Chapter 12 Flashcards
(44 cards)
1
Q
Genetic material must possess several key characteristics
A
- must contain complex information that is stable, but has the capacity to vary
- must replicate faithfully
- must encode the phenotype
2
Q
Who formalized the central dogma?
A
Francis Crick
3
Q
nucleotides
A
- what DNA consists of
- each has a sugar, phosphate, and a base
4
Q
tetranucleotide theory
A
- incorrect theory that DNA conisists of a series of four-nucleotide units, each containing all four bases, in a fixed sequence.
- it implied that DNA was not variable enough to be the genetic material
5
Q
Chargraff’s rules
A
- DNA from different organisms vary greatly
- there was a regularity in the ratios of the bases
- A-T
- G-C
6
Q
Hershey Chase experiment
A
- Radioactive isotopes of 32P and 35S.
- DNA contains phosphorus and protein contains sulfur
- grew two batches of. E Coli in medium with phosphorus and culture and infected with phage
- infected unlabeled E. Coli with the different phages
- placed E. Coli in blender to shear off empty phage ghosts from cell walls, then separated cells from protein coats
- Most of 35S was in protein ghosts. Most of 32P was found in the viral progeny
- Demonstrated that DNA, not protein is the genetic material of the phages.
7
Q
Wilkins Franklin experiment
A
- 3D structure of DNA studied using X ray diffraction
- indicated DNA is a helical structure
8
Q
Watson Crick experiment
A
- discovered three dimensional structure of DNA and created molecular models using wire and metal plates
- recognized adenine could bond with thymine, and guanine can bond with cytosine
- two strands of nucleotides wound around each other to form a right-handed helix, with sugars and phosphates on the outside and bases in the interior.
9
Q
covalent bond
A
- strongest chemical bonds, formed by sharing of electrons
- not spontaneous
- not affected by heat
10
Q
phosphodiester bonds
A
- covalently link the polynucleotide chain between the nucleotides
- join the 5’-phosphate group to the 3’ carbon atom of the next nucleotide
11
Q
Hydrogen bonds
A
- when an H atom is shared between two molecules
- weak bonds
- affected by heat
- bases pair through hydrogen bonds
12
Q
hydrophobic interactions
A
- nonpolar molecules cannot form hydrogen bonds with water. when present in aqueous solutions these non polar groups associate with each other because they are insoluble in water.
- stacked base pairs form a hydrophobic core
13
Q
sugar of DNA
A
- pentose sugars with five carbon atoms
- ribose has OH at 2’. deoxyribose has H there.
14
Q
nitrogen-containing base
A
- each base may be a purine or pyrimidine
- purine six-sided ring attached to five sided ring (AG)
- pyrimidine is one six-sided ring (CT,U)
15
Q
nucleoside
A
sugar and base together
16
Q
phosphate group
A
- phosphate atom bonded to four oxygen atoms
- found in every nucleotide
- carries a negative charge which makes DNA acidic
17
Q
Two strands of DNA secondary structure
A
- antiparallel
- complementary bases hydrogen bond
18
Q
polarity of DNA
A
- free phosphate group attached to 5’ carbon atom of sugar
- OH group attached to 3’ carbon atom of the sugar
19
Q
Forces holding the two strands together
A
- bonds - H bonds. Covalent phosphodiester bonds that link sugar and phosphate groups
- base stacking - hydrophobic interactions between bases.
20
Q
Difference between RNA and DNA
A
- Uracil instead of thymine
- RNA has an OH on 2’
21
Q
B-DNA
A
- structure described by Watson and Crick
- clockwise or right handed spiral
- 10 base pairs per turn
- most stable form of DNA and most predominant
- exists when plenty of water surrounds molecule
22
Q
Three levels of DNA structure
A
- DNA sequence
- double-stranded helix
- higher-order folding that allows packaging
23
Q
supercoiling
A
- a type of tertiary structure
- occurs when DNA is over or under wound
- takes up less space than relaxed DNA
24
Q
topoisomerase
A
enzymes which add or remove rotations from the helix by temporarily breaking the strands, rotating the ends around each other, and then rejoining the ends.
25
Bacterial DNA is not
attached to histone proteins
26
chromatin
Eukaryotic DNA in the cell closely associated with proteins
27
Euchromatin
- undergoes normal process of condensation and decondensation in the cell cycle
- majority of chromosomal material
- where most transcription takes place
28
Heterochromatin
remains in a highly condensed state throughout the cell cycle (only one state -hetero)
29
histones
- most abundant proteins in chromatin
| - small positively charged proteins of five major types
30
nonhinstone chromosomal proteins
a heterogenous assortment of proteins
31
nucleosome
- a core particle consisting of DNA wrapped about two times around an octomer of eight histone proteins
- connected by linker DNA
32
Treatment of chromatin with nuclease (DNase)
digests the linker DNA, leaving only the nucleosomes
33
30 nm fiber
- chromatin further condensed by nucleosomes folding upon themselves
34
Centromeres
- constricted region of the chromosome
| - binding site for the kinetochore, to which spindle fibers attach
35
Telomeres
- natural ends of chromosomes
- length varies from chromosome to chromosome and from cell to cell, suggesting that each telomere is a dynamic structure
36
C value
- the amount of DNA per cell
| - eukaryotes differ in this
37
C value paradox
C values differences not directly related to the complexity of the organisms
38
Three major classes of eukaryotic sequence elements
- single copy
- moderately repetitive
- highly repetitive
39
single copy DNA
- present once or a few times and interspersed through the genome
- includes sequences that encode proteins as well as DNA of unknown function
- comprises 25-50% of DNA in most organisms
40
Moderately repetitive DNA
- repeatable many thousands of times.
- several hundred bp in length
- includes ribosomal and transfer RNA genes and transposable elements as well as sequences of unknown function
- two examples are transposable elements like LINES and SINES
41
Highly repetitive DNA
- present in hundreds of thousands to million of copies that are repeated in tandem and clustered in certain regions of the chromosome, especially at centromeres and telomeres.
42
Mitochondrial genomes
- one circular molecule
- vary in size
- multiple mitochondria per cell and multiple mitochondrial genomes per mitochondrion
- genes encode: respiration and oxidative phosphorylation function, and components involved in translation, transcription, RNA processing, and protein important into the mitochondria.
43
Chloroplast genomes
- usually one circular molecule
- vary in size
- multiple chloroplasts per cell and multiple chloroplast genomes per organelle
- genes encode: photosynthesis and other function, and components involved in translation and transcription.
44
chromatosome
a nucleosome with one bound linker histone.
