AQA A-Level Biology 3.1.4: Protein Structure and Bonds

What are proteins composed of?

Proteins are composed of subunits called amino acids.

What groups are present in every amino acid?

Each amino acid has an amine group, a carboxyl group, and a side chain called the R group.

What is a dipeptide?

A dipeptide is formed when two amino acid monomers join with a peptide bond.

What type of reaction forms a dipeptide?

The formation of a dipeptide is a condensation reaction.

How are peptide bonds broken?

Peptide bonds are broken by an enzyme and water in a hydrolysis reaction.

What is a polypeptide?

A polypeptide is a chain of many amino acids linked together.

What is the primary structure of a protein?

The primary structure is the number and sequence of amino acids in the polypeptide chain.

What forms the secondary structure of a protein?

The secondary structure forms when the primary structure coils into an alpha helix or folds into beta pleated sheets, held together by hydrogen bonds.

What is the tertiary structure of a protein?

The tertiary structure is the specific 3D shape of a protein, held in place by ionic bonds, disulfide bridges, hydrophobic/hydrophilic interactions, and hydrogen bonds.

What characterizes the quaternary structure of a protein?

The quaternary structure forms when two or more polypeptides join together.

What is the function of Biuret reagent?

Biuret reagent is used to identify proteins; it turns purple in the presence of proteins.

What is an amine group?

The amine group is the -NH2 group of an amino acid.

What is a carboxyl group?

The carboxyl group is the -COOH group of an amino acid.

What type of bond is a peptide bond?

A peptide bond is a covalent bond formed between two amino acids.

What is a disulfide bridge?

A disulfide bridge is a bond formed between sulfur atoms in the R groups of amino acids.

What type of bond is an ionic bond?

An ionic bond is formed between a positive ion and a negative ion.

What is the role of hydrophobic and hydrophilic interactions in proteins?

Hydrophobic and hydrophilic interactions help maintain the shape of a globular protein.

What is the significance of the 2024 Nobel Prize in Chemistry?

It was awarded for research on predicting protein structures and designing new proteins.

Who were the recipients of the 2024 Nobel Prize in Chemistry?

David Baker, Demis Hassabis, and John Jumper.

What is AlphaFold?

AlphaFold is an AI developed to predict the structure of proteins with high accuracy.

What is the primary function of proteins in living organisms?

Proteins play vital roles in all living organisms, including structural and metabolic functions.

What is the importance of the sequence of amino acids in proteins?

The sequence of amino acids determines the shape and function of the protein.

What is the role of the Rosetta software?

Rosetta is used for designing proteins with desired structures.

What is the significance of hydrogen bonds in protein structure?

Hydrogen bonds stabilize the secondary and tertiary structures of proteins.

What is a polymer in the context of proteins?

A polymer is a large molecule made up of many repeating subunits, such as amino acids in proteins.

What is the relationship between proteins and enzymes?

Many enzymes are proteins that catalyze biochemical reactions.

What is the secondary structure of a protein?

Hydrogen bonds form between amino acids, causing the chain to coil into an α-helix or fold into a β-pleated sheet.

What is the quaternary structure of a protein?

The structure formed when two or more polypeptide chains are joined together.

What is an amino acid?

The monomer of a protein, consisting of a central carbon, an amine group, a carboxyl group, a hydrogen atom, and a variable R group.

What is the role of the R group in amino acids?

The R group determines the bonding and properties of the amino acid.

What bond is formed between two amino acids?

A peptide bond.

What type of reaction breaks down proteins?

Hydrolysis.

What elements are found in proteins that are not found in carbohydrates and lipids?

Nitrogen.

What is the significance of the primary structure in protein function?

It determines the 3D shape or tertiary structure, which affects the active site in enzymes.

What stabilizes the secondary structure of proteins?

Hydrogen bonds between amino acids.

What types of bonds are involved in the tertiary structure of proteins?

Hydrogen bonds, ionic bonds, and disulfide bridges.

What is the difference between primary and secondary structure of polypeptides?

Primary structure refers to the sequence of amino acids, while secondary structure involves coiling or folding due to hydrogen bonding.

What is a characteristic of proteins with quaternary structure?

They are made of more than one polypeptide chain.

What are examples of proteins with quaternary structure?

Antibodies and hemoglobin.

How does a change in the amino acid sequence affect protein structure?

It can alter the formation of secondary and tertiary structures due to different bonding patterns.

What is the general structure of an amino acid?

A central carbon atom, an amine group, a carboxyl group, a hydrogen atom, and a variable R group.

What is the unique feature of glycine among amino acids?

Its R group is just one hydrogen atom.

What is the process of forming a peptide bond?

A condensation reaction between the amine group of one amino acid and the hydroxyl group of another, releasing a water molecule.

What is the role of hydrogen bonds in protein structure?

They stabilize the secondary structure and contribute to the tertiary structure.

What is the difference between a polypeptide and a protein?

A polypeptide is a chain of amino acids, while a protein may consist of one or more polypeptide chains.

What is the significance of the tertiary structure in enzymes?

It creates a specific shape that is crucial for the enzyme's function.

What type of bond is a disulfide bridge?

A covalent bond that forms between the sulfur atoms of cysteine residues.

What is the role of ionic bonds in protein structure?

They help stabilize the tertiary structure by forming interactions between charged R groups.

What is the structure of the amino acid serine?

Serine consists of an amino group (NH2), a carboxylic acid group (COOH), a hydrogen atom, and a variable R group.

What happens when two amino acids join together?

They form a dipeptide and release a molecule of water.

What type of bond is formed between two amino acids?

A peptide bond.

How does a change in the primary structure of a globular protein affect its structure?

It can lead to a different three-dimensional structure due to changes in amino acid sequence affecting folding.

What is the primary evidence that keratin has a quaternary structure?

Keratin molecules consist of several polypeptide chains.

How do sulphur-containing amino acids contribute to keratin's strength?

They form disulfide bonds that provide structural stability.

Why do differences in primary structure result in keratins with different properties?

Different amino acid sequences lead to variations in folding and chemical properties.

What is a triglyceride composed of?

One glycerol molecule bonded with three fatty acids.

What distinguishes saturated fatty acids from unsaturated fatty acids?

Saturated fatty acids have no double bonds, while unsaturated fatty acids contain one or more double bonds.

What type of reaction forms a triglyceride?

A condensation reaction.

What reaction breaks down triglycerides?

A hydrolysis reaction.

What is the structure of phospholipids?

Similar to triglycerides but with one fatty acid replaced by a phosphate group.

What are the two distinct regions of a phospholipid?

A hydrophobic tail region and a hydrophilic head region.

What is the role of phospholipids in cell membranes?

They form a bilayer with hydrophilic heads facing outward and hydrophobic tails facing inward.

What are the building blocks of proteins?

Amino acids.

How many different amino acids are there?

There are about 20 different amino acids.

What are the two common secondary structures of proteins?

Alpha helix and beta-pleated sheet.

What stabilizes the tertiary structure of a protein?

Hydrogen bonds, ionic bonds, and disulfide bridges between R groups.

What are fibrous proteins?

Proteins that are long, straight chains and do not show tertiary structure.

What are globular proteins?

Rounded, soluble proteins that exhibit tertiary and quaternary structures.

What roles do globular proteins play in biological systems?

They function as enzymes, antibodies, hormones, and receptors.

What are proteins made of?

Proteins are polymers made up of monomers known as amino acids.

How many amino acids are present in all life forms?

There are twenty amino acids present in all life forms.

What is the simplest amino acid?

The simplest amino acid is glycine, which has a hydrogen atom as its R group.

What elements do proteins contain that carbohydrates and lipids do not?

Proteins contain nitrogen in their amine group.

What bond is formed when two amino acids join?

A peptide bond is formed.

What are dipeptides and polypeptides?

Dipeptides are two amino acids joined together, while polypeptides are longer chains of amino acids.

What reaction breaks down proteins?

Hydrolysis breaks down proteins.

What stabilizes the α-helix structure?

Hydrogen bonds between the -NH of one amino acid and the -CO of another stabilize the α-helix.

What types of bonds maintain the tertiary structure of proteins?

Hydrogen bonds, ionic bonds, disulfide bridges, and hydrophobic interactions maintain the tertiary structure.

What is an example of a fibrous protein?

Collagen is an example of a fibrous protein.

What are the characteristics of fibrous proteins?

Fibrous proteins have repetitive sequences, are insoluble in water, and serve structural roles.

What is an example of a globular protein?

Haemoglobin is an example of a globular protein.

What is the role of haemoglobin?

Haemoglobin transports oxygen in the blood.

What is the role of insulin?

Insulin regulates blood sugar levels.

What is the function of enzymes?

Enzymes catalyze biochemical reactions.

What is the significance of the R group in amino acids?

The R group varies between amino acids and determines their unique properties.

What happens to proteins when they are denatured?

Denaturation disrupts the protein's structure, affecting its function.

What is the bond formed between two cysteine amino acids?

A disulfide bridge is formed between two cysteine amino acids.

How many possible combinations can four amino acids have?

A four-amino-acid structure has 160,000 possible combinations.

What is the difference between primary and secondary structure?

Primary structure refers to the sequence of amino acids, while secondary structure refers to the shape formed by hydrogen bonds.

What maintains the structure of keratin?

Keratin is maintained by disulfide bridges and hydrogen bonds.

What is the role of collagen in the body?

Collagen provides structural support in tissues such as skin, tendons, and bones.