Proteins

Question 1

What are proteins made from

Answer 1

Monomers of proteins are amino acids, a dipeptide is formed when two amino acids join together. A polypeptide is formed when more than two amino acids join together. Proteins are made up of one or more polypeptides.

Question 2

Amino acid structure

Answer 2

Have the same general structure - a carboxyl group (-COOH), an amine, or amino group(-NH2) and an R group( variable group) attached to carbon atom. R groups generally contain carbon - only exception is glycine = just one hydrogen atom.
All living things share a bank of only 20 amino acids. Only difference is R group.

Question 3

Dipeptide and polypeptide formation

Answer 3

Amino acids are linked together by condensation reactions to form dipeptide and polypeptides. A molecule of water is release during reaction. Bonds formed between amino acids are called peptide bonds. The reverse reaction (hydrolysis) happens when dipeptides and polypeptides break down. OH from carboxyl group and H from amine group form a water molecule.

Question 4

Primary structure - proteins

Answer 4

Primary structure - sequence of amino acids in the polypeptide chain

Question 5

Secondary structure proteins

Answer 5

Secondary structure- polypeptide chain doesn’t remain flat and straight, hydrogen bonds form between amino acids in the chain, this makes it automatically coil into an alpha helix or fold into a beta pleated sheet. High temperatures and altered pH can split hydrogen bonds

Question 6

Tertiary structure

Answer 6

Tertiary structure - the coiled or folded chain of amino acids is often coiled or folded further. More bonds form between different parts of the polypeptide chain, including hydrogen bonds and ionic bonds. Altered pH can split ionic bonds. Disulfide bridges also form, whenever two molecules of the amino acid cysteine come close together- the sulfur atom in one cysteine bonds to the other sulfur atom in the other. Disulfide bridges are really strong, can be split using reducing agents. For proteins made from a singular polypeptide chain, the tertiary structure forms their final 3D structure.

Question 7

Quaternary structure- proteins

Answer 7

Made of several different polypeptide chains held together by bonds. Quaternary structure is way polypeptide chains are assembled together. For proteins made of more than one polypeptide chains, the quaternary structure is the proteins final 3D structure. Globular proteins form a spherical mass with a specific 3D shape. Fibrous proteins form a triple helix of polypeptide chains, the chains are held together by hydrogen bonds.

Question 8

Protein shape and function

Answer 8

Proteins shape determines its function. Eg haemoglobin is a compact soluble protein which makes it easy to transport. Makes it great for carrying oxygen around body.

Question 9

Examples of proteins shapes and functions

Answer 9

Enzymes - roughly spherical in shape due to tight folding of the polypeptide chains, soluble and often have roles in metabolism
Antibodies - involved in immune response and are found in blood, made up of two light polypeptide chains and two heavy polypeptide chains bonded together. Amino acids in antibody regions vary greatly
Transport proteins - eg channel proteins are present in cell membranes and contain hydrophobic and hydrophilic amino acids which cause protein to fold up and form a channel. Transport molecules and ions across membranes
Structural proteins - physically strong consist of long polypeptide chains lying parallel to each other with cross-links between them. Structural proteins include keratin and collagen. Collagen has three polypeptide chains tightly coiled together held by hydrogen bonds which makes it strong, supportive tissue in animals.

Question 10

the biuret test for proteins

Answer 10

the test solution needs to be alkaline, so first you add a few drops of sodium hydroxide solution
then add some copper(II) sulphate solution. if the protein is present, the solution turns purple, if there’s no protein the solution will stay blue.

Question 11

Fibrous proteins and globular proteins

Answer 11

Fibrous proteins are collagen silk keratin and chitin
- tend to be insoluble and strong
- have a structural role for support and protection
Globular proteins
Fold into a ball or globule like myoglobin and haemoglobin
-tend to be soluble
-most common are enzymes which control reactions in living cells (globular shale gas and active site)