proteins

Question 1

What are amino acids?

Answer 1

Amino acids are monomers and are joined together via peptide bonds to form dimers (dipeptides) and polymers (polypeptides)

Question 2

What are the function of amino acids?

Answer 2

• Enzymes- breakdown and synthesise molecules

•Antibodies -defence against infection and immune response

•Transport- some proteins can move molecules/ions across membranes e.g haemoglobin

• structural component- keratin and collagen, used to create strong fibres

• hormones- act as chemical messengers in the body

• muscle contraction- muscles are made up of proteins e.g actin

• storage

• membrane proteins e.g carrier proteins

Question 3

What are amino acids made up of?

Answer 3

An amino group (amine), R group and a carboxyl group

Question 4

What do R groups do?

Answer 4

Each amino acids has a different R group which determines its properties

Question 5

What is the general formula of an amino acid?

Answer 5

RCH(NH2)COOH

Question 6

What bonds are found in an amino acid?

Answer 6

Peptide bonds

Question 7

What is the synthesis and breakdown of a dipeptide?

Answer 7

A condensation reaction between two amino acids forms a dipeptide and a molecule of water

A hydrolysis reaction breaks the dipeptide back into 2 amino acids

Question 8

How is a peptide bond formed?

Answer 8

The hydroxyl (OH) in the carboxyl group of one amino acid reacts with the hydrogen (H) in the amino group of another amino acid. This releases a water molecule and forms a peptide bond between the carbon of one amino acid and the nitrogen of another.

Question 9

What solution do you use to test for a protein?

Answer 9

Biuret solution

Question 10

How do you test for a protein?

Answer 10

1. Placed food sample in a test tube
2. Add equal volume of biuret solution (sodium hydroxide and copper sulphate)
3. If proteins are present, it will turn from blue to purple/lilac

Question 11

What is a protein?

Answer 11

Proteins are large complex molecules with unique 3-D structures

Question 12

What is a protein made up of?

Answer 12

Amino acids

Question 13

What is the primary structure of a protein?

Answer 13

• unique sequence of amino acids in the polypeptide chain
• order of amino acids determines structure
• a change to just one amino acid can result in a change to the proteins function

Question 14

What is the secondary structure of a protein?

Answer 14

• a polypeptide chain can fold to form an alpha helix or a beta pleated sheet
• these folds are held together by hydrogen bonds

• weak hydrogen bonds form between partially positive hydrogen atoms and slightly negative oxygen atoms
• hydrogen bonds maintain stability

Question 15

What structures can be found in the secondary structure of a protein?

Answer 15

• alpha helix
• beta pleated sheet

Question 16

What is the tertiary structure of a protein?

Answer 16

• the tertiary structure forms when the polypeptide chain folds and twists further to create complex 3-D structure
• held together by bonds between the different R groups

Hydrogen bonds , ionic bonds, disulphide bridges, hydrophobic and hydrophilic interactions

Question 17

What bonds can be found in the tertiary structure?

Answer 17

• Hydrogen bonds- individually weak but provide strength in large numbers

• ionic bonds- these form between positive and negative R groups

• disulphide bridges- these form between R groups that contain sulphur (e.g cysteine)

• hydrophobic and hydrophilic interactions- these are weak interactions between polar and nonpolar R groups

Question 18

What is the quaternary structure of a protein?

Answer 18

Two or more polypeptide chains held together by the same bonds found in the tertiary structure

E.g haemoglobin

Question 19

What is a conjugated protein?

Answer 19

• A non-protein group attached (prosthetic group)

E.g haemoglobin
• 4 polypeptide chains (quaternary structure) each chain is conjugated
• heam group- iron which binds to oxygen
•

Question 20

What is the non-protein in a conjugated protein called?

Answer 20

Prosthetic group

Question 21

What roles do globular proteins have in the body?

Answer 21

Metabolic roles

Question 22

What is the structure of a globular protein?

Answer 22

Spherical/ball shaped, compact, soluble proteins

Question 23

What are examples of globular proteins?

Answer 23

Haemoglobin, insulin, amylase

Question 24

What is the structure and function of haemoglobin?

Answer 24

Structure: conjugated protein with a prosthetic group. Each of the four polypeptide chains in haemoglobin has a prosthetic group which contains iron which oxygen binds to.

Function: carries oxygen around the body in red blood cells

Question 25

What is the structure and function of insulin?

Answer 25

Structure: two polypeptide chains held together by disulphide bonds. When in the pancreas six of these molecules bonded together to form a large globular structure, precise shape to fit receptors Function: a hormone secreted by the pancreas, helps regulate the blood glucose levels

Question 26

What is the structure and function of amylase?

Answer 26

Structure: made up of a single chain of amino acids. Its secondary structure contains both alpha helix and beta pleated sheets Most enzymes are globular proteins function: amylase is an enzyme, catalyses the breakdown of starch in the digestive system

Question 27

What is the role of fibrous proteins in the body?

Answer 27

Structural support

Question 28

What is the structure of fibrous proteins?

Answer 28

Several polypeptide chains are twisted together like ropes Fibrous proteins form long strands which are insoluble Simple repeating sequence of just a few amino acids so that polypeptide chains can twist tightly like a rope

Question 29

What are examples of fibrous proteins?

Answer 29

Collagen, keratin, elastin

Question 30

What are the properties and function of collagen?

Answer 30

Properties: three polypeptide chains held together with hydrogen bonds, rope like structure, provides strength and flexibility to the molecule. It is a very strong molecule, minerals combined to the protein to increase rigidity e.g in bone Function: collagen is found in animal connective tissues such as bone, skin and muscle

Question 31

What are the properties and the functions of keratin?

Answer 31

Properties: it can be either be flexible (in skin) or hard and tough (in nails). Large numbers of cysteine- strong disulphide bonds- strong and insoluble molecules Function: found in many external structures of animal such as skin, hair, nails, feathers, horns

Question 32

What are the properties and the function of elastin?

Answer 32

Properties: it is elastic, so it allows tissues to return to their original shape after they’ve been stretched Function: it is found in elastic connective tissue, such as skin, large blood vessels and some ligaments

Question 33

How does a protein denature?

Answer 33

When a protein is denatured, it loses its tertiary structure permanently. Proteins can be denatured by high temperature and changes in pH. As the molecules gain energy they vibrate more and weak bonds will break. If a protein is denatured its shape is changed and it will no longer be able to function