CBS: Protein Structure and Function

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Questions and Answers

What is the main difference between the 20 universal structural amino acids?

Their R-group attached to the α-carbon (correct)

Their role in protein folding

Their molecular weight

Their ionization state at physiological pH

What is the functional importance of amino acid side chains?

They are involved in DNA replication

They define the properties and function of the amino acid (correct)

They are responsible for protein folding

They determine the molecular weight of the amino acid

What is the nature of the peptide bond between amino acids?

A covalent bond formed through the condensation of amino and carboxyl groups (correct)

A disulphide bond formed through oxidation

An ionic bond formed through electrostatic attraction

A non-covalent bond formed through hydrogen bonding

What is the role of hydrogen bonds in protein structure?

They are important for protein folding and stability Signup and view all the answers

What is the main structural feature of an α-helix?

A spiral staircase-like structure Signup and view all the answers

What is the result of defects in amino acid metabolism?

Disease Signup and view all the answers

What is the primary determinant of protein conformation?

The primary sequence of amino acids Signup and view all the answers

What is the nature of most folded proteins?

They are marginally stable Signup and view all the answers

What is the main difference between selenocysteine and cysteine?

The presence of Se instead of S Signup and view all the answers

What is the role of hydroxyproline in collagen?

It allows the formation of a triple helix structure Signup and view all the answers

What is the result of a defective phenylalanine hydroxylase enzyme?

Reduced production of tyrosine and hormones derived from it Signup and view all the answers

What is the characteristic of the peptide bond that allows for the formation of hydrogen bonds?

It has a partial negative charge on the oxygen atom and a partial positive charge on the nitrogen atom Signup and view all the answers

What is the role of enzymes in the formation of polypeptides?

They facilitate the formation of peptide bonds between amino acids Signup and view all the answers

What is the characteristic of the peptide bond that makes it resistant to rotation?

It is shorter than the standard C-N bond length Signup and view all the answers

What is the result of a defective tyrosinase enzyme?

Albinism Signup and view all the answers

What is the role of homocysteine in the synthesis of cysteine?

It is necessary for the synthesis of cysteine Signup and view all the answers

Study Notes

Amino Acids

Amino acids have an amino group (-NH2) and a carboxylic group (-COOH) attached to the same carbon (α-carbon)
There are 20 universal structural amino acids encoded in DNA
Each amino acid has a unique R-group attached to the α-carbon, which defines its properties and function
At physiological pH, the amino and carboxyl groups are ionized

Essential and Non-Universal Amino Acids

Some amino acids are essential for the human diet due to the lack of enzymes to synthesize them de novo
Other amino acids, such as hydroxyproline, selenocysteine, and homocysteine, exist in cells but are not universally encoded in DNA

Peptide Bond

Amino acids polymerize to form polypeptides (proteins) via the formation of peptide bonds between the alpha amino and alpha carboxylic groups of adjacent amino acids
The peptide bond is very strong and has some features of a double bond:
- It is shorter than the standard C-N bond length
- There is no rotation
- The R-groups are in the trans configuration
- There is a partial negative charge on the oxygen atom and a partial positive charge on the nitrogen atom
These partial charges are important in the formation of hydrogen bonds that are key for protein structure

Defects in Amino Acid Metabolism

Defects in metabolism result in a number of clinical conditions, such as:
- Phenylketonuria (PKU), due to defective phenylalanine hydroxylase
- Albinism, due to defective tyrosinase (tyr → melanin)

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Description

This quiz covers the structures of 20 common amino acids, their functional importance, and the nature of peptide bonds. It also explores the main structural features of an α-helix and its role in typical globular and membrane proteins.