BIOL 2051 Chapter : Chapter 3 Outline
Chapter 3 Cell Structure and Function
Read 3.3-3.7
Basic cellular structures:
1. Cytoplasm (water, electrolytes, protein)
2. Cytoplasmic membrane
3. Genetic info- nucleus (eukaryotic) or nucleoid region (prokaryotes- not membrane
bound)
4. Ribosomes- protein synthesis
5. Cell wall (optional)- found in plants & most prokaryotes; not in animals
Two types of cells:
1. Prokaryote
• Simpler internal structure
• Lack membrane enclosed organelles
• Bacteria & Archaea
2. Eukaryote
• Larger & more complex
• Membrane enclosed organelles (nucleus, chloroplast, mitochondria,
etc)
• Algae, fungi, protozoa, plants, animals
Viruses
• Non- cellular (not eukaryotic or prokaryotic)
• Reproduce only inside a host cell
• Lack many characteristics of living things
• Ex. HIV virus, Rhinoviruses (colds)
The Bacterial Cell
• Cytoplasm surrounded by envelope
o Cytoplasm contains DNA in nucleoid
• Envelope has lipid membrane boundary
o Plus structural cell wall
Bacterial cell structures
• cytoplasmic membrane- “fluid” selective permeability barrier made of
phospholipids and proteins that form a bilayer with hydrophilic (water liking)
exteriors and hydrophobic (doesn’t dissolve in water)interior
o CM is a phospholipid bilayer; each layer is a “leaflet”
o Phospholipid-
• Glycerol with ester links to 2 fatty acids
• Hydrophilic (dissolve in water) group faces cytoplasm or periplasm
• Hydrophobic (don’t dissolve in water) fatty acids line up inside
membrane
o Attraction of nonpolar fatty acid portions of one phospholipid layer for other
layer result in
selective permeability of cell membrane.
o Integral membrane proteins- span membrane
o Peripheral membrane proteins- are bound to surface of membrane
o Cytoplasmic Membrane: Functions
1. Permeability barrier:
a. Prevents leakage of cytoplasmic metabolites into environment.
b. Transport of substances (nutrients & waste products) into & out
of cell
• Due to hydrophilic outside of membrane, only water &
small uncharged particles can freely diffuse through
membrane
• Other compounds must be transported (active-use ATP
or passive-no energy required) by specific membrane
proteins
2. Structural support- site of many proteins involved in transport,
bioenergetics & chemotaxis
3. Energy conservation- site of generation & use of the proton
motive force
a. Respiration
• Eukaryotes have mitochondria to generate energy by
respiration
• In prokaryotes, respiration occurs in cytoplasmic
membrane
b. Photosynthesis
• Photosynthetic eukaryotes have chloroplasts to carry out
photosynthesis
• Photosynthetic prokaryotes carry out photosynthesis in
cytoplasmic membrane
o To reinforce the membrane:
- Eukaryotes have sterols such as cholesterol
- Bacteria have hopanoids
- Archaea have terpenoids which increase stability at high temp & low
pH
• The Bacterial Cell Wall (sacculus)
o made of peptidoglycan (murein)- a porous cage like structure
▪ sugar chains wrapped in circles around cell
• “glyco” = sweet
▪ Sugar chains linked to each other by short polymers of amino acids
• amino acid = peptide
o Structure of Peptidoglycan
▪ Backbone made of 2 sugars
▪ N-acetylglucosomine (NAG) and N-acetylemuramic (NAM)
▪ Sugars are arranged in
• M-G-M-G-M-G-M-G-M-G
▪ Chains held together by cross links (short chains of amino acids)
between N-acetylmuramic acids.
▪ Crosslinks differ among species
▪ Gram negative bacteria have unusual amino acid meso-
diaminopimelate (mDAP) in crosslink
o Functions- provides rigidity and shape to cell and prevents it from exploding
due to high pressure inside cell.
o Peptidoglycan as a target for antibiotics:
▪ Since peptidoglycan is unique to bacteria, it’s a great target for
antibiotics
▪ Example- penicillin inhibits transpeptidase which crosslinks the
peptides
▪ However, widespread use of antibiotics selects for resistant strain
▪ Example- Many organisms produce beta-lactamase which cleaves the
Lactam ring of penicillium, inactivating the penicillin
o Archaea
▪ lack peptidoglycan
▪ cell walls made of other polysaccharides
▪ Some Archaea cell walls contain pseudopeptidoglycan
▪ Other Archaea have a paracrystalline surface layer (s-layer) wall made
of protein
Document Summary
Basic cellular structures: cytoplasm (water, electrolytes, protein, cytoplasmic membrane, genetic info- nucleus (eukaryotic) or nucleoid region (prokaryotes- not membrane bound, ribosomes- protein synthesis, cell wall (optional)- found in plants & most prokaryotes; not in animals. Two types of cells: prokaryote, simpler internal structure, lack membrane enclosed organelles, bacteria & archaea, eukaryote, larger & more complex, membrane enclosed organelles (nucleus, chloroplast, mitochondria, etc, algae, fungi, protozoa, plants, animals. Viruses: non- cellular (not eukaryotic or prokaryotic, reproduce only inside a host cell, lack many characteristics of living things, ex. The bacterial cell: cytoplasm surrounded by envelope, cytoplasm contains dna in nucleoid, envelope has lipid membrane boundary, plus structural cell wall. The bacterial nucleoid: single loop of double stranded dna, ~4x106 bp (base pairs) in many bacteria, compacted via supercoiling, attached to cell envelope, no membrane separates dna from cytoplasm, replicates once for each cell division. Bacterial growth: growth of most microorganisms occurs by binary fission.
