Membrane and metabolism

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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

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H gradients across the membrane

• Proton Motive Force (PMF) is what drives ATP
  production in the cell
• (DpH1.4 0.14 V 23 KJ/mol)

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Figure 5.21
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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

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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

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• 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

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Gram cell wall
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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

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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

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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

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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

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Cell structure
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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 mm long in bacteria, while the
  organism is on the order of 1 mm long special
  enzymes called gyrases help coil it into a
  compact form

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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 mRNA mRNA then
translated into proteins.
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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.

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

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• Protein Formation
• The code on mRNA determines the sequence of
  protein assembly

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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.

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