Chapter 8 Flashcards
What are the characteristics of genetic material?
- Genetic material must provide information.
- Must be able to be passed on to the next generation (replicated).
- Must encode the phenotype.
- Must have the capacity to vary (mutate or change).
What is Chargaff’s rule?
Chargaff discovered that DNA (no structure yet) has a composition where the amounts of A=T and G=C.
Griffith’s experiments helped prove DNA as the hereditary material. His experiments helped develop the:
Transforming principle.
What did Griffith contribute to our understanding of DNA as hereditary material?
Experiment with bacterium was the first to reveal the “transforming principle,” which led to the discovery that DNA acts as the carrier of genetic information
How was Griffith’s experiment performed?
Mice were injected with a non-virulent R (rough) strain and a virulent S (smooth) strain. Griffith concluded some chemical components from the virulent S cells transformed the R cells into a more virulent S form. Griffith concluded when the R strain bacteria built a smooth shell from the instructions carried by DNA, it expressed a gene
How did Alfred Hershey and Martha Chase contribute to our understanding of DNA?
Found that the phosphorus-containing components are the genetic material of phages
How was the Avery, Macleod, McCarty experiment performed?
Inserted S-strain bacteria in different test tubes and then treated each tube with a different enzyme to see if it would degrade. They added R-strain bacteria, injected mice, and observed for illness.
If Avery, Macleod, and McCarty had found that
samples of heat-killed bacteria treated with
RNase and DNase transformed bacteria, but
samples treated with protease did not, what
conclusion would they have made?
Protein is the genetic material
How did the experiment of Avery, Macleod, and McCarty contribute to our understanding of DNA?
VERY strong evidence that DNA was the molecule responsible for Griffith’s transformation
DNA (not proteins) can transform the properties of cells, clarifying the chemical nature of genes. DNA provides the information necessary for the transformation
How was the Hershey - Chase experiment performed?
Radioactive phosphorus-labeled phages attach to bacterial cell membranes in a liquid solution and infect the bacteria. Using a centrifuge, Hershey and Chase rapidly spun the samples to separate the bacterial cells from the surrounding solution
How did Watson, Crick, Wilkins, and Franklin contribute to our understanding of DNA?
Co-discovered the double-helix structure of DNA, which formed the basis for modern biotechnology.
Watson and Crick- discovery of the 3D structure of DNA
Franklin- X-ray diffraction image of DNA
Did Watson and Crick perform any experiments for their original contribution?
No, they used experimental results found by others to help with their experiments.
What is the structure of DNA?
What are nucleic acids in the structure of DNA?
Polymers of nucleotides (RNA and DNA)
What are Nucleotides in the structure of DNA?
The two main types are Deoxyribonucleotides (DNA) and ribonucleotides (RNA).
Both contain a sugar group, a phosphate, and a base. The sugar group is the key identifier.
What are the five different nitrogenous bases?
Adenine, Guanine, Cytosine, Thymine (in DNA), Uracil (in RNA).
What are the phosphodiester bonds in the structure of DNA?
NMP=monophosphate, NDP=nucleotide diphosphate, NTP=nucleotide triphosphate
Nucleotides are linked together through phosphodiester bonds.
Provides a bridge between nucleotides in a nucleic acid. The 3’ OH of the sugar can be linked to the 5’ phosphate of the next nucleotide.
What are the Hydrogen bonds in DNA structure?
The base pairs are stabilized by hydrogen bonds; adenine and thymine form two hydrogen bonds between them, whereas cytosine and guanine form three hydrogen bonds between them.
What is the directionality of a DNA sequence?
The nucleic acid sequences are complementary and parallel, but they go in opposite directions,
What are complementary pairs in DNA?
A pairs with T
G pairs with C
What is the B form of DNA? (what are the other forms)
Right-handed double helix shape.
The right-handed helical shape of DNA at physiological condition (Identified by Watson and Crick).
Also A-form and Z-form. A-form is a right-hand helix, but more squat- often double-stranded RNA is A-form. Z-form is the left-hand helix and is more stretched.
What is DNA supercoiling and why is it important?
DNA supercoiling is important for DNA packaging within all cells. Refers to the additional twisting of a DNA strand. DNA must be tightly packed to fit in small spaces.
What is positive supercoiling?
Twisting DNA tighter.
What is negative supercoiling?
Underwinding of DNA.
What is topoisomerase and how is it involved?
It is the enzyme responsible for the adding and removing turns in the coil.
Normally, DNA has about 10 bp per
rotation. A DNA molecule 300 bp long
has 20 complete rotations. This DNA
molecule is:
Negatively supercoiled.
How is eukaryotic DNA packaged?
What are nucleosomes in the eukaryotic packaging of DNA?
“Beads” of DNA and histone protein complexed together.
What are histones?
Histones have arms that extend out from the histone core that can hold onto the DNA- and have a positive charge.
What is 2nm, 11nm, 30nm, metaphase chromosome?
The 2 nm DNA double helix winds around complexes of histone proteins to form an 11 nm nucleosome fiber. This then folds into a thicker, 25–30 nm fiber, and this ‘30 nm’ fiber then assembles into a series of ‘higher-order’ structures
Heterochromatin vs. Euchromatin and characteristics for eukaryotic packing of DNA.
Heterochromatin is highly condensed, gene-poor, has repeated sequences, and is transcriptionally silent, whereas euchromatin is less condensed, gene-rich, has unique sequences, and is more easily transcribed.
Neutralizing their positive charges would
have which effect on the histone
proteins?
They would bind less tightly to the DNA.
What is epigenetics?
they can change how your body reads a DNA sequence
Changes in chromatin structure. Can make a gene more or less available for expression. Example- the agouti gene in mice. All mice have the same alleles but the availability of the gene is different.
What is the centromere structure in eukaryotic chromosomes? Why are they important?
Constricted region of a chromosome where spindle fibers attach.
Directing the assembly of the microtubule-binding kinetochore and serving as the cohesion site between sister chromatids.
What is the telomere in eukaryotic chromosomes? Why are they important?
Ends of chromosomes; provide means to replicate the ends of linear chromosomes.
They protect chromosome ends from DNA degradation, recombination, and DNA end fusions, and they are important for nuclear architecture.
Which of the following is a characteristic
of DNA sequences at the telomeres?
a. One strand consists of guanine and adenine or thymine nucleotides.
b. They consist of repeated sequences.
c. One strand protrudes beyond the other,
creating some single-stranded DNA at the end.
d. All of the above.
All of the above.
How are genomes characterized?
Organisms differ in the amount of DNA per cell (c value).
GC-content (guanine-cytosine) is the percentage of nitrogenous bases in a DNA or RNA molecule that are either guanine or cytosine.
The higher the GC, the harder it is to take apart.
How do you simply determine the complexity of DNA?
DNA complexity can be analyzed through “melting” characteristics:
-Denaturation: an unwinding of DNA double-strand takes place, resulting in two separate single strands on applying high temperature, extreme pH, etc.
-Renaturation: the process when the single-stranded DNA reforms bonds with its complementary strand and rebuilds its original structure
What are the two main types of DNA sequences that eukaryotes have?
Unique Sequence DNA: usually has genes
Gene family- similar but not identical copies of unique DNA sequences that arose through duplication of an existing gene.
Repetitive DNA: moderately repetitive DNA (150-300 bp long) and highly repetitive DNA (less than 10 bp long)
Most of the genes that encode proteins are
found in:
Unique-sequence DNA
In double-stranded DNA, what is the appropriate complementary sequence for the sequence:
5’-GCCTAGCT-3’
5’-AGCTAGGC-3’
If a small length of double-stranded DNA contained 50 nucleotides (total between both strands) and also contained 10 cytosine bases, what is the composition of the remaining nucleotides?
15 A, 15 T, 10 G
In RNA, there would be a hydroxyl (OH) group at this position and not a hydrogen atom (H).
2’ carbon
In DNA, there would be a hydrogen atom (H) at this position and not a hydroxyl (OH) group.
2’ carbon
A purine base is connected at this position.
1’ carbon
A pyrimidine base is connected at this position.
1’ carbon
This position would be expected to be bonded to a phosphate group.
5’ carbon
In a single deoxynucleotide, not bonded to a longer nucleic acid, this position would be expected to be a hydroxyl (OH) group.
3’ carbon
What form of DNA spirals to the right and is the major form of naturally occurring DNA molecules?
B form
