Proteins

Question 1

Peptides + proteins

Answer 1

Polymers of amino acids molecules
Proteins consist of one or more polypeptides arranged as complex macromolecules
Contain carbon, hydrogen, oxygen and nitrogen

Question 2

Amino acids

Answer 2

All have the same basic structure
R groups result in different amino acids
20 amino acids found in cells
- 9 essential obtained from what we eat
- 5 non-essential as bodies make them from other amino acids
- 6 conditionally essential as they are only needed by infants and growing children

NH2CHRCOOH

Question 3

synthesis of peptides

Answer 3

Amino acids join when amine + carboxylic acid groups react
Peptide bond is formed between amino acids + water is produced (condensation reaction)
A dipeptide compound is produced
Peptide bonds break by hydrolysis (protease enzyme used to catalyse the reaction)

Question 4

Many amino acids joined together by peptide bonds

Answer 4

Makes a polypeptide

Reaction is catalysed by the enzyme peptides transferase present in ribosomes

Question 5

How are different proteins with different structures made.

Answer 5

Different R-groups of amino acids make up a protein are able to interact with each other (R-group interactions) forming different types of bonds
-bonds lead to a long chain of amino acids folding into complex shapes (proteins)
Different sequences of amino acids and different shapes or proteins change the function a protein has within a living organism

Question 6

Levels of protein structure

Answer 6

1. Primary
2. Secondary
3. Tertiary
4. Quaternary

Question 7

Primary structure

Answer 7

Sequence of amino acids 
Directed by information within DNA
Sequence of amino acids influence how polypeptides fold to give proteins their final shape
Determining proteins function 
Bonds involved = peptide bonds

Question 8

Secondary structure of proteins

Answer 8

Amino acids fold into regions with the repeating patterns
O,H,N atoms of the departing structure interact
Hydrogen bonds may firm within the amino acid chain pulling it into a coil shape (alpha helix) between 1&4 amino acid
Polypeptide chains can also lie parallel to one another joined by hydrogen bonds forming sheet like structures ( beta pleated sheets)

Contains peptide + hydrogen bonds

Question 9

Tertiary structure

Answer 9

• Folding of proteins into final shape
• Includes sections of secondary structure
• Coiling and folding of proteins into their secondary structure brings R groups of different amino acids closer together so they are close enough to interact and further folding of these sections will occur
• interactions include:
  Hydrophobic + hydrophilic interactions -weak interactions between polar and non polar r groups
  Hydrogen bonds
  Ionic bonds - form between oppositely charged r groups
  Disulphides bonds (bridges) - covalent + only form between R groups with sulfur atoms

Question 10

Subunit is in quaternary structure

Answer 10

Enzymes usually have 2 identical subunits
Insulin (hormone) has 2 different subunits
Hämoglobin has 4 subunits,

Question 11

Hydrophobic + hydrophilic interactions in proteins

Answer 11

Proteins are made in the aqueous environment of the cytoplasm
The way in which proteins fold depends on whether the r groups are hydrophobic or hydrophilic
Hydrophilic are in the outside of the protein
Hydrophobic are on the inside of the protein shielded from the water in the cytoplasm

Question 12

Main groups of proteins

Answer 12

Globular

Fibrous

Question 13

Globular proteins

Answer 13

Compact
Water soluble
Roughly spherical in shape

Form when proteins fold into their tertiary structures in such a way that hydrophobic r groups are kept away from the aqueous environment
Hydrophilic r groups are on the outside

Question 14

Insulin

Answer 14

Globular

Structure:
Compact, spherical shape
Primary structure amino acids do,dead in secondary structure alpha helixes which are further folded into tertiary structure

Function:
Hormone involved in regulation of blood glucose concentration
Soluble - hormone needs to be transported in blood stream
Need to have precise shapes to fit into receptors of cell membranes

Question 15

Conjugated proteins

Answer 15

Globular proteins that contain a non-protein component called prosthetic group

Proteins without a prosthetic group are called simple proteins

Question 16

Prosthetic groups

Answer 16

Lipids or carbohydrates can combine with proteins forming lipoproteins or glycoproteins
Metal ions and molecules derived from vitamins also reduce prosthetic groups

Haem groups contain iron(II) Ion (Fe2+)
Catalase and Hämoglobin both contain haem groups

Question 17

Haemoglobin

Answer 17

Red, oxygen carrying pigment found in red blood cells

Structure:
Made form four polypeptides (subunits)
(2 alpha, 2 beta)
Each subunit containing a prosthetic haem group
Haem group contains iron(II) ion capable of carryons one oxygen molecule

Function:
To carry and transport oxygen around the body
Picks up O2 in the lungs and transports it to where it is needed
Four subunits increases efficiency of oxygen transportation

Question 18

Catalase

Answer 18

An enzyme

Structure:
Consists of 4 identical subunits
contains 4 Haem prosthetic groups

Function:
Catalysts reactions
Presence of iron(II) allows catalase to interact with hydrogen peroxide and speed up its breakdown
Catalase makes sure hydrogen peroxide doesn’t accumulate as it is damaging to cells

Question 19

Fibrous proteins

Answer 19

Strand like proteins

Formed from long insoluble molecules
Due to presence of high proportion of amino acids with hydrophobic R groups in their primary structure
Contain a limited range of amino acids with small r groups (amino acid sequence is usually repetitive)
Leads to organ aided structures
Tend to make strong , long molecules NOT a folded into complex 3D shapes

Question 20

Keratin

Answer 20

Fibrous proteins
Contains large proportion of cysteine (sulfure containing amino acid)
Results in strong disulphides bonds/ bridges forming strong inflexible and insoluble materials
Degree of disulphide bonds determines flexibility EG hair has less than nails therefore is more flexible
Unpleasant smell of hair and skin burning is because of large quantities of sulfur
Present in hair, skin and nails

Question 21

Elastin

Answer 21

Fibrous proteins found in elastic fibres

Structure:
Quaternary protein made from many stretchy molecules called tropoelastin
Tropoelastin are able to stretch and recoil without breaking, acting as small springs
Contain alternate hydrophibic and lysine rich ares (stabilised by cross linking covalent bonds)

Function:
Elastic fibres are found in walls of blood vessels and in the alveoli of lungs - gives structures needed but to also return to their normal size (skin)

Question 22

Collagen structure + properties

Answer 22

Fibrous protein

3 polypeptides wound together in a triple helix structure to form a rope like structure

Every 3rd amino acid is glycine which is a small amino acid which allows the three protein molecules to form a closely packed helix structure
Staggered ends formed by hydrogen bonds between the polypeptide chains allow proteins to join end to end, forming long fibrils called tropocollagen (which cross-link to produce string fibres)
R groups in the amino acids, proline and hydroxyproline, repel each other, which adds to the stability of collagen

Question 23

Collagen function

Answer 23

Connective tissue found in skin, tendons connective tissue and ligament

In skin, collagen fibres form a mesh which is resistant to tearing