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Molecular 3rd year > Chpt 4: DNA, Chromosomes, and Genomes > Flashcards

Chpt 4: DNA, Chromosomes, and Genomes Flashcards

1
Q

what did Watson and Crick discover

A

the structure of DNA

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2
Q

what solved the problem of how info in DNA might be replicated

A

the double-helical structure

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3
Q

describe the first experimental demonstration that DNA is the genetic material

A
  • 2 strains of s. pneumoniae were used
  • one was smooth (S) and causes death, the other was rough (R) and is nonlethal
  • R cells were grown in the presence of heat-killed S, and some of the R transformed into S
  • molecules that can carry heritable info are present in S
  • R strain was incubated w various types of molecules purified from the S
  • RNA, protein, lipid, carbs all did not convert R. to S
  • DNA did convert R to S
  • DNA is the molecule that carries heritable info
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4
Q

what is gene expression

A

the process through which the info encoded in DNA is interpreted by the cell to guide the synthesis of proteins

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5
Q

what is the process through which the info encoded in DNA is interpreted by the cell to guide the synthesis of proteins

A

gene expression

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6
Q

what bonds hold the nucleotides together across diff strands

A

H bonds

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7
Q

what does DNA stand for

A

deoxyribonucleic acid

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8
Q

what is this

A

uracil

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9
Q

what is this

A

thymine

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10
Q

what is this

A

cytosine

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11
Q

what is this

A

adenine

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12
Q

what is this

A

guanine

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13
Q

what bonds hold the backbone together

A

covalent

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14
Q

where does the 3D structure of DNA arise from

A

the chem and structural features of its 2 polynucleotide chains

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15
Q

what enables the base pairs to be packed in the energetically most favourable arrangement in the interior of the double helix

A

complementary base pairing

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16
Q

there is one complete turn of the helix every _____ base pairs

A

10.4

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17
Q

a pre-existing strand of DNA works as a _______ for the synthesis of a new complementary strand

A

template

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18
Q

describe the structure of a cell nucleus

A
  • surrounded by a nuclear envelope
  • outer nuclear membrane is connected to endoplasmic reticulum
  • nuclear envelope is supported internally by the nuclear lamina
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19
Q

describe the structure of a chromosome in a eukaryotic cell

A

a single DNA molecule along w proteins

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20
Q

the complex of DNA and tightly bound protein is called what

A

chromatin

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21
Q

describe DNA structure in bacteria

A
  • carry their genes on a single DNA molecule (often circular)
  • w proteins that package and condense it (but diff than ones in eukaryotes)
  • this is cause they lack a special nuclear compartment
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22
Q

how many copies of each chromosome do we have

A

2 (except for gametes)

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23
Q

the maternal and paternal chromosomes of a pair are called what

A

homologous chromosomes (homologs)

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24
Q

what are the only nonhomologous chromosome pairs

A

sex chromosomes in males (Y from dad, X from mom)

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25
Q

what is an intron

A

Nucleotide sequence within a gene that is removed via RNA splicing during maturation of the final RNA product

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26
Q

what is an exon

A

Nucleotide sequence within a gene that becomes part of mature RNA molecule

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27
Q

how are all of the chromosomes typically displayed to produce an image

A

karyotype

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28
Q

what is a gene

A

a segment of DNA that contains the instructions for making a particular protein (this is a narrow def tho)

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29
Q

is there a correlation between the complexity of an organism and the number of genes in its genome

A

there can be (a lot of the differences is noncoding DNA tho)

30
Q

what accounts for the astonishing variations in genome size that we see when we compare one species with another

A

differences in the amount of noncoding DNA

31
Q

how much of the human genome codes for proteins

A

very little (about 1%)

32
Q

what size is the average gene size

A

large (about 26k nucleotide pairs)

33
Q

what ensures that genes are turned on or off at the proper time

A

regulatory DNA sequences

34
Q

do all RNA molecules produce proteins

A

no

35
Q

each DNA molecule that forms a linear chromosome must contain what

A
  • centromere
  • 2 telomeres
  • replication origins
36
Q

The highly condensed chromosomes in a dividing cell are known as what

A

mitotic chromosomes

37
Q

what is the name of the nucleotide sequence at which duplication of DNA begins

A

replication origin

38
Q

what is a centromere

A
  • specialized DNA sequence
  • allows one copy of each duplicated and condensed chromosome to be pulled into each daughter cell when a cell divides
39
Q

what attaches the chromosome to the mitotic spindle

A

kinetochore (a protein complex)

40
Q

what are some examples of specialized DNA sequences

A
  • centromere
  • telomere
41
Q

what is a telomere

A
  • specialized DNA sequence
  • the end of chromosomes
  • repeated nucleotide sequences that allow the ends of chromosomes to be efficiently replicated
  • protect the ends of chromosomes from being mistaken for a broken DNA molecule in need or repair
42
Q

the proteins that bind to DNA to form eukaryotic chromosomes are divided into which classes

A
  • histones
  • non-histone chromosomal proteins
43
Q

the complex of both classes of proteins with nuclear DNA of eukaryotic cells is known as what

A

chromatin

44
Q

what is chromatin

A

the complex of both classes of proteins with nuclear DNA of eukaryotic cells

45
Q

what are responsible for the 1st level of chromosome packing: nucleosome

A

histone

46
Q

describe the beads on a string visual

A
  • string is DNA
  • each bead is a nucleosome core particle (DNA wound around a histone)
47
Q

what is a nucleosome

A

DNA wound around a histone

48
Q

what is linker DNA

A

the DNA in between each nucleosome core particle

49
Q

describe the histones in the nucelosome core particle

A
  • histone octamer
  • 2 of each: H2A, H2B, H3 and H4 proteins
50
Q

describe the interface between DNA and histone

A

142 H bonds in each nucleosome

51
Q

describe the overall structure of histones

A
  • highly folded due to the basic AA
  • has a largely unstructed N-terminal AA “tail”
52
Q

what causes nucleosomes to stack on each other

A
  • nucleosome to nucleosome attractions
  • involve histone tails (often the H4 tail)
  • histone H1 is ofren present in a 1:1 ratio w nucleosome cores (called a linker histone)
53
Q

is chromatin structure static?

A
  • highly dynamic
  • must allow access to the DNA
  • some spontaneous wrapping/ unwrapping occurs
  • also through ATP-driven chromatin-remodling complexes
54
Q

what are ATP-driven chromatin-remodeling complexes

A
  • cells have a lot of these complexes
  • they allow nucleosome cores to be repositioned, reconstituted w diff histones, or completely removed to expose the underlying DNA
55
Q

are there multiple diff chromatin structures

A
  • a variety are possible
  • but in the chromosomes of eukaryotes, DNA is only in long strings of nucleosomes
56
Q

why is a variety of diff chromatin structures allowed

A

based on a large set of reversible covalent modifications of the 4 histones in the nucleosome core

57
Q

what modifications can be done on the 4 histones in the nucleosome core

A
  • mono-, di- and trimethylation of many diff lysine side chains
  • acetyl groups are added/ removed
  • methyl groups can be added/removed
58
Q

what facilitates the addition/removing of acetyl groups to histones

A
  • Added to specific lysines by histone acetyl transferases
  • Removed by histone deacetylase complexes
59
Q

what facilitates the addition/removing of methyl groups to histones

A
  • Added to lysine chains by histone methyl transferases
  • Removed by histone demethylases
60
Q

where is heterochromatin commonly found

A

around centromeres and telomeres (but can be elsewhere)

61
Q

what is heterochromatin, where is it found, and what is its relationship to transcription

A
  • Tightly packed form of DNA
  • Usually localized to the periphery of the nucleus
  • Was thought to be inaccessible to polymerases (not transcribed), but now we know that’s not true
62
Q

What is euchromatin, and what is its relationship to transcription

A
  • Lightly packed form of DNA
  • Often (but not always) under active transcription
  • “beads on a string”
63
Q

the enzymes that add/ remove modifications to histones in nucleosomes are part of what

A

multisubunit complexes

64
Q

after a modifying enzyme writes its mark on one or more neighbouring nucleosomes, what happens

A
  • writer enzyme works with a reader protein located in a protein complex
  • the reader contains a module that recognizes the mark and binds right to the newly modified nucleosome, activating an attached writer enzyme, and positioning it near an adjacent nucleosome
65
Q

what is a histone code

A

(a hypothesis) DNA transcription is largely regulated by post-translational modifications to these histone proteins

66
Q

describe how barrier action can occur for heterochromatin

A
  • tethering of a region of chromatin to a large fixed site (like a nuclear pore), forms a barrier that stops the spread of heterochromatin
  • tight binding of barrier proteins to a group of nucleosomes can make chromatin resistant to heterochromatin spreading
  • highly active histone-modifying enzymes can erase the histone marks that are required for heterochromatin to spread
67
Q

what is a key characteristic of heterochromatin

A

self propogating

68
Q

explain the heterochromatin propogation mechanism

A
  • a modifying enzyme writes its mark on one or more neighbouring nucleosomes
  • the reader contains a module that recognizes the mark and binds right to the newly modified nucleosome, activating an attached writer enzyme, and positioning it near an adjacent nucleosome
  • heterochromatin continues to spread until it reaches a barrier DNA sequence (then it stops)
  • reader-eraser proteins will then bind and remove heterochromatin specific marks and will return it to before
69
Q

done gene expression occur during mitosis

A

no (it shuts down completely)

70
Q

how do interphase chromosomes condense to form mitotic chromosomes

A
  • in early M phase, gene expression shuts down, and histones are modified (this helps reorganize chromatin)
  • cohesion proteins organize interphase chromosomes, which allows condensin to come in and form a linear chromosome axis
71
Q
A

Molecular 3rd year (9 decks)

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