Proteins and Amino Acids

Question 1

Protein types

Answer 1

Enzymatic proteins
Storage proteins 
Hormonal proteins 
Contractile and motor proteins 
Defensive proteins 
Transport proteins 
Receptor proteins 
Structural proteins

Question 2

Enzymatic proteins

Answer 2

Function: selective acceleration of chemical reactions
Example: Digestive enzymes catalyse the hydrolysis of bonds in food molecules.

Question 3

Storage proteins

Answer 3

Function: Storage of amino acids
Example: Casein is the protein in milk. It is the main source of amino acids for baby mammals.

Question 4

Hormonal proteins

Answer 4

Function: Coordination of an organisms activities
Example: Insulin (a hormone secreted by the pancreas) causes other tissues to take up glucose thus regulating blood sugar conc.

Question 5

Contractile and motor proteins

Answer 5

Function: Movement
Example: Motor proteins are responsible for the undulations of cilia and flagella. Actin and myosin proteins are responsible for the contraction of muscles.

Question 6

Defensive proteins

Answer 6

Function: Protection against disease
Example: Antibodies inactivate and help destroy viruses and bacteria

Question 7

Transport proteins

Answer 7

Function: Transport of substances
Examples: Haemoglobin (iron containing protein) transports oxygen from the lungs to other parts of the body. Other proteins transport molecules across cell membranes

Question 8

Receptor proteins

Answer 8

Function: Response of cell to chemical stimuli
Example: Receptors built in to the membrane of a nerve cell detect signalling molecules released by other nerve cells.

Question 9

Structural proteins

Answer 9

Function: Support
Examples: Keratin is the protein of hair, horns, feathers, and other skin appendages. Insects and spiders use silk fibres to make their cocoons and webs. Collagen and elastin proteins provide a fibrous framework in animal connective tissues

Question 10

Polypeptides

Answer 10

Unbranched polymers of amino acids.

Question 11

Proteins contain one or more polypeptide chains twisted and folded in to a unique shape

Answer 11

Each protein has a characteristic and unique amino acid sequence. 20 common amino acids give rise to diverse proteins.

Question 12

Primary structure

Answer 12

The primary structure of a protein is its unique sequence of amino acids

Question 13

Secondary structure

Answer 13

Found in most proteins consists of coils and folds in the polypeptide chain

Question 14

Tertiary structure

Answer 14

Determined by interactions among various side chains (R groups)

Question 15

Quaternary structure

Answer 15

Results when a protein consists of multiple polypeptide chains

Question 16

Amino Acids are:

Answer 16

Organic molecules with carboxyl (COOH) and amino (NH2) functional groups

Question 17

Amino acids have a central alpha carbon with each of these attached:

Answer 17

• R group (varies)
• Primary amine group (NH2)
• Carboxylic acid group (COOH)
• Hydrogen atom (H)

Question 18

Stereoisomers

Answer 18

Have the same formula but differ in their configuration

Question 19

Two types of stereoisomerism:

Answer 19

• Optical isomerism
• Geometric (cis-trans) isomerism

Optical isomerism is possible when a molecule contains one or more asymmetric carbon atoms

Question 20

A carbon atom has 4 valencies.

Answer 20

A carbon atom is said to be asymmetric or chiral when there are 4 different atoms or groups of atoms associated by covalent bonding

Question 21

Carbons 4 covalent bonds are tetrahedral in space. All the standard amino acids are also tetrahedral with 4 diff. groups bonded to the alpha carbon (except glycine)

Answer 21

When the four groups bonded to the carbon are different, the tetrahedral shape is asymmetric.

Question 22

There are 2 distinct ways to arrange the 4 bonds from carbon in 3D space. Two arrangements are non-superimposable mirror images called enantiomers (these are a type of stereoisomer)

Answer 22

These two stereoisomers are -D and -L amino acids.

Question 23

Defining the stereochemistry of amino acids is based on the mirror image enantiomers of glyceraldehyde. The middle carbon of glyceraldehyde is connected to 4 different atoms or groups of atoms (substituents) so it is asymmetrical or chiral.

Answer 23

This means that two forms (stereoisomers) of glyceraldehyde are possible called -D and -L isomers. -D and -L isomers rotate the plane of polarised light in equal but opposite directions

Question 24

-D and -L form of glyceraldehyde

Answer 24

• L form of glyceraldehyde- hydroxyl group is on the left of the molecule
• D form of glyceraldehyde- hydroxyl group is on the right of the molecule

Question 25

In an amino acid the position of the amino group on the left or right side of the alpha carbon determines the L or D designation

Answer 25

Amino acids in proteins are exclusively L stereoisomers. D amino acids are found in some small peptides including some peptides of bacterial cell walls.

Question 26

Amino acids R groups determine many of the chemical properties of the amino acid

Answer 26

They vary in structure, size, polarity, charge and water solubility.

Question 27

4 diff classes of amino acids determined by side chains

Answer 27

• Non-polar, uncharged
• Polar, uncharged
• Positively charged (basic)
• Negatively charged (acidic)