Symmetry II: Helical Symmetry Flashcards
Why is helical symmetry important? What does it do? Give examples.
Important for:
Proteins that place structural roles : tasks like cell rigidity, cell-cell adhesion, and cell mobility.
Ex. Actin in microfilaments and muscle.
Pilins in pili (fimbriae) on the surface of bacteria.
What distinguishes point symmetry from helical symmetry?
Helical symmetry leads to large unbounded complex unlike point symmetry. Meaning you can have an arbitrary number of molecules.
What defines and differs a Helix from an alpha-helix? (Hint functional difference)
Both have same shape and symmetry along the helical axis, but building blocks of an alpha helix are single amino acid residues, while a plain helix is made up of entire protein molecules and the interactions between subunits are formed by non-bonded interactions that allow for more dynamic formation and breaking down of these structures.
Alpha helix residues are covalently bonded together to form a chain.
What are microfilaments made of?
Actin polymers
Why are actin microfilaments important? What do they do?
Incredibly important helical assembly that comprises the cytoskeleton.
The network of fibers that give eukaryotic cells their shape .
They are flexible and relatively strong fibers and very versatile.
Important in cell division, cell movement, maintaining cell shape, and making changes to cell shape .
Define what a macrophage is?
Oh white blood cell crucial for the defense against pathogenic bacteria.
Explain how actin is crucial for macrophages.
The rate of Actin polymerization is greatest at the leading edge. This means they are changing the shape of the cell which allows these macrophages to move towards pathogens to fight.
What is the building block of actin fibers?
This building block has:
How many domains does it have?
How many amino acid residence does it have?
What are the two(kinda 3) things it binds to?
What is its most important property?
Globular Actin (G-Actin)
This building block has:
4 domains
~375 amino acid residues
Binds to ATP (can hydrolyze), and Ca++ [ or Mg++]
Its most important property is to be able to assemble/disassemble into fibers called microfilaments in non-muscle cells .
When G-Actin becomes a part of a fiber what is it?
Now apart of a microfilaments- F Actin. (Diameter of 70 Å)
How are actin microfilaments formed?
By the head-to-tail association of many copies of globular actin (g actin)
What form/shape are microfilaments? What’s the pitch? (Distance it takes for a complete turn of a molecule.)
Two strands of actin linked together intertwined with each other to form a RIGHT handed helical formation.
Pitch: 715 Å long, comprises 13 subunits long.
Means: about 55 Å per subunit.
Is f-actin(microfilaments) a polar molecule? If so what does that mean?
Yes it is. That means both ends are different.
For microfilaments specifically: present different interfaces and there’s a faster growing end and a slower growing end.
Besides icosahedral symmetry, what other symmetry do viruses use to store their genetics?
Helical symmetry.
Many proteins have partial symmetry and many proteins consist of different subunits, give two examples. Only AB5 toxins.
In an AB5 toxin, what symmetry does the B-subunits take?
C5 Cyclic Symmetry.
Where does the A-subunit bind in this 5B subunit?
In the middle.
Define what a nucleosome is.
A protien + DNA assembly.
The building blocks of chromosomes .
Define what histones are. And there structure.
The protein that organizes DNA. (The proteins in nucleosomes)
Histone is comprised of 4 proteins, 2 copies of each, for a total of 8 chains. (8 proteins total)
