Mcat biochem Nucleic Acid PDF

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Summary

Professor: Dr. Heather Tienson-Tseng
MCAT Nucleic Acids...

Description

Ch 7 | Nucleic Acids Tuesday, April 13, 2021

10:02 AM

Phosphorus Compounds -

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Phosphoric acid is an inorganic acid with three donatable protons ○ pKas 2.1, 7.2, 12.4 2○ At physiological pH, phosphoric acid is mostly in anionic form (HPO4 and H2PO4-) Phosphate alone is orthophosphate ○ When bound via anhydride linkage, two phosphates form a high energy pyrophosphate molecule

Nucleotides -

Nucleotides are NOT just DNA/RNA building blocks ○ ATP is the universal energy storage molecule ○ GTP is used for energy in protein synthesis ○ UTP is used in glycogenesis

DNA Structure -

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Precursor to the four basic nucleotides is dNTP where N is A, G, C, T ○ The nitrogenous base is linked to the sugar at the 1' carbon - making it a nucleoside § This is a B-N-glycosidic linkage Nitrogenous bases have a lot of hydrogen bonding potential ○ In aqueous environments, they bond to water ○ When compacted, they bond to each other Nucleosides become nucleotides when they have at least one phosphate group esterified onto them ○ They may be referred to by a name ending in ylate in the form with three phosphates § Ex. Thymidylate § ATP is also known as adenylate § Just know ylate means triphosphate Nucleotides are linked in the polymer by covalent phosphodiester bonds ○ These form between 3' hydroxy group in sugar of one nucleotide and the

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These form between 3 hydroxy group in sugar of one nucleotide and the 5' phosphate group of the sugar in the next nucleotide Nucleotide chains are written in the 5' to 3' direction § Ex. ACGT - T has the free 3' hydroxy group, A has the free 5' phosphate group

Watson and Crick Model -

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The theory that cellular DNA is a right-handed double helix held together by hydrogen bonds and hydrophobic forces ○ Ds-DNA is antiparallel, and h-bonding always occurs between a purine and pyrimidine ○ GC pairs and AT pairs take up the same amount of room in the helix ○ GC pairs are stronger due to being held by 3 hydrogen bonds while AT has 2 Tm - the temperature at which a solution of DNA molecules is 50 percent melted ○ Lower in a strand with less GC pairs and more AT Bases in the helix become hydrophobic because their polar nature disappears when their charge dipoles are occupied by H-bonding ○ This makes them hydrophobic in the helix and are able to interact with each other to stabilize ds DNA

Giemsa Stains -

Stain used on DNA where darker staining regions correspond to more densely packed chromatin, allowing us to map chromsomes Lighter areas replicate earlier/more often Used in karyotype production

RNA -

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Less stable than DNA because the 2' hydroxyl is capable of nucleophilic attack of thee backbone phosphate group ○ Important in lab because DNA is stable at a range of temperatures for long periods of time but RNA is harder to extract and is not stable for long Types of RNA to know ○ mRNA (and hnRNA) ○ tRNA ○ rRNA ○ Other less likely to show up on MCAT without explanation § snRNA - small nuclear □ Spliceosome components

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miRNA - micro RNA □ Post-transcriptional regulation of gene expression siRNA - small interfering RNA □ Post-transcriptional regulation piRNA- PIWI interacting RNAs □ Work with PIWI regulatory proteins to prevent transposons from moving Long ncRNA - control trascription levels and regulate posttranscriptional regulation □ Generally just gene regulation...