Polymers and Proteins

What are polymers?

Very large molecules with a carbone backbone

What are monomers?

Small molecules that combine to form polymers

Describe the polymerisation of addition polymers

• Monomers added together

• All atoms are used to form the polymer

• Alkenes undergo polymerisation

• The double bond is broken

  • New single C-C bonds are formed

• Involves use of a catalyst

• No small molecules/atoms eliminated

What is the general reaction for addition polymers?

(catalyst)

nR-C=C-R’ —> -(-C(R)-C(R’)-)n-

Describe the polymerisation of condensation polymers

• Reaction between monomers with two reactive groups (ie: diols, carboxylic acids, amines)

• Elimination of smaller molecules (H2O)

• 2 reactive functional groups remain at either end of growing chain

• Carboxylic acids + alcohols form polyesters

Describe the structure of polyethene

• Made of chains that vary in length and molecular mass

• Held together by dispersion forces

• Disp. forces stronger in regions where chains are arranged in orderly fashion

What is the equation for polyethene?

(catalyst)

nCH2=CH2 —> (-CH2-CH2-)n

What type of polymer is polyethene?

Addition polymer

What are the two types of polyethene?

Low Density Polyethene (LDPE)

High Density Polyethene (HDPE)

What is the structure of LDPE? How is it formed?

• Produced at high temperatures (200-300°C) and high pressures (1000-3000atm)

• Significant amount of branching (small side chains)

What are the properties of LDPE?

The significant amount of side chains:

• Reduce strength of dispersion forces

• Creates lots of space in the product

• Low MP, low density, soft and flexible

• Structure is amorphous (non-crystalline)

• Eg: cling wrap, flexible plastic bottles, plastic toys

What is the structure of HDPE? How does it form?

• Produced at lower temperatures (60°C) and low pressure (1-4atm)

• Unbranched chains allow close approach of polymer chains

• Held together by strong dispersion forces

What are the properties of HDPE?

• High mechanical strength

• Higher density

• Higher MP

• Eg: chopping boards, water pipes, buckets

What is a polyester?

A polymer with many ester links within the chain

What are the two configurations of polyester monomers?

• Single monomer: hydroxyl group at one end, carboxyl group at other

• Two different monomers: one has a diol, other is a dicarboxylic acid

Name this monomer unit

Benzene-1,4-dioic acid

What is the general formula for formation of polymers?

A + B —> (A+B)n + 2nH2O

What is PET?

Polyethylene terephthalate

What are the properties of PET?

• Permanent net dipole exists around each ester link

• IMF: dipole-dipole and dispersion forces

• Form crystalline structures when cool slowly, giving increased strength

What is a polyamide?

A condensation polymer where monomer units connect via amide linkages

What are the two configurations of polyamide monomers?

• Two different monomers - one is a diamine, one is a dicarboxylic acid

• Single monomer - amine group at one end, carboxylic acid at other end

What is needed for a protein to be considered a protein molecule?

Has 50+ amino acids

What is the primary structure of a protein?

Specific amino acid sequence

• Always listed from -NH2 end of molecule

• Determines how it will fold/curl in on itself

• Conformation governs how protein interacts with other molecules, determining its function

• Alteration in sequence affects conformation and ability to function correctly

What is the secondary structure of a protein?

Regular repeating structures

• Regular arrangement of various sections of the protein

• Structures include: Alpha-helix (coiled section), beta-pleated sheets (corrugated structure)

• Stabilised by C=O on one part of the chain and N-H group on another

Describe the structure of alpha-helix arrangement

Occur between lone pair of e- on O of C=O and H on N-H located four peptide links apart

Describe the structure of beta-pleated sheet arrangement

• Occur where alpha amino acid residues have smaller side chains

• Sections of protein chain can fit closely alongside each other

What is the tertiary structure of a protein?

Overall three-dimensional structure of a protein

• Can form several structures:

  • Long, narrow: fibrous proteins such as keratin

  • Spherical, globular: enzymes

• Caused by interactions between residue side chains

What are α-amino acids?

Contain both (-NH2) and (-COOH) groups

Form the backbone of proteins

What are the names of molecules that are formed from amino acid links?

Peptides

Can be dipeptides, tripeptides, polypeptides and proteins

What classifies a non-polar alpha amino acid?

Only C and H on side groups

• Ie: Ala, Gly, Ile, Leu, Phe, Val

What classifies a polar alpha amino acid?

Can either:

Form ions (ionic bonds in addition to all 3 IMF’s)

• Has extra -NH2, -COOH

Not form ions

• Has extra -OH, -C(=O)-NH2, S

What are the properties of alpha-amino acids?

• Soluble in water

• Solids at room temp (high MP)

• White, crystalline solids

What is a zwitterion?

A particle that has a net neutral charge, but has both a +ve and -ve charge on it

• Ie: N+H3-CH2-C(=O)-O-