inheritance and information flow

Question 1

what is vertical gene transfer

Answer 1

when two gametes fuse together and homologous chromosomes exchange genetic information- the genetic information is transferred from one generation to the next

Question 2

what is horizontal gene transfer

Answer 2

the transmission of genetic information between different organisms

Question 3

what are the three different ways prokaryotes exchange genetic information

Answer 3

1) transformation
2) conjugation
3) transduction

Question 4

what is transformation

Answer 4

when the prokaryotes uptakes DNA from the environment and recombines it within its own genome

Question 5

define a competent cell

Answer 5

cells which could take up DNA from the environment
it is a transient state depending on the cells physiological state

Question 6

who discovered transformation

Answer 6

Frederick Griffith 1928 using streptococcus pneumoniae

Question 7

outline the mthods of frederick griffiths experiment when discovering transformation

Answer 7

• involved injecting capsule free and capsuled bacteria into mice
  method A= live capsule free= mice died as well as bacteria
  method B=live capsule bearing=mice die bacteria live
  method c- heat treated dead capsule bearing = mice live
  method D- live capsule bearing injected with dead capsule bearing = mice die and bacteria live with a capsule

Question 8

what did frederick griffith conclude in his transformation experiment

Answer 8

R cells aquired the capsule gene from DNA released when s cells were killed by heat, therefore streptococcus pneumonia is naturall compotent

Question 9

outline the mechanism behind natural transformation

Answer 9

1) exogenous dsDNA binds to proteins of the competent cell membrane
2) the dsDNA is fragmented into smaller pieces
3) one strand of the DNA is degraded by nuclease while the other enters cells
4) the strand in the cell is coaded by transformation specific DNA binding proteins
5) the strand is homologous to existing DNA region so is intergrated in the chromosome
6) RecA invaded the hologous region in the chromosome displacing existing strands and replacing with DNA
6) when the cell divides only one daughter cell inherits transforming strand

Question 10

what is RecA

Answer 10

a protein essential for the repair and maintenance of DNA

Question 11

what is a nuclease

Answer 11

an enzyme which cleaves the chains of nucleotides into smaller acids therefore free DNA is short lived in the environment

Question 12

what is gene cloning

Answer 12

recombinant DNA is introduced into cells artificially

Question 13

how is DNA introduced into bacteria artificially

Answer 13

1) chemically competent cells and heat shock
2) electrocompetent cells and an electroporator

Question 14

outline the method of introducing DNA into bacteria using heat shock

Answer 14

1) cells are treated with chemicals (CaCl2) which alter the cell membrane permability allowing uptake
2) the calcium ions are attracted to negatively charged DNA and membrane producing a electrostaically neutral enviro

Question 15

outline the method of introducing DNA using electroporation

Answer 15

1) introduce the gene to the cell
2) apply an electric pulse which forms pores in the cell membrane allowing the gene to enter
3) after the electric pulse the pores reseal and the gene remains in the cell

Question 16

in cloning why are plasmids used more

Answer 16

the transformartion efficiency is higher as they cant be degraded by nucleases as they have no exposed ends compared to linear DNA which can be

Question 17

what is conjugation

Answer 17

a way of genetic exchange amoung microbes based on the ability of certain plasmids to transfer from cell to cell

Question 18

what is conjugation responsible for

Answer 18

1) horizontal gene transfer events
2) rapid spread of antibiotic resistance

Question 19

what is an F-plasmid/ F-factor/ sex factor

Answer 19

the conjugative plasmid

Question 20

how does conjugation in gram negative batceria work

Answer 20

1) the sex pilus of the donor (f+) attaches to recipient (f-)
2) the sex pilus retracts dragging the cells together
3) a single strand of plsamid is cut and unwound and the DNA is transferred to recipient cell and donor synthesises new strand
4) in the recipient a second strand is replicated where it becomes F+ and a new donor cell

Question 21

what are high frequency recombination cells

Answer 21

when the F-factor in the conjugative plasmid is integrated into the chromosome of the donor bacteria by site specific recombination
= the regions of plasmid sequecence and chromosome must be similar

Question 22

what does site specific recombination involve

Answer 22

1) specific DNA sequences
2) two DNA partners
3) a speacilised recombinase prtoein which is responsible for recognising the sites and breaking and rejoining the DNA

Question 23

outline conjugation in high frequency recombination cells

Answer 23

1) once integrated into theHfr cell the cell now contains the F-factor which can produce a sex pili
2) the cell connects with donor and gene in chromosome is transmitted to recipient
3) the length of time of attachemnt defines how much DNA is transferred
4) once in donor the DNA fragment integrates by homologous recombination in the chromosome

Question 24

what is the differences between conjugation in gram positive and negative bacteria

Answer 24

• mechanisms which establish celll to cell contact
• positive clump together to bring donor and recipient close, they dont form a sex pilus

Question 25

outline conjugation in gram positive bacteria

Answer 25

1) recipient produces a pheramone which interatcs with a plasmid of donor cell
2) plasmid in donor cell encodes for genes producing aggregation substances
3) these substances migrate to the cell surface
4) the substances bind to bidning substances on recipient membrane
5) cells clump and genetic exchange occurs

Question 26

what is quorum sensing

Answer 26

used by gram positive bacteria to locate donor cells for conjugation

Question 27

what is transduction

Answer 27

the transfer of gentic material by bacterial virus (a bacteriophage) where when the phage packs DNA during assembly it carries that DNA from one bacteria to the next

Question 28

what mistakes can occur during transduction

Answer 28

1) phages randomly pack and exchange any of the hosts genes (generalised transduction)
2) phages only pack and exchange specific genes from the host (specialised transduction)

Question 29

when does generalised transduction occur

Answer 29

during the lytic phase
1) phage injects DNA
2) phage enzymes degrade host DNA
3) cells synthesise new pahges and incroporate phage DNA and accidently some of the bacteria host DNA
4) tranducinh phage injects some of host DNA which is then incorporated into recpipient chromosome

Question 30

when does specialised transduction occur

Answer 30

during the lysogentic phase before phage excises

Question 31

outline the process of specialised transduction

Answer 31

1) phage DNA is integrated into bacterial chromosome as a prophage
2) normal phage excision produces a circular phage again
3) abnormal excision results in some of neighbouring bacterial DNA being carried over in the cirucalr phage

Question 32

what is homologous recombination

Answer 32

when genetic information is exchanged between two similar or identical molecules of double or single stranded nucleaic acids