Topic 1---A: Biological molecules- 5. proteins Flashcards
What are the monomers of proteins?
Amino acids
How is a dipeptide formed?
When two amino acids join together
How is a polypeptide formed?
When more than 2 amino acids join together
What are proteins made up of?
1 or more polypeptides
Amino acid (structure)
- Carboxl group (COOH)
- Amine group (H2N)
- R GROUP (1 of 20 varieties) attached to a carbon
- R GROUP consists of 1 hydrogen atom
H H O
\ I //
N -C-C
/ I \ OH
H R
How are amino acids linked together to form dipeptides and polypeptides?
By condensation reaction between amine and carboxyl group so a molecule of water is released during the reaction.
- Peptide bond is formed between the amino acids
What are the bonds between amino acids called?
Peptide bonds
When does hydrolysis happen?
When dipeptides and polypeptides are broken down
How is there 20 different amino acids?
-Because there are 20 different R groups
- Each R group is slightly different so each amino acid has different properties so proteins have a wide range of properties.
What are the 4 levels of structure in a protein?
- Primary
- Secondary
- Tertiary
- Quaternary
Primary structure (proteins)
This is the sequence of amino acids in a polypeptide chain
Secondary structure (proteins)
- Hydrogen bonds form between the amino acids in the chain between the amine and carboxyl groups
- This makes it automatically coil into a alpha helix or fold into a beta pleated sheet
- Hydrogen bonds hold the secondary structure in place
Tertiary structure (protein)
- The coiled or folded chain of amino acids is often coiled and folded further.
- More bonds form between different parts of the polypeptide chain including hydrogen and ionic bonds.
- Disulphide bonds also form whenever 2 molecules of the same amino acid cysteine come together
- For proteins made from a single polypeptide chain the tertiary structure forms their final 3D structure
Quaternary structure (protein)
-Protein made up of several different polypeptide chains held together by bonds
- It’s the way the polypeptide chains are assembled together
What is an example of a quaternary structure?
Haemoglobin (4 polypeptide chains associated together)
Why is the sequence of amino acids important?
- They determine the tertiary structure so therefore the overall 3D shape of the molecule due to the bonds forming in different locations.
What does a proteins shape determine?
Their function
Enzymes (protein example)
- Usually spherical in shape due to the tight-folding of the polypeptide chains.
- Their soluble and have roles in metabolism like breaking down large food molecules.
Transport proteins (protein example)
- Channel proteins are present in cell membranes
- They contain hydrophobic and hydrophilic amino acids
- This causes the protein to fold up and form a channel so they can transport molecules and ions across cell membranes.
Structural proteins (protein example)
- Physically strong
- Consist of long polypeptide chains lying parallel to each other with cross links between them.
- E.g. keratin and collagen
What happens when a protein denatures?
- Hydrogen and ionic bonds in secondary and tertiary structure break
- Lose the 3D shape
- E.g. from changes in temperature/ PH
Biuret test (proteins)
- Test solution needs to be alkaline so first you add a dew drops of sodium hydroxide solution
- Then add some copper (II) sulfate solution.
- If protein is present it will go from blue to purple
Ionic bonds
- Quite Strong
- Form between R groups
Hydrogen bonds
- Weak
- Easily broken by temperature or pH
Disulphide bridges
- Covalent (very strong)
- Form between sulphur atoms in the R group of cysteine
