A1.2

Strands

• DNA is double stranded while RNA is single stranded

Sugar

• Deoxyribose for DNA and ribose for RNA

Bases

• Base pairs for DNA are bonded through hydrogen bonds

• RNA has a single nucleobase

Function

• Long-term storage of genetic information = DNA

• Transfers genetic information for protein synthesis = RNA

Shape of DNA

• Each strand has a ‌sugar-phosphate backbone with nitrogenous bases projecting ‌inward

• The two strands wind around ‌each other to form a double ‍helix

Bases Pairing

• The bases ‍pair in a fixed way: ‌adenine with thymine, and cytosine ‍with guanine

• This is called complementary ‍base pairing.

• The base pairs are ‍joined by hydrogen bonds: ‍two between A and T, ‍and three between C and G.‍

Antiparallel Strands

• The two DNA strands run in ‌opposite directions.

• One strand runs 5'‍ to 3', while ‍the other runs 3' to ‌5'.

Drawing the Structure of ‍DNA

1. Antiparallel ‍strands, one labelled 5' ‌to 3' and the other ‍3' to 5'.‌

2. Complementary base pairing, with A ‍paired to T and C paired ‍to G, connected by hydrogen ‍bonds.

3. The sugar-phosphate backbone as a ‍continuous chain of alternating sugar and ‍phosphate groups.

Condensation Reaction

• Chemical reaction used to produce polymers

• Involves the loss/production of a water molecule

Condensation Reactions Link Nucleotides Into ‍a Polymer

1. Nucleotide monomers are joined by ‍condensation reactions

2. Each reaction forms a ‌phosphodiester bond and releases a molecule ‌of water

3. The polymer grows in ‍the 5' to 3' ‍direction as new nucleotides are ‌added to the 3' end.‌

4. Forms RNA polymer

Ligase

• Enzyme that joins two molecules together by forming a bond between them

• DNA ligase helps seal the sugar-phosphate backbone by joining DNA fragments

5’ to 3’

• Direction a nucleic acid strand is built and read

• 5' end = phosphate end

• 3' end = hydroxyl end

Basis ‍of the Genetic Code

• DNA ‌and RNA store genetic ‍information using nitrogenous bases

• Sequence ‌of these bases, ‌not the backbone, ‍that stores the code.

• Each letter gives us information for each protein

DNA Nitrogenous Bases

1. Adenine (A)

2. Thymine ‍(T)

3. Cytosine (C)

4. Guanine ‍(G)

RNA Nitrogenous Bases

• Same as DNA except thymine (T) = uracil (U)

Central Dogma

• 1. DNA stores the gene

• 2. Transcription copies the gene into mRNA

• 3. mRNA leaves the nucleus

• 4. Ribosomes read the mRNA in codons

• 5. tRNA brings amino acids

• 6. Amino acids join to form a polypeptide

• 7. The polypeptide folds into a functional protein

mRNA

• Messenger RNA

Phosphodiester Bond

• A covalent bond between nucleotides in a nucleic acid chain (polypeptide)

⁣Sugar Phosphate Backbone

• Gives nucleic acids structural framework

• sequence of ‍nitrogenous bases carries the genetic information.

DNA and RNA Directionality

• Backbone = chain with two “ends,” and each end is labeled by which carbon on the sugar is free

• 5' end has a free phosphate group\

• 3' end has a free hydroxyl group (-OH)

Purines

• Double ring bases

• Includes adenine (A) and guanine (G)

Pyrimidine

• Double ring bases

• Includes cytosine (C), thymine (T) for DNA, and Uracil (U) for RNA

Nucleotide

• The monomer that builds DNA and RNA

Parts of a Nucleotide

• Phosphate

• Sugar

• Base

Nucleotide Diagram

1. Start ‍With the Sugar (Pentagon)

   1. Draw a ‍pentagon in the centre to represent the ‍pentose sugar

   2. The sugar is the ‍core connection point for both the phosphate ‍group and the nitrogenous base

2. Add ‍the Phosphate Group (Circle)

   1. Attach a circle ‍to the sugar's carbon 5 ‌position (C5'), the upper ‍left corner

   2. This circle represents the ‍phosphate group, which lets nucleotides link ‌together in chains

3. Add the Nitrogenous ‍Base (Rectangle)

   1. Connect a rectangle to the ‌sugar's carbon 1 position (C1'‌), the upper right corner.

   2. This represents the nitrogenous base, ‍which determines the nucleotide's identity (A,‍ T, C, G,‍ or U)

Pentose sugar for RNA

• Ribose has an -OH on both 1’ and 2’ carbons

Pentose sugar for DNA

• Deoxyribose has a -OH on 1’ carbon and a H on 2’ carbon

DNA

• Stands for deoxyribonucleotide

• Double stranded molecule that stores + transmits genetic info in living organisms

RNA

• Stands for ribonucleic acid

• Single stranded nucleic acid

• Plays a key role in coding, decoding, regulation, and expression of genetic info

DNA Biomolecular Makeup

• A biopolymer constructed from monomer deoxyribonucleotides

RNA Biomolecular Makeup

• A biopolymer constructed from monomeric ribonucleotides