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REVIEW OF REPLICATION

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DNA as Genetic Material established by several critical

experiments Fred Griffith (1928) Oswald T. Avery, C. M. MacLeod, and M.

J. McCarty (1944) Alfred D. Hershey and Martha Chase

(1952)

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Fred Griffith 1928--Called the change fromrough to smooth by heat killed bacteria

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Avery and McCloud (1944) wanted to know whatin Griffiths

This suggested that DNA was responsiblefor

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Alfred Hershey/Martha Chase*

**

*

* **

During infection phage DNA went into E. coli ,

phage protein

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DNA Bases

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Chain growth:DNA

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DNA Structure Summary

nitrogenous bases A, T, G, C

pentose sugar deoxyribose

chain of nucleotides linked byphosphodiester bonds

usually a double helix, composedof two complementary, antiparallel strands

base pairing rules A with T G with C

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Some Facts

error frequency = 10 -9 or 10 -10 perbase pair replicated

due to proofreading activity of DNApolymerases III and I

occurs very rapidly 750 to 1,000 base pairs/second in

procaryotes

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Schematic of DNA Polymerase III

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TRANSCRIPTION &

TRANSLATION1 st Semester 2008-2009

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RNA Structure

nitrogenous bases A, G, C, U (instead of T) pentose sugar

ribose

usually consists of single strand of nucleotides linked by phosphodiesterbonds

can coil back on itself

forms hairpin-shaped structures withcomplementary base pairing and helicalorganization

base pairing rules A with U

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The Genetic Code the manner in which genetic

instructions for polypeptide synthesisare stored within genome

colinearity sequence of base pairs in DNA

corresponds to the amino acid sequence

of polypeptide encoded

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Establishment of Genetic

Code codon

genetic code word specifies an amino acid

codon meanings deciphered by

Marshall Nirenberg, et al. in 1960s

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Organization of the Code code degeneracy

up to six different codons can codefor a single amino acid

sense codons the 61 codons that specify amino

acids stop (nonsense) codons

the three codons used as translationtermination signals

do not encode amino acids

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Wobble loose base

pairing 3 rd position

of codon lessimportantthan 1 st or2 nd

eliminatesneed forunique tRNA Figure 11.19

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Gene Structure

gene linear sequence of nucleotides with a

fixed start point and end point encodes a polypeptide, a tRNA, or an

rRNA cistron gene that encodes a polypeptide

reading frame organization of codons such that they

can be read to give rise to a geneproduct

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Figure 11.20

Importance of reading

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Genes That Code for tRNA andrRNA

Figure 11.24a

tRNA precursor

tRNAgenes have

promoter,

leader,coding,spacer, andtrailer regions

leader, spacer, and trailer removed during maturation process

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