3.6 Structure of proteins Flashcards
What are peptides?
Polymers made up of two or more amino acid molecules
What do proteins consist of?
One or more polypeptides arranged as complex macromolecules
*What elements do proteins contain
Carbon, hydrogen, oxygen, nitrogen
What are R-groups?
Variable groups on amino acids
How many amino acids are found in cells?
20
How many amino acids are non-essential? What does this mean?
5 - our body can make them from different amino acids
How many amino acids are essential? What does this mean?
9 - only obtainable from food
How many amino acids are conditionally essential? What does this mean?
6 - only needed by growing children
Describe what happens during synthesis of peptides
*(Refer to Figure 2 on p.g. 59)
-Amino acids join when amine and carboxylic acid groups react
-Hydroxyl in the carboxylic acid group of one amino acid reacts with a hydrogen in the amine group of another amino acid
-Peptide bond forms between amino acids and water is produced (this is an example of a condensation
reaction)
-The resulting compound is a dipeptide
What is a peptide bond?
The bond formed between 2 amino acids
What happens when many amino acids are joined by peptide bonds?
A polypeptide forms
Polypeptide - chains of 3 or more amino acids
What enzyme catalyses the reaction which forms peptide bonds?
Peptidyl transferase, found in ribosomes
Define R-group interaction. What does this result in?
- Different R-groups in the amino acids making up one protein can interact
- Forming different types of bonds
-These bonds cause the long amino acid chains (polypeptides) to fold into complex structures
(proteins)
What does the presence of different amino acid sequences lead to?
Different structures with different shapes being produced
Why does a protein’s shape have to be specific?
Vital for the protein to carry out its function
*What is thin layer chromatography (TLC) used for?
To separate individual components of a mixture
e.g. identify a mixture of amino acids in a solution
*What are the 2 phases in TLC? What happens at each phase?
- Stationary phase
- Thin layer of silica gel/any other adhesive substance is applied to a rigid surface e.g. sheet of glass
- Amino acids are added to one end of the gel
- This end is submerged in organic solvent - Mobile phase
- The organic solvent moves through the silica
*What is the rate at which amino acids move dependent on?
- Interactions the amino acids have with the silica during the stationary phase
- Amino acid’s solubility during the mobile phase
- Since these vary, the amino acids move different distances in the same period of time
*How do you carry out the procedure to separate and identify a mixture of amino acids in solution?
- Whilst wearing gloves, draw a baseline 2cm from the bottom in pencil on the chromatography plate (handle the plate by its edges)
- Mark 4 equally spaced points along the baseline
3.
Explain what the primary structure of a protein is
- Sequence in which amino acids are joined
- Directed by information carried within DNA
- Amino acids in the sequence influence how the polypeptide folds to give the protein’s final shape - this determines its function
- Only contains peptide bonds
Explain what happens in the secondary structure of a protein
- Oxygen, hydrogen and nitrogen atoms of the amino acid structure interact
- Hydrogen bonds form within the amino acid chain, pulling it into a coil shape known as ‘alpha helix’
- Result of hydrogen bonds
What is the secondary structure a result of?
Hydrogen bonds
Where does the secondary structure form?
At regions along long protein molecules, depending on the amino acid sequence
What forms a beta pleated sheet?
Polypeptide chains parallel to each other joined by hydrogen bonds, forming sheet-like structures
What happens in the tertiary structure?
The protein is folded into its final shape
