3.1.4 Proteins

Question 1

What are proteins made out of?

Answer 1

Amino acids

Question 2

What is a dipeptide

Answer 2

2 amino acids

Question 3

What’s a polypeptide?

Answer 3

More than 2 amino acids

Question 4

What is a protein ?

Answer 4

One or more polypeptides

Question 5

What elements make up proteins?

Answer 5

C, H, O, N
Some have S

Question 6

Draw and amino acid

Answer 6

H H O
\ | //
H - N-C-C
/ | \
H R O

COO is carboxyl
R=R-group (variant)
NH3 = amino

Question 7

How many R groups are there?
And how many amino acids?

Answer 7

20 R groups
20 amino acids

Question 8

Peptide bonds are formed between which groups?
What type of reaction?

Answer 8

Amino and carboxyl
Condensation

Question 9

Which elements hold the peptide bond?

Answer 9

Nitrogen and carbon

Question 10

Describe the first level of protein structure

Answer 10

Primary structure

Order of amino acids in a polypeptide

Determines shape and function of protein

A change in 1 amino acid can change the shape and may stop its function

Linked by only peptide bonds

Question 11

Describe the 2nd level of protein structure

Answer 11

Chains fold into 2 different shapes:
Alpha helices(most common)
Beta pleated sheets(less common)

Hydrogen bonds between CO and NG of adjacent amino acids (no r groups involved )

Found in all proteins

R groups are stuck out to the side ready for bonding in the tertiary structure

Secondary structure

Question 12

Describe the 3rd level In protein structure

Answer 12

Further folding caused the R group bonding and forms a 3D shape

Contains hydrogen bonds(weak) ionic bonds (stronger but vulnerable to changes in PH) Disulphide bridge(very strong covalent bonds)

This makes a globular protein(3D)

Has hydrophobic interactions

Tertiary structure

Question 13

What is a disulphide bond?

Answer 13

2 sulfur atoms bonded (split by reducing agents)

Question 14

What is the 4th level of protein structure?

Answer 14

Quaternary structure

2 or more polypeptide chains combine

Joined by bonds same as tertiary (H, disulphide bonds, ionic)

Only some proteins exhibit quaternary structure

Example: haemoglobin consists of 4 polypeptide chains held by disulphide bonds bridges and non protein prosthetic group

Question 15

Protein shape to function

Answer 15

Roles depends upon their molecular shape-2 types:
Fibrous- proteins like collagen have structural roles - polypeptide chains linked in parallel chains or sheets with numerous cross linked to make fibres

Globular- perform metabolic functions- shape is compact and folded spherical

Question 16

Fibrous - globule similarities and differences

Answer 16

Fibrous:
Structural function
Regular repetitive sequences
H bonding
Cross linked to form long fibres
Stable
Insoluble in water

Globular:
Metabolic function
Irregular sequences (spherical shape)
H, ionic and disulphide bridges/bonding-hydrophobic bonds
Depressions(other molecules can fit in)
Relatively unstable
Soluble in water

Question 17

Function of proteins

Answer 17

Transport
Movement
Sensitivity and coordination (nervous system and hormone system)
Reproduction
Protection(immune system)

Question 18

Method to test for proteins

Answer 18

Place sample of solution in test tube and add equal volume of biurets reagent

If present then solution is purple/lilac

Of negative results solution stays blue