Ch 16 WarmUp 1 Draw and label a

Ch. 16 Warm-Up 1. Draw and label a nucleotide. 2. Explain the semiconservative model of DNA replication. 3. What is the complementary DNA strand to: DNA: A T C C G T A T G A A C

Chargaff’s Rules: If cytosine makes up 21% of the nucleotides, then adenine would make up ___ % ? A. B. C. D. 21% 42% 58% 29%

THE MOLECULAR BASIS OF INHERITANCE Chapter 16

What you must know The structure of DNA. The major steps to replication. The difference between replication, transcription, and translation. The general differences between the bacterial chromosome and eukaryotic chromosomes. How DNA is packaged into a chromosome.

Edwin Chargaff (1947) Chargaff’s Rules: DNA composition varies between species Ratios: %A = %T and %G = %C

Rosalind Franklin (1950’s) Worked with Maurice Wilkins X-ray crystallography = images of DNA Provided measurements on chemistry of DNA

James Watson & Francis Crick (1953) Discovered the double helix by building models to conform to Franklin’s X-ray data and Chargaff’s Rules.

Structure of DNA = double helix “Backbone” = sugar + phosphate “Rungs” = nitrogenous bases

Structure of DNA Nitrogenous Bases Adenine (A) Guanine (G) Thymine (T) Cytosine (C) purine pyrimidine Pairing: purine + pyrimidine A=T GΞC

In analyzing a number of different bases in a DNA sample, which result would be consistent with base pairing rules? A. B. C. D. E. A=G A+G=C+T A+T=G+T A=C G=T

Structure of DNA Hydrogen bonds between base pairs of the two strands hold the molecule together like a zipper.

Structure of DNA Antiparallel: one strand (5’ 3’), other strand runs in opposite, upside-down direction (3’ 5’)

DNA Comparison Prokaryotic DNA Double-stranded Circular One chromosome In cytoplasm No histones Supercoiled DNA Eukaryotic DNA Double-stranded Linear Usually 1+ chromosomes In nucleus DNA wrapped around histones (proteins) Forms chromatin

Problem: How does DNA replicate?

Replication: Making DNA from existing DNA 3 alternative models of DNA replication

Replication is semiconservative

DNA Replication Video http: //www. youtube. com/watch? v=4 jtm. OZa. I v. S 0&feature=related

A biochemist isolates and purifies the molecules needed for DNA replication. When she adds some DNA, replication occurs, but each DNA molecule is a normal strand paired with segments of DNA a few hundred nucleotides long. What has she probably forgotten? A. B. C. D. E. DNA polymerase DNA ligase Nucelotides Okazaki fragments primase

Major Steps of Replication: 1. Helicase: unwinds DNA at origins of replication 2. Initiation proteins separate 2 strands forms replication bubble 3. Primase: puts down RNA primer to start replication 4. DNA polymerase III: adds complimentary bases to leading strand (new DNA is made 5’ 3’) 5. Lagging strand grows in 3’ 5’ direction by the addition of Okazaki fragments 6. DNA polymerase I: replaces RNA primers with DNA 7. DNA ligase: seals fragments together

1. Helicase unwinds DNA at origins of replication and creates replication forks

3. Primase adds RNA primer

4. DNA polymerase III adds nucleotides in 5’ 3’ direction on leading strand

Replication on leading strand

Elongation of the leading strand during DNA synthesis… A. B. C. D. E. Progresses away from the replication fork Occurs in the 3’ 5’ direction Produces Okazaki fragments Depends on DNA polymerase Does not require a template strand

Leading strand vs. Lagging strand

Bio. Flix: DNA Replication http: //media. pearsoncmg. com/bc/bc_0 medi a_bio/bioflix. htm? 8 apdnarep