Unit 6, 4 - amino acid and proteins

Question 1

what is amino acid

Answer 1

has 2 functional groups
- carboxyl group = COOH
- amino group = NH2

they are amphoteric = have both acidic and basic properties

acidic = because carboxyl group can donate proton COO-
basic = because amino group - can accept proton - NH3+

Question 2

zwitterions

Answer 2

dipolar ion
- both positive and negative charge are in different part of the molecule

Question 3

zwitterions and amino

Answer 3

• only find zwitterions near AA isoelectric point

an amino acid = zwitterions when amino group is protonated into NH3+ and it’s COOH group is deprotonated to COO-

Question 4

isoelectric point

Answer 4

• the ph when net charge of AA is zero

Question 5

condition when zwitterion in AA produced

Answer 5

• in more acidic than isoelectric point - NH2 is likely to be protonated and COOH remain unchanged - so AA carry positive charge
• in more basic than isoelectric point - COOH deportenated into COO- hwile NH2 remains unchanged - carry negative charge
• only near the isoelectric point are bo0th carboxyl and amino group likely to be ionised -forming zwitterion

Question 6

seperating mixtures of amino acid

Answer 6

• can seperate by thin layer chromotaphy
• diff AA = diff solubility in same solvent = diff r group

AA colourless - can’t identify
- use ninhydrin solution on plate - causes AA to purple
- use plate wiht flurescnet dye - AA spot appear dark under UV light

Question 7

Identifying amino acids

Answer 7

find Rf value
distance of sub / distance of solvent

Question 8

proteins

Answer 8

• condensation polymers of amino acid - joined toge by peptide bond
• 2 diff AA combine diff = 2 diff dipeptide will form , AA can join either side
• dipeptide sitll has NH2 group to one end and COOH group at other end - can undergo further conden R

Question 9

Hydrolysis of protien

Answer 9

• forms AA
  need to use harsh condition
• add aqueous 6 mol dm-3 of HCl
• heat the mixture under reflux for 24 hours

Question 10

protein stu

Answer 10

• big and complicated mole
• • into diff stu - primary , sec ….

Question 11

primary structure

Answer 11

• seq of AA in ling chain that makes up protein3

Question 12

secondary protein

Answer 12

• peptide link = form hydrogen bonds with each other
• make a helix and beta pleadted sheets

Question 13

tertiary structure

Answer 13

• chain of AA itself often coiled and folded in characteristic way that idnetifies the protein
• extra bond bet diff part of polypeptide chain = give 3D stu

Question 14

hydrogen bonding

Answer 14

• type of IMF
• holds protein in shape

H only exist between polar groups like OH- AND NH2
- group contains ele neg atoms which induce partial positive charge on H

H atractesd to lone pair of electron on the adjacent polar groups

Question 15

Disulfide bonding

Answer 15

• AA part of protein = residue
• disulfide bonding = occurs bet residues of AA cysteine
• cystene - contains thiol group and join toge to from disulfode ( S-S ) bond with another thiol group

these disulfide bonds link together diff parts of the protein chain and help to stabilise tertiary structure