H+ are pumped out of the cell by the respiratory chain.
§ The cytoplasmic membrane is impermeable to H+, which creates a high [H+] on the outside the cell
and a low [H+] inside the cell – the proton motive force.
§ H+ is taken back in through passive transporters, e.g. ATPases which generate energy in the form of
ATP.
§ Energy is NOT required as this is along the concentration gradient.
The cell wall
Function
Strength (protection against osmotic lysis)
The cytoplasmic membrane allows accumulation of solutes inside
the cell, generating up to 2 atmospheres of osmotic pressure (car
tyre). But, how does the cell not burst?
- The cytoplasmic membrane is semi-fluid and easily ruptured.
§ Peptidoglycan surrounds the cytoplasmic membrane and prevents cell lysis.
§ Peptidoglycan is composed of chains of sugars and short peptides which are crosslinked together,
creating strength.
Cell rigidity and shape
, In addition to preventing lysing, the cell wall gives rigidity and shape.
- The peptidoglycan layer can be bent by interaction with proteins, forming characteristic shapes.
Structure
Peptidoglycan is key as strings of alternating sugars.
i. N-acetylglucosamine (GlcNAc) (G)
ii. N-acetylmuramic acid (MurNAc) (M)
- These are crosslinked by short peptides to form a
lattice-like structure.
§ The long glycan chains run parallel to each other
around the circumference of the cell.
§ The short peptide crosslinks can have two
different arrangements, one for gram-negative
and one for gram-positive.
Two general organisations of the cell wall
The thick peptidoglycan layer is anchored to the cytoplasmic membrane, termed Gram positive.
The thin peptidoglycan layer is surrounded by second outer membrane, termed Gram negative.
