Mutations and Cytosol Function in Cells

Bacterial Cell Structure and Function

• Bacteria are minute, single-celled organisms with diverse shapes (cocci, bacilli, spirals).
• Bacteria range in size from 0.2 to 2.0 µm in diameter and 2 to 8 µm in length.
• Essential structures present in all bacteria:
  • Cytoplasm containing ribosomes.
  • Cytoplasmic membrane (plasma membrane).
  • Rigid cell wall (except in mycoplasmas).
  • Nucleoid (circular chromosome).
• Structures present in some bacteria (variable features):
  • Flagella.
  • Spores.
  • Inclusion granules.
  • Fimbriae.
  • Sex pili.
  • Glycocalyx (capsule or slime layer).

Glycocalyx

• A sticky, sugary layer (polysaccharides/polypeptides) surrounding the bacteria.
• Can be firmly attached (capsule) or loosely attached (slime layer).
• Aids in adherence to surfaces, crucial in biofilms.
• Important for pathogenicity.

Cell Wall

• The outermost layer, common to all bacteria except Mycoplasma.
• Rigid structure made of peptidoglycan.
• Provides shape and protection for the cell.
• Gram-positive bacteria have a thicker peptidoglycan layer than gram-negative bacteria; also have teichoic acid.

Cytoplasmic Membrane

• Encloses the cytoplasm and organelles.
• Controls passage of molecules into and out of the cell (selective permeability barrier).
• Site of enzyme and toxin secretion.

Flagella

• Long, whip-like appendages that allow bacteria to move.
• Composed of protein and powered by a motor within the cell membrane.
• Various arrangements (monotrichous, lophotrichous, amphitrichous, peritrichous) depending on the position and number on the bacterium.

Fimbriae and Pili

• Short, hair-like appendages found on the bacterial surface.
• Used for attachment to surfaces, host cells, and other bacteria.
• Sex pili are longer and used for DNA transfer (conjugation).

Ribosomes

• Sites of protein synthesis.
• 70S in bacteria (50S and 30S subunits).
• Different from eukaryotic ribosomes (80S).
• Target of some antibiotics.

Mesosomes

• Infoldings of the cytoplasmic membrane.
• Involved in cell division.

Cytoplasm

• Gel-like substance inside the cell, containing ions, molecules, and macromolecules.
• Contains machinery for cell maintenance and reproduction.

Granules

• Storage structures within the cytoplasm, used for nutrient storage.

Nucleoid (Bacterial Chromosome)

• Single, circular DNA molecule.
• Contains the genetic material responsible for reproduction, metabolism, and other cell functions.

Nucleic Acids (DNA and RNA)

• Two main types: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).
• DNA: double helix, deoxyribose sugar, specific base pairing (A-T, G-C).
• RNA: single helix, ribose sugar, uracil instead of thymine.
• Different types of RNA: mRNA (messenger), tRNA (transfer), rRNA (ribosomal).

Mutations

• Permanent change in DNA sequence.
• Can affect the phenotype (observable characteristics).
• Types: substitution, insertion, deletion.
• Can be spontaneous or induced by chemical or environmental agents.

Bacterial Genetic Recombination

• Exchange of genetic material between bacteria.
• Mechanisms: transformation, transduction, conjugation.

Plasmids

• Extra-chromosomal, circular DNA molecules that replicate independently.
• Can carry genes for antibiotic resistance, toxin production, and other traits.
• Often involved in horizontal gene transfer between bacteria.

Spores

• Dormant survival structures formed by some bacteria.
• Highly resistant to environmental stressors (heat, radiation, chemicals).
• Can germinate into vegetative cells when conditions improve.