Nucleic Acids: Cell Overview and Core Topics

Outline I.Cellular Overview II.Anatomy of the Nucleic Acids 1.Building blocks 2.Structure (DNA, RNA) III.Looking at the Central Dogma 1.DNA Replication 2.RNA Transcription 3.Protein Synthesis

Cellular Overview DNA and RNA in the Cell

Classes of Nucleic Acids: DNA  DNA is usually found in the nucleus  Small amounts are also found in: mitochondria of eukaryotes chloroplasts of plants  Packing of DNA: 2-3 meters long histones  genome = complete collection of hereditary information of an organism

Classes of Nucleic Acids: RNA FOUR TYPES OF RNA mRNA - Messenger RNA tRNA - Transfer RNA rRNA - Ribosomal RNA snRNA - Small nuclear RNA

Anatomy of Nucleic Acids THE BUILDING BLOCKS

Nucleic acids are linear polymers. Each monomer nucleotide consists of: 1. a sugar 2. a phosphate 3. a nitrogenous base

Nitrogenous Bases

DNA (deoxyribonucleic acid): adenine (A)guanine (G) cytosine (C)thymine (T) RNA (ribonucleic acid): adenine (A)guanine (G) cytosine (C)uracil (U) Why ?

Properties of purines and pyrimidines: 1.keto – enol tautomerism 2.strong UV absorbance

Pentoses of Nucleic Acids This difference in structure affects secondary structure and stability. Which is more stable?

Nucleosides linkage of a base and a sugar.

Nucleotides - nucleoside + phosphate - monomers of nucleic acids - NA are formed by 3’-to-5’ phosphodiester linkages

Shorthand notation: - sequence is read from 5’ to 3’ - corresponds to the N to C terminal of proteins

Nucleic Acids: Structure DNA

Primary Structure nucleotide sequences

DNA Double Helix Maurice Wilkins and Rosalind Franklin James Watson and Francis Crick Features: two helical polynucleotides coiled around an axis chains run in opposite directions sugar-phosphate backbone on the outside, bases on the inside bases nearly perpendicular to the axis repeats every 34 Å 10 bases per turn of the helix diameter of the helix is 20 Å Secondary Structure

Double helix stabilized by hydrogen bonds. Which is more stable?

Axial view of DNA

A and B forms are both right-handed double helix. A-DNA has different characteristics from the more common B-DNA.

left-handed backbone phosphates zigzag Z-DNA

Comparison Between A, B, and Z DNA:  A-DNA: right-handed, short and broad, 11 bp per turn  B-DNA: right-handed, longer, thinner, 10 bp per turn  Z-DNA: left-handed, longest, thinnest, 12 bp per turn

Major and minor grooves are lined with sequence-specific H-bonding.

Supercoiling relaxed DNA supercoiled DNA Tertiary Structure

Consequences of double helical structure: 1. Facilitates accurate hereditary information transmission 2.Reversible melting melting: dissociation of the double helix melting temperature (T m ) hypochromism annealing

Structure of Single-stranded DNA Stem Loop

Nucleic Acids: Structure RNA

Secondary Structure transfer RNA (tRNA) : Brings amino acids to ribosomes during translation

Transfer RNA Extensive H-bonding creates four double helical domains, three capped by loops, one by a stem Only one tRNA structure (alone) is known Many non-canonical base pairs found in tRNA

ribosomal RNA (rRNA) : Makes up the ribosomes, together with ribosomal proteins. Ribosomes synthesize proteins All ribosomes contain large and small subunits rRNA molecules make up about 2/3 of ribosome Secondary structure features seem to be conserved, whereas sequence is not There must be common designs and functions that must be conserved

messenger RNA (mRNA) : Encodes amino acid sequence of a polypeptide

small nuclear RNA (snRNA) :With proteins, forms complexes that are used in RNA processing in eukaryotes. (Not found in prokaryotes.)