Proteins (Cambridge (CIE) AS Biology): Flashcards
Exam code: 9700
1/330Still learning
Know0
Describe the general structure of an amino acid.
Was this flashcard helpful?
Cards in this collection (33)
Describe the general structure of an amino acid.
A central carbon bonded to:
an amino group (–NH~2~), a carboxyl group (–COOH), a hydrogen atom and an R group (variable side chain).
How is a peptide bond formed?
By a condensation reaction between the amino group of one amino acid and the carboxyl group of another.
A molecule of water is released.
How is a peptide bond broken?
By hydrolysis — a molecule of water is added, splitting the peptide bond.
Define dipeptide.
A dipeptide is two amino acids joined by a peptide bond.
A peptide bond forms by a reaction between two amino acids.
A peptide bond forms by a condensation reaction between two amino acids.
True or False?
The R group is the same in every amino acid.
False.
The R group (side chain) varies between amino acids and gives each its properties.
Define the primary structure of a protein.
The sequence of amino acids in a polypeptide chain.
Define the secondary structure of a protein.
The folding of the polypeptide into an α-helix or β-pleated sheet, held together by hydrogen bonds.
Define the tertiary structure of a protein.
The overall 3D shape of a single polypeptide, held by hydrogen bonds, ionic bonds, disulfide bonds and hydrophobic interactions.
Define the quaternary structure of a protein.
The arrangement of two or more polypeptide chains (and any prosthetic groups) in a protein.
Which bonds hold the secondary structure of a protein in place?
Hydrogen bonds.
The sequence of amino acids in a protein is its structure.
The sequence of amino acids in a protein is its primary structure.
Name the four types of interaction that hold a protein in shape.
Hydrophobic interactions, hydrogen bonds, ionic bonds and covalent (disulfide) bonds.
Define disulfide bond.
A disulfide bond is a strong covalent bond between the sulfur atoms of two cysteine R groups.
Where do ionic bonds form in a protein?
Between oppositely charged R groups (side chains).
Strong covalent bonds between two cysteine side chains are called bonds.
Strong covalent bonds between two cysteine side chains are called disulfide bonds.
True or False?
Hydrogen bonds are the strongest interactions holding a protein in shape.
False.
Covalent disulfide bonds are the strongest; hydrogen bonds are individually weak.
Compare globular and fibrous proteins.
Globular proteins are generally soluble and have physiological (metabolic) roles.
Fibrous proteins are generally insoluble and have structural roles.
Define globular protein.
A generally soluble protein with a compact, rounded shape and a physiological role (e.g. haemoglobin).
Define fibrous protein.
A generally insoluble protein with a long, strand-like shape and a structural role (e.g. collagen).
proteins are generally insoluble and have structural roles.
Fibrous proteins are generally insoluble and have structural roles.
True or False?
Globular proteins are generally insoluble.
False.
Globular proteins are generally soluble; it is fibrous proteins that are generally insoluble.
Describe the quaternary structure of haemoglobin.
Four polypeptide chains — two α (alpha)-globin and two β (beta)-globin chains.
Each chain holds a haem group.
Why is haemoglobin an example of a globular protein?
It has a compact, rounded 3D shape and is soluble, with a physiological role (oxygen transport).
How is the structure of haemoglobin related to its function?
Each of its four haem groups contains an iron ion (Fe^2+^) that binds one O~2~ molecule.
So one haemoglobin molecule can carry four oxygen molecules.
Why is iron important in haemoglobin?
The Fe^2+^ ion in each haem group is where oxygen binds, allowing haemoglobin to transport oxygen.
Each haem group in haemoglobin contains an ion that binds oxygen.
Each haem group in haemoglobin contains an iron ion that binds oxygen.
True or False?
Haemoglobin is made of four polypeptide chains.
True.
Two α-globin and two β-globin chains give haemoglobin its quaternary structure.
Describe the structure of a collagen molecule.
Three polypeptide chains wound together in a triple helix.
The chains are held together by hydrogen bonds.
How are collagen molecules arranged into fibres?
Many collagen molecules line up in parallel, with covalent cross-links between them.
Their staggered ends add strength, forming strong collagen fibres.
How is the structure of collagen related to its function?
The triple helix and cross-links give very high tensile strength.
This makes it a strong structural protein in tendons, skin and artery walls.
A collagen molecule is made of three polypeptide chains wound into a helix.
A collagen molecule is made of three polypeptide chains wound into a triple helix.
True or False?
Collagen is a soluble globular protein.
False.
Collagen is an insoluble fibrous protein with a structural role.
Sign up to unlock flashcards
or