LIFESCI 7A Lecture Notes - Lecture 5: Central Dogma Of Molecular Biology, Transfer Rna, Complementary Dna
3.1: Major Biological Functions of DNA
● DNA can transfer biological characteristics from one organism to another.
○ transformation The conversion of cells from one state to another, as from nonvirulent to
virulent, when DNA released to the environment by cell breakdown is taken up by recipient
cells. In recombinant DNA technology, the introduction of recombinant DNA into a recipient cell.
○ Series of experiments led scientists to deduct that DNA carries biological hereditary information,
not proteins/RNA, etc.
● DNA molecules are copied in the process of replication.
○ replication The process of copying DNA so genetic information can be passed from cell to cell
or from an organism to its progeny.
■ Faithful replication is critical in that it allows DNA to pass genetic information from cell to
cell and from parent to offspring.
■ To make a mistake is to make a mutation
○ mutation Any heritable change in the genetic material, usually a change in the nucleotide
sequence of a gene.
■ A single mutation could have a deadly result, but sometimes may actually be favorable
and therefore passed down via natural selection
● Genetic information flows from DNA to RNA to protein.
○ DNA indirectly directs the activities of a cell and growth of an organism. They have the code for
all proteins, which carry out all the work
○ ribonucleic acid (RNA) A molecule chemically related to DNA that is synthesized by proteins
from a DNA template.
■ Intermediary between DNA and protein synthesis
○ central dogma The theory that information transfer in a cell usually goes from DNA to RNA to
protein. (though exceptions exist)
1. transcription The synthesis of RNA from a DNA template.
a. template A strand of DNA or RNA whose squence of nucleotides is used to
synthesize a compementary strand.
b. Both molecules use same language of nucleic acids
2. translation a molecule of RNA is used as a code for the sequence of amino acids in a
protein; occurs in ribosome
a. Here we see a change in language, from nucleic acids to amino acids
○ All cells carry all DNA, but central dogma is very regulated and does not occur at all times;
some genes are expressed and some are not at very specific times in specific cells
■ Prokaryotes: both transcription and translation in the cytoplasm
■ Eukaryotes: transcription in nucleus, translation in cytoplasm
● Separation of time/space allows for even MORE reguation
■ These processes are really similar and must’ve evolved very early on
● ANIMATION NOTES
○ DNA uses nucleic acids A/T, G/C
○ RNA uses nucleic acids A/U, G/C
○ Transcription: DNA splits, mRNA makes template for complementary strand
■ In prokaryotes, mRNA goes straight to translation
■ In eukaryotes, mRNA is modified first, then sent out to cytoplasm
○ Translation: ribosome attatches to mRNA, adding one amino acid at a time to the growing chain
(per three nucleic acids of mRNA)
■ Synthesized protein released from ribosome into cytoplasm
■ Multiple ribosomes can read the same mRNA at once!
3.2: Chemical composition and structure of DNA
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● Structure of DNA allows it to carry out the huge amount of tasks it does! structure=function!!!
● VIDEO NOTES
○ Double-stranded DNA (dsDNA); two strands intertwine to form double helix
■ Most common form of dsDNA is B-form DNA
○ Each DNA strand is made up of nucleotides, each consisting of
■ 5-carbon sugar
■ Phosphate
■ One of four possible nitrogenous bases: adenine, guanine, thymine, cytosine
● Always attached to 1-carbon of the 5C sugar
● Phosphate between the 5’ of the 5C and the 3’ of another 5C
○ DNA sugars (deoxyribose) missing OH- at the 2’ position
■ Nucleotides bond together linearly with phosphodiester bonds
● Phosphate of one nucleotide binds to 3’ of another nucleotide
○ Complementary strands are backwards (5’ to 3’ watson vs 3’ to 5’ crick)
■ Covalent bonds in the backbone bind nucleotide to its backbone, but nucleotides interact
to eachother (complementary strands bond) via hydrogen bonding
■ A/T 2 hydrogen bonds; G/C 3 hydrogen bonds
● T and C are pyrimidines (one ring); A and G are purines (2 rings)
■ Symmetrical base pairing allow for stacking
○ Each turn of double helix is about 10 base pairs; pi-pi interactions occur when rings of base
pairs share electrons with eachother;
○ MAJOR and MINOR GROOVES; 2 repeating/alternating spaces
■ Base pair recognition and binding sites for proteins and enzymes; allow for proteins to
correctly attach and carry out their functions int he genome
■ Major: base/pair specific information, minor: base/pair nonspecific
● A DNA strand consists of subunits called nucleotides.
○ nucleotide DNA’s subunitsA constituent of nucleic acids, consisting of a 5-carbon sugar, a
nitrogen-containing base, and one or more phosphate groups.
■ 5 carbon sugar: deoxyribose in DNA, ribose in RNA
■ phosphate group A chemical group consisting of a phosphorus atom bonded to four
oxygen atoms.
● nucleoside A molecule consisting of a 5-carbon sugar and a base. Nucleoside+
(1 or more) phosphate group=nucleotide
■ Nitrogenous base gives nucleotide identity: A, T, G, C, or even U
● purine In nucleic acids, either of the bases adenine and gunanine, which have a
double-ring structure.
● pyrimidine In nucleic acids, any of the bases thymine, cytosine, and uracil,
which have a single-ring structure.
● DNA is a linear polymer of nucleotides linked by phosphodiester bonds.
○ phosphodiester bond A bond that forms when a phosphate group in one nucleotide is
covalently joined to the sugar unit in another nucleotide.
■ 3’ of one 5C carbon attaches to the 5’ phosphate group of another
■ relatively stable and form the backbone of a DNA strand.
■ Give DNA its polarity (asymmetry
● 5′ end The end of a nucleic acid strand containing a free 5′ phosphate group.
● 3′ end The end of a nucleic acid strand that carries a free 3′ hydroxyl.
○ Need to specifify which end:
■ 5′-AGCT-3′ or equivalently 3′-TCGA-5′.
■ Without labelling, AGCT is assumed 5′-AGCT-3′
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● Cellular DNA molecules take the form of a double helix.
○ Double helix causes major grooves and minor grooves; uneven spaces
■ proteins that interact with DNA often recognize a particular sequence of bases by
making contact with the bases via the major or minor groove or both
○ DNA strands in helix are antiparallel: Oriented in opposite directions;
■ Pyrimidines always pair with purines and vice versa; double helix stays even throughout
(preserves the distance between the backbones along the length of the entire molecule)
● complementary Describes the relationship of purine and pyrimidine bases, in
which the base A pairs only with T and G pairs only with C.
○ 5′-ATGC-3′
○ 3′-TACG-5′
○ base stacking Stabilizing hydrophobic interactions between bases in the same strand of DNA.
● The three dimensional structure of DNA gave important clues about its functions.
○ there is no restriction on the sequence of bases along a DNA strand
■ Infinitely many different combinations of just 4 nucleotides!
○ Because of pairings, the numbers of A in a DNA strand must equal number of T’s; C’s must
equal G’s
■ %A = %T and %G = %C
○ It’s double helix structure allows for DNA to unwind and be copied onto RNA‘
● Cellular DNA is coiled and packaged with proteins.
○ Circular DNA in prokaryotic cells can form supercoils to compress itself
■ topoisomerase enzymes that regulates the supercoiling of DNA by cleaving one or both
strands of the DNA double helix, and later repairing the break.
○ Linear DNA in eukaryotic cells form chromosomes (one chromosome=one DNA molecule)
■ chromatin A complex of DNA, RNA, and proteins that gives chromosomes their
structure; chromatin fibers are either 30 nm in diameter or, in a relaxed state, 10 nm.
● Chromatin interact with DNA despite sequence;
● evolutionarily conserved Characteristics that persist relatively unchanged
through diversification of a group of organisms and therefore remain similar in
related species.
○ are very similar in sequence from one organism to the next
○ Evolutionary conserved RNA, DNA, and protein suggests that they are
fundamental and have not evolved much over time
13.4: Organization of Genomes
We need to be able to compress a LARGE amount of genentic information while still not tampering with its
function; how is the (eukaryotic) genome stored?
● Bacterial cells package their DNA as a nucleoid composed of many loops.
○ Circular bacterial DNA forms supercoils (thanks to topoisomerase (II)
■ topoisomerase II An enzyme that breaks a DNA double helix, rotates the ends, and
seals the break.
■ Supercoils form nucleoid, which has multiple loops
● Eukaryotic cells package their DNA as one molecule per chromosome.
○ Linear eukaryotic DNA forms a single chromosome per DNA molecule
■ DNA is packed with proteins (histones) to form chromatin
● chromatin A complex of DNA, RNA, and proteins that gives chromosomes their
structure; chromatin fibers are either 30 nm in diameter or, in a relaxed state, 10
nm.
1. DNA wrapped twice around histone proteins
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Document Summary
In recombinant dna technology, the introduction of recombinant dna into a recipient cell. Series of experiments led scientists to deduct that dna carries biological hereditary information, not proteins/rna, etc. Dna molecules are copied in the process of replication. Replication the process of copying dna so genetic information can be passed from cell to cell or from an organism to its progeny. Faithful replication is critical in that it allows dna to pass genetic information from cell to cell and from parent to offspring. To make a mistake is to make a mutation. Mutation any heritable change in the genetic material, usually a change in the nucleotide sequence of a gene. A single mutation could have a deadly result, but sometimes may actually be favorable and therefore passed down via natural selection. Genetic information flows from dna to rna to protein. Dna indirectly directs the activities of a cell and growth of an organism.
