Proteins Flashcards
What is a protein?
A macromolecule consisting of the elements carbon, hydrogen, oxygen and nitrogen, made of one or more polypeptide chains.
If the monomer is an amino acid, what is the polymer?
A peptide
Which groups are constant in an amino acid and which change to determine what amino acid it is?
Constant - amine, carboxyl, hydrogen
Change - R group
How many amino acids found in cells?
20
How many nonessential amino acids? Why are they non essential?
5, can be synthesised from other amino acids
How many essential amino acids? Why are they essential?
9, can only be found in our diet
How many ‘conditionally’ essential? Why are they thus?
6, only needed in infants and growling children
What are the terminals in an amino acid?
N terminal- amine group
C terminal- carboxyl group
What can an amino acid do in terms of hydrogens (protons)? WHAT IS THIS CALLED?
it can lose hydrogens from the CARBOXYL group, it can ‘mop up’ hydrogens from the AMINE group - AMPHOTERIC
Which groups in amino acids react to form peptides? What do they each give?
The amine group and carboxyl group.
The amine group gives H
The carboxyl group gives OH
What is the bond formed between two amino acids?
Peptide bond
O H
|| |
C—N
What is formed when two amino acids react?
A dipeptide
What is formed when more than 2 amino acids join?
A polypeptide.
What are the levels of protein synthesis?
Primary, Secondary, Tertiary, Quaternary
What is the primary structure?
The SEQUENCE of amino acids in the polypeptide chain.
What importance does the primary structure have?
It influences the shape the proteins fold into, and so influences the protein’s function.
Influences WHERE the hydrogen bonds form
What is the secondary structure?
The secondary structure is the result of formation of hydrogen bonds between different amino acids in the same chain
Where are the hydrogen bonds in an alpha helix
Between every first and fourth amino acid in the same polypeptide chain
Where are the hydrogen bonds in beta pleated sheet?
Between layers of the same polypeptide chain
How do hydrogen bonds formed between amino acids?
Between the double bonded oxygen and the hydrogen between R groups
What is the tertiary structure of a protein?
This is the interaction of Rgroups between different amino acids in the same polypeptide chain to determine the proteins shape when it folds
Name the different types of R group interactions in the tertiary structure, form weakest to strongest
Van der Waals (hydrophobic/hydrophilic)
Hydrogen
Ionic
Disulfide bridges (covalent)
How do you disulphide bridge bonds arise?
When the protein contains cysteine , which contains sulfur.
What determines whether the amino acid chain forms an alpha helix or beta pleated sheet?
The load/sequence of amino acids in the chain.
What does high-temperature do to proteins?
High temperature will break the Van der Waals - hydrophobic/hydrophilic - attractions in the tertiary structure and the protein will unravel and lose its shape and will not be able to perform its function anymore
What is quaternary structure of a protein?
This is the interactions between different polypeptide chains
What is quaternary protein?
A protein consisting of more than one polypeptide chain
What are the quaternary proteins we are supposed to know?
Catalase, haemoglobin, insulin, collagen, keratin, elastin
What is a globular protein?
Soluble proteins with a roughly spherical shape
Name the globular proteins we need to know
Haemoglobin catalase insulin
Why are globular proteins spherical in shape?
Due to the tertiary structure. The hydrophobic amino acids abounded towards the interior whereas the hydrophilic amino acids are towards the exterior and there is an equal proportion of hydrophobic and hydrophilic amino acid that the protein had a globular shape.
Why are globular proteins soluble?
The hydrophilic amino acids face outwards and can interact with the water molecules
What is the structure of haemoglobin
- 4 polypeptide chains, 2 alpha globin 2 beta globin
- Each polypeptide chain has a haem group associated with it
- the haem group is a prosthetic group which contains iron
What is a conjugated protein and give examples?
A conjugated protein is a protein with a prosthetic group which is a non-protein component
Haemoglobin Catalase
What is the role of iron in haemoglobin and why is this useful?
Iron allows haemoglobin to bind with oxygen reversibly which is useful because the blood may need to be oxidised or reduced depending on its pH
Describe the function of haemoglobin
Haemoglobin transports oxygen around the blood
What is the structure of catalase?
Catalase is a tetramer which means it has four polypeptide chains
- 4 haem groups
- Very similar to haemoglobin except the haem groups are not attached to the polypeptide chains
What is the function of catalase?
Catalase breaks down hydrogen peroxide which is a natural waste product in the human body and is poisonous
What does the iron do in catalase?
It catalyses the breakdown of hydrogen peroxide
Why is catalase being an antioxidant important?
It breaks down hydrogen peroxide into water and oxygen and this is important because oxidation leads to free radicals which produces chain reactions which are dangerous
Describe what insulin is (cell)
Insulin is a peptide hormone
it cannot diffuse through the phospholipid bilayer so must attach to a receptor with a complimentary shape outside the cell so it can enter
Describe the structure of insulin
2 polypeptide chains one starts with alpha helix and one ends with a beta pleated sheet
- disulfide bonds between chains due to cysteine
What is a fibrous protein?
It is a long and insoluble protein
Why are fibrous proteins long
They are made up of a repetitive, limited range of amino acids
Why are fibrous proteins insoluble?
They have a higher proportion of hydrophobic R groups then hydrophilic R groups so cannot fully arrange themselves so that the hydrophobic R groups are in the interior of the protein
CANNOT INTERACT W WAER
Where is collegan and found?
Skin tendons Cartilage
What is the structure of collagen
2 polypeptide chains wrapped around each other in a helix
Hydrogen bonding between the chains stabilises and strengthens the structure
Cross linking covalent between collagen molecules stabilises
What is the structure of keratin
2 polypeptide chains with lots of cysteine and so lots of disulphide bridges
lots of covalent bonds
so very strong and rigid
inflexible
Where is keratin found
Hair skin nails
What does keratin do in the -skin and what is it doing the -nails and hair
Skin- gives epithelial cells strength
Hair and nails- gives strength and inflexibility
What does keratin do to compensate for a lack of sulphur
It makes saline and hydrogen bonds to connect the polypeptide chains
Where is elastin found
Blood vessels, alveoli, arteries
What does elastin do
It expands and contracts and allows the structure to return back to its original length/shape
What is the structure of elastin
Many monomers calld tropoelastin connected together via interactions between the hydrophobic areas which is stabilised by cross links (covalent bonds) between lysine rich areas
What does elastin do in arteries
When blood passes through with lots of pressure all the elastin expands and when the blood goes back the artery contracts again
which amino acids dont end with an -ine and why
if they have an acidic R group
describe the peptide bond
- due to electron arrangement, acts as a double bond
- stiff and limited rotation
