Proteins Flashcards
(36 cards)
Draw and label a diagram of an amino acid.
Alpha carbon atom in the centre, with a carboxly group (COOH) and an amino group (NH2) off to the side, plus a hydrogen atom above or below the alpha the carbon. A variable R group also above or below the alpha carbon.
Identify the part of an amino acid which is variable.
The R group
State how many amino acids occur in life.
There are 20 variations of amino acids.
Describe the different types of amino acid in life.
Unclear
Draw a labelled diagram demonstrating the condensation of peptide bonds. (Explain and draw out)
A peptide bond connects amino acids together when the carboxyl group on one reacts with the amino group on another. The R groups are not involved at this point. The hydroxly from the carboxyl group and the hydrogen from the amino group react to form a dipeptide. Water is released. This is an example of a condensation reaction.
Draw a labelled diagram demonstrating the hydrolysis of peptide bonds.
Breaking peptide bonds by addding a water molecule. The amino and carboxyl groups are reformed.
Draw a dipeptide and label the peptide bond.
Two amino acids connected with a bond between the carbon atom and the nitrogen.
Explain how the variety of amino acids leads to a wide range of dipeptides and very quickly to an incredible variety of polypeptide chains.
The R group of an amino acid is variable, so when they are sequenced together in a condensation reaction the resulting polypeptide chain is different each time.
Define the term “polypeptide chain”
A molecule formed from more than two amino acids
Define the term ‘‘protein’’
One or more polypeptide chains arranged as a complex macromolecule
Describe how one end of a polypeptide chain differs from the other end
In a polypeptide the NH and the CO groups are polar. The H atom is slightly postive and the O atom is slightly negative (delta). So hydrogen bonding can form between them (they are polar)
Define the term “primary structure” of a protein and describe how it is held together.
The primary structure is the sequence and number of amino acids in the polypeptide chain. Different proteins have different sequences as amino acids in its primary structure. The primary structure is held together by peptide bonds.
Define the term “secondary structure” of a protein.
The folding of the polypeptide chain/primary structure into an alpha helix or a beta pleated sheet due to hydrogen bonds between N-H and C=O groups of amino acids in the same polypeptide chain.
No interactions between R-groups
Describe the structure of an alpha helix coil.
Hydrogen bonds may form within the amino acid chain, pulling it into a coil shape.
Describe the structure of a beta pleated sheet.
Different region on a long polypeptide chain can parallel to each other. Hydrogen bonds join these regions together, forming a sheet-like structure. The pattern formed by individual amino acids causes the structure to appear pleated.
Define the term “tertiary structure” of a protein.
Further folding of the polypeptide chain/secondary structure due to bonds forming between R-groups on the same polypeptide chain, resulting in a 3D shape.
(The R-groups are brought close enough together to react when the protein coils or fold into the secondary structure.)
State all the interactions that can occur in the tertiary structure.
- Hydrophobic and Hydrophilic interactions
- hydrogen bonds
- ionic bonds
- disulphide bonds
Describe the hydrophobic and hydrophilic interactions in the tertiary structure.
When hydrophobic R groups are close together in the protein they tend to clump together. This means that hydrophilic R groups are more likely to be pushed to the outside which affects how the protein folds up into its final structure. `
Describe the hydrogen bonds in the tertiary structure.
These weak bonds form between slightly negatively charged atoms in R-groups and slightly positively charged hydrogen atoms in other R-groups on the polypeptide chain.
Describe the ionic bonds in the tertiary structure.
Much stronger than hydrogen bonds. They form between oppositely charged R-groups on different parts of the molecule.
Describe the disulphide bonds in the tertiary structure.
These are covalent and the strongest of the bonds but only form between R-groups that contain sulfur atoms.
Explain how the primary structure of a protein determines its tertiary structure.
The tertiary is structure is defined by R-group interactions. The primary structure sets the sequence of these R-groups as it is the order of the amino acids, therefore, the tertiary structure is reliant on the primary structure
Define the term “quaternary structure” of a protein, and describe how it is held in place. Include all possible bonds.
Interactions between R-groups of more than one polypeptide chain.
- disulphide bridges
- hydrogen bonds
- hyrophobic/ hydrophilic interactions
- ionic bonds
- covalent bonds
Define the term“globular protein”.
- Spherical, water soluble proteins.
- Form when proteins fold into their tertiary structure so that hydrophobic R-groups are folded up inside the protein (away from the aqueous environment) and the hydrophilic R-groups are on the outside.
- This makes them soluble and so easily transported.
- Normally have a metabolic role
(any enzyme is a globular protein).
