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MBG* 2040 Pt. 2 > Transposable Elements > Flashcards

Transposable Elements Flashcards

1
Q

Transposable elements

A

Segments of DNA capable of moving from one location in the chromosomes do another or even to a different chromosomes
also called jumping genes
Found in many organisms
Can constitute a significant portion of the genome
Can lead to chromosomal breakage and insert in new locations
becomes a major source of mutations

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2
Q

Why are transposon’s important in the generation of some human diseases?

A

Due to their ability to alter gene function

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3
Q

General characteristics of transposable elements

A
  1. Create staggered, breaks in target DNA.
  2. Attaches to single stranded ends of DNA.
  3. DNA is replicated at the gaps.
    Flanking direct repeats
    The transposase enzyme
    Terminal inverted repeats
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4
Q

Flanking direct repeats

A

3-12 bp long
Generated in the process of transposition
Don’t belong to the transposable element
Created by dna replication of the staggered single stranded pieces of dna

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5
Q

Transposase enzyme

A

Often encoded by the transposable element
Makes the staggered break in the dna and catalyses the transposition

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6
Q

Terminal inverted repeats

A

9-40 bp long
Inverted and complimentary
- Found at the ends of (within) many transposable elements
- Recognized by the enzymes that catalyze transposition (like transposase)

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7
Q

Two classes of transposable elements

A

Based on DNA or RNA
Class I. - retrotransposons (RNA intermediate)
Class II. DNA transposing - catalyze by transposase
Includes:
- nonreplicative transposons and
- replicative transposons

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8
Q

Class I transposons

A

Aka retrotransposons (RNA intermediate)
- rna is transcribed from the transposable element (DNA)
- Dna copy of element made from rna by reverse transcription and then inserted into a new chromosomal site
Requires a reverse transcriptase - reverse flow of genetic information from rna to dna
(RNA dependent DNA polymerase)

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9
Q

Class II transposons

A

Dna transposons catalyze by transposase
Includes
Nonreplicative transposons
And
Replicative transposons

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10
Q

Non replicative transposons

A

Sub class of class II transposons
Element is physically cut out of one side in a chromosome or plasmid and pasted into a new site
Cut and paste
Number of transposable elements is preserved

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11
Q

Replicative transposons

A

Element is replicated with one copy and inserted at a new site and one remains at original site
Copy and paste
Number of transposable elements increases (new copy at new site, old copy remains)

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12
Q

Structure of class one transposable elements

A

Long terminal direct repeats,

short, flanking, direct repeats at target site

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13
Q

Structure of class two transposable elements

A

Short terminal, inverted repeats,
short, flanking, direct repeats at target site

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14
Q

Genes encoded by class I (retrotransposons)

A

Reverse transcriptase gene (and sometimes others)

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15
Q

What genes are encoded by class II transposons

A

Transposase gene (and sometimes others)

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16
Q

Which class of transposons are more common in eukaryotes

A

Eukaryotes contain both dna transposons and retrotransposons but retrotransposons are more common

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17
Q

What kind of transposons are present in bacteria

A

Just DNA transposons

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18
Q

What are the mechanisms in place to control or limit transposition

A
  1. DNA is methylated where transposon’s are common
    - Methylating DNA suppresses transcription
    - Prevents production of a transpose enzyme
  2. Alterations in the chromatin structure (eg. heterochromatin) prevent transcription
  3. Control of the transposes translation by piwi interacting RNAs (piRNAs) Bind to piwi proteins in Arabic translation of transposase mRNA.
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19
Q

Why are transposable elements mutagenic

A

Due to their ability to insert themselves into DNA, they are mutagenic
Transposition is a spontaneous mutation
Transposition entails the exchange of dna sequences and recombination
Leads to dna rearrangements such as duplications, deletions, inversions and translocations

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20
Q

What is the cause of hemophilia

A

Insertion of the L1 transposable element into the blood clotting factor VIII gene causes hemophilia (frameshift/nonsense mutation)
Insertion can cause a loss of function mutation (disrupts the coding sequence of a gene)

21
Q

How can insertion cause a gain of function mutation

A

By activating a nearby gene
Beneficial: ex activating a channel to pump out insecticide in insects
Detrimental: ex. Activating protooncogene (cancerous)

22
Q

What causes black pigment in grapes

A

Lack of transposons
black pigment in the grapes is due to anthocyanins in the skin

23
Q

What causes a green/white grapes?

A

Gret1 Transposon inserted near the VvmybA1 gene disrupts the gene and synthesis of the anthocyanins that encode the black pigment
Results in no anthocyanin production

24
Q

What causes red grape colour?

A

Red grapes came about from a partial removal of retro transposon, allowing the summer, but not full production of anthocyanin

25
Q

How does can transposons lead to deletion

A

Pairing of direct repeats can result in deletion

26
Q

How can transposons lead to an inversion

A

Pairing of inverted repeats can lead to inversion

27
Q

What are the affects of misalignment and e equal exchange between transposable elements located on sister chromatids

A

Leads to one chromosome with a deletion and another with a duplication

28
Q

Corepressor

A

A small molecule that binds to a repressor, and it allows the repressor complex to bind to the operator which inhibits transcription used in negative repressible, operon

29
Q

What does negative mean for negative regulation?

A

The regulator protein is an inhibitor or repressor

30
Q

Positive control

A

Regulator protein is an activator activator, binds operator and induces transcription alternatively, an activator combined upstream of the operator to influence transcription

31
Q

CAP

A

Catabolite activator protein
A positive activator of transcription
Binds just upstream of the promoter and enhances the binding of rna polymerase to the promoter

32
Q

What does lac Y encode

A

Permeate
Transports lactose across the bacterial cell membrane

33
Q

Lac Z

A

B-galactosidase
enzyme that catabolizes Break down into glucose and galactose
Can also convert lactose into allolactose

34
Q

Lac A

A

Thiohalactoside transacetylase
Function is unclear

35
Q

LacP

A

Common promoter of the lac Y, lac z and lac A

36
Q

Lac operon in the absence of lactose

A

Very little of the operon is transcribed (but not none)
Repressor protein (lac I) binds to the operator (lacO) and inhibits transcription

37
Q

Coordinate induction

A

The simultaneous synthesis of several proteins by a specific mlc called the inducer

38
Q

Two major groups of transposable elements in bacteria

A

Simple and complex

39
Q

Simple transposable elements

A

Major group of transposable elements in bacteria only carries information required for movement,
insertion sequence contains the transposes gene
contain terminal, inverted repeats,
and flanked by direct repeats at the target site

40
Q

Complex transposable elements

A

Major group in bacteria
Includes composite and non composite

41
Q

Composite transposons

A

Any sequence that is flanked by 2 simple transposable elements
Composite transposons is flanked by direct repeats
Ex. Tn 10

42
Q

Non-composite transposable elements

A

Possess transposase gene and have terminal inverted repeats
Contain extra dna not related to transposition
Tn3 is an example
Carries ampicillin resistance gene

43
Q

Barbara McClintock

A

Discovered chromosome breakage caused usually clear kernels to become mosaic
Genetic analysis of the mechanism of chromosome breakage led her to discover the cut and paste Ds and Ac elements that moved around in the genome

44
Q

Ac gene

A

Activator gene
Contains terminal inverted repeats
Has transposase gene
Autonomous transposition
Stimulates chromosome breakage at site of Ds

45
Q

Ds gene

A

Dissociation gene
Similar to Ac
Possesses inactivated transposase gene
Requires transposase from Ac to transpose
Nonautonomous transposition

46
Q

P elements

A

In drosophila flies
Possess terminal inverted repeats
Contain both a transposase and a repressor of transposition
Creates phenomenon of

47
Q

Hybrid Dysgenesis

A

Occurs when p elements are introduced into a cell that does not have them in its genome
Sudden appearance of numerous mutations burst
Chromosome aberrations
Sterility
Repressor protein is a cytoplasmic protein that inhibits transposition
Repressor protein is incorporated into the cytoplasm of the egg

48
Q

SINES

A

Most common transposable element in human genome is Alu
Identified as mutagenic in more than 20 genetic diseases
I Roz from RNA intermediate, contain shorten, five prime end
Have a short flanking repeats (100-300bp) when sequences inserted into DNA

49
Q

LINES

A

Have shortened sequences but longer than SINES (900-6000bp)

MBG* 2040 Pt. 2 (9 decks)

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