Proteins Flashcards
What are 4 roles of amino acids and give an example for each?
Structure: muscle
Catalytic: enzymes
Cell signalling: hormones
Immunological: antibodies
What is the general structure of an amino acid?
On the left is the amino group: 2 separate hydrogen atoms are single bonded to a nitrogen atom
On the bottom is the R group which is represented by R
On the right is the carboxylic acid group: an OH is single bonded to a carbon and an Oxygen is double bonded to the same carbon
In the middle is a Carbon that the nitrogen and carbon from the other groups bind to and above it is a hydrogen atom
How do amino acids form and break?
Form: During a condensation reaction 2 amino acids will be joined to together by a peptide covalent bond and form a dipeptide molecule
Break: During a hydrolysis reaction the peptide covalent bond is broken and water is added which causes two amino acids to be formed
How many naturally occurring amino acids are there?
20
What are polypeptides and how are they formed?
They are long chains of amino acids which are formed as more amino acids are added to dipeptides through condensation reactions that release water and form peptide bonds
What is the primary structure of a protein?
The order of amino acids that is held together by peptide bonds
What is the secondary structure of proteins?
The areas of initial folding. The structure is held together by hydrogen bonds in main structures called alpha helix and beta pleated sheets
What is the tertiary structure of proteins?
Interactions of the R groups, it is given a 3D shape as it is held together by 4 bonds and interactions: hydrogen bond, disulphide bridge, ionic bond and a cluster of hydrophobic groups behind the hydrogen bond
How are hydrogen bonds formed and how strong are they?
Slightly +charged H and slightly -charged O come into close contact it forms hydrogen bonds.
They are very weak
How are ionic bonds formed and how strong are they?
Ionic bonds are formed when oppositely charged R groups come into close contact with one another.
They aren’t particularly strong
How are disulphide bonds/bridges formed?
A disulphide bond is formed between cysteine molecules which contain sulfur. When the cysteines are close they form double covalent bonds.
They are very strong and heard to break
Where do hydrophobic and hydrophilic interactions take place?
In a water based environment hydrophobic amino acids will be most stable when there is no water present.
The hydrophilic amino acids will be found on the outside and hydrophobic in the inside
What is the quaternary structure of a protein?
The product of two or more polypeptides joining together or if a prosthetic group is present.
How does denaturing occur and what does it do?
Denaturing occurs when the bonds of a protein are broken
It mostly happens in hydrogen and ionic bonds as they are the weakest
It can be caused by changes in temperature, pH or salt concentration
Fibrous proteins lose their structural strength when denatured whereas globular proteins become insoluble and inactive
What are globular proteins and what is their structure like?
Spherical proteins that are caused by tightly folded polypeptide chains
The chains are usually folded so that hydrophobic groups are on the inside and hydrophilic groups on the outside which makes most globular proteins soluble in water
What are the roles of globular proteins and give an example for each?
Transport proteins such as haemoglobin
Enzymes such as amylase
Hormones such as insulin
Haemoglobin is a globular protein, describe its structure
Made of 4 polypeptide chain subunits: 2 alpha, 2 beta
within 4 subunits there are 4 prosthetic groups which each contain Fe2+
It’s a conjugated protein as it is a globular protein with a prosthetic group
It is soluble
Amylase is an enzyme made from a globular protein, describe its structure and its function
It is soluble
It is made from a single chain of amino acids
Its secondary structure has alpha helices and beta pleated sheets
It only works if the co-factor Cl- is bound to it
Its function is to break down starch into maltose
Insulin is a hormone made from a globular proteins, describe its structure and its function
It is soluble
It is made of 2 amino acid chains that are joined together by disulphide bonds
Its function is to turn glucose into glycogen and store it in muscle tissue and the liver
What are the functions of Fibrous proteins?
They make up keratin and elastin
What is the structure of fibrous proteins like?
Formed from parallel polypeptide chains that are held together by cross-links
They form long, rope-like fibres, with high tensile strength
Generally insoluble in water
What is the use of keratin? Give 3 examples
Provides protection on animals
Hair, claws, feathers, hooves, nails
What is the function of elastin? Give 3 examples
Major component in tissues that require elasticity
Arteries, lungs, bladder, skin, cartilage
What are 3 characteristics of fibrous proteins?
Insoluble
Elongated
Forms cross-links
High tensile strength
Flexible
What are 4 characteristics of globular proteins?
Soluble
Spherical
3D shape
Complementary to another molecule
Sensitive to pH and temperature
Can contain a prosthetic group
Hydrophilic on the outside
