Amino Acids

Question 1

What is the structure of an amino acid?

Answer 1

Central carbon
Amine group
Carboxyl group 
Hydrogen
R group

Question 2

When is the central carbon a chiral centre?

Answer 2

If the four groups bonded to it are different

Question 3

How many different amino acids are commonly found in proteins?

Answer 3

20

Question 4

When are two molecules stereoisomers?

Answer 4

When they are made of the same atoms connected in the same sequence but the atoms are positioned differently in space

Question 5

What are the names of the two forms of stereoisomers and what do they tell you about their positioning?

Answer 5

L- (amine group on the left of the central carbon)

D- (amine group on the right of the central carbon)

Question 6

How are amino acids classified?

Answer 6

By their R groups

Question 7

What are the different types of R groups an amino acid can have?

Answer 7

Non polar, aliphatic R groups
Polar R groups 
Aromatic R groups 
Positively charged R groups 
Negatively charged R groups

Question 8

Describe and give examples of amino acids with non polar aliphatic R groups.

Answer 8

Aliphatic = chains with a high density of carbons and hydrogens
Aliphatic chains can be straight, branched or in ring structures
Non polar = they cannot form hydrogen bonds
Hydrophobic
Examples ; Glycine, Proline (distinctive cyclic side chain structure)

Question 9

Describe and give examples of amino acids with polar R groups.

Answer 9

Polar = they can form hydrogen bonds with water
Hydrophilic
Examples ; Glutamine, Asparginine, Cysteine

Question 10

Describe and give examples of amino acids with aromatic R groups.

Answer 10

Aromatic = a substance consisting of or more rings that contain alternating single and double bonds
Only amino acids that absorbs UV light
Relatively non polar
Examples ; Tyrosine, Tryptophan

Question 11

Describe and give examples of amino acids with positively charged R groups.

Answer 11

‘Basic’ amino acids
Hydrophilic
Examples ; Lysine, Arginine, Histidine

Question 12

Describe and give examples of amino acids with negatively charged R groups.

Answer 12

Acidic
Hydrophilic
Examples ; Aspartate, Glutamate (both have a second carboxyl group)

Question 13

How does selenocysteine differ from cysteine?

Answer 13

Similar to cysteine but has a selenium group in place of the sulphur group

Question 14

Name the four types of mutations that occur in proteins.

Answer 14

Silent
Conservative
Non conservative
Nonsense

Question 15

What is a silent mutation?

Answer 15

A change in DNA but no change in the amino acid sequence

Question 16

What is a conservative mutation?

Answer 16

A change in DNA and a change in amino acid but within the same classification

Question 17

What is a non-conservative mutation?

Answer 17

A change in DNA and a change in amino acid from another classification

Question 18

What is a nonsense mutation?

Answer 18

A change in DNA that causes the insertion of a stop codon

Question 19

What happens to the red blood cells of a person with sickle cell anemia?

Answer 19

They are sickle shaped

Question 20

What type of mutation results in sickle cell anemia?

Answer 20

Non-conservative (glutamate is changed to valine)

Question 21

What happens to amino acids when the pH of its environment is changed?

Answer 21

Groups within the amino acid become protonated or deprotonated

Question 22

What does a pKa value indicate?

Answer 22

The strength of an acid

Question 23

What is the pKa of carboxylic acid?

Answer 23

4.8

Question 24

What is the pKa of the amine group?

Answer 24

10.6

Question 25

What is the isoelectric point?

Answer 25

The pH at which an amino acid is charged neutral

Question 26

What R groups are affected by changes in pH?

Answer 26

R groups with an explicit positive or negative charge

Question 27

How do you calculate PI?

Answer 27

the sum of the pKa's either side of the PI / 2

Question 28

Name 3 buffer systems and where they work.

Answer 28

Phosphate - intracellular Bicarbonate - blood and small intestine Histidine - in neutral pH's

Question 29

What form is nitrogen found in the atmosphere?

Answer 29

N2

Question 30

What is the equation of nitrogen fixing?

Answer 30

N2 + 3H2 = 2NH3

Question 31

How many ATP molecules are used in nitrogen fixing?

Answer 31

16

Question 32

What is the equation for the production of glutamate from ammonia?

Answer 32

Ammonia + alpha-ketoglutarate + NADPH = glutamate + NADP + water

Question 33

What is the equation for the production of glutamine from ammonia?

Answer 33

Ammonia + glutamate + ATP = glutamine

Question 34

What compound supplies nitrogen to most reactions?

Answer 34

Glutamine

Question 35

What compound allows nitrogen to be transported in the blood without being in the form of ammonia?

Answer 35

Glutamine

Question 36

How is glutamine synthetase regulated?

Answer 36

Allosterically - glutamine provides nitrogen for the production of other compounds, these compounds inhibit the conversion of glutamate to glutamine

Question 37

What is protein turnover?

Answer 37

The balance between protein synthesis and protein degradation

Question 38

Describe the process of transamination.

Answer 38

Amino acids lose their amine group | The amine group is transferred to alpha-ketoglutarate to produce glutamate and alpha-keto acid

Question 39

What enzyme catalyses the production of glutamate from an amine group?

Answer 39

Glutamate dehydrogenase

Question 40

Where is the carbon backbone (amino acid without amine group) metabolised?

Answer 40

In the krebs cycle

Question 41

What enzyme catalyses the production of glutamine from glutamate and ammonia?

Answer 41

Glutamine synthase

Question 42

Where is glutamate synthesised?

Answer 42

In all cells other than skeletal muscle

Question 43

Describe the steps in the glucose alanine cycle.

Answer 43

1. Glucose is metabolised to pyruvate in skeletal muscle 2. Pyruvate is converted to alanine by the addition of an amine group 3. Alanine is transported to the liver 4. The liver breaks down alanine to pyruvate and an amine group 5. The amine group is used to form urea 6. Pyruvate is used to make glucose

Question 44

Why is the glucose alanine cycle important?

Answer 44

It prevents the build up of lactic acid

Question 45

Why is it more efficient to transport nitrogen in the form of glutamine rather than glutamate?

Answer 45

Because glutamine contains two nitrogens where as glutamate only contains one

Question 46

What three substrates donate an amine group amine group during the urea cycle?

Answer 46

Glutamine Glutamate Aspartate (Alanine is converted to glutamate which then donates an amine group)

Question 47

Describe the process of the urea cycle.

Answer 47

Glutamate undergoes oxidative deamination producing alpha-ketoglutarate and ammonia Ammonia combines with carbon dioxide to form urea Urea is transported to the kidney where it is converted to urine and excreted

Question 48

How many nitrogen molecules are transported for one urea molecule?

Answer 48

2

Question 49

What is the name of amino acids that are used to make glucose?

Answer 49

Glucogenic amino acids

Question 50

What is the name of amino acids that are used to make acetyl CoA?

Answer 50

Ketogenic amino acids

Question 51

Name the only two amino acids that are explicitly ketogenic.

Answer 51

Leucine | Lysine

Question 52

What is acetyl CoA used for?

Answer 52

To make ketone bodies | In the krebs cycle

Question 53

What are ketone bodies?

Answer 53

A form of energy used when glucose levels are low

Question 54

What inability do people with Phenylketonuria (PKU) have?

Answer 54

An inability to metabolise phenylalanine

Question 55

What inability do people with maple syrup urinary disease have?

Answer 55

An inability to degrade branched amino acids (valine, leucine)