Eukaryotic Genes Vs Prokaryotic

Question 1

What is it called when prokaryotic mrna has clustered genes on it and codes for many proteins involved in same processes?

Answer 1

Polycistronic

Question 2

Eukaryotic mrna is monocistronic. What does that mean

Answer 2

Each gene is seperate on mrna. It has its own promoter and terminator

Question 3

How does the polycistronic and monocistronic organisation affect genetics

Answer 3

In prokaryotes, if one promoter is damaged or lost many genes will not be transcribed due to clustered

In eukaryotes only the gene associated affected

Question 4

What are transcription promoters

Answer 4

Nucleotide sequences on 5’ end which allows transcription factors and therefore rna polymerase to bind

Question 5

In prokaryotes, the sigma factor recognises a conserved sequence on promoter region. How does this allow transcription

Answer 5

The sigma factor then binds and allows the positioning of rna polymerase to initiate transcription

Question 6

What does the mix of rna polymerase and sigma factor in prokaryotes represent

Answer 6

A holo enzyme

Question 7

There are 3 rna polymerase in eukaryotes vs 1 in prokaryotes. Name and explain what they transcribe

Answer 7

Rna pol 1- transcribes rrna genes

Rna pol 2- transcribes all protein coding genes

Rna pol 3- transcribes tRNA,rRNA, other non coding rnas

Question 8

What is rna polymerase 2 promoter comprised of

Answer 8

Repeating sequences /motifs such as the TATA box- TATATATATATATA sequence

Question 9

What binds to the tata box in eukaryotic promoter site to initiate rna polymerase 2

Answer 9

The transcription factor 2D complex

Which then recruits rna polymerase 2

Question 10

What is the terminator sequence in eukaryotes and what happens

Answer 10

AAUAAA

Rna at this point is cut by endonucleases from the dna

Question 11

How is gene expression altered in prokaryotes using sigma factors

Answer 11

Sigma factors have ability to direct rna polymerase to specific genes. By using alternative sigma factors, they recognise different sequences and so could affect whether gene is transcribed or not.

Question 12

What would a mutation to sigma factor do

Answer 12

Affect expression of all the sets of genes it regulates (eg in a cluster)

Question 13

How do eukaryotes alter gene expression using many different transcription factors

Answer 13

The TFs bind to the motifs in the promoter region which influences ability for rna polymerase to bind

These regulate each promoter/gene. More is needed for transcription than just the TATA box and tf 2D complex

Question 14

How would you analyse patters of transcription

Answer 14

Isolate mrna from different organisms and replicate them

The mrna is labelled with eg fluorescent dye

The mrna are then hybridised and analysed in a microarray - dna in genes spotted on a slide

Question 15

When do changes in gene expression occur

Answer 15

Diseases like cancer
Different tissues = different genes expressed
During development different genes expressed

Question 16

Splicing removes introns in between exons. Explain the structure of an intron which allows splicing

Answer 16

Before intron and after intron there are conserved sequences
These are splice sites

The splice site after intron usually has pyrimidines such as A or G

Question 17

What are splice sites for (conserved sequences)

Answer 17

They define where introns are and recruit the spliceosome

Question 18

What cuts dna in splicing

Answer 18

Spliceosome

Question 19

Do protein genes only encode for 1 protein? Why not?

Answer 19

No - due to alternative splicing

Question 20

Due to alternative splicing and alternative promoters, mrna can have many different versions. What are these called

Answer 20

The transcriptome

Question 21

After transcriptomes undergo post translational modifications, what are all the proteins called

Answer 21

The proteome

Question 22

Which base does translation always start at

Answer 22

Methionine

Question 23

What is an open reading frame

Answer 23

The sequence of bases translated from the start to stop codon

Question 24

What does the small subunit do

Answer 24

Reads and recognises the start codon at mrna (start of orf) - AUG

Pairs trna to complementary codon

Question 25

What does the large subunit do

Answer 25

House the PEPTIDYL TRANSFERASE CENTRE (synthesis of protein)

Question 26

How are ORF identified in prokaryotes in translation

Answer 26

Each gene in a cluster has its own shine dalgarno sequence before the AUG start. This is recognised by the small subunit via base pairing

Question 27

How does the small subunit recognise the shine dalgarno sequence

Answer 27

Through base pairing - complementary sequence

Question 28

Why would a mutation of the shine dalgarno sequence only affect 1 gene is the prokaryotes are polycistronic

Answer 28

Each gene has its own ORF. Independent translation of all of them

Question 29

When Is a poly A tail added to eukaryotic mrna?

Answer 29

After mrna is cut by endonucleases at the terminator region in transcription

Question 30

What is the importance of the poly A tail on mrna

Answer 30

It increases its stability

Question 31

What is the 5’ cap on eukaryotic mrna for

Answer 31

It allows the small subunit to bind in translation

Question 32

In eukaryotic translation, after the small subunit binds to the cap, which sequence later in the mrna is recognised by small subunit

Answer 32

The Kozak consensus sequence (before the AUG)

Question 33

Where does translation start in eukaryotes

Answer 33

The kozak consensus sequence

Question 34

Why does transcription affect translation in prokaryotes but not eukaryotes

Answer 34

In prokaryotes they are paired. Translation occurs whilst mrna could still be getting transcribed from dna

In eukaryotes, the mrna is cut and has to transport to the cytoplasm where translation occurs- they are seperate processes