Proteins Flashcards
How do proteins exist?
Not as long straight chains because the R group causes the polypeptide to fold
Why do R groups interact with each other?
Their different properties and this causes the poly tide to fold to form final protein
What is primary structure?
The sequence of amino acids in a polypeptide
How are amino acids held together?
By peptide bonds
What does the sequence of amino acids determine?
Where certain R groups occur which determines which bonds can occur and where, deciding the shape of the final protein e.g. enzymes and their active site
What is secondary structure?
The folding and coiling caused by hydrogen bonding between hydrogen and oxygen of nearby amino acids
What is an alpha helix?
It is when hydrogen bonds pull the peptide chain into coils
What are beta pleated sheets?
Polypeptide chains lying parallel in sheets held together by hydrogen bonds where the pattern forms pleats
What is tertiary structure?
Brought about by further folding of secondary structure caused by bonds and interactions between R groups
What are the 4 types of bonds within tertiary structure?
Hydrogen bonds, hydrophobic interactions, ionic bonds and disulfide bonds
What are hydrogen bonds?
Weak attraction caused by H being shared between 2 atoms
What are hydrophobic interactions?
Weak association between R groups that do not dissolve in water
What are ionic bonds?
Weak attraction between groups of opposite charge
What are disulfide bonds?
Strong covalent bonds between cysteine amino acids
What happened when all bonds break in tertiary structure?
Te protein experiences denaturalisation and the whole protein unravels
What is the order the bonds within tertiary structure break?
- Hydrophobic interactions
- Hydrogen bonds
- Ionic bonds
- Disulfide bonds
Where do hydrogen bonds form?
Also between hydrogen and nitrogen?
What do disulfide bonds form?
Between R groups containing -SH groups
What is quaternary structure?
The level of structure where two or more polypeptide subunits are bonded together, and the subunits can be identical or different.
What are 4 examples of quaternary structure?
Insulin - two different subunits, haemoglobin - two sets of identical subunits, antibodies - light and heavy chains and catalase with 4 different subunits.
What are the two shapes of proteins?
Globular or fibrous
What are characteristics of globular proteins?
Usually soluble in water and have metabolic roles
What are examples of globular proteins?
Haemoglobin, enzymes and antibodies
What are characteristics of fibrous proteins?
Usually insoluble and have structural roles
What are examples of fibrous proteins?
Silk, collagen and keratin
What type of protein is haemoglobin?
A conjugated protein
What is the structure of haemoglobin?
It has a quaternary structure with 2 alpha polypeptides, 2 beta polypeptides and 4 haem prosthetic groups
How is haemoglobin shaped?
It is ball shaped with a hydrophilic group towards the exterior and hydrophobic towards the interior so is soluble.
Where is haemoglobin located?
Within red blood cells
What is the role of haemoglobin?
Transports oxygen from the lungs to be released in the tissue
How many oxygen molecules can bind to haemoglobin?
One oxygen molecule to each iron in the 4 haem groups
How is the shape important?
It is important to how well it can bind and release oxygen
Where is the haem located?
In the centre of each subunit, so it’s protected from being oxidised and destroyed by the oxygen it transports
What is insulin?
A hormone involved in blood glucose regulation
Where is insulin transported?
In the blood so it needs to be soluble
What do hormones do?
They fit into the specially shaped receptor proteins on cell surface membranes
What does tertiary structure do for hormones?
It gives the hormone a precise shape to fit the receptor
What is catalase?
An enzyme specific to a particular reaction
What is catalase’s substrate?
Hydrogen peroxide
Where does hydrogen peroxide come from?
ApIt is a common by-product of metabolism but it damages cells and organelles
What is the structure of catalase?
It is a quaternary protein with 4 haem prosthetic groups
How does catalase work?
Iron (II) ions are present which allows catalase to interact with hydrogen peroxide and speed up its breakdown which produces oxygen and water
Where is catalase found?
In all cells
What is the equation for the breakdown of hydrogen peroxide?
2H₂O₂ -> 2H₂O + O₂
What are features of fibrous proteins?
They are insoluble molecules with high proportions of hydrophobic R groups and are not folded into complex 3D shapes, their amino acids usually have a limited range of small amino acids which leads to a very organised structure.
What are examples of fibrous proteins?
Keratin, elastin and collagen
Where is keratin found?
In hair, skin and nails
Where is elastin found?
Walls of blood vessels and alveoli
Where is collagen found?
Skin, tendons, ligaments and nervous tissue
What does keratin contain?
A large proportion of sulfur containing amino acids with many strong bonds
What is keratin like as a protein?
It is strong, inflexible and insoluble
What determines the flexibility of keratin?
The number of bonds
Where is elastin present?
Elastic fibres
What is the structure of elastin?
It has a quaternary structure made of many stretchy molecules called tropoelastin
Why is elastin flexible?
It is essential for lining arteries which need to expand and return to its original shape
What is the structure of collagen?
It has a quaternary structure with each polypeptide chain a coil made of 1000 amino acids which 3 of the r wish together in a triple helix to form a molecule
What are the amino acids in collagen?
Every 3rd amino acid is glycine and there are as many prolines and hydroxyproline amino acids and the R groups are small
What do collagen molecules form?
Hydrogen bonds and covalent bonds called cross links with two other collagen molecules to form fibrils
What do crosslinks do?
They are staggered along the molecules to give strentgh and flexibility
What do fibrils for,?
They are joined by together to form a collagen fibre of quaternary structure
What is collagen a component of?
Bone, cartilage, tendons and wall of arteries providing mechanical strength such as tendons, ligaments and skin
What are tendons and ligaments?
They are mostly collagen with many fibres in large bundles and they connect skeletal muscle to bone, forming strong connections to pull bones for movement
What is collagen’s purpose in skin?
The fibres form a mesh that is resistant to tearing
How are bones formed?
From collagen plus calcium phosphate to make them hard
How is collagen used cosmetically?
It is injected for example into lips to make them look fuller
