site on bacterial chromosome actually contains 2 separate genes GroEL GroES

Site on bacterial chromosome actually contains 2

This preview shows page 37 - 39 out of 40 pages.

site on bacterial chromosome actually contains 2 separate genes, GroEL & GroES that encode 2 separate proteins, GroEL & GroES 1. Under EM, purified GroEL protein appeared as cylindrical assembly consisting of 2 disks 2. Each disk was composed of 7 subunits arranged symmetrically around central axis D. Several years later – study on pea plants hinted at existence of similar assembly-promoting protein in plant chloroplasts 1. Rubisco is large chloroplast protein that catalyzes reaction in which CO 2 molecules taken up from atmosphere are covalently linked to organic molecules during photosynthesis 2. Rubisco comprises 16 subunits: 8 small subunits (molecular mass of 14,000 daltons) & 8 large subunits (55,000 daltons) 61
Image of page 37
3. Large Rubisco subunits, synthesized in chloroplast, are not present in independent state, but associated with huge protein assembly consisting of identical 60,000 dalton (60 kDa) subunits 4. Researchers considered possibility that complex formed by large Rubisco subunit & the 60-kDa- polypeptide was an intermediate in the assembly of a complete Rubisco molecule E. Separate study on mammalian cells – revealed existence of proteins that appeared to assist assembly of multisubunit proteins 1. Like Rubisco, antibody molecules consist of a complex of 2 different types of subunits, smaller light chains & larger heavy chains 2. Like large Rubisco subunits, heavy chains of antibody complex become associated with another protein not found in the final complex 3. This protein, which associates with newly synthesized heavy chains, but not with heavy chains that are already bound to light chains, was named binding protein (BiP) 4. BiP was subsequently found to have a molecular mass of 70,000 daltons (70 kDa) F. 1986 – 2 lines of investigation (heat-shock response & proteins that promote protein assembly) came together 1. Shown that very prominent heat shock response protein, heat-shock protein 70 (hsp70) due to its molecular mass, was identical to BiP, the protein implicated in antibody molecule assembly III. Even before heat-shock response was known, protein structure was known to be sensitive to temperature A. A small rise in temperature could cause delicate proteins to begin to unfold 1. Unfolding exposes hydrophobic residues previously buried in protein core 2. Hydrophobic residue patches on protein surfaces attract each other like fat droplets 3. Thus, when cell is heat shocked, soluble proteins are denatured & form aggregates B. 1985 report showed that after temperature elevation, newly synthesized hsp70 molecules enter cell nucleus & bind to nuclear protein aggregates 1. They then act like molecular crowbars to promote disaggregation 2. Due to their role in assisting protein assembly by preventing undesirable interactions, hsp70 & related proteins were named molecular chaperones IV. Soon demonstrated that bacterial heat-shock protein GroEL & Rubisco assembly proteins in plants are homologous proteins A. The 2 proteins share same amino acids at nearly half of >500 residues in their respective molecules 1.
Image of page 38
Image of page 39

You've reached the end of your free preview.

Want to read all 40 pages?

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Stuck? We have tutors online 24/7 who can help you get unstuck.
A+ icon
Ask Expert Tutors You can ask You can ask You can ask (will expire )
Answers in as fast as 15 minutes