Describe the key molecular processes that occur when a cell grows and divides (Section 5.1). - ANS -
Cell division is a complex process requiring several proteins referred to as Fts proteins. Fts proteins
interact to f
...
Describe the key molecular processes that occur when a cell grows and divides (Section 5.1). - ANS -
Cell division is a complex process requiring several proteins referred to as Fts proteins. Fts proteins
interact to form an apparatus called the divisome, the key protein of which is FtsZ. FtsZ shows structural
similarities to the eukaryotic tubulin protein, and its synthesis results in ring formation during cell
elongation before division. Depolymerization of FtsZ occurs as cell constriction begins at the septum.
Min proteins, especially MinE, is involved in directing FtsZ to the cell midpoint.
Describe the role of proteins present at the divisome (Section 5.2). - ANS - Fts proteins interact to form
a division apparatus called the divisome. FtsZ polymerizes in a ring structure in the middle of the cell
and helps coordinate divisome assembly and cell division. ZipA anchors FtsZ to the cytoplasmic
membrane. FtsA also connects FtsZ to the membrane, but it additionally recruits other proteins to the
divisome. FtsI functions in the synthesis of new peptidoglycan. FtsK functions to help partition the
newly synthesized chromosomes into each daughter cell.
In what way do derivatives of the rod-shaped bacterium E. coli carrying mutations that inactivate the
protein MreB look different microscopically from wild-type (unmutated) cells? What is the reason for
this (Section 5.3)? - ANS - The protein MreB is the key shape-determining protein in prokaryotes,
forming an actin-like cytoskeleton. MreB forms spiral-shaped bands just inside the cytoplasmic
membrane and defines the cell's shape. Mutations in E. coli MreB protein would result in a spherical
shape in the mutant. Support for this can be found in the fact that spherical cells, such as
Staphylococcus, lack a gene coding for an MreB-like protein.
Describe how new peptidoglycan subunits are inserted into the growing cell wall. How does the
antibiotic penicillin kill bacterial cells, and why does it kill only growing cells (Section 5.4)? - ANS -
Glycan tetrapeptides are delivered to the outside of the membrane using the hydrophobic molecule
bactoprenol. Autolysins cleave glycosidic bonds in old peptidoglycan so that the new peptidoglycan
subunits can be inserted by a transglycosylase. Transpeptidation adds cross-linking peptide bonds to add
strength to the peptidoglycan. Penicillin prevents transpeptidation by binding to the transpeptidase
responsible for connecting the interpeptide bridges between adjacent peptidoglycan chains, thus
weakening the cell wall. As autolysins continue to remove old cell wall units and new glycan
tetrapeptide units are laid down, the failure to form interpeptide bridges results in lysis of the cell due to
its internal turgor p
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