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Human Molecular B > Lecture 6: Structure Of Eukaryotic Genes > Flashcards

Lecture 6: Structure Of Eukaryotic Genes Flashcards

1
Q

What is a gene?

A

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

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2
Q

What is interrupted genes?

A

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

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3
Q

What do many genes encode?

A

Functional RNAs that are not translated into protein

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4
Q

What is primary (RNA) is

A

The original I modified RNA product corresponding to a transcription unit

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5
Q

What is RNA splicing?

A

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

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6
Q

What is an Exon?

A

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

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7
Q

What is an Intron?

A

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

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8
Q

What is mature transcript?

A

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

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9
Q

How are introns removed?

A

RNA splicing which occurs in cis in individual RNA molecules

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10
Q

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

A

Yes

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11
Q

What does mutation in the exons affect?

A

Polypeptide sequence

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12
Q

What does mutations in introns affect?

A

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

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13
Q

How can introns be detected?

A

When genes are compared with their RNA transcription products

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14
Q

What is cDNA?

A

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

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15
Q

What are the methods that detect introns?

A

Restriction mapping Electron microscopy Sequencing

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16
Q

How many exons and introns does the ovalbumin gene contain?

A

8 exons and 7 introns

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17
Q

What does complementary regions between DNA and mRNA form?

A

DNA-RNA hybrid

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18
Q

What can genes be interrupted by?

A

Segments not present in mRNA

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19
Q

When are the positions of introns usually conserved?

A

When homologous genes are compared between different organisms

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20
Q

What do introns not usually encode?

A

Proteins

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21
Q

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

A

The conservation of the positions of the introns

22
Q

What is the organisation of the mammalian genes for DHFR?

A

Short exons and very long introns

23
Q

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

A

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

24
Q

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

A

Dot matrix comparison

25
Q

Why does intron evolve much more rapidly then exons?

A

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

26
Q

Under positive selection what sequence vary and what are conserved?

A

Exons- vary Introns - conserved

27
Q

What are individuals under positive selection do?

A

Advantage survive (produce more fertile progeny)

28
Q

What genes are uninterrupted but interrupted in multicellular eukaryotes?

A

S. Cerevisiae

29
Q

What do genes show?

A

A wide distribution of sizes

30
Q

What tends to be uniform in size between organisms?

A

Exons

31
Q

Exons

A

Usually short, typically encoding fewer than 100 amino acids

32
Q

What tends to vary in size between organisms?

A

Intron size

33
Q

What is the overall length of a gene determined by?

A

It’s introns

34
Q

What does the predominance of introns in multicellular eukaryotes mean?

A

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

35
Q

What does a simple eukaryotic transcription unit produce?

A

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

36
Q

What lies between exons?

A

Introns and are removed during processing of primary transcript

37
Q

How are multiple variants of a polypeptide chain produced?

A

The use of alternative start or stop codons

38
Q

What is overlapping gene?

A

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

39
Q

How can 2 proteins be generated from a single gene?

A

Starting or terminating transcription at different points

40
Q

What can complex eukaryotic transcription unit produce?

A

A primary transcript that can be processed in alternative ways

41
Q

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

A

Processed into MRNAS with alternative 3’ exons

42
Q

What is differential (alternative) splicing?

A

When certain exons are included or excluded

43
Q

What does alternative splicing use?

A

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

44
Q

What is alternative splice sites?

A

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

45
Q

What does alternative splicing produce?

A

Proteins with altered function

46
Q

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

A

10-12

47
Q

are alternative transcripts expressed at the same level?

A

No

48
Q

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

A

75%

49
Q

What are examples of Alternative Splicing?

A

Striated muscle mRNA Smooth muscle mRNA Fibroblast mRNA Brain mRNA

50
Q

What can proteins consist of?

A

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

Human Molecular B (13 decks)

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