Proteins

Question 1

What elements do proteins contain?

Answer 1

Carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur.

Question 2

What are the sub-units from which proteins are formed?

Answer 2

Amino acids.

Question 3

What is the generalized structure of an amino acid?

Answer 3

H2N, COOH, and a carbon-containing side group R.

Question 4

How many different commonly occurring amino acids are there in living organisms?

Answer 4

20.

Question 5

What groups do all amino acids have?

Answer 5

• Amine group (NH2)
• Carboxylic acid group (COOH)

Question 6

What type of bond joins amino acids together?

Answer 6

Peptide bonds (-CONH-).

Question 7

What reaction forms a dipeptide?

Answer 7

Condensation reaction between two amino acids.

Question 8

What do many amino acids joined together form?

Answer 8

A polypeptide.

Question 9

What may a protein consist of?

Answer 9

One or more polypeptides.

Question 10

What process can hydrolyze proteins?

Answer 10

Heating with acid or using enzymes (proteases).

Question 11

Fill in the blank: Amino acids are joined together by _______.

Answer 11

Peptide bonds.

Question 12

True or False: Proteins can only be hydrolyzed by heating with acid.

Answer 12

False.

Question 13

What determines the primary structure of proteins?

Answer 13

The sequence of amino acids in the polypeptide chain

The primary structure is crucial as it dictates the protein’s shape and function.

Question 14

What are the two main types of secondary structures in proteins?

Answer 14

Alpha helix and beta-pleated sheet

These structures arise from hydrogen bonding between amino acids.

Question 15

What type of bonds contribute to the tertiary structure of proteins?

Answer 15

Hydrogen bonds, ionic bonds, and disulfide bonds

The tertiary structure is influenced by the sequence of amino acids in the primary structure.

Question 16

How does the tertiary structure of an enzyme affect its function?

Answer 16

It determines the shape of its active site

The active site shape is critical for enzyme-substrate interactions.

Question 17

What characterizes globular proteins?

Answer 17

They are soluble and consist of a highly folded and coiled polypeptide chain

Examples include enzymes and antibodies.

Question 18

What is the quaternary structure of proteins?

Answer 18

When proteins consist of more than one polypeptide chain

These chains are held together by ionic bonds, hydrogen bonds, and sometimes disulfide bonds.

Question 19

Fill in the blank: The _______ structure refers to the sequence of amino acids in the polypeptide chain.

Answer 19

primary

The primary structure is foundational for protein formation.

Question 20

True or False: The secondary structure of proteins is solely determined by the primary structure.

Answer 20

True

The folding and coiling in secondary structure arise from interactions dictated by the primary structure.

Question 21

What is the significance of the R groups of amino acids in protein structure?

Answer 21

They determine the formation of tertiary structure through bonding

The unique interactions between R groups lead to the specific shape and function of proteins.

Question 22

List the types of bonds involved in stabilizing tertiary structure.

Answer 22

• Hydrogen bonds
• Ionic bonds
• Disulfide bonds

These bonds contribute to the protein’s overall stability and functionality.

Question 23

What type of protein structure is characterized by more than one polypeptide chain?

Answer 23

Quaternary structure

This structure is important for the function of many multi-subunit proteins.

Question 24

What is denaturation of proteins?

Answer 24

An alteration in the tertiary structure of a protein, leading to a loss of its three-dimensional shape and functionality.

Denaturation is often irreversible.

Question 25

What usually causes denaturation of proteins?

Answer 25

Breaking of hydrogen and ionic bonds, high temperatures above the optimum, extreme changes in pH, and heavy metals. ## Footnote Heavy metals can also contribute to denaturation.

Question 26

Are disulfide bonds broken during protein denaturation at typical temperatures?

Answer 26

No, disulfide bonds are not broken at the temperatures that break hydrogen and ionic bonds. ## Footnote Some proteins can have disulfide bonds remain unbroken at 70 °C.

Question 27

What is the Biuret test used for?

Answer 27

To test a sample for the presence of protein. ## Footnote A specific reagent is used in this test.

Question 28

What indicates the presence of protein in the Biuret test?

Answer 28

A purple or lilac color indicates protein is present. ## Footnote If the solution remains blue, no protein is present.

Question 29

Fill in the blank: Denaturation is often _______.

Answer 29

irreversible

Question 30

What happens to the functionality of a protein after denaturation?

Answer 30

The protein is no longer functional. ## Footnote This is a key consequence of denaturation.

Question 31

True or False: Denaturation can be caused by extreme changes in pH.

Answer 31

True

Question 32

List three factors that can lead to protein denaturation.

Answer 32

* High temperatures above the optimum * Extreme changes in pH * Heavy metals