Lecture 10 - bacterial genes & genetics (chromosomes plasmids & gene transfer)

Question 1

Are spontaneous mutations always readily visible?

Answer 1

no (however pigment formation in Streptomyces is visible) - sometimes mutations aren’t as easily identifiable

Question 2

What is fundamental in the development of molecular biology?

Answer 2

genetics of bacteria and their viruses

Question 3

What were historical misconceptions about DNA?

Answer 3

e.g. bacterial genetics has nothing to do with eukaryotes

Question 4

What is the first choice for basic bacterial genetics?

Answer 4

E. coli

Question 5

Describe the size of chromosomes in bacteria that are parasitic

Answer 5

Small chromosomes

Question 6

Describe the size of chromosomes in bacteria in a stable environment

Answer 6

larger chromosomes

Question 7

Describe the size of plasmids

Answer 7

smaller than chromosomes

Question 8

Describe the difference in chromosomes between eukaryotes and prokaryotes

Answer 8

• bacterial chromosome is tightly packed with coding genes with mobile elements and a little unused sequence
• human DNA has a lot of non-coding DNA (total of 20,000 of genes)

Question 9

In what bacteria is there big differences in gene distribution?

Answer 9

Salmonella enterica

Question 10

Describe the genetic organisation of bacteria’s genes, operons & regulons

Answer 10

• organisation of a single gene & surrounding regions
• one single gene makes a moncistronic message (for one protein)
• an operon of 3 genes makes a polycistronic message (for 3 proteins)
• in a chromosome, genes and operons may form a regulon controlled by a common regulatory proteins

Question 11

Is a nucleiod a nucleus?

Answer 11

no

Question 12

How does a nucleiod become supercooled?

Answer 12

• supercooling of a 300bp circular DNA molecule
• enzymes (Topoisomerase) make a double-strand break in the circle, passes another part of DNA through the break, then reseals it.

Question 13

Describe semi conservative replication

Answer 13

at the replication fork, DNA synthesis machine separates the 2 strands while extending the new growing strands. Each daughter duplex is checked for accuracy before segregation to the two cells

Question 14

Describe DNA replication from a single origin

Answer 14

1. Replication starts at origin
2. Replication bubble forms - forks progress in opposite directions
3. One strand at each fork is synthesised continuously, 5’ to 3’
4. Second strand is made discontinuously 5’ to 3’ Okazaki fragments
5. Replication ends at terminus

Question 15

How is DNA replication terminated?

Answer 15

1. terminator region for DNA replication on the E. coli chromosome
2. there are less than 8 arrest sites at the terminus
3. Replication forks moving clockwise are trapped in terB. C F G J
4. Counterclockwise - moving forks are trapped by terA. D E H I

Question 16

What are the rings called after replication?

Answer 16

concatamers