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Applied Genetics > Gene Structure > Flashcards

Gene Structure Flashcards

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Biology 101 flashcards
1
Q

what is glycocalyx

A

a glycoprotein, polysaccharide that surrounds the cell membranes of some bacteria, epithelia and other cells

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2
Q

what are histones

A

family of basic proteins that associate with DNA in the nucleus and help condense into chromatin

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3
Q

what is UASs

A

upstream activator sequences

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4
Q

what are eukaryotic gene systems

A
  • transport of stable RNA from nucleus to cytoplasm

- transcription in nucleus and translation in cytoplasm

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5
Q

what is the eukaryotic gene structure like

A

DNA: associated with histones, linear, genes may contain introns, in nucleus

Internal structures have membrane-bound organelles (mitochondria, chloroplasts, vacuoles)
Ribosomes are 80S

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6
Q

what types of reproduction are there in eukaryotic gene systems

A

> asexual (mitosis)
sexual (meiosis)
DNA usually paired (diploid or more)

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7
Q

what are the two short sequences in the core promoter structure of prokaryotes

A

> at -10 (Pribnow box, or -10 element) usually 6 nt: TATAAT, and absolutely essential for transcription start
at -35 (-35 element) usually 6 nt: TTGAGA, is present, transcription is very high

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8
Q

what is the structure of eukaryote gene DNA

A 
Promoter 
Transcription start
5’ UTR
Exons and introns 
3’ UTR
Transcription end point
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9
Q

what do eukaryote promoters contain

A
  1. TATA box (TATAAA) to form RNA polymerase transcription complex
  2. CAAT box
  3. Enhancers, silencers and other upstream activator sequences (UASs) differs from those of prokaryotic genes
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10
Q

what are the promoters like in eukaryotes

A

diverse and complex; regulatory elements can be several kilo base pairs in length from ATG = bending of DNA

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11
Q

what is the termination in prokaryotes

A
  1. Rho-dependent

2. Rho-independent

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12
Q

what is the transcription termination in eukaryotes

A

not known but two models proposed

  1. torpedo model
  2. allosteric model
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13
Q

what is the torpedo model

A

Protein factors recognise terminator signals associated with RNA polymerase II triggering termination process

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14
Q

what is the allosteric model

A

Poly A signals transcribed to mRNA and two proteins transfer Carboxyl terminal domain of RNA polymerase II to polymerase A signal

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15
Q

how is mRNA made in eukaryotes

A
  1. mRNA capped (methyl guanosine at 5’ end)
  2. mRNA tailed (polyadenosine at 3’ end, usually 200nt of As)
  3. mRNA spliced (intron boundaries are cut and rejoined to remove intron sequences from the nascent mRNA). Eukaryotic nuclear genes, this is carried out by spliceosome. Prokaryotes, introns are much rarer and of different type
  4. mature mRNA is transported from nucleus to cytoplasm, where translation will over
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16
Q

what is the Shine-Delgarno sequence

A

AGGAGGU - AUG (3-10 nucleotides)
prokaryotes, consensus sequence in mRNA
to which ribosomes bind

17
Q

what makes up a mRNA cap and where is it

A

Cap is an extra guanosine triphosphate joined backwards (5’ end to 5’ end) onto front of mRNA

18
Q

what is the capping structure like in prokaryotic mRNA

A

very few prokaryotic mRNAs, mainly from viruses that infect eukaryotic cells, have specific site in 3’ UTR of mRNA, which ribosome can bind
Most do not, have a cap structure. One subunit of ribosome (plus other factors) binds to cap and move along mRNA looking for first AUG

19
Q

what are the nucleotides like in the original mRNA

A

Nucleotide and first couple of nucleotides in the original mRNA have methyl groups attached to them

20
Q

how does tailing of mRNA in type II genes occur

effect

A

no terminator of transcription

  • transcription continues beyond end of gene. mRNA is cut and string of couple of hundred adenosines (poly A tail) is added
  • ribosome can’t bind to cap until whole set of proteins (initiation factors) have bound there
21
Q

what is molecules are capped and tailed

A

only mRNA

22
Q

what is the role of cap and tail

A

help ribosomes bind

23
Q

what occurs if the mRNA cap and tail are removed

A

removed won’t translate efficiently, or translate at all

24
Q

what does the capping and tailing protect

A

mRNA from nucleases

25
Q

what determines the end of tRNA and rRNA

A

specific terminator sequences

26
Q

what are genes transcribed by that don’t make functional proteins and why

A

genes transcribed by RNA polymerase I and those translated by RNA polymerase III do not encode proteins so don’t need to be translated – don’t have these structures or mechanism of termination

27
Q

examples of eukaryote proteins additional processing

and why

A

usually addition of molecules to them in order to make them functional, e.g.

  1. Phosphorylation (addition of phosphate)
  2. Methylation (addition of methyl groups)
  3. Glycosylation (addition of carbohydrate chains)
28
Q

how can proteins be activated

A

by post-translational proteolysis (trimming of N or C termini or internal cleavage to yield one, or more smaller polypeptides)

29
Q

how may eukaryote proteins be targeted intracellularly

A
  • out of cell
  • to the endomembrane system (vacuole, protein bodies or lysosomes)
  • to other organelles (mitochondria and plastids)
30
Q

why aren’t proteins intracellularly targeted the same in prokaryotes as eukaryotes

A

prokaryotes don’t have most of these cellular compartments

Applied Genetics (20 decks)

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