Proteins

Question 1

What makes up an amino acid?

Answer 1

an amino group
a carbocylic group
its R group

Question 2

How many different naturally occurring amino acids exist?

Answer 2

20

Question 3

How are Polypeptides formed? (4)

Answer 3

 Amino acids joined together by a condensation reaction

 A molecule of water is lost

 A peptide bond is formed between the two amino acids

 Many amino acids joined together form a polypeptide chain

Question 4

How are proteins formed? (4)

Answer 4

 One or more polypeptide chains folded together in a 3-D
shape

 The shape is held together by bonds such as
o Hydrogen bonds
o Ionic bonds
o Disulphide bridges/bonds

Question 5

What is a dipeptide?

Answer 5

Two amino acids bonded together by a peptide bond

Question 6

Where are the peptide bonds formed?

Answer 6

Between Carboxyl (COOH) group on one amino acid and the amino (NH2) Group on another group[

Question 7

What are the three additional bonds proteins may have?

Answer 7

Hydrogen bonds
Disulphide bridges
Ionic bonds

Question 8

How do Hydrogen bonds form?

Answer 8

these bonds form because of the tiny negative
charges (dipoles) on the oxygen of the carboxyl groups and the
positive charges on the hydrogen atoms of the amino groups.
These are weak intermolecular bonds, but because there are a
lot of them they can hold the protein together firmly. Hydrogen
bonds give rise to alpha helices and beta pleated sheets.

Question 9

How are Disulphide bridges formed?

Answer 9

occur when an oxidation reaction happens
between two sulphur-containing amino acids (cysteine or
methionine). These are strong covalent bonds.

Question 10

How are Ionic bonds formed?

Answer 10

these bonds can occur between some of the
strongly positive and negative amino acid side chains found in
proteins

Question 11

What are the 4 types of protein structures?

Answer 11

primary, secondary, tertiary and quaternary

Question 12

Definition of Primary Structure.

Question 12

Definition of Secondary Structure.

Question 13

Definition of Tertiary Structure.

Question 14

Definition of quaternary Structure.

Question 15

What are conjugated proteins?

Answer 15

these are proteins that have another
chemical group associated with their polypeptide chains e.g.
haemoglobin and myoglobin

Question 16

How does the sequence of amino acids determine how the chain will fold up into a
specific shape?

Answer 16

 The primary structure is the sequence of
aminoacids joined together by peptide bonds

 The sequence of the amino acids and their R
groups determine the position of the hydrogen
bonds, ionic bonds and disulphide bonds, that
determine how the chain will fold up into a
specific shape

 The polar R groups will be found on the outside
part of the protein and the non-polar R groups on
the inside

Question 16

Which amino acids are hydrophobic?

Answer 16

Non-polar

Question 16

How are FIbrous proteins formed?

Answer 16

Fibrous proteins are formed from parallel polypeptide chains held
together by cross-links. These form long, rope-like fibres, with high
tensile strength and are generally insoluble in water.

Question 16

Name 3 Globular proteins

Answer 16

• transport proteins– such
  as haemoglobin, myoglobin
  and those embedded in
  membranes.
• enzymes–such as lipase
  and DNA polymerase.
  8
• hormones– such as
  oestrogen and insulin.

Question 17

Which amino acids are hydrophelic?

Answer 17

polar

Question 18

What is a globular protein and why are they soluble most of the time?

Answer 18

Globular proteins usually have a spherical shape caused by
tightly folded polypeptide chains.

The chains are usually folded so that hydrophobic groups are on
the inside, while the hydrophilic groups are on the outside. This
makes many globular proteins soluble in water

Question 19

Name 3 Fibrous Proteins.

Answer 19

• collagen– the main
  component of connective
  tissue such as ligaments,
  tendons, cartilage.
• keratin– the main
  component of hard
  structures such as hair,
  nails, claws and hooves.
  234
• silk– forms spiders’ webs and silkworms’ cocoons.

Question 20

Structural properties of collagen?

Answer 20

Collagen has a triple helix – the helices are
crosslinked. Collage is made up of many parallel
strands that lie side by side. This makes collagen very
strong

Question 21

Compare and contrast Haemoglobin and Collagen.

Answer 21

Haemoglobin  Quaternary structure  Consist of 4 polypeptide chains known as subunits  2 alpha-helix and 2 beta pleated sheets  It’s a conjugated protein (proteins that contain a non aminoacid part on them called prosthetic group)  Has 4 iron-containing haem groups, one on each chain so that the oxygen will bind on them Collagen  Quaternary structure  Consists of 3 polypeptide chains  All 3 a-helix wrapped around each other forming a triple helix  Extremely strong fibres have high tensile strength

Question 21

Compare and contrast globular and fibrous proteins.

Answer 21

Globular  Polypeptide chains have tertiary structure and fold into a compact shape  Bonds = H-bonds, ionic, disulphide, hydrophobic interactions  Each protein has its own specific shape and length of chains  Soluble in water  Easily changed chemically, so not stable  Metabolic functions  E.g haemoglobin Fibrous  Polypeptide chains parallel with little or no tertiary folding  Bonds = usually H-bonds  Different proteins may have similar shapes and lengths of chains of same protein may vary  Insoluble in water  Stable and tough  Structural functions  E.g collagen

Question 21

What causes denaturation?

Answer 21

Changes in temperature, pH or salt concentration can all denature a protein, although the specific conditions will vary from protein to protein.

Question 22

How does denaturation affect globular and fibrous proteins?

Answer 22

Fibrous proteins lose their structural strength when denatured, whereas globular proteins become insoluble and inactive.