The Structure And Replication Of Dna

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Genes

Back 1

Sequences of DNA that encode proteins (occasionally encode RNA to construct ribosomes)

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Genome

Back 2

Is comprised of chromosomes, DNA in organelles, and extra chromosomal DNA called plastids

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Somatic cells

Back 3

All cells except gamete producing cells

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Germ cells

Back 4

Gamete producing cells

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What are genes made of?

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•Genes are made of the nucleic acid DNA
•cells nucleus contains large amounts of nucleic acid
•somatic cells contain same amount of DNA
•germ cells contain half the amount of DNA than somatic cells

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Structure of DNA

Back 6

DNA is composed of building blocks called nucleotides
•Four possible bases
•Purine
•Pyrimidine
Adenine, Guanine, Thymine, Cytosine

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Purine

Back 7

Double ring base (Adenine, Guanine)

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Pyrimidine

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Single ring base (Thymine, Cytosine)

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Griffith's experiment

Back 9

Mice were injected with different strains of bacteria that cause pneumonia. Results- live avirulent strain R was transformed to a virulent strain S by picking up genetic material from a dead virulent strain S

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Transforming principal

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Rough strain on pneumonia picked up DNA for capsule from heat killed smooth strain, and was able to avoid getting killed

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Hershey and Chase experiment

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Showed that a virus that attacks bacteria (bacteriophage) does so by injecting its DNA into the bacterial cell. Demonstrated that DNA was the genetic material

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Bacteriophage

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A virus that attacts bacteria

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Nucleotide

Back 13

Is composed of a five carbon sugar that is bonded to a phosphate group and to a nitrogenous base. The carbons in the sugar are designated as 1'-5'. The phosohate is bound to the 5' carbon, and a hydroxyl (OH) group is attached to the 3' carbon of the sugar.

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DNA

Back 14

Exist as a double chain structure. The two chains are held together by hydrogen bonding between the nitrogenous bases. The sequence of bases in one strand determines the sequence of bases in the opposite strand, they are complementary to each other. The polarity of the two strands is opposite, one runs 5' to 3' thus the DNA chains are antiparallel

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Rosalind Franklin

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Produced the first X-ray diffraction pattern of the DNA

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Francis Crick

Back 16

Had developed mathematical methods for interpreting the X-ray patterns. Used these photographs to deduce that DNA is a helix

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James Watson and Crick

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Developed a model of the structure of the DNA

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Chargaff

Back 18

Biochemist who noted that the proportion of cytosine in a DNA fragment always matched the proportion of guanine, and the same holds true for thymine

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DNA replication

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The process that copies the nucleotide sequence of a double-stranded parent DNA molecule into a two double-stranded daughter DNA molecules

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Semi-conservative replication

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Each daughter molecule contains one strand from the parental molecule (conserved strand) and one newly synthesized

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DNA gyrase

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An enzyme that unwinds the DNA of two parental strands. Enzyme that relaxes super coiled DNA

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Origin

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Specific site where DNA begins to unwind

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DNA polymerase

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(komberg enzyme) ensures complenentarity by adding complementary nucleotides to the new strand. DNA polymerase can only add nucleotides in the 5'->3' direction

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Primer

Back 24

A short RNA segment that is synthesized near the replication fork and the DNA polymerase extends the primer by adding deoxyribonucleotides to form a short 5'->3' strand of DNA

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Primers removed

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Primers are removed by the DNA polymerase and are linked by DNA ligase

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Continuous manner

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The 3' end of the new strand is elongated by DNA polymerase in a continuous manner

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Discontinuous manner

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The 5' end is elongated in a discontinuous manner

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DNA replication in eukaryotes

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In Eukaryotic cells, which have linear chromosomes, replication of DNA starts at many sites on the molecule with the formation of replication bubble

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SSB protein

Back 29

Binds SS DNA---> Keeps SS

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Helicase

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Breaks hydrogen bonds

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DNA primase

Back 31

Builds RNA primer, is an enzyme

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DNA polymerase II

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Main replication enzyme

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DNA polymerase I

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Enzyme that will remove primers and build DNA, fragments form continuous line by using DNA ligase

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DNA ligase

Back 34

Forms phosphodiester bond

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Okazaki fragments

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The lagging strands being built (200 bases in length)