Amino acids, proteins, DNA and enzymes

Question 1

draw structure of an amino acid

Answer 1

H2N-CRH-COOH

Question 2

What are zwitterions?

Answer 2

Have both positively charged end and a negatively charged end

Question 3

In what pH are there predominately dipolar ions (zwitterions)?

Answer 3

pH7

Question 4

What do zwitterions go to in acidic solutions?

Answer 4

In acidic solutions with more alcohol it accepts a proton due to increased H+ in solution

Forms cation
H3N-CRH-COOH

Question 5

What do zwitterions go to basic solutions?

Answer 5

In basic solutions with less alcohol, less H+ in solution so loses a proton

Forms anion
H2N-CRH-COO-

Question 6

Define isoelectric point?

3

Answer 6

pH at which amino acid is a zwitterion- usually pH7

Different for each amino acid due to difference in R groups

Means they can be separated by electrophoresis

Question 7

Physical properties of amino acids?
Bonding?
2

Answer 7

• Electrostatic attraction between oppositely charged parts of ions
• -> high melting points
  eg: glycine (smallest amino aicd) = 290*C

Question 8

What is special about glycine (smallest amino acid)?
isomers?
2

Answer 8

It is the only amino acid that is not chiral (4 different R groups on C)

• > no optical isomers
• this is the exception, all other amino acids are chiral

Question 9

Amino acid + NaOH?

Answer 9

Carboxylate

Makes COOH group lose proton –> COO-

Question 10

Amino acid + HCl?

Answer 10

Protonate everything

Makes NH2 group gain proton –> NH3+
COOH =COOH

Question 11

Amino acid + methanol w/ small amount of conc H2SO4?

Answer 11

Esterification

C=OOH group —> C=OO-CH3
NH2 = NH2

Question 12

Amino acid + ethanoyl chloride?

Answer 12

Acylation

Will produce N-substituted amide
Add on to N side

H3C-C=O-NH-……

Question 13

Define proteins?

3

Answer 13

Naturally occurring polymers of amino acids

Have amine bond / peptide link

Further react on each end to form polyamide/polypeptide

Question 14

Isomers of chiral amino acids (all except glycine)?

3

Answer 14

They are tetrahedral

So have optical isomers

Enantiomer pairs

Question 15

Describe primary protein structure?
2
Bonding?
2

Answer 15

• Sequence of amino acids
• -> polypeptide chain
• Covalent peptide bonds
• -> amine and COOH groups of adjacent AA

Question 16

Importance of primary protein structure?

Answer 16

It controls all subsequent levels of protein organisation because it determines the nature of interactions between R groups

Question 17

Describe secondary protein structure?
2
Bonding
1

Answer 17

• The way polypeptides fold in a repeating arrangement
• -> alpha helix and beta pleated sheet or random coil

-H bonds between amine and COOH groups of non-adjacent AA

Question 18

Importance of secondary protein structure?

Answer 18

Mechanical stability

Question 19

Describe tertiary protein structure?
1
Bonding
2

Answer 19

-Polypeptide coils and turns to form a 3D shape

• BC of interactions bewteen R groups
• -> H bonds, ionic interactions, disulfide bonds, hydrophobic interactions

Question 20

Importance of tertiary protein structure?

2

Answer 20

Relative amino acid positions important

Important for function of protein due to shape
—> eg: enzyme

Question 21

Describe quaternary protein structure?
1
Bonding
1

Answer 21

• Multiple polypeptides or prosthetic groups interact to form a single, larger, biologically active protein
• Have a variety of bonds similar to tertiary

Question 22

What are prosthetic groups (proteins)?

Answer 22

inorganic compounds involved in protein structure/function eg: heme in haemoglobin

Question 23

What are conjugated proteins?

Answer 23

Protein with prosthetic group

Question 24

Hydrolysis of proteins: conditions? what forms?

Answer 24

• Boil protein/peptide w/ 6moldm-3 HCl for 24 hours

- Breaks down to a mix of amino acids as the HCl hydrolyses peptide linkages

Question 25

What groups form H bonds?

Answer 25

-C=O and -N-H

Question 26

What groups form ionic bonds?

Answer 26

-COO- and -NH3+

Question 27

What groups form sulfur-sulfur bonds?

Answer 27

• CH2SH and HSCH2

- > -CH2-S-S-CH2

Question 28

What type of protein are enzymes?

Answer 28

Globular

Question 29

How do proteins work?
How do they decrease Ea
2

Answer 29

The substrate is complementary and forms temporary bonds by intermolecular forces w/ enzyme

These forced promote movement of electrons w/in substrate which decreases Ea

Question 30

What is spectrospecificity?

Answer 30

Means they form stereoisomers

1 or the other of a pair of enantiomers bc of how important shape is, the other one wont work

Question 31

Structure of a nucleotide?

Answer 31

Phosphate group

Pentose sugar/ 2-deoxyribose

Base

Question 32

Name the 4 DNA bases?

Answer 32

Adenine
Guanine
Cytosine
Thymine

Question 33

What is cis-platin?

Answer 33

A very effective drug to fight cancer

Question 34

How does cis-platin work?

2

Answer 34

The platinum binds to the N in guanine

Stops DNA replication as it bind the two strands together

Question 35

Describe bonding of platinum in cis-platin to guanine?
3
What is it called?
1

Answer 35

1. Nitrogen atoms of guanine have lone pairs so will form dative covalent bonds w/ platinum
2. The chloride ions on cis-platin are displaced by water
3. the water ligands are displaced by N on guanine
   - > called ligand substitution