Proteins 1.1

Question 1

How many diff. amino acids are there?

Answer 1

20

Question 2

Describe what proteins made up of?

Answer 2

chains of amino acids
-monomer: amino acid
-2 form a dipeptide
-chain of 2 or more amino acids bonded together = polypeptide
-multiple polypeptides form a protein
(if a protein is made up of one type of polypeptide, it has a tertiary final structure)

Question 3

what is the primary structure of a protein?

Answer 3

the amino acid sequence of the polypeptide chain

Question 4

Draw the structure of an amino acid. Give an example.

Answer 4

Question 5

Name an exception to the amino acids.

Answer 5

Glycine is the only only amino acid that dosen’t have carbon in its side group. It’s R group consists of just one hydrogen atom.

Question 6

How does the second structure of a protein form?

Answer 6

Hydrogen bonds form between the amino acids in a polypeptide chain, which allows them to automatically coil into an alpha helix or fold into a beta pleated sheet.

Question 7

Explain how a dipeptide is formed, giving a diagram.

Answer 7

Question 8

Explain what is meant by quarternary structure.

Answer 8

• The quaternary structure of a protein is the way several different polypeptides are arranged together.
• These polypeptides are held together by bonds.
• e.g. insulin, collagen, haemoglobin
• The quarternary structure serves as the final 3D structure of the protein.

Question 9

Describe the general structure of structural proteins.

Answer 9

Structural proteins are made up of long polypeptide chains that lie parallel alongside each other with cross-links between them.

Question 10

Describe how different types of bonds contribute towards the tertiary structure of a protein.

Answer 10

There are three different types of bonds that occur during folding. Hydrogen bonds and ionic bonds form between the different parts of the polypeptide chains. Disulfide bridges also form between sulfur atoms in the R groups of two cysteine amino acids.

Question 11

When is the tertiary structure considered the final 3D structure of a protein?

Answer 11

For proteins made up of a single polypeptide chain, the tertiary structure forms their final 3D structure.

Question 12

Which of the following levels of structure forms haemoglobin’s final 3D structure?
A. primary B. secondary C. tertiary D. quaternary

Answer 12

D. quaternary. As haemoglobin is made up of more than one polypeptide chain, it’s the way that these chains are assembled together which forms the protein’s final 3D structure.

Question 13

Answer 13

Protein A could be a transport protein that transports molecules and ions across cell membranes. These proteins have a mixture of hydrophobic and hydrophilic amino acids in them. This allows the protein to fold up and create a channel.

Question 14

Describe the test for proteins and its results.

Answer 14

Question 15

Wht do you need to remember when testing for proteins?

Answer 15

In order to work correctly, the test solution used for a Biuret test needs to be alkaline. The first student did not add any alkalising agent, such as sodium hydroxide solution, to the sample. This prevented the colour change in the copper(II) sulfate from happening in the presence of protein.

Question 16

What are antibodies?

Answer 16

Antibodies are proteins that bind onto antigens (proteins found on the surface of cells) as part of the immune response. They have variable regions which form their antigen binding sitesand make them complementary to one specific antigen.

Question 17

Explain what makes antibodies specific?

Answer 17

Specificity is dependent on the unique tertiary structure (the different amino acid sequences) of the variable regions.

As amino acids contain unique R groups, different sequences of amino acids will change the way in which the polypeptide chains in the variable regions fold up and form bonds between themselves. This creates the unique tertiary structures found in the variable regions, meaning that each antibody will only bind to one complementary antigen.

Question 18

What are the different types of proteins and what are their functions?

Answer 18

1. Enzymes - e.g. of role: metabolism - synthesise large food molecules or break them down.
2. Antibodies - immune response
3. Transport proteins - form channels in cell membranes to transport molecules and ions across.
4. Structural proteins - form structure, e.g. keratin (hair, nails), collagen (connective tissue).