22 - penicillin and cross links

Question 1

what percentages of antibiotics contain penicllin

Answer 1

80%

• more than 30,000 have been synthesized
• more than 100 sold as drugs (semi-synthetic)

Question 2

explain alexander flemings discovery in 1929

Answer 2

• fleming had bunch of agar plates with different bacteria
• he went away on vacation and when he got back , found out one of the plates had developed a mold
• zone of death around the mold - preventing bacterial growth
• his actual discovery: two colonies of bacteria present in the agar plate, but only one was able to grow at the top of the plate
• thought the mold was able to purify bacteria

Question 3

what did howard florey and ernst chain figure out in 1941 and how

Answer 3

• figured out that penicillin could be used to treat bacterial infections
• got a sample of flemings mold and successfully isolated its chemical structure to get penicillin
• tested on infected mice (mice that were given penicillin survived, mice that were left untreated die)

Question 4

when was penicillin discovered and when was it brought to the market

Answer 4

• discovered in 1929 and made available to public in 1944

Question 5

what characteristics do bacterial cells have

Answer 5

• rigid outer layer
• has lots of strength
• resists osmotic pressure

Question 6

what characteristics do human cells have

Answer 6

• no cell wall
• do not have strength
• large and unable to resist osmotic pressure

Question 7

describe the difference in osmotic pressures between human cells and bacteria cells

Answer 7

• human cells have low internal pressure (keep the concentration on the inside of the cell relatively low
• bacterial cells have high internal pressure (require cell wall to contain the pressure)

Question 8

describe the cell wall structure in bacteria

Answer 8

• two polysaccharide chains (sugars joined together)
• amino acids joined by peptide cross links
• polysaccharide chains are attached together through peptide cross links

Question 9

explain the formation of the cell wall

Answer 9

• two polysaccharide chains come together forming a cross linked structure
• enzyme does this job → called transpeptidase (target for penicillin)

Question 10

what are polymers

Answer 10

• monomers linked together through a chemical reaction

Question 11

what are spaghetti-like mixtures

Answer 11

long spaghetti-like molecules can slide past each other. the structure these make is flexible because the molecules can move relative to each other

Question 12

explain cross-linking between the spaghetti strands

Answer 12

cross-links form connections between strands (or even between different parts of same strand). this makes a rigid three dimensional network in which the molecules can no longer move very much. this structure is much stronger and more rigid than the original matieral

Question 13

explain the cross link formation

Answer 13

• amino acids in the peptides have very unusual structural features
• remarkable structure features here
• this is an ancient structure (comes from a time when d-amino acids existed)

Question 14

explain what L-amino acids and D-amino acids are

Answer 14

• L: has the side chain always in the back, almost all “natural” amino acids have this configuration
• D: has the side chain always in the front, rare in nature

Question 15

explain the Transpeptidase reaction and how it links two peptide strands together

Answer 15

• takes amino group (H2N) from 1st chain and reacts it with the D-Ala (carboxylic group) on the 2nd chain
• oxygen bond breaks and reforms, kicks off 2nd D-Ala as a leaving group on 2nd chain
• water comes and clips another D-Ala off the 2nd chain
• cross link formed using an amino group