Proteins Quiz

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Questions and Answers

What type of bonds connect amino acids in a protein?

Peptide bonds (correct)

Ionic bonds

Hydrogen bonds

Disulfide bonds

What percentage of the dry weight of cells do proteins constitute?

30%

60%

20%

50% (correct)

What is unique about glycine among the 20 common amino acids?

It is the largest amino acid

It is the simplest amino acid (correct)

It is an imino acid

It is the only D-isomer

What is the term for the process by which amino acids are connected to form a protein?

Protein synthesis Signup and view all the answers

What type of amino acids are the most common?

α-amino acids Signup and view all the answers

What is the meaning of the Greek word 'proteios', from which the term 'protein' is derived?

First of importance Signup and view all the answers

What is the characteristic feature of chiral carbon centers in amino acids?

Attached to four different substituents Signup and view all the answers

What is the characteristic of L-amino acids found in the body?

Amino group on the left Signup and view all the answers

What type of proteins are derived from simple or conjugated proteins through physical or chemical means?

Derived proteins Signup and view all the answers

What is the primary difference between complete and incomplete proteins?

Adequacy of essential amino acids Signup and view all the answers

What is the process called when peptide bonds are broken by treatment with aqueous acid, base, or certain enzymes?

Protein hydrolysis Signup and view all the answers

What is the term for proteins that lack one or more essential amino acids in correct proportion?

Incomplete proteins Signup and view all the answers

What is the effect of heat on protein structure?

It cleaves hydrogen bonds Signup and view all the answers

What is the purpose of combining two or more incomplete proteins?

To create a complete protein Signup and view all the answers

What is the primary structure of a protein that remains intact during denaturation?

Primary structure Signup and view all the answers

What is the effect of reducing agents on protein structure?

They break disulfide bonds Signup and view all the answers

What is the primary role of the amino acid leucine in the body?

Maintenance of nitrogen balance and energy supply Signup and view all the answers

Which amino acid is involved in calcium absorption and tissue repair?

Lysine Signup and view all the answers

What is the term for the amino acid that is in shortest supply in relation to need?

Limiting amino acid Signup and view all the answers

Which of the following amino acids has hepatoprotective properties?

Methionine Signup and view all the answers

What is the primary function of proteins in the body?

To provide structure and strength to cells and tissue Signup and view all the answers

Which of the following foods is a rich source of the limiting amino acid lysine?

Grains Signup and view all the answers

What is the consequence of a shortage of a limiting amino acid?

Decreased protein synthesis Signup and view all the answers

Which amino acid is involved in neuronal function and immunity?

Tryptophan Signup and view all the answers

Study Notes

Proteins

Complex organic macromolecules containing carbon, hydrogen, oxygen, nitrogen, and usually sulfur
Linear polymers of amino acids connected by peptide bonds
Diverse and abundant class of biomolecules, making up about 50% of the dry weight of cells
Not stored in the body, so they must be consumed daily

Amino Acids

Organic compounds containing an amino group (NH2) and a carboxylic acid group (COOH)
Building blocks of proteins
20 common amino acids, with most being chiral molecules
Most amino acids are α-amino acids, and all amino acids in the body are L-isomers
Exceptions: Glycine (simplest amino acid, achiral) and Proline (imino acid)

Classification of Proteins

According to composition: derived proteins (e.g. denatured proteins and peptides)
According to nutritional basis:
- Complete proteins: contain all essential amino acids in correct proportion (e.g. meat, fish, dairy, egg)
- Incomplete proteins: lack one or more essential amino acids in correct proportion (e.g. grains, nuts, beans, seeds, peas, corn)
- Complementary proteins: combining two or more incomplete proteins to create a complete protein

Properties of Proteins

Denaturation: loss of secondary, tertiary, and quaternary structures, but primary structure remains intact
Factors that cause protein denaturation: heat, detergents, acids and bases, salts, reducing agents, heavy metal ions, alcohol, and mechanical stress

Protein Hydrolysis

Breaking peptide bonds by treatment with aqueous acid, base, or certain enzymes
Primary structure of protein is cleaved by the addition of water
Involved in the development of antibodies and has important antiviral properties

Specific Amino Acids

Leucine: helps maintain nitrogen balance and energy supply, supports muscle building, and lowers cholesterol and LDL levels
Limiting amino acids: amino acids in shortest supply in relation to need, inhibits protein synthesis, and usually found in incomplete proteins

Examples of Limiting Amino Acids

Lysine: involved in growth, tissue repair, and collagen synthesis
Threonine: involved in lipid metabolism and intestinal health
Methionine: involved in detoxification, antioxidant functions, and liver health
Tryptophan: involved in neuronal function, immunity, and gut homeostasis

Functions of Proteins

Structure: provides strength to cells and tissue, chief constituents of skin, bones, hair, and nails
Other functions: enzymatic, transport, storage, and defense-related functions

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Description

This quiz covers the basics of proteins, including their composition, structure, and properties. Learn about the complex organic macromolecules that are essential for life.