Amino acids

Question 1

What is an amino acid?

Answer 1

Molecule that contains at least one amine group and one carboxylic acid group
These groups are bonded to 1 carbon in between = alpha amino acid
This carbon has an r group

Question 2

Essential amino acids

Answer 2

Amino acids that cannot be synthesised by the body but must be obtained in diet

Question 3

Neutral amino acids

Answer 3

1 basic NH2 group and 1 acidic COOH group

Question 4

Acidic amino acids

Answer 4

One basic NH2 group and 2 acidic COOH groups

Question 5

Basic amino acids

Answer 5

Two basic NH2 groups and 1 COOH group

Question 6

Naming amino acids

Answer 6

Carbon Number the amine group is
- amino
Branching
Carboxylic acid

Question 7

Pure amino acids at room temperature state

Answer 7

Solid

Question 8

What do amino acids exist as?

Answer 8

Zwitterions

Question 9

What are zwitterions?

Answer 9

When the COOH group transfers H+ to the basic NH2 group:
COOH becomes COO-
NH2 becomes NH3+

Question 10

Overall charge of a zwitterion

Answer 10

Neutral: positive NH3+ balanced by negative COO-
But the separate groups in the molecule have a charge

Question 11

Zwitterions attraction to each other

Answer 11

Positive charge on NH3+ is attracted to negative charge on COO- of the neighbouring zwitterion
Forms ionic interactions between oppositely charged ions

Question 12

Why are amino acids solid at room temperature?

Answer 12

Because the Zwitterions can form strong ionic bonds between each others charges which require lots of energy to overcome
So these are much stronger than hydrogen bonds which are weaker

Question 13

Why are Zwitterions soluble in water?

Answer 13

Because ion-dipole forces of attraction are formed between hydrogen dipoles and the charges on the Zwitterions

Question 14

Adding an alkali to amino acid solution

Answer 14

We have a zwitterion in solution
The OH- acts as a base and removes H+ from NH3+ (acts as conjugate acid) to form water, and the amine group on amino acid becomes NH2 as a result
COO- stays as is
= overall, now has negative charge

Question 15

Adding an acid to amino acid solution

Answer 15

H+ is donated to the COO- (conjugate base) to form COOH
NH3+ stays as is
Overall positive charge

Question 16

Acid/alkali to amino acid always forms..

Answer 16

A Salt of amino acid
Acid added = positive amino acid ion+ anion from acid-
Alkali added = cation from acid+ neg amino acid ion

Question 17

Isoelectronic point

Answer 17

The pH at which the zwitterion exists in aqueous solution
Where the NH2 becomes NH3+ and COOH becomes COO-

Question 18

Do amino acids have a chiral carbon?

Answer 18

Most of them do:
COOH, NH2, H and the R group bonded to a chiral carbon

Question 19

What happens if amino acids have a chiral carbon?

Answer 19

They can display optical isomerism:
Exist as non superimposable mirror images of each other that rotate the direction of plane polarised light in opposite but equal directions

Question 20

Racemic mixture of amino acids

Answer 20

Contain equal concentrations of 2 enantiomers
so the rotational effect of plane polarised light in opposite but equal directions is therefore cancelled out: has no effect on the plane of plane polarised light

Question 21

A peptide bond

Answer 21

Formed in a condensation reaction between the COOH group of 1 amino acid and the NH2 group of a different amino acid
Releases H2O (eliminated)

Question 22

Peptide bond symbol

Answer 22

C-N

Question 23

What type of reaction is the formation of a peptide bond?

Answer 23

Acid base condensation polymerisation reaction
H+ from amine group donated and accepted by OH- group from COOH group to form water
Water is eliminated to join 2 molecules = condensation polymerisation

Question 24

Dipeptide

Answer 24

Condensation reaction between 2 amino acids to form this molecule
Contains a peptide bond

Question 25

Tripeptide

Answer 25

Condensation reaction between 3 amino acids to form this molecule Contains 2 peptide bonds

Question 26

How can we break a peptide bond?

Answer 26

In a hydrolysis reaction which uses water to break the bond and reform the constituent amino acids

Question 27

How can we separate the amino acids formed?

Answer 27

By chromatgraphy

Question 28

How do you hydrolyse the polypeptide into amino acids

Answer 28

By refluxing for a long period of time wit concentrated HCl Protonates the NH2 groups

Question 29

Polypeptides

Answer 29

Molecule formed from a Condensation polymerisation reaction between 4 or more amino acids, joined by peptide bonds

Question 30

Amphoteric

Answer 30

A substance that acts as both a base and an acid

Question 31

What does the solubility in water depend on, outside of forming ion dipole forces to water?

Answer 31

The size and nature of the R group

Question 32

Why do amino acids not dissolve in non polar solvents?

Answer 32

Because there is a lack in attraction between non polar molecules and zwitterions. So cannot pull zwitterions apart in the ionic lattice

Question 33

Optical activity of amino acids

Answer 33

Most have a chiral carbon so can form different enantiomers which rotate the plane of plane polarised light in opposite but equal directions

Question 34

Will the extra COOH (in acidic amino acids) or NH2 (in basic amino acids) react when acid/alkaline is added?

Answer 34

YES

Question 35

Drawing dipeptides from 2 different amino acids

Answer 35

For any two different amino acids there are two possible combinations of the amino acids in the dipeptide Depending on which one is added first etc