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III. DNA, RNA, and Chromosome Structure
A. DNA and RNA Structure
III. DNA, RNA, and Chromosome Structure
A. DNA and RNA Structure
Avery, McCarty, and MacLeod
Chase and Hershey
III. DNA, RNA, and Chromosome Structure
A. DNA and RNA Structure
Watson and Crick
Pauling
Wilkins
Franklin
III. DNA, RNA, and Chromosome Structure
A. DNA and RNA Structure
DNA is the genetic material in all forms of life
(eubacteria, archaea, protists, plants, fungi, and
animals).
Those quasi-living viruses vary in their genetic
material. Some have double-stranded DNA
(ds-DNA) like living systems, while others have
ss-DNA, ss-RNA, and ds-RNA.
RNA performs a wide array of functions in living
systems. Many of these functions have only
been discovered in the last few years.
III. DNA, RNA, and Chromosome Structure
A. DNA and RNA Structure
1. monomers are “nucleotides”
three parts:
- pentose sugar (ribose in RNA, deoxyribose in DNA)
III. DNA, RNA, and Chromosome Structure
A. DNA and RNA Structure
1. monomers are “nucleotides”
three parts:
- pentose sugar (ribose in RNA, deoxyribose in DNA)
- nitrogenous base (A, C, G, U in RNA A, C, G, T in DNA)
III. DNA, RNA, and Chromosome Structure
A. DNA and RNA Structure
1. monomers are “nucleotides”
three parts:
- pentose sugar
- nitrogenous base
Nitrogenous base
binds to the 1’ carbon
III. DNA, RNA, and Chromosome Structure
A. DNA and RNA Structure
1. monomers are “nucleotides”
three parts:
- pentose sugar
- nitrogenous base
- phosphate group
PO4 binds to the
5’ carbon
III. DNA, RNA, and Chromosome Structure
A. DNA and RNA Structure
1. monomers are “nucleotides”
three parts:
- pentose sugar
- nitrogenous base
- phosphate group
Diphosphates and triphosphates
occur, also. In fact, here is ATP,
the energy currency of the cell.
The nucleotides exist as free
triphosphates before they are
linked into a nucleic acid chain.
III. DNA, RNA, and Chromosome Structure
A. DNA and RNA Structure
1. monomers are “nucleotides”
2. polymerization occurs by ‘dehydration synthesis’
OH
O-P-O
O
OH
O-P-O
O
Between the PO4 (which always has free H+
ions binding and unbinding) of the free
nucleotide and the –OH group on the 3’
carbon of the last sugar in the chain.
OH
OH
O-P-O
O
H2O
OH
Energy released by cleaving the diphosphate group can be used to
power the dehydration synthesis reaction
III. DNA, RNA, and Chromosome Structure
A. DNA and RNA Structure
1. monomers are “nucleotides”
2. polymerization occurs by ‘dehydration synthesis’
Polymerization results in a
polymer of DNA (or RNA).
This single polymer is a singlestranded helix
5’
It has a ‘polarity’ or ‘directionality’;
it has different ends… there is a
reactive phosphate at one end (5’)
and a reactive –OH at the other
(3’). So, the helix has a 5’-3’
polarity.
3’
III. DNA, RNA, and Chromosome Structure
A. DNA and RNA Structure
1. monomers are “nucleotides”
2. polymerization occurs by ‘dehydration synthesis’
3. most DNA exists as a ‘double-helix’ (ds-DNA)
(although some viruses have genetic material that is signle-stranded DNA (ss-DNA))
a. The nitrogenous bases on the two helices are ‘complementary’ to one
another, and form weak hydrogen bonds between the helices.
A purine (A or G) always binds with a
pyrimidine (T or C)
In fact, A with T (2 h-bonds)
And G with C (3 h-bonds)
III. DNA, RNA, and Chromosome Structure
A. DNA and RNA Structure
1. monomers are “nucleotides”
2. polymerization occurs by ‘dehydration synthesis’
3. most DNA exists as a ‘double-helix’ (ds-DNA)
a. bases are complementary
b. the strands are anti-parallel: they are aligned with opposite polarity
5’
III. DNA, RNA, and Chromosome Structure
A. DNA and RNA Structure
1. monomers are “nucleotides”
2. polymerization occurs by ‘dehydration synthesis’
3. most DNA exists as a ‘double-helix’ (ds-DNA)
4. RNA performs a wide variety of functions in living cells:
a. m-RNA is a ‘copy’ of a gene, read by the ribosome to make a protein
III. DNA, RNA, and Chromosome Structure
A. DNA and RNA Structure
1. monomers are “nucleotides”
2. polymerization occurs by ‘dehydration synthesis’
3. most DNA exists as a ‘double-helix’ (ds-DNA)
4. RNA performs a wide variety of functions in living cells:
a. m-RNA is a ‘copy’ of a gene, read by the ribosome to make a protein
b. R-RNA is made the same way, is IN the Ribosome, and ‘reads’ the m-RNA
III. DNA, RNA, and Chromosome Structure
A. DNA and RNA Structure
1. monomers are “nucleotides”
2. polymerization occurs by ‘dehydration synthesis’
3. most DNA exists as a ‘double-helix’ (ds-DNA)
4. RNA performs a wide variety of functions in living cells:
a. m-RNA is a ‘copy’ of a gene, read by the ribosome to make a protein
b. r-RNA is made the same way, is IN the Ribosome, and ‘reads’ the m-RNA
c. t-RNA is made the same way, and brings amino acids to the ribosome
III. DNA, RNA, and Chromosome Structure
A. DNA and RNA Structure
1. monomers are “nucleotides”
2. polymerization occurs by ‘dehydration synthesis’
3. most DNA exists as a ‘double-helix’ (ds-DNA)
4. RNA performs a wide variety of functions in living cells:
a. m-RNA is a ‘copy’ of a gene, read by the ribosome to make a protein
b. r-RNA is made the same way, is IN the Ribosome, and ‘reads’ the m-RNA
c. t-RNA is made the same way, and brings amino acids to the ribosome
d. mi-RNA (micro-RNA) and si-RNA (small interfering RNA) bind to m-RNA and
splice it; inhibiting the synthesis of its protein. This is a regulatory function.
III. DNA, RNA, and Chromosome Structure
A. DNA and RNA Structure
1. monomers are “nucleotides”
2. polymerization occurs by ‘dehydration synthesis’
3. most DNA exists as a ‘double-helix’ (ds-DNA)
4. RNA performs a wide variety of functions in living cells:
a. m-RNA is a ‘copy’ of a gene, read by the ribosome to make a protein
b. r-RNA is made the same way, is IN the Ribosome, and ‘reads’ the m-RNA
c. t-RNA is made the same way, and brings amino acids to the ribosome
d. mi-RNA (micro-RNA) and si-RNA (small interfering RNA) bind to m-RNA and
splice it; inhibiting the synthesis of its protein. This is a regulatory function.
e. Sn-RNA (small nuclear RNA) are short sequences that process initial m-RNA
products, and also regulate the production of r-RNA, maintain telomeres,
and regulate the action of transcription factors. Regulatory functions.
III. DNA, RNA, and Chromosome Structure
A. DNA and RNA Structure
B. Chromosome Structure
1. Prokaryotes
- usually one circular chromosome, tethered to the membrane, with some
associated, non-histone proteins.
III. DNA, RNA, and Chromosome Structure
A. DNA and RNA Structure
B. Chromosome Structure
1. Prokaryotes
2. Eukaryotes – usually many linear chromosomes, highly condensed
with histone proteins into several levels of structure.
III. DNA, RNA, and Chromosome Structure
A. DNA and RNA Structure
B. Chromosome Structure
1. Prokaryotes
2. Eukaryotes – usually many linear chromosomes, highly condensed
with histone proteins into several levels of structure.
a. Level 1: ds-DNA is wrapped
around histone proteins, creating
the “beads on a string’ level of
organization.
III. DNA, RNA, and Chromosome Structure
A. DNA and RNA Structure
B. Chromosome Structure
1. Prokaryotes
2. Eukaryotes – usually many linear chromosomes, highly condensed
with histone proteins into several levels of structure.
a. Level 1: ds-DNA is wrapped
around histone proteins,
creating the “beads on a string’
level of organization.
III. DNA, RNA, and Chromosome Structure
A. DNA and RNA Structure
B. Chromosome Structure
1. Prokaryotes
2. Eukaryotes – usually many linear chromosomes, highly condensed
with histone proteins into several levels of structure.
a. Level 1: ds-DNA is wrapped
around histone proteins,
creating the “beads on a string’
level of organization.
b. Level 2: string is coiled, 6
nucleosomes/turn (solenoid)
III. DNA, RNA, and Chromosome Structure
A. DNA and RNA Structure
B. Chromosome Structure
1. Prokaryotes
2. Eukaryotes – usually many linear chromosomes, highly condensed
with histone proteins into several levels of structure.
a. Level 1: ds-DNA is wrapped
around histone proteins,
creating the “beads on a string’
level of organization.
b. Level 2: string is coiled, 6
nucleosomes/turn (solenoid)
c. Level 3: the coil is ‘supercoiled’
III. DNA, RNA, and Chromosome Structure
A. DNA and RNA Structure
B. Chromosome Structure
1. Prokaryotes
2. Eukaryotes – usually many linear chromosomes, highly condensed
with histone proteins into several levels of structure.
a. Level 1: ds-DNA is wrapped
around histone proteins,
creating the “beads on a string’
level of organization.
b. Level 2: string is coiled, 6
nucleosomes/turn (solenoid)
c. Level 3: the coil is ‘supercoiled’
d. Level 4: the supercoil is folded
into a fully condensed
metaphase chromosome
III. DNA, RNA, and Chromosome Structure
A. DNA and RNA Structure
B. Chromosome Structure
1. Prokaryotes
2. Eukaryotes – usually many linear chromosomes, highly condensed
with histone proteins into several levels of structure.
To read a gene, the chromosome must be diffuse
(uncondensed) in that region. Even when
condensed, these ‘euchromatic’ coding
regions are less condensed and more lightly
staining than non-coding regions.
DNA that has few genes can remain condensed
and closed (heterochromatic), and appears as
dark bands on condensed chromosomes.
Study Questions:
1) Diagram the parts of an RNA nucleotide.
2) Show how two nucleotides are linked together by dehydration
synthesis reactions.
3) Why does the purine - pyrimidine structure relate to the complementary
nature of double-stranded DNA?
4) Draw a DNA double helix, showing three base pairs and the antiparallel
nature of the helices.
5) Describe the higher levels of eukaryotic chromosome structure,
including the terms nucleosome and solenoid.
6) What are two differences between euchromatin and hetochromatin?