Proteins Flashcards
What are amino acids?
They are the monomers of all proteins, and all amino acids have the same basic structure
What bond is formed when 2 amino acids are joined by a condensation reaction?
Peptide bond
Give information about proteins
Large polymers compromised of long chains of amino acids
Both plants and animals need amino acids to make proteins but most ingest others “essential amino acids”
What is the structure of amino acid?
Carbon, nitrogen, hydrogen, oxygen
Some may contain sulfur
20 are found as protein
Each protein chain of amino acids has 1 amino group (-NH2) and a carboxyl group (-COOH)
Most amino acid names end in -ine, except when the R group is acidic (contains free -H+ ions)
How are the peptide bond formed?
Enzymes catalyses the condensation reaction
Protease enzyme in the intestines break peptide bond during digestion
They also break down protein hormones so that their effects are not permanent
A protein may consist of a single polypeptide chain or more than 1 chain bonded together
What is a dipeptide?
2 amino acids joined together
What is a polypeptide?
Many amino acids joined together
What is the primary structure?
The sequence of amino acid found in a chain
What is the secondary structure?
The coiling and folding of an amino acid chain, which arises often as a result of hydrogen bond formation between different parts of the chain
What is the tertiary structure?
The overall 3D shape of a protein molecule. Its shape arises due to interactions including H-bonding, disulfide bridges, ionic bond and hydrophilic/hydrophobic interactions
What is the quaternary structure?
Protein structure where a protein consists of more than 1 polypeptide chain
Describe the bonding in proteins with reference to the different structures
Chains of amino acid in primary structure are held together by peptide covalent bonds, which are strong
Other types of bond form between amino acid in difference parts of the polypeptide chain:
Secondary structure is primarily held together by H-bonds
Tertiary and quaternary structure are held together by H-bonds andmany others
Describe hydrogen bonds
Form between slightly positive hydrogen atoms and other atoms with a slight negative charge
In amino acids H-bonds are formed in hydroxyl, carboxyl, and amino groups
Describe Ionic bond
They form between those carboxyl and amino groups that are part of R groups
These ionis into NH3+ and COO- groups
Positive and negative groups like this are strongly attracted to each other
Describe disulfide links
The R group of the amino acid cysteine contain sulfur
Disulfide bridges are formed between the R group od 2 cysteines - strong covalent bonds
Describe hydrophobic and hydrophillic interactions
These interactions cause twisting of the amino acid chain, which changes the shape of the protein
Important: most proteins are found in water-based environments
What are fibrous proteins?
They have a relatively long, thin structure, they are insoluble in water and metabolically inactive.
They have a regular, repetitive sequence of amino acids and are usually insoluble in water. These features enable them to form fibres which tend to have a structural function
What are globular proteins?
Has molecules of a relatively spherical shape, which are soluble in water, and often have metabolic roles within the organism
Any hydrophobic R groups are turned inwards towards the center of the molecule, while hydrophilic groups are on the outside. This makes the protein water soluble because water molecules can easily cluster around and bond to them. They often have very specific shapes, which helps them to take up roles as enzymes, hormones (such as insulin) and hemoglobin
What structures fall into the two categories of fibrous proteins and globular proteins?
3D tertiary and quaternary structure
Is collagen a fibrous protein or a globular protein?
Fibrous
What is the function of collagen?
To provide mechanical strength:
In artery walls, layer of collagen prevents the artery from bursting when it has to with stand high pressure from blood being pumped by the heart
tendon are made often collagen
Is haemoglobin a fibrous protein or a globular protein?
Globular
Describe the structure of haemoglobin
Quaternary structure - 4 polypeptides - 2 alpha globin chain, 2 beta globin chains - each of these with a tertiary structure
At one position on the outside of each chain, there is a space in which a haem group (essential) is sheld = called prosthetic group
Not made of amino acids
Haem group contains iron ion
A protein is associated with this kind of group is called a conjugated protein
Give information about keratin
It is rich in cysteine (a type of protein) so lots of disulfide bridges form between its polypeptide chains. Alongside hydrogen bonding, this makes the molecule very strong.
Hard and strong
Provides mechanical protection, but also provides an impermeable barrier to infection and, being waterproof, also prevents entry of water-borne pollutants
Give information about elastin
Cross-linking and coiling make the structure of elastin strong and extensible.
They can stretch and adapt their shape as part if life processes
e.g. Skin can stretch around our bone and muscles because of elastin. Without it, skin would not go back to normal after being pinched
Like collage, elastin helps our blood vessels to stretch and recoil as blood is pumped through them, helping maintain the pressure wave of blood as it passes through
Describe the structure of insulin
It is made of 2 polypeptides chain. The A chain begins with a section of alpha-helix and B chain ends with a section of beta-pleat. Both chains fold into a tertiary structure and are then joined together by disulfide links. Amino acids with hydrophilic R groups are on the outside of the molecule, which makes it soluble in water.
Insulin binds the glycoprotein receptors on the outside of the muscle and the fat cells to increase their uptake of glucose from the blood, and their rate of consumption of glucose.
Give information about pepsin
It is an enzyme that digests protein in the stomach. The enzyme is made io if a single polypeptide chain 327 amino acids, but it folds in a symmetrical tertiary structure.
Stable in an acidic environment in the stomach
Its tertiary structure is also held together by H-bonds and 2 disulphide bridges
