Lecture notes 9


I. Cell Wall and Membrane Protein
a. Integral Membrane Proteins
i. Proteins that span width of, or are fully embedded in, cell membrane
ii. Transmembrane pumps and pores: made of integral membrane proteins:
1. Pump chemicals into or out of the cell
b. Peripheral membrane proteins
i. Only attach to part of the cell membrane, or are only partially embedded of the cell wall

Lab experiments this week:
• E. Coli bacteria are killed by a virus (T4 bacteriophage)
o Infection of E. Coli with T4 bacteriophage:
• Gram-Negative bacteria (E. Coli)
• E. Coli has a lot of proteins - embedded in the cell wall, outer membrane, and plasma membrane - allowing things to go in and out of the cell
• 1st Step of infection: T4 adheres to a protein on the outer surface of the bacteria
• Enzymes needed for DNA replication
• Ribosomes
• 2nd Step of infection: Pokes a hole all the way through all the layers of the cell envelope of our E. Coli bacterium. Through that hole it’s going to inject it’s own DNA
• 3rd Step: The DNA belonging to the T4 is copied by bacterium enzymes and translated by the bacterial ribosomes
• This will give us many many many copies of T4 inside of the E. Coli
• 4th Step: A direct consequence of all of the coping of T4 bacteriophage inside of the E. Coli causes the death of E. Coli (blows up) releasing all of the virus particles into the world to infect more E. Coli
• Can the E. Coli become resistant to the T4 bacteriophage?
• Assuming they do become resistant: Why is it that they do?
o Is it just that some E. Coli are randomly “born” resistant to T4?

II. Bacterial adhesion to surfaces
a. “Adhesins” are usually integral or peripheral membrane proteins
i. Cell wall/membrane proteins used to stick to surfaces, typically peripheral membrane proteins
ii. Ex. Adhesins on ends of Pili
b. Pili
i. Retractable extensions from bacterial cell envelope
1. One of ways bacteria can move itself
ii. Attachment to surfaces and motility
1. Extend and Retract (interpretive dance in class)
iii. Use in conjugation (bacterial sex) by some species
1. Pili extensions touching other bacteria
2. Copy what we want to share and send across the bridge (extension) to the other bacteria
3. Bacteria detach and move on

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