1.6- PROTEINS Flashcards
What is the size of proteins usually?
usually very large molecules
How are the types of carbohydrates and lipids in all organisms in terms of number + structure?
relatively few and they are very similar
Something about the shape of proteins in comparison to each other?
shape of any one type of protein molecule differs from that of all other types of proteins
How significant are proteins in living organisms?
very important
What does the word “protein” mean in greek?
“of first importance”
How involved are enzymes?
enzymes involved in almost every living process
What is amino acids used as?
basic monomer units which combine to make up a polymer
What is the name of the polymer made up of amino acids?
polypeptide
When polypeptides are combined what do they form?
proteins
About how many amino acids have been identified?
about 100 amino acids
How many amino acids occur naturally in proteins?
20
What does the fact that the same 20 amino acids occur in all living organisms provide indirect evidence for?
evolution
What does every amino acid have?
a central carbon atom to which are attached four different chemical group
What are the four different chemical groups attached to the carbon in an amino acid?
-NH₂
-COOH
-H
R group
Through what process do amino acid monomers combine to form a dipeptide?
condensation reaction
How is the water formed in the condensation reaction between amino acids?
combining an -OH from carboxyl group of one amino acid with -H from amino group of another amino acid
How do the two amino acids become linked?
by a peptide bond
Where is the peptide bond between?
between the carbon atom of one amino acid and nitrogen atom of other
How can a peptide bond of a dipeptide bond be broken and what is left?
through hydrolysis to give two constituent amino acids
What is the process called when a series of condensation reactions happen, joining many amino acid monomers?
polymerisation
What is the resulting chain of many hundreds of amino acids called?
polypeptide
What is the primary structure of any protein?
sequence of amino acids in polypeptide chain
How is the sequence of amino acids in a polypeptide chain determined?
determined by DNA
How is there a limitless number of primary protein structures?
as polypeptides have many (usually hundreds) of the 20 naturally occurring amino acids joined in different sequences, there’s a limitless number of combinations
What does the primary structure determine?
its ultimate shape and hence its function
What can a change in a single amino acid in the primary sequence lead to?
lead to a change in the shape of protein + may stop it from carrying out function
What is the protein’s shape very specific to?
its function
What can happen if the shape of a protein is changed?
it will function less well or differently
What may a simple protein consist of?
consist of a single polypeptide chain
More commonly, what does a protein consist of?
made up of a number of polypeptide chains
What does the linked amino acids that make up a polypeptide possess?
-NH and -C=O groups on either side of peptide bond
What overall charge does the hydrogen on -NH have?
an overall positive charge
What overall charge does the O of -C=O group have?
overall negative charge
Due to the charge of the hydrogen on -NH and charge of O on -C=OH what happens?
readily form weak bonds called hydrogen bonds
What does the hydrogen bond between the O and H cause?
the long polypeptide chain to be twisted into a 3D shape
What can the 3D shape?
alpha helix or beta pleated sheets
What happens in the tertiary structure?
secondary protein structure can be twisted and folded even more
What does the further folding and twisting produce?
gives a complex, and often specific 3D structure of each protein
How is the tertiary structure maintained?
by a number of different bonds
How is where the bonds in the tertiary structure determined?
depends on the primary structure of protein
What are the bonds in the tertiary structure?(3)
disulfide bridges
ionic bonds
hydrogen bonds
How strong are disulfide bridges?
fairly strong so not easily broken
Where are ionic bonds formed?
Formed between any carboxyl and amino groups that are not involved in forming peptide bonds
How strong are ionic bonds and how are they broken?
weaker than disulfide bonds and easily broken by change in pH
How strong are hydrogen bonds + numbers?
numerous but easily broken
What is important for the function of protein?
3D shape of protein
What does the 3D shape allow?
makes each protein distinctive and allows it to recognise, and be recognised by other molecules
What does proteins being able to interact with other molecules enable?
it can interact with them in a very specific way
What do large proteins often form?
form complex molecules containing a number of individual polypeptide chains that are linked in various ways
What other groups may also be associated with the molecules in the quaternary structure?
non-protein (prosthetic) groups
Example of prosthetic group on protein?
iron-containing haem group in haemoglobin
What determines the 3D structure in the first place?
the sequence of amino acids (primary structure)
What is the most reliable test for proteins?
Biuret test
What does the Biuret test detect?
peptide bonds
