Prokaryote and Extra-chromosomal Genetics

Question 1

How is a prokaryotic chromosome stored within the cell?

Answer 1

As a nucleoid (non-compartmentalised).

Question 2

How many chromosomes do prokaryotes typically have?

Answer 2

One.

Question 3

How do prokaryotic chromosomes compare in terms of size?

Answer 3

Much smaller.

Question 4

Describe the shape of prokaryotic chromosomes.

Answer 4

Circular.

Question 5

How are aggregates of cells produced?

Answer 5

Via binary fission.

Question 6

Define the term prokaryotic genetics.

Answer 6

Constant segregation and assortment of genetic information via cellular level gene transfer.

Question 7

Define the term plasmid.

Answer 7

An extra-chromosomal circle of DNA containing non-essential genes.

Question 8

What genetic information is stored on plasmids?

Answer 8

Genes allowing replication/segregation of the plasmid.

Genes that confer auxiliary metabolic pathways.

Question 9

How many origins of replication do prokaryotic chromosomes have?

Answer 9

Usually one.

Question 10

Define the term conjugate plasmid.

Answer 10

A plasmid containing genes that allow the plasmid to transfer a copy of itself to another cell.

Question 11

What is the name given to genes that allow conjugation?

Answer 11

Transfer genes.

Question 12

What are plasmid - strains?

Answer 12

Cells lacking a specific conjugative plasmid.

Question 13

What are plasmid + strains?

Answer 13

Cells possessing a specific conjugative plasmid.

Question 14

What do tra genes encode?

Answer 14

Proteins called pilins that extrude from the cell to form pili.

Question 15

Where are tra genes found?

Answer 15

On plasmids.

Question 16

How do pili function?

Answer 16

They recognise and adhere to the plasmid to form a channel between cells.

Question 17

What are transposable elements?

Answer 17

Mobile DNA sequences that are able to jump from one location to another within a cell.

Question 18

What are inverted repeats?

Answer 18

Flanking identical short DNA sequences.

Question 19

What do transposase enzymes recognise?

Answer 19

Inverted repeats.

Question 20

What do transposase enzymes do?

Answer 20

Catalyse transposition.

Question 21

What are the simplest transposable elements?

Answer 21

Insertion sequences.

Question 22

What genes do insertion sequences contain?

Answer 22

tnp genes which encode for transposases.

Question 23

Define the process of replicative transposition.

Answer 23

Creating a new copy of the transposable element.

Question 24

Define the process of non-replicative transposition.

Answer 24

A transposable element jumping from one position to another.

Question 25

How are transposable elements "selfish gene" parasites?

Answer 25

They proliferate throughout the genome by jumping between/within chromosomal and plasmid locations.

Question 26

How is a transposon formed?

Answer 26

Two insertion sequences flank a gene which disrupts the normal function of transposases.

Question 27

Define the term transposon.

Answer 27

A transposable element carrying extra genes.

Question 28

How do transposons get transferred between chromosomes and plasmids?

Answer 28

Transposases have no specific DNA target.

Question 29

How can genes on a chromosome be transferred between cells?

Answer 29

The genes could become part of a transposon and then become incorporated into the plasmid. This plasmid can then be transferred to other cells via conjugation.

Question 30

What happens when there is no selection for a plasmid?

Answer 30

A mixed population will be formed: some cells will have the plasmid, some won't.

Question 31

What happens when selection for a plasmid occurs?

Answer 31

Those with the advantageous plasmid survive and spread the plasmid within the population.

Question 32

What is meant when a pilus is described as promiscuous?

Answer 32

It means that it has the potential for conjugation between species.

Question 33

What is a reciprocal strand exchange?

Answer 33

Homologous recombination between a chromosome and plasmid as a result of the two aligning because of identical genes.

Question 34

What is sometimes formed from reciprocal strand exchange?

Answer 34

A co-integrated molecule (the chromosome and plasmid combine).

Question 35

What is meant by plasmid excision?

Answer 35

The plasmid separating from the co-integrated molecule. Opposite of reciprocal strand exchange.

Question 36

Define the term episomal plasmid.

Answer 36

A plasmid with sequences homologous to a host cell | chromosome, capable of reversible integration and excision.

Question 37

Define the process of transduction.

Answer 37

The transfer of genes via viral transfer as a result of incorporating sections of the host genome.

Question 38

Define the process of transformation.

Answer 38

The deliberate uptake of DNA from the external environment and its incorporation into the host cell chromosome.

Question 39

What is the term given to the ability to take up DNA?

Answer 39

Competence.

Question 40

Eukaryotic gene transmission is vertical. How do prokaryotes compare?

Answer 40

Gene transmission in prokaryotes can be both vertical and horizontal.

Question 41

Define vertical gene transmission (VGT).

Answer 41

Transfer of genetic information down a lineage (generation to generation)

Question 42

Define horizontal gene transmission (HGT).

Answer 42

Transfer of genetic information between lineages (between living cells).

Question 43

What processes allow horizontal gene transmission (HGT) in prokaryotes?

Answer 43

Conjugation, transduction and transformation.

Question 44

Define the mobilome.

Answer 44

The genetic material that can actively move within a genome and between individuals.

Question 45

What could be classed as part of the mobilome?

Answer 45

Plasmids, transposons, DNA transduced by viruses and DNA in the environment.

Question 46

How is horizontal gene transfer restricted (HGT)?

Answer 46

Conjugation is generally limited to one species. Cells have mechanisms to select DNA. Prokaryotes have immune systems to destroy foreign DNA.

Question 47

What is quorum sensing?

Answer 47

A form of HGT prevention. The cell only becomes competent when it senses other similar cells growing nearby.

Question 48

Why do prokaryotes often contain restriction endonucleases?

Answer 48

They cleave foreign DNA in order to prevent the cell being harmed.

Question 49

How is host cell DNA protected from restriction endonucleases?

Answer 49

Host DNA is modified by DNA methylase so isn't recognised.

Question 50

Where do the organelles and cytoplasm originate from in a eukaryotic cell?

Answer 50

From the maternal gamete.

Question 51

What shape are mitochondrial chromosomes?

Answer 51

Circular.

Question 52

What shape are chloroplast chromosomes?

Answer 52

Circular.

Question 53

What are the evolutionary origins of mitochondria and chloroplasts?

Answer 53

They were originally bacteria that entered into | a symbiotic relationship with archaeal-like cells.

Question 54

Why do maternally-inherited organelle traits show phenotypic variability?

Answer 54

Variability in the number of mitochondrial chromosomes in each mitochondrion.

Question 55

What is one technique that can be used to avoid maternally inherited diseases?

Answer 55

"3 parent" IVF combined with transplant of healthy mitochondria.

Question 56

What is Wolbachia?

Answer 56

An alpha-proteobacteria that is an endosymbiont in | arthropod and nematode cells.

Question 57

How are Wolbachia cells transmitted?

Answer 57

Maternally via egg cell cytoplasm.

Question 58

How does Wolbachia proliferate?

Answer 58

It increases the proportion of females as it is passed on maternally.