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Molecular Genetics > Lecture 12 - Genetic Recombination > Flashcards

Lecture 12 - Genetic Recombination Flashcards

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1
Q

Why do genes need to have stability?

A

Genome conservation, DNA repair, void cancer and genetic disorders

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2
Q

Why is genetic diversity needed?

A

Meiosis, antibody diversity, adaptation and evolution

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3
Q

What are the 5 mechanisms of genetic recombination?

A

Homologous recombination, non-homologous end joining, transposition, site-specific recombination and independent assortment of chromosomes.

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4
Q

Homologous recombination - what happens after a double strand break?

A

The ends are processed by a nucleuses - the RecBCD complex.

The broken DNA can then invade an intact homologous DNA

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5
Q

Homologous recombination - what helps strand invasion?

A

Recombinant (RecA)

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6
Q

Homologous recombination - what happens after invasion?

A

The broken DNA is repaired by using the intact DNA as a template for replication and faithfully synthesise missing DNA.

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7
Q

Homologous recombination - what are Holliday junctions?

A

The 4 DNA branch structures

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8
Q

Homologous recombination - what can cleave Holliday junctions?

A

Resolvable called RuvABC

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9
Q

Homologous recombination - where can ruvABC cleave?

A

It has the choice between side ways and above/below - this will make different molecules

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10
Q

Homologous recombination - what happens if both Holliday junctions are cleaved on the same strand?

A

No-crossover - REMEMBER CHANGE STRANDS AT THE ARROWS

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11
Q

Homologous recombination - what happens if the RuvABC cuts different strands?

A

Crossover - REMEMBER YOU FOLLOW THE ARROWS

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12
Q

When does Homologous recombination take place?

A

DS break, ds DNA fragment, DNA single stranded gap

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13
Q

Non-Homologous end Joining - what does this repair

A

double stranded break and is good for diversity

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14
Q

Non-Homologous end Joining - what happens after a DS break?

A

The end are protected by Ku which keeps the ends next to each other.

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15
Q

Non-Homologous end Joining - what happens after Ku has bonded?

A

Sometimes they will naturally ligaments together, other times they need to be processed first

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16
Q

Non-Homologous end Joining - what happens during end processing?

A

This is carried out by different enzymes - nucleotides are added due to polymerase and removed by nucleuses. Nucleotides can be modified by phosphotase. This changes the original DNA

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17
Q

Non-Homologous end Joining - what happens after end processing?

A

Lig4 ligands the ends together.

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18
Q

What is transposition?

A

Movement of transposable elements within and between elements.

This is an origin of genetic diversity

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19
Q

site-specific recombination - what does it need at specific target sites to work?

A

Recombinase

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20
Q

site-specific recombination - what does recombinase do?

A

Binds at specific target sites and cleaves DS DNA at specific sequences which allows the change of order before they rejoin once more

21
Q

site-specific recombination - what does the nature of the change rely on?

A

The orientation of the target sites - head to head or head to tail

22
Q

site-specific recombination - what does a target site orientation of head to head mean?

A

They are going in the opposite orientation

23
Q

site-specific recombination - what does head to tail orientation mean?

A

They are in the same orientation

24
Q

site-specific recombination - what are the consequences of inversion (head to head) recombination?

A

There is an inversion of the sequence between the two target sites

Part of the target sites are also exchanged (arrows)

25
Q

site-specific recombination - what are the consequences of deletion/ integrate (head to tail) recombination?

A

Line up the arrows - whether this is a deletion or an integration depends on the molecule.

The recombinase lines up the target sits creating a loop. This then leads to 2 products - a circle containing the DNA sequence between the 2 target sites (and one Target site) being excised and the original molecule without the DNA which previously sat between the target sites and only one target site.

26
Q

site-specific recombination - can the 2 products recombine to form the original strand?

A

Yes

27
Q

site-specific recombination in nature - e.coli replicate on the inside of the circle which means straight DNA can be bad for them. What template is used for the repair?

A

The inside one

28
Q

site-specific recombination in nature e.coli - what is the product of this repair?

A

Non-crossover or crossover - these are still circular

29
Q

site-specific recombination in nature - e.coli - what happens if there is crossover?

A

They can’t go into their own cell and therefore must be unlinked before that.

30
Q

site-specific recombination in nature - e.coli - how do they unlink crossed DNA?

A

Site specific recombination - a specific head to head target site called dif and the recombination is done by xerCD recombinase which causes a second crossover which then lets them unlink.

31
Q

Following infection of bacteria wha can bacteriophage lambda do?

A

Use its host to replicate in the lambic cycle or insert its DNA and force the host to replicate that.

32
Q

How does the lambda bacteriophage integrate or excised from the bacteria it is infecting?

A

Site specific recombination

33
Q

Lambda genomes recircularise after entering the bacteria genome. This now makes them able to enter e.coli chromosomes - how?

A

They line up their attp site with attB sites on the e.coli chromosomes and uses the int protein to insert themselves.

34
Q

Is lambda and e.coli genome recombination reversible?

A

Yes

35
Q

What are the composite sites formed called?

A

AttL and attR

36
Q

Are attp and attB sites different?

A

Yes which means more enzymes need to be used for integration

37
Q

Site specific recombination in flagellar phase variation in Salmonella? - where are the target sites?

A

Head to head

38
Q

Site specific recombination in flagellar phase variation in Salmonella? - what does the fljb gene encode?

A

Protein which makes flagellum

39
Q

Site specific recombination in flagellar phase variation in Salmonella? What does fljA encodes?

A

Regulator protein which represses fljc

40
Q

Site specific recombination in flagellar phase variation in Salmonella? - what does fljc encode?

A

Another flagellum protein

41
Q

Site specific recombination in flagellar phase variation in Salmonella? Where is the promoter of fljb?

A

In between 2 head to head target sites

42
Q

Site specific recombination in flagellar phase variation in Salmonella? - what happens if the promoter is in front of fljb?

A

The flagellum is made up of fljb protein

43
Q

Site specific recombination in flagellar phase variation in Salmonella? - what happens when the signal is inverted?

A

Fljb and fljA proteins aren’t produced and therefore fljc is no longer repressed and we can form fljc flagellum’s.

44
Q

Bacteriophage Mu tail fibre variation - what type of recombination event - head to head or head to tail?

A

Head to head

45
Q

Bacteriophage Mu tail fibre variation - this is made up of many protein - what codes for the constant part?

A

sc

46
Q

Bacteriophage Mu tail fibre variation - this is made up of lots of proteins - what codes for the variable part?

A

so or sv+

47
Q

Bacteriophage Mu tail fibre variation - what is the second protein?

A

U or U+

48
Q

Bacteriophage Mu tail fibre variation - what does gin seen on the end of the tail encode?

A

Recombinase which can interrupt the genome between the target sites to encode either scSvU or ScSv+U+

Molecular Genetics (20 decks)

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