Proteins & Polymers (Exam 4 Essay Questions) - Chemistry

Elasticity 

The ability of a material/object to return to intro original shape when an applied force (such as a stretch) is removed. 

when a force is applied, the chain uncoils, causing the covalent bonds to bend and twist, when the force is removed it recoils

What is required for a polymer to have elasticity?

elastic polymers must have long, flexible chains, and covalent cross links

What is a cross-link? What does a cross-link do?

a small molecule binding two different polymer chains 

cross-link makes a material more solid and rigid by restricting the movement/ability for the polymers to slide past each other

What does an amino acid consist of?

amine, carboxylic acid, and R (side) group

Are amino acids polar or nonpolar?

VERY polar (can vary in hydrophilic or hydrophobic)

How do we determine if an amino acid is hydrophobic or hydrophilic?

by looking at its R-group

Levels of protein structures

primary, secondary, tertiary, quaternary

Primary Structure

linear, covalent sequences of amino acids, polyamide forms, and hydrophilic and hydrophobic categorization.

Secondary Structure

regular, repeating structure held together by H-bonds formed by a backbone of a carbonyl, oxygen, and hydrogen bonded to the nitrogen of an amide group

a-helix (secondary structure)

spiral-like

• the amino acids are not reacting w/ the amino acids right next to it (abt 4 aa away)

• r-groups  point out of the helix (R-groups tend to be bigger)

B-sheet (secondary structure)

pleated sheet (long amino acids)

• every other r-group is pointing out (above/below backbone)

• antiparllel (stronger b/c of hairpin turns)

• even further distance of amino acids interacting with each other

Tertiary Structure

Folding of the entire portein in it’s secondary structure held together by intramolecular forces b/w R-groups 

• hydrophobic effect for water soluble proteins on the interior

• ion-ion/salt bridge, ion-dipole, and HB on the exterior

• creates pockets that provide binding sites 

• will not have 4 structure

Quaternary structure

when two or more polypeptides in their tertiary structures are held together. (separate polypeptides = subunits of the whole protein)

• hydrophobic effect effect holds the protein together if it’s a water soluble protein (stabilizing)

• ion-ion, salt bridge, ion-dipole, HB it its a lipid soluble protein

• some do not have 4 structure

Hydrophobic effect

the amount of added energy required for a hydrophobic region to expose itself to a hydrophilic environment; important in water soluble proteins

• LDF important because when placed in an aqueous environment, the hydrophobic regions are further stabilized by the hydrophobic effect 

How can heat cause denaturation?

the addition of energy overcomes intramolecular forces in the 3 and 4 structure. Protein will unfold (loss of shape = loss of function) and the hydrophobic regions will be exposed and stick to each other, leading to coagulation and solidification

How can a change in pH cause denaturation?

changing the pH changes the charge of the side groups because of a gain or loss of H+. This changes the intramolecular forces, causing a change in shape

During which type of folding is when hydrophobic/hydrophilic categorization matters?

Secondary structure

Why do we categorize by hydrophobic or hydrophilic?

B/c during secondary structure, the polymer forms in such a way that the R-groups face out and the backbone is hidden

What type of compound is the most common monomer unit for addition polymers?

Alkene: the pi bond that reacts in the polymerization reaction

Are proteins condensation or addition polymers?

Condensation polymers b/c they lose a water molecule with each polymerization reaction

What is crystallinity?

Molecules ability to form in a structural form/arrangement among the individual polymer molecules

Physical properties of highly branched polymers

weaker IMF (cannot pack closely together), and have difficulty forming solids b/c branches get in the way, less dense, more flexible

Phyical properties of linear branched polymers

rigid, stronger IMF (can pack closely together), more dense, and crystalline

How does heat denature a protein?

heat is the addition of energy until there is enough to overcome the intramolecular forces holding 2, 3, and 4 structure (never 1 structure)

-loss of shape causes loss of function

-unfolding exposes hydrophobic regions which will then stick to each other causing coagulation and solidfiication

How does Mechanical Agitation denature protiens?

The addition of energy until there is enough to overcome intramolecular forces holding 3 and 4 structures

-loss of shape causes loss of function

-unfolding exposes hydrophobic regions which will then stick to each other causing coagulation and solidification.

How do hygroscopic molecules denature a protein?

are molecules that make very strong IMF with water (salts, urea, small alcohols, etc)

-denatures protein by pulling away water from the protein, weakening hydrophobic effect

-loss of shape causes loss of function

-unfolding exposes hydrophobic regions that will then stick together, causing coagulation and solidification

-affects 3 and 4 structure

How does pH denature a protein?

-changing ph changes charges of side chains by changing proton [H+] concentration

-changes strength of intramolecular force and where intramolecular force occurs

-loss of shape causes loss of function

-proteins unfolding at ambient temperatures exposing hydrophic regions that will stick together and cause coagulation and solidification. 

-affects 3 and 4 structure

How does detergent/soap denature a protein?

the soaps hydrophobic tails insert themselves into the middle of the protein, which changes the intramolecular forces

-loss of shape causes loss of function

-affects 3 and 4 structure

-proteins unfolding exposes hydrophobc regions which will then stick together causing coagulation and solidification

addition polymer

polymer constructed without the loss of any mass form the monomer (will always have a double bond and.a 2-carbon backbone)

Condensation polymer

polymer constructed with the loss of small molecule (will have a carbonyl-containing and a non-carbonyl containing functional group)

• must have same atomic-make up: the same atoms in repeating unit of the monomer

Explain what happens when you stretch a plastic garbage bag until it tears.

You are breaking intermolecular forces (LDF) as you stretch the bag. It was each because the polymers were less dense, less rigid, highly branched, and flexible, allowing the polymers to easily slide past each other. As you continue to stretch it, you create less and less overlap between the polymers.

Explain what happens when slime “drips”

The hydrogen bonds in slime are just weak enough so that gravity can break those intermolecular forces, allowing polymers to slide past each other. As gravity acts, there is less and less overlap of polymers.

Explain why some newspaper strips will tear in a straight path but if you cut the paper strips at 90 degrees, it will be more difficult to tear it straight.

Newspaper behaves this way because of the organization of the polymers. When tearing the paper, you are breaking the intermolecular forces (HB) and so tearing with he polymer organization occurs easily compared to tearing against the organization, which causes it to veer off towards the edges because it much work around the big polymers.

Explain why nylon had a high tensil strength yet could easily be frayed.

Nylon fibers are linked with hydrogen bonds. Breaking the fibers along the axis is much more difficult because you have to break multiple hydrogen bonds at once where as at the ends, you can break individual hydrogen bonds at a time, causing fraying.

What is the cross link was used in Slime? Silly putty? Latex?

slime - hydrogen bonds cross-link with guar gum and borax

silly putty - ion dipole cross-link with glue and borax

latex - covalent cross-link with O2

what were the physical properties of Slime? Silly putty? Latex?

slime - not moldable, not elastic

silly putty - more solid, moldable, a little elastic

latex - not moldable after cross links fromed, elastic, very solid/rigid

Explain why adding salt to water doesn’t cause a noticeable change

Small is a small molecule that can easily zip past other molecules, meaning the water will not thicken with salt, so it acts like a liquid.

Explain why adding guar gum to water causes the solution to be viscious

Guar gum is a larger molecule that requires more energy to move because you will have to move whole polymers, thickening the solution

Explain why adding diaper polymer to water causes the solution to become a gel. Why does the polymer “absorb” so much water?

Diaper polymer is a larger molecule that creates a gel-like solution because the ions of the diaper polymer bind up more water together, so the polymers can’t move past each other.

Explain why adding borax to glue (silly putty) solution caues it to somewhat solidify

Borax was a cross-linking agent which does ion-dipole binding, a higher IMF that restricts polymers from sliding past each other

Explain why adding salt to the diaper polmer/gel causes it to become watery

Salt draws water molecules out of the polymer, causing the polymers to stick together and drop out of solution. Therefore, all that is left is water surrounding salt, so the gel returns to its liquid state.