Unit 3, Day 2: Nucleic acid structure

3. What bases are found in DNA and RNA?

•DNA: A, G, C, & T. •RNA: A, G, C, & U.

2.How is the sugar group of DNA different from that of RNA?

•DNA: Each nucleotide is composed of a sugar-phosphate covalently linked to a base. •RNA: Based on the sugar ribose and contain bases.

1.How is the structure of a nucleotide different from the structure of a nucleoside?

•Nucleotide: Has 3 phosphates linked in a series by 2 phosphoanhydride bonds. Includes a nucleoside with a series of one or more phosphate groups linked to its sugar. •Nucleoside: Molecule made of a nitrogen-containing ring compound attached to a sugar.

6.Describe the basic flow of genetic information (i.e. the central dogma) described by Francis Crick and outlined in Figure 7-1.

•The flow of genetic information from DNA to RNA (transcription) and from RNA to protein (translation) occurs in all living cells. It was Francis Crick who dubbed this flow of information "the central dogma". The segments of DNA that are transcribed into RNA are called genes.

Deoxyribose

The sugar component in the side chains of DNA, in contrast to the ribose in the side chains of RNA.

Purine

A double-ringed, nitrogen-containing compound found in DNA and RNA. Examples are adenine and guanine.

Polynucleotide

A molecular chain of nucleotides chemically linked by a series of phosphodiester bonds. A strand of RNA or DNA.

Pyrimidine

A nitrogen-containing, six-membered ring compound found in DNA and RNA. Examples are thymine, cytosine, and uracil.

Nucleotide

Basic building block of the nucleic acids, DNA and RNA; includes a nucleoside with a series of one or more phosphate groups linked to its sugar.

Complementary

Describes two molecular surfaces that fit together closely and form non-covalent bonds with each other. Examples include complementary base pairs, such as A and T, and the two complementary strands of a DNA molecule.

Antiparallel

Describes two similar structures arranged in opposite orientations, such as the two strands of a DNA double helix.

5'end

Designates the end of the DNA or RNA strand that has the fifth carbon in the sugar-ring of the deoxyribose or ribose at its terminus. A phosphate group attached to the 5′-end permits ligation of two nucleotides, i.e., the covalent binding of a 5′-phosphate to the 3′-hydroxyl group of another nucleotide, to form a phosphodiester bond.

DNA (Deoxyribonucleic Acid):

Double-stranded polynucleotide formed from two separate chains of covalently linked deoxyribonucleotide units. It serves as the cell's store of genetic information that is transmitted from generation to generation.

Ribose

Found in RNA, is a "normal" sugar, with one oxygen atom attached to each carbon atom.

3'end

Identifies one end of a single-stranded nucleic acid molecule. It's that end of the molecule which terminates in a 3' phosphate group.

Nucleic Acid

Macromolecule that consists of a chain of nucleotides joined together by phosphodiester bonds; RNA or DNA.

Nucleoside

Molecule made of a nitrogen-containing ring compound attached to a sugar, either ribose (in RNA) or deoxyribose (in DNA).

RNA (Ribonucleic Acid):

Molecule produced by the transcription of DNA; usually single-stranded, it is a polynucleotide composed of covalently linked ribonucleotide subunits. Serves a variety of structural, catalytic, and regulatory functions in cells.

5.How did the Watson-Crick double helix model of DNA structure confirm Chargaff's rules?

The structure immediately revealed how DNA might be copied or replicated and it provided the first clues about how a molecule of DNA might encode the instructions for making proteins.

Phosphodiester Bond

Strong covalent bond that forms the backbone of DNA and RNA molecules; uses choline attached to a phosphate as its head group.

Double Helix

The typical structure of a DNA molecule in which the two complementary polynucleotide strands are wound around each other with base-baring between the strands.

Base Pairing

Two complementary nucleotides in an RNA or DNA molecule that are held together by hydrogen bonds. For example, G with C and A with T or U.

Hydrogen Bonding

Weak non-covalent interaction between a positively charged hydrogen atom in one molecule and a negatively charged atom, such as nitrogen or oxygen, in another; these interactions are key to the structure and properties of water.

4.Describe the structure of a DNA molecule using the terms: sugar-phosphate backbone, purine and pyrimidine bases, base-pairs, antiparallel, complementary, hydrogen bonds, phosphodiester bond, 3' end, 5'end.

•Sugar-Phosphate Backbone: The nucleotides are covalently linked together in a chain through the sugars and phosphates, which form a backbone of alternating sugar-phosphate-sugar-phosphate. All the bases are therefore on the inside of the double helix, with the sugar phosphate backbones on the outside. •Purine & Pyrimidine Bases: A bulkier two-ring base (a purine) is paired with a single-ring base (a pyrimidine). •Base Pairs: Each purine-pyrimidine pair is called a base pair and this complementary base-pairing enables the base pairs to be packaged in the energetically most favorable arrangement in the interior of the double helix. •Antiparallel: The members of each base pair can fit together within the double helix because the two strands of the helix run antiparallel to each other. This means that they are oriented with opposite polarities. •Complementary: Each strand of a DNA double helix contains a sequence of nucleotides that is exactly complementary to the nucleotide sequence of its partner strand. An A always matches with T on the opposite strand, and C always matches a G. •Hydrogen Bonds: The two polynucleotide chains in the DNA double helix are held together by hydrogen-bonding between the bases on the different strands. •Phosphodiester Bond: Is a strong covalent bond that forms the backbone for a DNA molecule. •3' & 5' End: Two ends of the strand can be easily distinguished as one will have a hole ('3 hydroxyl) and the other knob (the 5' phosphate). This polarity in a DNA strand is indicated by referring to one end as the 3' end and the other as the 5' end.