Chpt 4: DNA, Chromosomes, and Genomes Flashcards
1
Q
what did Watson and Crick discover
A
the structure of DNA
2
Q
what solved the problem of how info in DNA might be replicated
A
the double-helical structure
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
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
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
6
Q
what bonds hold the nucleotides together across diff strands
A
H bonds
7
Q
what does DNA stand for
A
deoxyribonucleic acid
8
Q
what is this
A
uracil
9
Q
what is this
A
thymine
10
Q
what is this
A
cytosine
11
Q
what is this
A
adenine
12
Q
what is this
A
guanine
13
Q
what bonds hold the backbone together
A
covalent
14
Q
where does the 3D structure of DNA arise from
A
the chem and structural features of its 2 polynucleotide chains
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
16
Q
there is one complete turn of the helix every _____ base pairs
A
10.4
17
Q
a pre-existing strand of DNA works as a _______ for the synthesis of a new complementary strand
A
template
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
19
Q
describe the structure of a chromosome in a eukaryotic cell
A
a single DNA molecule along w proteins
20
Q
the complex of DNA and tightly bound protein is called what
A
chromatin
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
22
Q
how many copies of each chromosome do we have
A
2 (except for gametes)
23
Q
the maternal and paternal chromosomes of a pair are called what
A
homologous chromosomes (homologs)
24
Q
what are the only nonhomologous chromosome pairs
A
sex chromosomes in males (Y from dad, X from mom)
25
what is an intron
Nucleotide sequence within a gene that is removed via RNA splicing during maturation of the final RNA product
26
what is an exon
Nucleotide sequence within a gene that becomes part of mature RNA molecule
27
how are all of the chromosomes typically displayed to produce an image
karyotype
28
what is a gene
a segment of DNA that contains the instructions for making a particular protein *(this is a narrow def tho)*
29
is there a correlation between the complexity of an organism and the number of genes in its genome
there can be (a lot of the differences is noncoding DNA tho)
30
what accounts for the astonishing variations in genome size that we see when we compare one species with another
differences in the amount of noncoding DNA
31
how much of the human genome codes for proteins
very little (about 1%)
32
what size is the average gene size
large (about 26k nucleotide pairs)
33
what ensures that genes are turned on or off at the proper time
regulatory DNA sequences
34
do all RNA molecules produce proteins
no
35
each DNA molecule that forms a linear chromosome must contain what
- centromere
- 2 telomeres
- replication origins
36
The highly condensed chromosomes in a dividing cell are known as what
mitotic chromosomes
37
what is the name of the nucleotide sequence at which duplication of DNA begins
replication origin
38
what is a centromere
- specialized DNA sequence
- allows one copy of each duplicated and condensed chromosome to be pulled into each daughter cell when a cell divides
39
what attaches the chromosome to the mitotic spindle
kinetochore (a protein complex)
40
what are some examples of specialized DNA sequences
- centromere
- telomere
41
what is a telomere
- 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
the proteins that bind to DNA to form eukaryotic chromosomes are divided into which classes
- histones
- non-histone chromosomal proteins
43
the complex of both classes of proteins with nuclear DNA of eukaryotic cells is known as what
chromatin
44
what is chromatin
the complex of both classes of proteins with nuclear DNA of eukaryotic cells
45
what are responsible for the 1st level of chromosome packing: nucleosome
histone
46
describe the beads on a string visual
- string is DNA
- each bead is a nucleosome core particle (DNA wound around a histone)
47
what is a nucleosome
DNA wound around a histone
48
what is linker DNA
the DNA in between each nucleosome core particle
49
describe the histones in the nucelosome core particle
- histone octamer
- 2 of each: H2A, H2B, H3 and H4 proteins
50
describe the interface between DNA and histone
142 H bonds in each nucleosome
51
describe the overall structure of histones
- highly folded due to the basic AA
- has a largely unstructed N-terminal AA "tail"
52
what causes nucleosomes to stack on each other
- 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
is chromatin structure static?
- highly dynamic
- must allow access to the DNA
- some spontaneous wrapping/ unwrapping occurs
- also through ATP-driven chromatin-remodling complexes
54
what are ATP-driven chromatin-remodeling complexes
- 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
are there multiple diff chromatin structures
- a variety are possible
- but in the chromosomes of eukaryotes, DNA is only in long strings of nucleosomes
56
why is a variety of diff chromatin structures allowed
based on a large set of reversible covalent modifications of the 4 histones in the nucleosome core
57
what modifications can be done on the 4 histones in the nucleosome core
- **mono-, di- and trimethylation of many diff lysine side chains**
- acetyl groups are added/ removed
- methyl groups can be added/removed
58
what facilitates the addition/removing of acetyl groups to histones
- Added to specific lysines by histone acetyl transferases
- Removed by histone deacetylase complexes
59
what facilitates the addition/removing of methyl groups to histones
- Added to lysine chains by histone methyl transferases
- Removed by histone demethylases
60
where is heterochromatin commonly found
around centromeres and telomeres (but can be elsewhere)
61
what is heterochromatin, where is it found, and what is its relationship to transcription
- 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
What is euchromatin, and what is its relationship to transcription
- Lightly packed form of DNA
- Often (but not always) under active transcription
- "beads on a string"
63
the enzymes that add/ remove modifications to histones in nucleosomes are part of what
multisubunit complexes
64
after a modifying enzyme writes its mark on one or more neighbouring nucleosomes, what happens
- *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
what is a histone code
(a hypothesis) DNA transcription is largely regulated by post-translational modifications to these histone proteins
66
describe how barrier action can occur for heterochromatin
- 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
what is a key characteristic of heterochromatin
self propogating
68
explain the heterochromatin propogation mechanism
- 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
done gene expression occur during mitosis
no (it shuts down completely)
70
how do interphase chromosomes condense to form mitotic chromosomes
- 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
