11/ bacterial genetics 1

Question 1

how is genetic info organised in a bacteria

Answer 1

• in a nucleoid
• loops of supercoiled dna, anchored in the middle by histone-like anchoring proteins
• looks like a flower
• supercoiling is relaxed in a nicked strand

Question 2

how is supercoiling achieved

Answer 2

• enzymes (topoisomerases) make double stranded break in the circle
• passes another part of DNA through the break
• reseals it

Question 3

how long can it take to replicate bacterial genome

Answer 3

15 mins

Question 4

how does dna replication occur in bacteria

Answer 4

• oric (origin point) recognised
• replication bubble forms
• semiconservative replication, clockwise and anticlockwise direction
• one strand okazaki fragment - dna pol 5’ to 3’ only
• terminates at termination points

Question 5

what are the termination points for e coli

Answer 5

• over 8 arrest sites
• replication forks moving clockwise trapped by terB, C, F, G, J
• anticlockwise forks trapped by terA, D, E, H, I

Question 6

intracellular organisms

Answer 6

have to live inside another organism bc its genome is so small

Question 7

difference between pro and euk coding vs non coding genes

Answer 7

• only 5% of genes in humans code for proteins, coding regions separated by introns, ancient genes decayed to pseudogenes.
• bacterial chromosome tightly packed w coding genes, few mobile elements, little unused sequence

Question 8

what are operons and regulons in bacteria

Answer 8

• operons are multiple genes controlled by same promotor that make a polycistronic message that codes for multiple proteins
• (individual genes make monocistronic mrna)
• genes and operons may form a regulon controlled by a common regulatory protein - dif genes in dif operons cand be simultaneously activated