Proteins Flashcards
1
Q
What are proteins ?
A
- Polymers made from the monomers amino acids by the formation of peptide bonds due to condensation reactions
- contain the elements carbon, hydrogen, oxygen, nitrogen and sulfur
2
Q
How is a peptide bond formed?
A
- the OH from the carboxylic group of one amino acid with the H from the anime group of another carboxylic acid
- condensation reaction
- removal of water
3
Q
Describe the primary function of proteins
A
- sequence of amino acids
- due to translation at ribosome
4
Q
Describe the secondary structure of proteins
A
- the oxygen and hydrogen and nitrogen form hydrogen bonds
- the bonds cause the polypeptide to coil into an alpha helix
- if the polypeptides lie parallel then hydrogen bonds form and this forms a beta pleated sheet
- there is a repeated pattern in beta pleated sheets because of the structure of the amino acids
- initial folding of the protein
5
Q
Describe the tertiary structure of proteins
A
- The R groups are now close enough to interact
- formation of ionic bonds, disulphides bonds, hydrogen bonds, hydrophilic and hydrophobic interactions
- final folding of the protein into its 3D shape
6
Q
Why is the tertiary structure of proteins important?
A
- specific shape determines their function
- eg. For enzymes tertiary structure determines the shape of their active site which gives them their specificity for the metabolic reaction they catalyse
7
Q
What is the quarternary structure of proteins?
A
- when more than one polypeptide joins or cofactor and then it gets called subunits
- the subunits are held together by the same interactions as in the tertiary structure.
8
Q
Give examples of quarternary proteins and describe them
A
- insulin has two different subunits
- enzymes have two identical subunits
- haemoglobin has four subunits of which their are two pairs … alpha helices subunits and beta pleated sheets subunits
9
Q
Describe the hydrolysis of polypeptides
A
- addition of water to break polymer into its constituent monomers
- uses protease enzymes
10
Q
Describe the test for proteins
A
- Biuret test
- biuret reagent contains copper ions in an alkaline solution so copper sulfate
- add the biuret reagent drop by drop until sample turns blue
- leave for five minutes
- if a violet complex forms, protein is present
11
Q
Describe the structure of collagen
A
- three polypeptide chains held together by hydrogen bonds in a triple helix known as a tropocollagen
- every third amino acid is glycine which is the smallest amino acid with a small r group and it allows the polypeptides in the triple helix to be arranged very close together
- there are covalent cross links between the triple helices to form fibrils
- there are staggered ends in these fibrils
- many fibrils are arranged together to form a collagen fibre
12
Q
Describe the properties of collagen
A
- it is a flexible protein
- it has a high tensile strength because there are many hydrogen bonds holding the polypeptide chains in the triple helix
- as it is a fibrous protein, it is long as so is insoluble in water
- the staggered ends provide strength
13
Q
Does collagen have a prosthetic group?
A
No
14
Q
What is the function of collagen?
A
- collagen is the most common structural protein
- it is found in tendons, bones, walls of blood vessels, connective tissue
15
Q
What is the shape of globular vs fibrous proteins?
A
- globular is spherical and soluble
- fibrous is long and insoluble… they don’t have much of a tertiary structure
- it is insoluble because it has a high proportion of hydrophobic r groups
