Lecture 16 Eukaryotic Gene Structure Flashcards

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1
Q

Eukaryotes: endosymbiotic theory

A

Eukaryotes are more complex, have organelles with own bacteria. Thought that 1-1.5 billion years ago anaerobic eukaryote engulfed an aerobic eubacterium and evolved symbiosis with it (mitochondria/chloroplasts) organelles therefore have their own genomes.

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2
Q

Mitochondrial genome

A

Size varies between species
50 to millions per cell
Mitochondria grow/divide independently of the cell - maternal inheritance

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3
Q

Chloroplast genome

A

Much larger than mitochondrial genome
Up to 60 per cell
Grow and divide independently from cell

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4
Q

Organelle genome DNA barcoding

A

Organelle genomes evolve/change more slowly than nuclear genomes so are more commonly used for DNA barcoding species

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5
Q

Length of DNA

A

one big DNA molecule per chromosome: x chromosome is ~150 million BP = 5.07cm in length h.
Average human nucleus is 6micrometres (0.000006M) in diameter
46 chromosomes = 2.3m of DNA
It requires specialist packaging

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6
Q

Nuclear chromatin structure

A

At simplest level chromatin is helical dsDNA (2nm wide)
DNA is complexed with histones to form nucleosomes. Each nucleosome has 8 histone proteins w/DNA wrapped around 1.65 times (11nm)
Nucleosomes fold to form 30 nm chromatin fibre
That forms 300nm loops
Compressed and folded to 250nm wide fibre 700nm tall
Finally compacted into a 1400nm chromosome - more condensed means less accessible

Chromatin contains 2x as much protein as DNA

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7
Q

Histones

A

Abundant basic proteins
Have positive charge
5 main types H1 H2A H2B H3 & H4
4 pairs of histone proteins= 1 nucleosome
Evolutionarily conserved

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8
Q

Non histones

A

All other proteins associated with DNA
Differ in type/ structure
Amount and mass vary
Have other functions including scaffolding

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9
Q

DNA needs to be loosened for access

A

Polytene V. Large chromosomes sometimes seen in drosophila have “puff” regions where DNA has uncoiled and there’s visible high level gene activity - product of rapid replication w/out cell division keeping up

Same can happen in regular chromosomes

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10
Q

Heterochromatin Vs euchromatin

A

Hetero/Eu

Highly packed/ uncoiled chromatin
Genetically inactive/ active (transcribed)
Only in eukary/ in eukary and prokary

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11
Q

Degree of condensation

A

Changes during cell cycle and packing changes locally during transcript & replication

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12
Q

Histone modification

A

Histone tails can be modified by addition of small molecules - reversible
Lysine residues can be acetylated (CH3COO-) or methylated (CH3-)
Serine residues can be phosphorylated (PO4²-)

Modifications are interactive and summative (they add up to give diff effects)

Acetylation can shift heterochromatin to euchromatin

Methylation can silence gene expression

Phosphorylation is necessary for meiosis/mitosis

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13
Q

Chromatin “remodeling” exposed binding sites for regulation proteins

A

Chromatin remodeling complex binds to DNA and repositions nucleosomes exposing transcription factor binding site

Transcription apparatus assembles at binding site and transcription initiated

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14
Q

Eukaryotic gene expression v. Complex

A

Eukaryote DNA packaged
Cells have compartments

Complex organisms need to respond transcriptionally w/wide range of responses to multiple diff situations relevant to cell function

Eukaryotes that are multicellular usually diff cells have diff purposes and need diff proteins

E.g. skin cell forms keratin and tongue cell does not.

Only proteins appropriate to external condition/function produced

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15
Q

Plants

A

Have rapid transcriptional control to adapt to surroundings as cannot move e.g. touch stimulus in mimosa or Venus fly trap.

Respond to drought/flood, temp., Ozone and salt

Genes may be expressed in some cells and not others and produced when necessary e.g. hormones

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16
Q

Eukaryotic transcription and translation in different areas

A

Transcript - nucleus
Transcribe - ribosomes in cytoplasm

17
Q

Eukaryotes have all 3 RNA polymerase forms

A

Aminitin toxin in mushroom used to study RNA

RNA pol l: in nucleolus synthesises rRNA
No alpha aminitin sensitivity

RNA pol ll : in nucleoplasm synthesises hnRNA (protein coding genes)
Inhibited by alpha aminitin

RNA pol lll: in nucleoplasm synthesises tRNA and other small nuclear RNA
Partially inhibited by alpha aminitin

Note: dedicated RNA pol for chloroplasts and mitochondria so exist and are similar to bacterial ones

18
Q

Summary

A

Eukaryotes: complex DNA packing partially reversed for transcriptiom

Multiple RNA Pols and RNA pol ll codes nuclear genes

Cell specific gene expression to produce required proteins