LECTURE 5 BIOLOGY.doc

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20 Apr 2012
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LECTURE 5 (Chapter 21)
PROKARYOTES
- Prokaryotes play a crucial role in ecosystems, recycling nutrients and
breaking down compounds that no other organism can.
- Many live in very extreme environment.
- Make up tow of the three domains of life: Bacteria and Archaea
- Archaea share some cellular features with eukaryotes and some with
bacteria
- Many of the Archaea live under very extreme conditions that no other
organism can, including bacteria.
PROKARYOTES STRCTURE AND FUNCTION
- prokaryotes are the smallest organisms in the world
- despite the size, they dominate life on Earth, they colonize every niche
on Earth that support life
- Prokaryotic cells appear simple in structure compared with Eukaryotic
cells: 3 cell shapes are common among prokaryotes: SPIRAL (spirilla),
SPHERICAL (coccoid), and CYLINDRICAL (bacilli).
- Have no cytoplasmic organelles equivalent to the mitochondria,
endoplasmic reticulum, or Golgi complex of eukaryotic cell.
INTERNAL STRUCTURE
- The genome of most prokaryotes consists of a single, circular DNA
molecule and contains small circles of DNA called PLASMID.
- Plasmids contain genes for beneficial functions such as antibiotic
resistance, they replicate independently of the cell’s chromosomes and
can be transferred from one cell to another. (horizontal transfer)
- Horizontal transfer allows antibiotic resistance and other traits to spread
very quickly in bacterial population.
- Like Eukaryotic cell, Prokaryotes contain ribosomes
- Bacterial ribosomes are smaller than eukaryotic ribosome but carry out
protein synthesis like those of eukaryotes.
- Archaea ribosomes are like bacteria’s ribosomes in size but different in
structure. Protein synthesis in Archaea is a combination of bacterial and
eukaryotic process.
PROKARYOTIC CELL WALLS
- Most prokaryotes have a cell wall that lies outside their plasma
membrane.
- Primary component of bacterial cell walls is PEPTIDOGLYCAN, a polymer
of sugars and amino acids in a linear chain form.
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