Membrane and metabolism• As the membrane is the focus of gradients, this is where

electron transport reactions occur which serve to power the cell in different ways

• Many enzymes important to metabolic activity are membrane bound

H+ gradients across the membrane

• Proton Motive Force (PMF) is what drives ATP production in the cell

(pH=1.4 = 0.14 V = 23 KJ/mol)

Figure 5.21

Membrane functions (other)

• In addition to directing ion/molecule transport and providing the locus for energy production, membranes are also involved in:– Phospholipid & protein synthesis for membrane– Nucleoid division in replication– Base for flagella– Waste removal– Endospore formation

• Though very small, the membrane is critical to cell function Lysis involves the rupture of this membrane and spells certain death for the organism

Cell Wall• Cell wall structure is also chemically quite

different between bacteria and archaea• Almost all microbes have a cell wall –

mycoplasma bacteria do not• Bacteria have peptidoglycan, archaea use

proteins or pseudomurein• The cell wall serves to provide additional

rigidity to the cell in order to help withstand the turgor pressure developed through osmosis and define the cell shape as well as being part of the defense mechanisms

• Cell wall structure• Two distinct groups of bacteria with very different

cell walls– Gram negative has an outer lipid membrane (different

from the inner, or plasma membrane) – Gram positive lacks the outer membrane but has a

thicker peptidogycan layer

Gram – cell wall

Peptidoglycan layer• This layer is responsible for the rigidity of the cell wall,

composed of N-Acetylglucosamine (NAG) and N-acetylmuramic (NAM) acids and a small group of amino acids.

• Glysine chains held together with peptide bonds between amino acids to form a sheet

Outer membrane – Gram (-)

• Lipid bilayer ~7 nm thick made of phospholipids, lipopolysaccharides, and proteins

• LPS (lipopolysaccharides) can get thick and is generally a part that is specifically toxic (aka an endotoxin)

• LPS layers are of potential enviornmental importance as a locus of chelators and electron shuttles

• Porins are proteins that are basically soluble to ions and molecules, making the outer layer effectively more porous than the inner membrane, though they can act as a sort of sieve

External features

• Glycocalyx (aka capsule – tightly bound and adhering to cell wall, or slime layer – more unorganized and loosely bound) – helps bacteria adhere to surfaces as well as provides defense against viruses

• Flagella – ‘tail’ that allows movement by rotating and acting as a propeller

• Pili – thin protein tubes for adhesion (colonization) and adhering to surfaces

Inside the cell• Cytoplasm – everything inside the membrane• Nucleoid/Chromosome – DNA of the organism – it

is not contained by a nuclear membrane (as eukaryote cell)

• Ribosomes – made of ribosomal RNA and protein these are responsible for making proteins

• Vacuoles or vesicles – spaces in the cytoplasm that can store solids or gases

• Mesosomes/Organelles –a membrane system internal to the cell which facilitates protein function; there are these structures specifically for photosynthesis

Cell structure

Cytoplasmic inclusions

Where found Composition Function

glycogen many bacteria e.g. E. coli polyglucose reserve carbon and energy source

polybetahydroxyutyric acid (PHB)

many bacteria e.g. Pseudomonaspolymerized hydroxy

butyratereserve carbon and energy source

polyphosphate (volutin granules)

many bacteria e.g. Corynebacteriumlinear or cyclical

polymers of PO4reserve phosphate; possibly a reserve of high

energy phosphate

sulfur globulesphototrophic purple and green sulfur

bacteria and lithotrophic colorless sulfur bacteria

elemental sulfurreserve of electrons (reducing source) in

phototrophs; reserve energy source in lithotrophs

gas vesicles aquatic bacteria especially cyanobacteriaprotein hulls or shells

inflated with gasesbuoyancy (floatation) in the vertical water

column

parasporal crystals

endospore-forming bacilli (genus Bacillus)

protein unknown but toxic to certain insects

magnetosomes certain aquatic bacteriamagnetite (iron oxide)

Fe3O4 orienting and migrating along geo- magnetic

field lines

carboxysomes many autotrophic bacteriaenzymes for autotrophic

CO2 fixationsite of CO2 fixation

phycobilisomes cyanobacteria phycobiliproteins light-harvesting pigments

chlorosomes Green bacterialipid and protein and

bacteriochlorophylllight-harvesting pigments and antennae

Nucleoid

• Single strand of DNA, usually circular, usually looks like a big ball of messed up twine…

• Size – smallest organism yet discovered (Nanoarchaeum equitans) 490,889 base pairs; e. coli 4.7 Mbp, most prokaryotes 1-6 million base pairs (1-6 MBp); Humans 3300 MBp

• DNA is around 1000 m long in bacteria, while the organism is on the order of 1 m long – special enzymes called gyrases help coil it into a compact form

Ribosomes• Ribosomal RNA is single stranded • RNA is a single stranded nucleic acid

– mRNA- messanger RNA – copies information from DNA and carries it to the ribosomes

– tRNA – transfer RNA – transfers specific amino acids to the ribosomes

– rRNA – ribosomal RNA – with proteins, assembles ribosomal subunits

DNA is transcribed to produce mRNAmRNA then translated into proteins.

RNA and protein construction

• The nucleotide base sequence of mRNA is encoded from DNA and transmits sequences of bases used to determine the amino acid sequence of the protein.

• mRNA (“Messenger RNA”) associates with the ribosome (mRNA and protein portion).

• RNA (“Transfer RNA”) also required• Codons are 3 base mRNA segments that specify a

certain amino acid.• Most amino acids are coded for by more than one

codon.• Translation ends when ribosome reached “stop codon”

on mRNA.

TranscriptionRNA polymeraze takes the DNA and temporarily unwinds it, templates the transfer RNA from that, using ribonucleoside triphosphates to assemble…

Translation• mRNA is coded for one or more specific

amino acids and moves to the ribosome to assemble amino acids into proteins

• On mRNA, codons are 3 bases, coded to specific amino acids

• On tRNA, the anticodon

latches to the codon

on the mRNA

Protein Formation

• The ‘code’ on mRNA determines the sequence of protein assembly

rRNA

• Ribosomes are made of proteins and rRNA, the tRNA and mRNA come to it and assemble the proteins

• rRNA plays a structural role, serving as a support for protein construction, and a functional role

• rRNA consists of two subunits, one 30S in size (16S rRNA and 21 different proteins), one 50S in size (5S and 23S rRNA and 34 different proteins). The smaller subunit has a binding site for the mRNA. The larger subunit has two binding sites for tRNA.