A5. Proteins

Question 1

What are proteins made from?

What are the monomers of proteins?
What is a dipeptide?
What is a polypeptide?
Proteins are made up of…?

Answer 1

The 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

What is the general structure?

Figure 2: The general structure of an amino acid

Answer 2

Amino acids have the same general structure-a carboxyl group (-COOH), an amine or amino group (-NH) and an R group (also known as a variable side group) attached to a carbon atom.

Question 3

Dipeptide and polypeptide formation (3 things)

Figure 3: Dipeptide formation.

Answer 3

• Amino acids join to make dipeptide/polypeptides in a
• Condensation reaction
• With peptide bonds

Question 4

Primary structure (1 thing)

Answer 4

Primary structure
This is the sequence of amino acids in the polypeptide chain.

Question 5

Secondary structure (2 things)

Answer 5

• Hydrogen bonds form between the amino acids in the chain.
• making it coil into an alpha helix or fold into a beta pleated sheet

Question 6

Tertiary structure (3 things)

Answer 6

• The coiled or folded chain of amino acids is often coiled and folded further.
• Ionic and hydrogen bonds form between different parts of the polypeptide chain
• Disulfide bridges also form whenever two molecules of the amino acid cysteine come close together.

Question 7

Quaternary structure (1 thing)

Answer 7

more than one polypeptide chain are assembled together

Question 8

Tip: ____________ bridges are covalent bonds between sulfur atoms. They’re a lot __________than the ionic and hydrogen bonds in proteins.

Answer 8

Tip: Disulfide bridges are covalent bonds between sulfur atoms. They’re a lot stronger than the ionic and hydrogen bonds in proteins.

Question 9

Examples of proteins (4 types with large description)

Answer 9

Enzymes - They’re usually roughly spherical in shape due to the tight folding of the polypeptide chains. They’re soluble and often have roles in metabolism, eg, some enzymes break down large food molecules (digestive enzymes) and other enzymes help to synthesise (make) large molecules.

Antibodies - Antibodies are involved in the immune response and are found in the blood. They’re made up of two light (short) polypeptide chains and two heavy (long) polypeptide chains bonded together. Antibodies have variable regions - the amino acid sequences in these regions vary greatly.

Transport proteins - Eg. channel proteins are present in cell membranes. Channel proteins contain hydrophobic (water hating) and hydrophilic (water loving) amino acids, which cause the protein to fold up and form a channel. These proteins transport molecules and ions across membranes.

Structural proteins - Structural proteins are physically strong. They consist of long polypeptide chains lying parallel to each other with cross-links between them. Structural proteins include keratin (found in hair and nails) and collagen (found in connective tissue). Collagen has three polypeptide chains tightly coiled together, which makes it strong. This makes it a great supportive tissue in animals.

Question 10

Test for proteins

Answer 10

1) Add sodium hydroxide and copper(II) sulfate solution (buiret reagent)
2) If protein present = turn lilac