iGenetics_chapter2acidonucleico como material geentico.ppt

ADN como material genético

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Chapter 2: DNA The
Genetic Material
Linnea Fletcher Ph.D.
BIOL 2316

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Review Principal Points
What is the sugar for DNA? RNA?
What are the possible bases?
What are the possibilities for genetic arrangement?
How are bacterial chromosomes compacted?
Define karyotype
What is the composition of eukaryotic genomes; what
is constant between cells of a particular organism and
what varies?
What is the role of the centromere?
What is the composition of the telomere?
Compare and contrast the prokaryotic genome with
the eukaryotic genome.

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What color are the phosphate, oxygen, carbon, nitrogen and hydrogen
atoms?

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The Search for Genetic
Material
What are the three principal
characteristics for genetic materials?
Stable form
Replicate accurately
Capable of change

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Understand the experiments
performed by:
1928 Griffith
1944 Avery, McCarty, & MacLeod
1947 Chargaff
1954 Wilkins, Franklin, Watson, &
Crick

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Griffith’s Transformation Experiment

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Avery’s Transformation Experiments

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What does it tell you when A=T and G=C?

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What did the X-ray diffraction patterns analyzed by
Rosalind Franklin INITIALLY reveal about the DNA
molecule?
It is of uniform diameter about 2 nm wide and has a
highly repetitive structure that repeats every 3.5 nm
It is a helical molecule with paired bases in the center
It is double-stranded with antiparallel strands
It is acidic, phosphate-rich, and very large
It contains the hereditary information
Can you answer this multiple choice question?

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. An understanding of the molecular basis of
inheritance allows us to develop a detailed
knowledge of how this works.
Describe the structural features of DNA and RNA.
How are they similar, and how are they different?
How do purines differ from pyrimidines? Which base-
pair with each other?
How do nucleosides differ from nucleotides?
What type of covalent bonding combines the
monomers into polymers?
Why is the DNA double helix referred to as being
“antiparallel”?

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DNA vs RNA sugar moiety

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Know the difference between a purine and a pyrimidine and
Which bases are purines and pyrimidines----------
But don’t memorize the exact structures

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Be able to draw
a double-stranded
DNA for the
test using P
for the phosphate
Group, drawing
the ribose sugar,
A one letter
Descriptor for the
Base, and
lines for the no.
of hydrogen
bonds between
the bases

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Be able to draw this!
Using the symbols
Previously indicated
Don’t forget to indicate
5’ P ends and 3’ OH
ends.

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Know the bases,
But do not memorize the
Structure of the bases

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a.Describe the three oligomers that the
DNA double helix can assume: A-
from, B-form and Z-form. Which has
the most compact structure, and
which is the most elongated? Which
are found in living cells?

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A is A-DNA; b is B-DNA; c is Z-DNA

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The organization of nucleic acids in
genomes varies with the level of
complexity of the organism
What form is the chromosome of most
prokaryotes? (circular)
How is supercoiling created in a
circular chromosome?
Compare the size of the haploid
genome (C-value) of humans with
other organisms.
What is the C value paradox?

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Figure 2.21 Electron
micrographs of a circular DNA
molecule, showing relaxed and
supercoiled states. (a) Relaxed
(nonsupercoiled) DNA. (b)
Supercoiled DNA. Both
molecules are shown at the
same magnification.

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Figure 2.22 Model for the structure of the circular bacterial (prokaryotic)
chromosome. The chromosome is organized into looped domains, the bases
of which are anchored in an unknown way.

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Notice the C
Value for ameoba
Vs homo sapien

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Compaction of chromosomes is important in
eukaryotes, due to the large size of the eukaryotic
genome.
What are the two types of molecular components of
chromatin?
What are the most abundant proteins in chromatin and
what role do they play in the structure of the
chromosome?
How long would the diploid set of human
chromosomes from one cell be if they were not
compacted and where place end-to-end in a straight
line? How does this compare to the diameter of the
nucleus of a human cell?
Describe the structures of the 10-nm and 30-nm
chromatin fibers.
Describe how scaffold=associated regions (SARs) are
arranged by non-histone proteins in a condensed
chromosome. About how many looped domains does
the average human chromosome have? What is the
approximate diameter of the metaphase chromosome?

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Figure 2.23 Electron micrograph of unraveled chromatin, showing the nucleosomes
in a “beads-on-a-string” morphology.

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Figure 2.24 Basic eukaryotic chromosome
structure. (a) Histone core for the
nucleosome. (b) Diagram of nucleosomes in
“beads-on-a-string” chromatin. A nucleosome
is (c) Chromosome condensation brought
about by the binding of histone H1.

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Figure 2.27 Looped domains in metaphase chromosomes. (a) Fiber loops
30 nm attached at scaffold-associated regions to the chromosome
scaffold by nonhistone proteins. (b) Schematic of a section of the
metaphase chromosome. Shown is the spiraling of looped domains.

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What affect does compaction of a
chromosome have on its transcriptional
activity?
Compare the staining of euchromatic,
compared to heterochromatic, regions of a
chromosome by dyes.
Which is transcriptionally more active:
euchromatin or heterochromatin?
What are two types of constitutive
heterochromatin and what roles do they
play? What structural features do they
share, and how are they different?
What is an example of facultative
heterochromatin?

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To make learning easier:
Make a table that compares the copy number and the
relative amounts of unique-sequence, moderately
repetitive, and highly repetitive DNA in the human
genome.
In a separate column, indicate which category has
these of DNA: genes, SINEs, LINEs, centromeres,
telomeres, rRNAs, tRNAs.
How are tandemly repeated sequences different from
interspersed repeat sequences of DNA?
Compare the structures of LINEs with that of SINEs.
What is the most abundant of each in the human
genome, and about how many times are they repeated
in the haploid human genome?