Replication, Transcription, Translation 2.6 and 4.4

Gene Expression DNA Transcription RNA Translation Protein Replication – copying of the DNA prior to cell division.

DNA and Proteins DNA and RNA are nucleic acids The monomers of nucleic acids are nucleotides Each nucleotide has a nitrogen base Adenine, thymine, cytosine, and guanine in DNA Adenine, uracil, cytosine, and guanine in RNA The monomers of proteins are amino acids. The sequence of bases in the DNA determines the sequence of amino acids in the protein. The sequence of bases is unique for each person, which leads to different proteins being produced, which gives each person unique characteristics.

Replication The message encoded within the sequence of bases in DNA must be copied so that it can be passed to the next generation of cells Occurs in the nucleus The DNA strands are separated and free nucleotides are added to both strands following the complementary base pair rules by an enzyme called DNA polymerase. Results in two DNA molecules that are identical to each other and to the original DNA molecule

Enzymes in Replication Helicase – seperates the two original strands DNA Polymerase – constructs the new strands using free nucleotides. Can only add nucleotides on the 3’ end of the strand it is constructing Ligase – joins sections called Okazaki fragments together on the lagging strand

The 3’ and 5’ end of the DNA has to do with the carbon atoms that are in the sugar in the backbone. The two strands in a DNA molecule are always opposite each other.

Leading and Lagging Strand The leading strand can be constructed continuously. The lagging strand has to be constructed in sections called Okazaki fragments.

Replication

Two daughter DNA molecules Figure 10.5A Parental DNA molecule Origin of replication Parental strand Daughter strand “Bubble” Figure 10.5A Multiple bubbles in replicating DNA Two daughter DNA molecules 14

A parental molecule of DNA Figure 10.4A_s1 A T C G G C A T T A A parental molecule of DNA Figure 10.4A_s1 A template model for DNA replication (step 1) 15

A parental molecule of DNA Figure 10.4A_s2 A T T A A T C G C G G C G C G C C A A T A T Free nucleotides T A T A A parental molecule of DNA The parental strands separate and serve as templates Figure 10.4A_s2 A template model for DNA replication (step 2) 16

A parental molecule of DNA Figure 10.4A_s3 A T T A A T A T A T C G C G G C G C G C G C G C C G C G C A A T A T A T A T Free nucleotides T A T A T A T A A parental molecule of DNA The parental strands separate and serve as templates Two identical daughter molecules of DNA are formed Figure 10.4A-s3 A template model for DNA replication (step 3) 17