Proteins

Question 1

What are amino acids?

Answer 1

Monomers of all proteins, and all amino acids have the same basic structue.

Question 2

What are peptide bonds?

Answer 2

A bond formed when two amino acids are joined by a condensation reaction. Peptide bonds are broken by hydrolysis reactions when water is removed.
Peptide bonds are a type of covalent bonds.

Question 3

What are proteins?

Answer 3

Proteins are large polymers comprised of long chains of amino acids.
Both plants and animals need amino acids to makes proteins. Animals can make some amino acids, but must ingest others (called essential amino acids). Plants can make all the amino acids they need, but only if they can access fixed nitrogen.

Question 4

What is the function of proteins?

Answer 4

They form structural components of animals in particular. For example, muscles are made of proteins.
Their tendency to adopt specific shapes makes proteins important as enzymes, antibodies and some hormones.
Membranes have protein constituents that acts as carriers and pores for active transport across the membranes and facilitated diffusion.

Question 5

What is the structure of amino acids?

Answer 5

Each amino acids contains the elements carbon, hydrogen, oxygen and nitrogen. Some amino acids contain Sulphur.
Proteinogenic- amino acids that are found in proteins.
Each protein chain of amino acids has and amino group (-NH2), a carboxyl (-COOH), and R-group.
H- H = O
N-C-C
H- R - OH

Question 6

What is the Primary structure of Proteins?

Answer 6

The sequence of amino acids found in a molecule.
The number and order of amino acids in a protein chain is important, as changing just one amino acid can alter the function of the protein. The order of amino acids in the primary structure will determine the shape of the protein molecule, through its secondary, tertiary and quaternary structure.
The primary structure is held together by peptide bonds.

Question 7

What is the Secondary structure of Proteins?

Answer 7

The coiling or folding of an amino acid chain, which arises often as a result of hydrogen bond formation between different parts of the chain. The main forms of secondary structure are an a-helix and a b-pleated sheet.
The bonds in the a-helix and b-pleated sheet are hydrogen bonds.
Both the a-helix and the b-pleated sheet are stable structures at optimal temperature and pH.

Question 8

What is the Tertiary structure of Proteins?

Answer 8

The overall three-dimensional shape of a protein molecule. Its shape arises due to interactions including hydrogen bonding, disulfide bridges, ionic bonds and hydrophobic interactions.

Question 9

What is the Quaternary structure in Proteins?

Answer 9

A Protein structure where a protein consists of more than one polypeptide chain. For example, insulin has a quaternary structure.

Question 10

What are Hydrogen bonds in Proteins?

Answer 10

Hydrogen bonds- they form between hydrogen atoms with a slight positive charge and other atoms with a slight negative charge. These form in hydroxyl, carboxyl and amino groups. They are involved in keeping the tertiary and quaternary structure of the protein in the correct shape. The presence of lots of hydrogen binds can give protein molecules a lot of strength.

Question 11

What are Ionic bonds in Proteins?

Answer 11

Ionic bonds can form between those carboxyl and amino groups that are part of the R groups.
These ionise into NH3+ and COO- groups.
Positive and negative groups like this are strongly attracted to each other to form an ionic bond.

Question 12

What are Disulfide links in Proteins?

Answer 12

The R group of the amino acid cysteine contains Sulphur. Disulfide bridges formed between the R groups of two cysteine.
These are strong covalent bonds.

Question 13

What are Hydrophobic and Hydrophilic interactions?

Answer 13

Hydrophobic parts of the R groups tend to associate together in the centre of the polypeptide to avoid water.
Hydrophilic parts are found at the edge of the polypeptide to be close to the water.
Hydrophobic and hydrophilic interactions cause twisting of the amino acid chain, which changes the shape of the protein.

Question 14

What are Fibrous Proteins?

Answer 14

They have a relatively long, thin structure. It is insoluble in water and are metabolically inactive, often having a structural role within an organism.
These features enable them to form fibres, which tend to have a structural function.
Examples include collagen and elastin (in the connective tissue) and keratin (in the hair).

Question 15

What are Globular Proteins?

Answer 15

They have molecules of a relatively spherical shape, which are soluble in water, and often have metabolic roles within the organism.
The hydrophobic R groups are turned inwards towards the centre of the molecule, while the hydrophilic groups are on the outside.
They often have very specific shapes, which helps them to take up roles as enzymes, hormones (such as insulin) and Haemoglobin.

Question 16

Collagen:

Answer 16

In artery walls, a layer of collagen prevents the artery from bursting when withstanding high pressure from blood being pumped by the heart.
Tendons are made of collagen and connect muscles to bones, allowing them to pull on bones.
Bones are made from collagen, and then reinforced with calcium phosphate, which makes them hard.
Cartilage and connective tissue are made from collagen.

Question 17

Keratin:

Answer 17

Keratin is rich in cysteine so lots of disulfide bridges form between its polypeptide chains. This and hydrogen bonding makes it very strong.
Keratin is found wherever a body part needs to be hard and strong. It is found in finger nails, hair, claws, hoofs, horns, scales, fur and feathers. It provides mechanical protection, but also provides an impermeable barrier to infection and, being waterproof, also prevents entry of water-borne pollutants.

Question 18

Elastin:

Answer 18

Cross-linking and coiling make the structure of elastin strong and extensible. It is found in living things where they need to stretch or adapt their shape as part of life processes.
Skin can stretch around our muscles and bones because of the elastin. Without elastin, skin would not go back to normal after being pinched.
Elastin in our lungs allows them to inflate and deflate, and in our bladder helps it to expand to hold urine.
Like collagen, 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

Question 19

Haemoglobin:

Answer 19

This overall structure of Haemoglobin is quaternary. It is made up of two a-globin chains and two b-globin chains, which each have their own tertiary structure.
Haem groups are held together by the prosthetic groups.
The Haem group contains an iron ion. A protein associated with this kind of group is called a conjugated protein.
The function of Haemoglobin is to carry oxygen from the lungs to the tissues. In the lungs, an oxygen molecule binds to the iron in each of the four haem groups in the Haemoglobin molecule. When it binds, the Haemoglobin turns from a purple red colour to bright red. The oxygen is released by the Haemoglobin when it reaches the tissues.

Question 20

Insulin:

Answer 20

Insulin is made from two polypeptide chains ( a-helix and b-sheet). 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 to glycoprotein receptors on the outside of muscle and fat cells to increase their uptake of glucose from the blood, and to increase their rate of consumption of glucose.

Question 21

Pepsin:

Answer 21

Is an enzyme that digests protein in the stomach.
The enzyme is made up of a single of polypeptide chin of 327 amino acids, but it folds into a symmetrical tertiary structure.
Pepsin has very few amino acids with basic R groups, whereas it has 43 amino acids with acidic R groups. This helps to explain why it is so stable in the acidic environment of the stomach, as there are few basic groups that accept H+ ions.
The tertiary structure is held together by hydrogen bonds and two disulfide bridges.