Proteins Flashcards
(44 cards)
Size of proteins
Usually very large
Each organism…
Makes its own unique proteins. It’s proteins that give the organism their characteristics and allow key functions to occur
Proteins are key biological molecules - why?
The shape is highly specific and there fore different to other type of types
Monomers of proteins
Amino acids
Amino acids contain which elements?
Nitrogen (N), Carbon (C), Oxygen (O), Hydrogen (H) and sometimes sulphur (S)
Variety of proteins: Different roles
-Haemoglobin -> Transports oxygen by binding to it
-Antibodies -> Defends the body against infection
-Enzymes -> Biological catalysts
-Actin and myosin -> Involved in muscle contraction
Variety of proteins: Structural role
-Keratin -> Found in nails, hair and hooves
-Collagen -> Found in tendons
How many types of amino acids?
20 different types of amino acids, all with the same general structure
Essential and non-essential amino acids
You must ingest the essential amino acids in your diet, non-essential amino acids can be synthesised by your body
General amino acid structure
H H O
| | | |
H—-N—-C—-C—-OH
|
R
Each amino acid contains
A central carbon and 4 different chemical groups
-A nitrogen containing amine group (NH^2 or H^2N)
-A carboxyl group (COOH)
-A hydrogen atom (H)
-A ‘R’ variable side chain or group
What is different in amino acids in the general structure?
‘R’ variable side chain. Each R group has a different size and are grouped together by different properties e.g. charge and polarity
Formation of a peptide bond
Two amino acids joined together to form a dipeptide by a condensation reaction. The hydroxyl group (OH) from the carboxyl group of one amino acid reacts with a hydrogen (H) from the amine group of the second amino acid via a condensation reaction. The water is removed in the formation of a PEPTIDE BOND
Many (hundreds of) amino acids form what?
Form a polypeptide chains as a result of many condensation reactions
Important points of peptide bonds
-A peptide chain will always have an amine group at one end (N terminus) and a carboxyl at the other end (C terminus)
-Number of peptide bonds in the chain will be one less than the number of amino acids originally joined together
Proteins structure
Primary -> Secondary -> Tertiary -> Quaternary
What is the primary structure?
-The number and sequence of amino acids in a polypeptide chain. Because there is 20 amino acids, there is a limitless number of possible sequences
-Determines the positions of the bonds = Hydrogen, ionic and disulphide -> between R groups and final shape of protein
-Specific shape indicates it’s function
-PROTEINS ARE DIFFERENT FROM EACH OTHER BECAUSE OF THE PRIMARY STRUCTURES BEING DIFFERENT
what is the secondary structure?
-The linked amino acids all have -NH and -C=O groups on either side of the polypeptide chain. NH group has overall positive charge and C=O has an overall negative charge.
-A hydrogen bond forms between the slight positive charge on the H and the slight negative charge on oxygen
-These 2 groups form weak hydrogen bonds through put the polypeptide but because there is so many they are strong
-Due to hydrogen bonding the chain coils into alpha helices or folds it’s beta pleated-sheets
What is the tertiary structure?
-This is the further folding of the secondary structure into a specific, complex 3D shape. Determined by the R groups
-Held together by bonds and interactions between R groups of different amino acids
-Hydrogen bonds = weak bonds
-Ionic bonds = Weak, Bonds form between oppositely charged R groups
-Disulphide bonds = covalent bonds which form between sulphur atoms
-Specific tertiary structure which gives them specific shape necessary for their function
What is the quaternary structure?
-When proteins form complex molecules that contain more than one polypeptide chain that are also linked hydrogen, ionic and disulphide bridges
-Haemglobin -> made up of 4 polypeptide chain and also contain non-protein groups (contains Fe 3+), Called a haem group and is where oxygen binds to
-Keratin is made up of 3 polypeptide chains held together by many hydrogen bonds between each chains. Produces a strong structural proteins
Why is denaturing of enzymes important?
It changes the shape of proteins which is essential to its function. When bonds break it changes the specific tertiary shape
Why do enzymes denature at high temperatures?
Increases in temperature increases the kinetic energy of the molecules causing them to vibrate more. This means it can break the weak hydrogen bonds that hold the structure together. As these bonds break the tertiary shape is lost
What is denaturation?
When the specific tertiary structure shape is lost
What is denaturation caused by pH change?
It disrupts the ionic and hydrogen bonds in the tertiary structure
