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Molecular Bio > module 3 - Genomes > Flashcards

module 3 - Genomes Flashcards

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Biology 101 flashcards
1
Q

what is a genome?

A

the complete set of DNA molecules possessed by an organism

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2
Q

what is the function of DnaA in e.coli

A
  • bind close to the origin of replication
  • DNA becomes wound around protein - forces bases to break at replication origin
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3
Q

what is the function of DnaB in e.coli

A
  • forms prepriming complex by attatching to origin
  • DnaB acts as helicase
  • breaks base pairs so replication fork moves away from origin
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4
Q

what is the primosome?

A
  • complex that makes the RNA primers that initiate replication of the 2 leading strands
  • formed by the attatchment of 2 primase enzymes
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5
Q

what happens at the replication fork in e.coli?

A
  • helicase (DnaB) breaks base pairs
  • single strand binding proteins protect bare single strands
  • DNA topoisomerase unwinds strands
  • primase forms primers on leading + lagging strands
  • DNA Pol III synthesises DNA
  • DNA Pol I and DNA ligase removes primers + joins okazaki fragments
  • gamma complex (clamp loader) attatches + detatches DNA Pol III from lagging strand
  • beta complex (sliding clamp) holds DNA Pol III to template - allows it to slide
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6
Q

what is the function of the gamma complex?

A

clamp loader
- attatches + detaches DNA Pol III from lagging strand

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7
Q

what is the function of the beta complex?

A

sliding clamp
- holds DNA Pol III to the template - allows it to slide

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8
Q

what happens at the replication fork in humans?

A
  • helicase breaks base pairs
  • single strand binding proteins protect bare single strands
  • DNA topoisomerase unwinds strands
  • primase/DNA Pol alpha forms primers on leading + lagging strands
  • DNA Pol delta synthesises DNA
  • FEN1 + DNA ligase removes primers + joins okazaki fragments
  • proliferating cell nuclear antigen (PCNA) sliding clamp that holds DNA Pol delta to the DNA
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9
Q

what shape is the E.Coli genome?

A

circular

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10
Q

what is a Tus protein?

A

a protein that allows a replication fork to pass in one direction but not the other
- has a permissive and a non-permissive face

tusks on a boar - can’t get past head on bc tusks face forwards, but can run past from the back

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11
Q

what do Tus proteins bind to?

A

terminator sequences

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12
Q

what happens as a result of two adjacent Tus proteins?

A

creates a region where the replication fork gets trapped
- Tus lock domain
- allows replication to stop in circular DNA

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13
Q

what is chromatin?

A

DNA extracted from the nucleus
- digestion with an endonuclease shows that chromatin is actually a DNA-protein complex

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14
Q

what are histones?

A

the proteins within chromatin

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15
Q

what are the 5 histone proteins?

A

H1
H2A
H2B
H3
H4

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16
Q

what is a nucleosome?

A
  • octamer - made up of 8 proteins
  • made up of two each of H2A, H2B, H3, and H4
17
Q

what is the role of histone H1?

A

linker histone - attatches outside nucleosome

18
Q

what is a chromatosome?

A

the composition of a nucleosome + DNA wrapping around it + linker histone on top

19
Q

why are histones important?

A
  • allows a vast amount of DNA to be packed into nucleosomes and other higher order DNA structures
20
Q

what is euchromatin?

A

contains active genes as 30nm fibre (less densely packed)

21
Q

what is heterochromatin?

A

contains inactive genes (more densely packed)

22
Q

what is the difference between constitive and facultative heterochromatin?

A

Con - contains DNA that is always tightly packed in all cells
Fac - cotains DNA that is tightly packed only in some cells

23
Q

what is the function of the centromere in a chromosome?

A
  • holds daughter chromosomes together
  • contains special histones - CENP-A instead of H3
  • attatchment point for microtubules + spindle fibres that pull chromosomes apart
24
Q

what is the function of telomeres in chromosome?

A
  • telomeres protect the ends from exonuclease attack or from being mistaken for chromosome breaks and being joined together by DNA repair mechanisms

Molecular Bio (8 decks)

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