Proteins Flashcards
What are the type of bonds formed between amino acids?
Peptide bonds
What are proteins composed of?
- Carbon, hydrogen, oxygen and nitrogen
- sometimes sulphur and phosphorus to
Name the different examples of proteins?
- Enzymes
- Cell membrane
- Structural protein (eg.collagen)
- Hormones
- Antibodies
- Transport (eg. haemoglobin)
- Muscle Contractions (Actin and Myosin proteins)
What is the general structure of an amino acid?
Amine group (NH2)
Central carbon and hydrogen
Carboxyl group (COOH)
R-Group
What is an R-Group?
It’s the variable group which differs with the 20 different amino acids
How do different R-Groups change the properties of amino acids?
- Non-Polar
- Polar
- Acidic
- Bases/basic
How do peptide bonds form?
A condensation reaction between two amino acids forms a peptide bond
What forms when a condensation reaction occurs between two amino acids?
One water molecule
Dipeptide chain
What always forms at either end of a dipeptide/polypeptide chain?
An amine group is ALWAYS at one end and a Carboxyl group is ALWAYS at the other end
How do you test for proteins?
Add a few drops of biuret reagent (1=sodium hydroxide ) and biuret reagent (2=copper sulphate ) to the sample
This should look blue
When added to the test solution if a purple/lilac colour develops it indicates the presence of peptide bonds
What is biuret reagent composed of?
Copper Sulphate
Sodium Hydroxide
Why won’t an amino acid show a positive result in the biuret test?
The biuret test - tests for peptide bonds which are not present in an single amino acid
What does a semi-quantitative test mean?
It means that with observation you can determine that the concentration is higher or lower
How do you make a semi-quantitative food test more accurate?
Use a colorimeter to measure colour
What’s the primary structure of proteins?
The SEQUENCE of amino acids found in A proteins polypeptide chain
What’s the secondary structure of proteins?
The primary structure is pulled into the secondary structure due to hydrogen bonds forming between the double bonded oxygen and single bonded hydrogen of nearby peptide bond. This forms an Alpha Helix or Beta Pleated Sheet
What does the secondary structure form?
- Alpha Helix
- Beta Pleated Sheet
What’s the tertiary structure of proteins?
R-Group interactions pull the secondary structure into a more complex 3D shape held in place by disulphide bridges, ionic bonds, hydrogen bonds and hydrophobic/hydrophilic interactions.
What is a disulphide bridge?
A bond which forms between two sulphurs molecules in the R-group of amino acids.
This causes bends/folds in the structure
What is an ionic bond in the Tertiary structure ?
A bond which forms between a positive and negative charge of the R-Group
This also causes folds/turns in the structure
What is the hydrogen bond in the tertiary structure?
A bond which forms between nearby peptide bonds (between O and H)
How do hydrophobic and hydrophilic interactions affect the structure of proteins?
Hydrophobic molecules fold inwards to avoid contact with water
Hydrophilic molecules push out due to attraction with water
What’s the quaternary structure of proteins?
When two or more polypeptide chains are bonded together.
Prosthetic groups may also be present to form large, complex protein molecules
How does the tertiary structure impact the function of a protein?
The tertiary structure aids to determine the shape of the molecule which affects its function (eg. Enzymes active site)
What are the two types of proteins?
Globular
Fiborous
What function does a globular structure give proteins?
It forms a
Spherical shape
Compact Structure
And aids metabolic function
Name two globular proteins?
Enzymes
Haemoglobin
What structure does haemoglobin have?
It has a quaternary structure as 4 polypeptide chains are bonded together around an iron ion
What function does a fibrous proteins have?
The long strands/chains which run parallel to one another are linked by cross-bridges which make them strong and stable. They are also insoluble
Name a fiborous protein?
Collagen ( has structural function)
Why are globular proteins usually soluble in water?
The hydrophobic R-Groups fold in and cluster on the inside whilst the hydrophilic R-Groups push towards the outside to make attractions with the water molecules
Why is collagen strong?
Bonds occur between amino acids of adjacent polypeptide chains
Also the point where individual collagen molecules begin and end is spread throughout the fibre rather than all being in the same place hence providing strength
What do conjugated proteins have?
A prosthetic group
What is a prosthetic group?
They are cofactors that are permanently bound to the enzyme itself
