Lecture 6: Structure Of Eukaryotic Genes

Question 1

What is a gene?

Answer 1

Entire DNA sequence transcriptional unit required for synthesis of a functional protein or RNA molecule

Question 2

What is interrupted genes?

Answer 2

A gene in which the coding sequence is not continuous due to the presence of introns

Question 3

What do many genes encode?

Answer 3

Functional RNAs that are not translated into protein

Question 4

What is primary (RNA) is

Answer 4

The original I modified RNA product corresponding to a transcription unit

Question 5

What is RNA splicing?

Answer 5

The process of excising introns from RNA and connecting the Exxon’s into a continuous mRNA

Question 6

What is an Exon?

Answer 6

A segment of DNA that is transcribed and retained in the mature RNA product

Question 7

What is an Intron?

Answer 7

A segment of DNA that is transcribed, but later removed from within the transcript by splicing together the sequences on either side of it

Question 8

What is mature transcript?

Answer 8

A modified RNA transcript. Modification may include the removal of intron sequences and alterations to the 5’ and 3’ ends

Question 9

How are introns removed?

Answer 9

RNA splicing which occurs in cis in individual RNA molecules

Question 10

Do exons remain in the same order in MRNA as in DNA?

Answer 10

Yes

Question 11

What does mutation in the exons affect?

Answer 11

Polypeptide sequence

Question 12

What does mutations in introns affect?

Answer 12

RNA processing - influence the sequence and/or production of a polypeptide

Question 13

How can introns be detected?

Answer 13

When genes are compared with their RNA transcription products

Question 14

What is cDNA?

Answer 14

Single-stranded DNA complementary to RNA, synthesised from it by reverse transcription in vitro

Question 15

What are the methods that detect introns?

Answer 15

Restriction mapping Electron microscopy Sequencing

Question 16

How many exons and introns does the ovalbumin gene contain?

Answer 16

8 exons and 7 introns

Question 17

What does complementary regions between DNA and mRNA form?

Answer 17

DNA-RNA hybrid

Question 18

What can genes be interrupted by?

Answer 18

Segments not present in mRNA

Question 19

When are the positions of introns usually conserved?

Answer 19

When homologous genes are compared between different organisms

Question 20

What do introns not usually encode?

Answer 20

Proteins

Question 21

Genes that share a common ancestry have similar organisations with what?

Answer 21

The conservation of the positions of the introns

Question 22

What is the organisation of the mammalian genes for DHFR?

Answer 22

Short exons and very long introns

Question 23

What has been observed by doing comparisons of related genes in different specifies?

Answer 23

Sequencers of the corresponding exons are usually conserved but the sequences of the introns are much less similar

Question 24

In what form can the homology of 2 genes be plotted?

Answer 24

Dot matrix comparison

Question 25

Why does intron evolve much more rapidly then exons?

Answer 25

Lack of selective pressure to produce a polypeptide with a useful sequence

Question 26

Under positive selection what sequence vary and what are conserved?

Answer 26

Exons- vary Introns - conserved

Question 27

What are individuals under positive selection do?

Answer 27

Advantage survive (produce more fertile progeny)

Question 28

What genes are uninterrupted but interrupted in multicellular eukaryotes?

Answer 28

S. Cerevisiae

Question 29

What do genes show?

Answer 29

A wide distribution of sizes

Question 30

What tends to be uniform in size between organisms?

Answer 30

Exons

Question 31

Exons

Answer 31

Usually short, typically encoding fewer than 100 amino acids

Question 32

What tends to vary in size between organisms?

Answer 32

Intron size

Question 33

What is the overall length of a gene determined by?

Answer 33

It’s introns

Question 34

What does the predominance of introns in multicellular eukaryotes mean?

Answer 34

Genes can be much larger than the sum total of the exons

Question 35

What does a simple eukaryotic transcription unit produce?

Answer 35

Single monocistronic MRNA which is translated into a single protein which extends from the 5’ cap sire to the 3’poly(A) site

Question 36

What lies between exons?

Answer 36

Introns and are removed during processing of primary transcript

Question 37

How are multiple variants of a polypeptide chain produced?

Answer 37

The use of alternative start or stop codons

Question 38

What is overlapping gene?

Answer 38

A gene in which part of the sequence is found within part of the sequence of another gene

Question 39

How can 2 proteins be generated from a single gene?

Answer 39

Starting or terminating transcription at different points

Question 40

What can complex eukaryotic transcription unit produce?

Answer 40

A primary transcript that can be processed in alternative ways

Question 41

What happens when primary transcript has 2 poly (A) sites?

Answer 41

Processed into MRNAS with alternative 3’ exons

Question 42

What is differential (alternative) splicing?

Answer 42

When certain exons are included or excluded

Question 43

What does alternative splicing use?

Answer 43

Same pre-mRNA to generate mRNAs that have different combinations of exons

Question 44

What is alternative splice sites?

Answer 44

mRNA has same 5’ and 3’ exons but different internal exons

Question 45

What does alternative splicing produce?

Answer 45

Proteins with altered function

Question 46

On average, how many expressed alternative transcripts per protein coding gene are there?

Answer 46

10-12

Question 47

are alternative transcripts expressed at the same level?

Answer 47

No

Question 48

What percentage of protein coding genes have at least 2 dominant/major alternative transcripts ?

Answer 48

75%

Question 49

What are examples of Alternative Splicing?

Answer 49

Striated muscle mRNA Smooth muscle mRNA Fibroblast mRNA Brain mRNA

Question 50

What can proteins consist of?

Answer 50

Independent functional modules, the boundaries which can be equated with those of exons