Proteins

Question 1

Proteins : elements, monomer, function

Answer 1

CHON(S), Amino acids, structural fibres, enzymes, hormones, antibodies,

Question 2

what does a protein in its Primary structure look like

Answer 2

A sequence of amino acids (polypeptide chain) held together by peptide bonds. Different sequences of amino acids form different proteins in primary structure.

Question 3

what does a protein in its Secondary structure look like

Answer 3

Hydrogen bonds that form between O and H of carboxyl and amine groups make the chain coil into an alpha helix or fold into a beta pleated sheet

Question 4

what does a protein in its Tertiary structure look like

Answer 4

chains are folded and coiled Further. more bonds are formed between parts of the polypeptide chains. Forming a 3-D structure.

Question 5

explain Ionic bonds in proteins

Answer 5

attractions between negatively charged R groups and positively charged R groups

Question 6

explain Disulphide bonds in proteins

Answer 6

Whenever two molecules of the amino acid cysteine come close together the sulphur atom in one cysteine bonds to the other one

Question 7

Hydrophobic and hydrophilic interactions

Answer 7

in a soluble protein When hydrophobic r groups clump together inside the molecule repelling water, hydrophilic r groups are pushed to the outside. this affects how the protein folds up in its tertiary structure

Question 8

Hydrogen bonds in tertiary proteins

Answer 8

weak bonds form between polar r groups

Question 9

Quaternary structure

Answer 9

Made of several polypeptide chains held together by cross-link covalent bonds.

Question 10

Globular proteins

Answer 10

• are round and compact
• The hydrophilic R groups of the amino acids are pushed to outside of the molecules making them soluble
• so they are easily transported in fluids
• also have metabolic function
• can be conjugated ( contains a non-protein group (prosthetic group)
• Irregular amino acid sequence
• more sensitive to changes eg in heat or pH (reactive)

Question 11

what are some of the roles of globular proteins

Answer 11

• metabolic role as enzymes that catalyse reactions eg amylase which catalyses breakdown of starch in the digestive system
• hormones/receptors for cell signalling eg insulin which regulates blood glucose level
• transport substances across cell membrane eg carrier/ channel proteins
• transport substances in the blood eg haemoglobin carries oxygen

Question 12

Fibrous proteins

Answer 12

• Tough and long and narrow rope shaped
• Strong as long strands have high tensile strength
• hydrophilic R groups face inwards - insoluble
• Are structural/ protection proteins so must be fairly unreactive
• contains no conjugated proteins
• little and repetitive amino acid sequence
• Less sensitive to changes eg in heat or pH (unreactive)

Question 13

what are some of the roles of fibrous proteins

Answer 13

• for structure eg as collagen in bone, cartilage, connective tissue,
• for protection eg as keratin in skin, nails and hair
• to give elasticity eg as elastin in blood vessels, alveoli, or cartilage

Question 14

Globular protein examples

Answer 14

Haemoglobin, insulin, Amylase

Question 15

Fibrous protein examples

Answer 15

Collagen, keratin, elastin, actin

Question 16

Structure and function of Haemoglobin

Answer 16

• It is a conjugated protein in quaternary structure
• all four polypeptide chains in haemoglobin has a prosthetic group called haem which contains iron ions which oxygen binds to.
• this allows it to transport oxygen around the body in red blood cells.
• it changes shape during loading and dissociation of oxygen
• Contains the amino acid cysteine

Question 17

What is the function and structure of Insulin (globular)

Answer 17

• a hormone secreted by the pancreas that regulates the blood glucose level
• consist of two polypeptide chains which are held together by disulphide bonds
• when they’re in the pancreas, six of these molecules bind together to form large globular structure.

Question 18

Function and structure of Amylase (globular)

Answer 18

• enzyme that catalyses the Hydrolysis of starch in the digestive system.
• It is made of a single chain polypeptide in its secondary structure, contains both alpha and beta sheets

Question 19

Function and structure of Collagen (fibrous)

Answer 19

• forms animal connective tissues such as bone skin and muscle.
• minerals can bind to the protein to increase its rigidity eg in bones.
• forms a triple helix then a fibre
• made mostly of glycine

Question 20

Function and structure of Keratin (fibrous)

Answer 20

• Found in many external structures of animals eg skin, hair, nails, feathers, and horns
• it can be flexible eg skin or hard and tough eg nails

Question 21

Function and structure of Elastin (fibrous)

Answer 21

• Found in elastic connective tissue such as skin, large blood vessels and some ligaments
• It is elastic so allows tissues to recoil to their original shape after being stretched

Question 22

Explain how the globular structure of haemoglobin makes it suited to its function

Answer 22

The hydrophilic side chains are on the outside of the molecule making it soluble in water which makes it easily transported and it carries oxygen around the body in the blood

Question 23

What is meant by glycoprotein?

Answer 23

A protein combined with a carbohydrate

Question 24

Explain how the structure of collagen contributes to its strength And how it suited to its function

Answer 24

Many hydrogen bonds and strong covalent bonds keep triple helix together, this form a tight coiled helix which will form fibers. This allows it to form strong rigid structures like bone

Question 25

State 4 properties of a globular protein that are different to those of a fibrous protein

Answer 25

Soluble reactive Has many different amino acids Can contain a prosthetic group

Question 26

Explain how the structure of insulin makes it soluble

Answer 26

The hydrophobic R groups on the amino acids of the insulin clump together causing the hydrophilic groups to be pushed to the outside of the molecule making it soluble

Question 27

How to test for a protein

Answer 27

Add a few drops of biuret Regent (NaOH and CuSO4) to the sample, Blue to purple is a positive result

Question 28

Compare the bonding in secondary and tertiary structure of a protein

Answer 28

Secondary structure only has hydrogen bonds but tertiary structures also contain ionic sulphide hydrophobic and hydrophilic interactions

Question 29

what part (groups) of amino acids are involved in condensation to form primary structure of a protein

Answer 29

Amine group and carboxyl group

Question 30

A student uses Biuret test to detect the presence of Enzymes, How is the structure of enzyme allowing it to be detected

Answer 30

Enzymes are globular proteins, the hydrophilic r groups are on the outside making it easy for the reagent to interact with the molecule

Question 31

a doctor suspects haemoglobin in the urine, How can they confirm

Answer 31

haemoglobin is a protein used the biuret test which goes from blue to purple if present

Question 32

examples of proteins

Answer 32

enzymes, anti bodies, carrier proteins

Question 33

Describe in detail how two amino acids bond

Answer 33

A peptide covalent bond would form by condensation between the C from the carboxyl group and the N from the amine group the OH from carboxyl group of one amino acid and the H from amine group from another amino acid releasing a water molecule

Question 34

How do r groups Interact to determine the tertiary structure of a protein

Answer 34

- the S from one R group forms a disulfide bond to another S from a different R group - hydrogen makes a hydrogen bond to a partially negative molecule - Hydrophobic r groups repel water and therefore bundle up causing hydrophilic r groups to surround on the outside - negatively charged molecule forms ionic bond with positively charged molecule

Question 35

Describe what a conjugated protein is

Answer 35

It's a protein with a non protein prosthetic group attached eg Iron attached by Ionic interactions/ hydrogen bonds/ covalent bonds