III. DNA, RNA, and Chromosome StructureA. DNA and RNA Structure

III. DNA, RNA, and Chromosome StructureA. DNA and RNA Structure

Avery, McCarty, and MacLeod

Chase and Hershey

III. DNA, RNA, and Chromosome StructureA. DNA and RNA Structure

Watson and Crick

Pauling

FranklinWilkins

III. DNA, RNA, and Chromosome StructureA. 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 StructureA. DNA and RNA Structure

1. monomers are “nucleotides”three parts: - pentose sugar (ribose in RNA, deoxyribose in DNA)

III. DNA, RNA, and Chromosome StructureA. 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 StructureA. 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 StructureA. 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 StructureA. 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.

OHO-P-O O

OH

OHH2O

III. DNA, RNA, and Chromosome StructureA. DNA and RNA Structure

1. monomers are “nucleotides”2. polymerization occurs by ‘dehydration synthesis’

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.

OHO-P-O O

OHO-P-O O

Energy released by cleaving the diphosphate group can be used to power the dehydration synthesis reaction

5’

3’

III. DNA, RNA, and Chromosome StructureA. 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 single-stranded helix

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.

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 StructureA. 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.

5’

III. DNA, RNA, and Chromosome StructureA. 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

III. DNA, RNA, and Chromosome StructureA. 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 StructureA. 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 StructureA. 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 StructureA. 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 StructureA. 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 StructureA. DNA and RNA StructureB. Chromosome Structure

1. Prokaryotes - usually one circular chromosome, tethered to the membrane, with some

associated, non-histone proteins.

III. DNA, RNA, and Chromosome StructureA. DNA and RNA StructureB. Chromosome Structure

1. Prokaryotes2. Eukaryotes – usually many linear chromosomes, highly condensed

with histone proteins into several levels of structure.

III. DNA, RNA, and Chromosome StructureA. DNA and RNA StructureB. Chromosome Structure

1. Prokaryotes2. 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 StructureA. DNA and RNA StructureB. Chromosome Structure

1. Prokaryotes2. 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 StructureA. DNA and RNA StructureB. Chromosome Structure

1. Prokaryotes2. 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 StructureA. DNA and RNA StructureB. Chromosome Structure

1. Prokaryotes2. 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 StructureA. DNA and RNA StructureB. Chromosome Structure

1. Prokaryotes2. 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 StructureA. DNA and RNA StructureB. Chromosome Structure

1. Prokaryotes2. 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?