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Genetics Chapter 2
Terms in this set (74)
a heritable change in the genetic material.
the threadlike structures found in nuclei
carriers of hereditary information
composed of protein and nucleic acids
A specific set of sequences at the end of a linear chromosome, stabilizes the chromosome and is required for replication.
Two telomeres on each chromosome, one at each end.
Region of a chromosome containing DNA sequences to which mitotic and meiotic spindle fibers attach.
unique - sequence DNA
present in one to a few copies in the genome.
ex) two copies per diploid cell.
moderately repetitive DNA
present in a few to about 10^5 copies in the genome
Highly Repetitive DNA
Present in about 10^ 5 to 10^7 copies in the genome.
Dispersed (or Interspersed) Repeated
Dispersed repeated DNA
Interspersed Repeated DNA
DNA sequences that can be arranged within the genome distributed at irregular intervals.
-Consist of families of repeated sequences interspersed through the genome with unique - sequence DNA.
long interspersed elements (LINEs)
Short interspersed elements (SINEs)
Long interspersed elements
The sequences in the families are about
1,000 - 7,000 bp long.
In all eukaryotic organisms
Short interspersed Elements
in which all the sequences in the families are
100-400 bp long.
In all eukaryotic organisms
Griffths experiment injecting a mixture of dead and live bacteria into mice demonstrated that
A factor was capable of TRANSFORMING one bacterial cell type to another
Tandemly Repeated DNA
DNA sequences that can be arranged within the genome clustered together so that the sequence repeats many times in a row.
arranged one after the other in the genome in a head to tail organization.
mainly associated with centromeres and telomeres.
Common in eukaryotic genomes
In the 1920s while working with Streptococcus pneumonia, Grifith injected mice with different types of bacteria. For each of the following bacteria types inject, indicate whether the mice lived or died.
type IIR + heat-killed IIIS
IIR - living (nonvirulent)
IIIS - died (virulent)
heat-killed IIIS - Lives (nonvirulent)
type IIR + heat-killed IIIS - dies (IIR transformed to IIIS)
In the key transformation experiment performed by Griffith, mice were injected with living IIR bacteria mixed with heat - killed IIIS bacteria.
a) what was recovered?
b) What result would you expect if living IIR bacteria had been mixed with heat killed IIS bacteria?
a) IIIS bacteria was recovered.
b) IIS bacteria would be recovered
Explain why, for griffith to interpret his results as evidence of transformation, it was necessary for him to mix living IIR bacteria with dead IIIS bacteria and not dead IIS bacteria.
This was essential for Griffith to distinguish between spontaneous mutation and transformation, as spontaneous mutation of R-type bacteria can produce S-type bacteria.
List steps that show DNA from dead S.pneumoniae cells were responsible for the change from the nonvirulent to virulent state.
(experiment performed by Avery &McCarty)
-Made extracts from IIIS bacteria & showed that exposing living IIR bacteria to these extracts could transform IIR bacteria into IIIS bacteria
-The extracts contained different cellular macromolecules.
- They showed that Nucleic acids were the only macromolecular component that could transform the IIR cells.
- They treated the nucleic acid component with either ribonuclease or deoxyribonuclease, showing that the transforming principle co-purified with DNA.
What role did enzymes play in Avery & McCartys experiment.
Enzymes were used to destroy one of the two components of the nucleic acid mixture.
Ribonuclease did not destroy the transforming principle. Deoxyribose did destroy transforming activity.
This supported the hypothesis that DNA was the genetic material.
Did Avery & McCartys work confirm or disconfirms Griffiths work?
Their work affirmed Griffiths transforming principle of being DNA.
What genome composition do you expect in a:
A) unknown multi-ceulluar organism to have
B) Uni - cellular Organism
C) Bacteriophage or virus
All known cellular organisms use double stranded DNA, so any newly discovered multicellular or unicellular organisms are expected to have double stranded DNA. However bacteriophages and viruses can be single or double stranded DNA or RNA
How could you use radioactively labeled molecules to determine if the genome of a newly identified bacteriophage that infects E.coi is RNA or DNA?
How might you determine if it is composed of single stranded or double stranded nucleic acid?
DNA has thymine & RNA doesn't.
RNA has Uracil & DNA doest.
To evaluate if it has DNA genome - infect the bacteriophage with radioactively labeled dTTP in which has a thymine base.
To evaluate if it has a RNA genome - infect the bacteriophage with radioactively labeled UTP.
Collect the progeny and see if they are radioactively labeled.
Take the molar ratios of AT for DNA or AU for RNA and see if whether C & G are equal. These are expected to be equal in a double stranded genome and unequal in single stranded genome.
The X-ray diffraction data obtained by Rosalind Franklin suggested that
DNA is a helix with a pattern that repeats every 3.4 nm.
What evidence do we have that, in the helical form of the DNA molecule, the base paris are composed of one purine and one pyrimidine?
From analyzed double stranded DNA
Amount of Purines = Amount of Pyrimidines
Amount of Adenine = Amount of Thymine
Amount of Cytosine = Guanine.
The diameter of the double helix is constant throughout out its length at 2nm. This is the right size to accommodate a purine paired with a pyrimidine.
What exactly is deoxyribonucleotide made up of, and how many different deoxyribonucletoides are there in DNA? Describe bonding mechanism of the molecule.
2 - deoxyribose plus a phosphate group
5 carbon plus a nitrogenous based attached to its 1 carbon.
On the sides of the ladder the 5 carbon of one deoxyribose is connected by a covalent phosphodiester bond to the 3 carbon of another.
Hydrogen bonds hold the complementary strands together. (A-T & G-C)
Since there are four different nucleotides in DNA (A,T,C,G) there are four nucleotides.
Base pairing occurs in pyramydines and purines so why is not possible for A-C and G-T pairs to form?
They do not form because of their hydrogen bonding.
A-T pairs have two H bond & C - G pairs have three H bonds.
Describe the bonding properties of G-C and T-A. Which base pair would be harder to break apart? Why?
A- T pairs have two H bond & C- G pairs have there hydrogen bonds, so C-G an bonds would be harder to break apart.
Suppose the ratio of (A+T) to (G+C) in a particular DNA is 1.0. Does this ratio indicate that the DNA is probably composed of two complementary strands of DNA, or a single strand of DNA, or is more information necessary?
More information is needed. If the DNA were single stranded there are no restrictions on the relative amounts of the different bases, so there are many ways in which 1 could be observed.
The percentage of cytosine in a double - strand DNA is 17. What is the percentage of adenine in that DNA?
That would mean
C + G = 34 %
leaving 66% A- T base pairs.
66/2 x 100 = 33% A
A double stranded DNA polynucleotide contains 80 thymidylic acid and 110 deoxyguanylic acid residues. What is the total number in this DNA fragment.?
80 T = 80 A
110 G = 110 C
80 + 80 + 110 + 110 = 380 nucleotides
380 / 2 = 190 base pairs
Analysis of DNA from a bacterial virus indicates that it contains:
Interpret these data.
First, notice (A) doesn't = (T) and (G) doesn't = (C).
Thus, the DNA is not double strand. The bacterial virus appears to have a single stranded DNA genome.
The following are melting temperature for different double stranded DNA molecules:
Arrange these molecules from lower to higher content of G-C pairs.
G-C pairs have 3 hydrogen bonds.
A-T pairs have 2 hydrogen bonds.
Consequently G-C base paris are stronger than A=T
Double stranded molecules with more G-C base pairs require more thermal energy to break the hydrogen bonds, so they dissociate into single strands at higher temperatures.
Higher GC content = Higher melting temperature.
Order from lowest to highest is : B, D, E , C
What are the molecular attributes of
A - DNA:
Right Handed double helix
Base Pairs Per helical turn: 11
Diameter: 2.2 nm
Major Groove: Narrow, very deep
Minor Groove: Wide, shallow
What are the molecular attributes of
Right handed double helix
Base Pairs per helical turn: 10
Diameter: 2.0 nm
Major Groove: Wide, similar depth to minor
Minor Groove: Narrow, similar depth to major
Thinner and longer than A-DNA for the same amount of base pairs
What are the molecular attributes of
Left handed double helix
Base Pairs per helical turn: 12
Diameter: 1.8 nm
Major Groove: Not distinct (to close to Helix surface)
Minor Groove: Deep
Thinner & longer than both A-DNA and B-DNA
Which form is closest in structure to most of DNA found in living cells? Why isn't cellular DNA identical to this form?
Crystallized B-DNA = 10 base pairs
DNA in solution = 10.5 base pairs
When if ever does cellular DNA have one of the other two forms? What do you infer from this information about the potential cellular role of the other DNA forms?
DNA can assume A - DNA structure in certain DAN - protein complexes.
A- DNA might be important in replication, packaging, and transcribing.
There is debate where Z-DNA exists in cells and what its significance is.
If a virus particle contains 200,000 bp of double stranded DNA, how many complete 360 turns occur in its genome?
(use the value of 10bp per turn in your calculation.)
200,000/10 = 20,000
A double stranded DNA molecule is 100,000 bp long.
a) how many nucleotides does it contain?
b) how many complete turns are there in the molecule?c) How many nm long is the DNA molecule?
a) each base pair has two nucleotides, so the molecules has 200,000
b) There are 10 base pairs per complete 360, turn, so there will 100,000/10 = 10,000 complete
c) There is 0.34 nm between the centers of adjacent base pairs.
There will be 100,000 x 0.34 nm = 3.4 x 10^ 4 = 34 micrometers.
If nucleotides were arranged at random in a piece of single strand dRNA 10^6 nucleotides long, and if the base composition of this RNA was
How many times would you expect the specific sequence 5'-GUUA-3' to occur?
The chance of finding the sequence 5- GUUA - 3 is
(0.30 x 0.25 x 0.25 x 0.20) = 0.00375
In a molecule 10^6 nucleotides long, there are nearly 10^6 groups of four bases:
The first group of four is bases 1,2,3 & 4 the second group is bases 2,3 , 4, and 5, etc. Thus, the number of times this sequence is expected to appear is 0.00375 x 10^6 = 3,750.
Define topoisomerases, and list the functions of these enzymes.
Topoisomerases are a class of enzymes that convert one topological form of DNA to another.
Topoisomerases untwist relaxed DNA to produce negative supercoils or twist negatively supercoiled DNA to convert it to a more relaxed state. These enzymes allow DNA to be converted between negatively supercoiled, compact DNA and a more relaxed, less compact state.
What is the relationship between cellular DNA content and the structural or organizational complexity of the organism?
Paradoxically, there is no simple relationship between the haploid DNA content of a cell and its structural or organizational complexity. This is the "C - value paradox." While organisms in some taxa show little variation, organisms in other taxa show as much as tenfold variation in their C-Values. In addition, organisms do not have C-Values corresponding to their organizational or structural complexity. At least one reason for this is the conferable variation in the amount of repetitive - sequence DNA in the genome.
In a particular eukaryotic chromosome:
a) heterochromatin and euchromatin are regions were genes make functional gene products
b) Heterochromatin is inactive, but euchromatin is active
c) Heterochromatin is inactive, but euchromatin is active
d) both heterochromatin and euchromatin are inactive
c) Hetetrochromatin is inactive but Euchromatin is active
What are the components and structure of a nucleosome and the composition of a nucleosome core particle? Explain how nucleosomes are used to package DNA hierarchically.
Nucleosome are the fundamental unit of DNA packaging in eukaryotic chromosomes.
Histone proteins from many different eukaryotes are highly similar in their amino acid sequence, making the among the most highly conserved eukaryotic proteins. what functional properties of histone proteins might limit their diversity.
What are the main molecular features of yeast centromeres?
Telomeres are unique repeated sequences. Where on the DNA strand are they found? Do they serve a function?
Would you expect to find most protein coding genes in unique sequence DNA, in moderately repetitive DNA, or in highly repetitive DNA?
You would find most protein-coding genes in unique-sequence DNA, as most protein coding genes exist only in one copy per haploid.
DNA and RNA are polymers of
A molecule consisting of ribose covalently bonded to a purine or pyrimidine base is a
The transforming principle was found to be
a cellular material that could alter a cells heritable characteristic
When Griffith injected mice with a mixture of live R pneumococcus derived from a IIS strain and heat killed IIIS bacteria.
the mice died, but he recovered live type IIIS cells.
In the Hershey - Chase experiment, T2 phage were radioactively labeled with either 35S or 32 P and allowed to infect E.Coli. What results proved that DNA was the genetic material?
The 35S was found in phage ghosts, and the 32P was found in page ghosts
Analysis of the bases of a sample of nucleic acid yielded these percentages:
The sample must be:
Single stranded DNA
Which of the following is not true about a linear molecule of double stranded DNA?
At one end, two 5' phosphate groups can be found.
Which kind of DNA is not likely to be found in cells?
Two double stranded 25 base pair DNA fragments are heated in solution. Fragment A has 60% GC, and fragment B has 40% Gc. Which observations, might e made as the solution temperature increase?
B will separate into single strands at a lower temperature than A
The chromosome of E.coli is packaged in the nucleoid region in a
Topoisomerases are enzyme that do all of the following except:
a) untwist relaxed DNA.
b) introduce negative supercoils into relaxed DNA
c) introduce positive supercoils into relaxed DNA
d) change the topological form of the DNA, but not the DNA sequence.
C) introduce positive supercoils into relaxed DNA.
Controls the amount and type of DNA supercoiling. Causes the DNA to become more compact.
Found in all organisms.
Either type of supercoiling causes the DNA to becomemore compact.
The total amount of DNA in the haploid genome of any organism is
its C- Value
Total amount of DNA in the haploid genome of a species.
The fundamental unit of chromatin packaging in eukaryotes is:
a) histone protein
b) a nucleosome
c) a 30nm chromatin fiber
d) a looped domain.
a) is always inactive
b) is inactive only in certain cells
c) Contains only moderately repetitive DNA
d) can contain unique -sequence DNA
e) both b & d
e) both b & d
Examples of tandemly repeated DNA sequences include all of the following except
a) genes for ribosomal RNA
c) genes for histones
d) simple telomeric sequences
Which type of chromatin contains expressed genes?
Complete set of metaphase chromosomes in eukaryotic cell.
Play a crucial role in chromatin packing.
Most abundant proteins in chromatin.
5 types: H1, H2A, H2B, H3, H4
Amount of histone = Amount of DNA
Non - histone
Apart from histones, non - histones are another major source of protein.
double helix is twisted in space about its own axis.
DNA & Protein ( stainable material in acell nucleus)
chromosomes or region of chromosomes that show the normal cycle of chromosome condensation and de-condensation in the cell cycle.
Most of the genome of an active cell is in the form of euchromatin.
- Euchromatic DNA is actively transcribed (genes within it an be expressed
-is devoid of repetitive sequences
chromosomes or chromosomal regions that usually remain condensed throughout the cell cycle, even in the interphase.
-will stain darker then euchromatin
-Usually transcriptionally inactive.
present in all cells at identical positions on both homologous chromosomes of a pair.
-Mostly repetitive DNA
-Exemplified by centromeres and telomeres.
Varies in state in different cell types, developmental states, or from one homologous chromosome to another.
-Represents condensed and therefore inactivated, segments of euchromatin.
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