Lecture 11: DNA and the Genetic Code

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35 Terms

1
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what is nuclein

the old name for DNA → identified as weakly acidic, phosphorous-rich material from nuclei of human white blood cells

2
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what was the major component of nuclein determined to be

DNA

3
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what does the Schiff reagent do

stains DNA red → it was used to show it was almost exclusively located in the chromosomes

4
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what do chromosomes consist of

DNA and proteins (DNA is compacted around proteins)

5
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<p>what does this experiment show</p>

what does this experiment show

microbes need to be ALIVE to cause disease

<p>microbes need to be ALIVE to cause disease</p>
6
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what is transformation

the ability of a substance to change genetic characteristics of an organism

  • the genetic alteration of a cell resulting from the direct uptake and incorporation of exogenous material

<p>the ability of a substance to change genetic characteristics of an organism</p><ul><li><p>the genetic alteration of a cell resulting from the direct uptake and incorporation of exogenous material</p></li></ul><p></p>
7
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which experiment showed transformation of streptococcous

  • heat killed S cells (disease causing variant of strep)

  • incorporated R cells w them (non disease causing variant of strep)

  • when gave “harmless” R cells to mice it killed them

  • when analyzed mice tissue it showed living S cells

8
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explain the transforming principle

the thing that made R streptococcus cells S streptococcus cells

  • the transforming principle could be added to living R cells and S cells would be produced given sufficient time → they were getting their genetic info somehow → that genetic info is the transforming principe (the thing that sparked the transformation)

9
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how did people initially determine what the transforming principle was (include what proteases, RNase, DNase, and ultracentrifugation do)

they isolated and purified the transforming principle then ran a series of tests with diff samples, each destroying a substance that might have been the transforming principle, then seeing if R cells were transformed into S cells once the samples were introduced to an R colony

  • protease → destroys proteins

  • RNase → destroys RNA

  • DNase → destroys DNA

  • ultracentrifugation → destroys fats

transformation only didn’t occur when samples of purified transforming principle were treated with DNase

therefore the transforming principle was DNA

<p>they isolated and purified the transforming principle then ran a series of tests with diff samples, each destroying a substance that might have been the transforming principle, then seeing if R cells were transformed into S cells once the samples were introduced to an R colony</p><ul><li><p>protease → destroys proteins</p></li><li><p>RNase → destroys RNA</p></li><li><p>DNase → destroys DNA</p></li><li><p>ultracentrifugation → destroys fats</p></li></ul><p>transformation only didn’t occur when samples of purified transforming principle were treated with DNase</p><p>therefore the transforming principle was DNA</p>
10
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what are viruses

  • not alive (do not have cells)

  • made up of only protein and DNA or RNA (protein + 1 type of nucleic acid)

11
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what are bacteriophages

viruses that infect bacteria

  • often called “phages” for short

12
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explain the lifecycle of a bacteriophage

  1. phage attaches to bacterium (host)

  2. injects its genes into host

  3. phase DNA replicates, new phage proteins are made

  4. phage particles assemble

  5. cell bursts, releasing new phages

note: genetic material used to replicate phages is inside the bacterial host

another note: after injection, ghost particle of phage remains attached to the outer surface of the bacterial cell

13
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after injection, where does the ghost particle of a bacteriophage go

it remains attached to the outer surface of the bacterial cell

14
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how were bacteriophages used to further distinguish DNA from protein as the transforming principle (the genetic material of a cell)

injected one bacteriophage (T2 phage) into a phosphorous containing medium (so as they grew they would use that P to make their DNA

  • radiolabels DNA

injected another bacteriophage into a sulphur containing medium so they would use sulphur to make their proteins

  • radio labelled proteins

after infection, phage ghosts and bacterial cells were separated via centrifugation

  • bacterial cells end up in pellet

  • phage ghosts end up in supernatant

looked for which of these substances was found in the infected bacterial cell

→ radiolabeled P :. DNA was in the pellet (bacterial cells)

→ radiolabeled S :. proteins were in the supernatant

so DNA carried genetic info

15
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what are the 3 components of DNA

deoxyribose sugar

phosphate group

nitrogenous base

16
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what are the 4 types of nitrogenous bases

  • Adenine (A)

  • Guanine (G)

  • Thymine (T)

  • Cytosine (C)

17
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what is each “building block” of DNA called

a nucleotide

18
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how are nucleotides linked

in a directional chain

  • phosphodiester bonds form covalent link btwn 3’ carbon of one nucleotide and 5’ carbon of the next nucleotide

19
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in what direction are nucleotide sequences written in by convention (unless stated otherwise)

5’ to 3’

20
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what pieces get incorporated into DNA during DNA synthesis

deoxyribonucleoside triphosphates (dNTPs)

  • contain 3 phosphate groups (instead of 2 when on DNA)

  • P groups hold a lot of energy

    • the E gained by cleaving those bonds gives it energy to add them to the larger DNA molecule

21
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which nitrogenous bases repeatedly occur at basically the same rates and what does that mean

A/T and C/G → means they bind tg

22
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what is the diameter of DNA

20 angstroms

23
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what does x-ray difraction of purified DNA show

that DNA was spiral-shaped (helical)

24
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what is the basic structure of DNA

  • anti-parallel strands held tg by hydrogen bonding btwn base pairs

  • one complete turn every 34 angstroms

25
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how big is an angstrom

1 angstrom is 1 ten-billionth of a meter

26
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t/f: double helixes can have many alternative forms

true

<p>true</p>
27
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which form of a double helix is the form DNA takes the majority of the time

the B-form

<p>the B-form</p>
28
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t/f: chromosome structure varies

true

29
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where are linear, double-stranded chromosomes found

eukaryotic nuclear genomes

30
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where are circular, double stranded chromosomes found

most bacteria, mitochondria, chloroplasts

31
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where is single-stranded DNA usually found

many viruses

32
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what things have no DNA in them

retroviruses (RNA viruses) → have RNA genomes

33
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what kinds of bonds are involved in complimentary base pairing

hydrogen bonds

34
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in double stranded DNA molecule, if 18% of bases are thymine (T) what percent are guanine (G)

knowt flashcard image
35
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if a DNA molecule of 422 base pairs contains 88 adenosine bases (A) how many guanine bases (G) will it have

334