Let s start with some background. Don t copy this down!

Transcription

1 DNA Structure

2 Let s start with some background. Don t copy this down!

3 DNA (deoxyribonucleic acid) is a molecule that encodes the genetic information of living things. Francis Crick and James Watson are credited for discovering the structure of DNA and ultimately how it works. However, it was largely the work of Franklin Rosalind that led to this important discovery.

4 DNA (deoxyribonucleic acid) is a molecule that encodes the genetic information of living things. Francis Crick and James Watson are credited with for discovering the structure of DNA. However, it was largely the work of Rosalind Franklin that led to this important discovery. X-ray photograph of DNA crystal Model of DNA

5 DNA Structure The basic units that make up the DNA (deoxyribonucleic acid) molecule are nucleotides. Each nucleotide is made up of 3 components: nitrogenous base phosphate group This you copy! five carbon sugar (deoxyribose) Figure 4 pg. 276

6 DNA contains 4 different nucleotides. What makes these nucleotides different from each other are their nitrogenous bases. Adenine (A) and Guanine (G) are double-ringed structures known as purines. Thymine (T) and Cytosine (C) are single-ringed structures known as pyrimidines. Figure 5 pg. 276

7 According According This is known to to the the asmodel model Chargaff's proposed proposed ruleby by and James James it means Watson Watson thatand and if you Francis Francis know Crick, the Crick, nucleotides nucleotides nucleotide Theform sequence form base22pairs antiparallel antiparallel ofare oneheld strand, strands. strands. together you The can The by hydrogen nitrogenous deduce nitrogenous thebonds. sequence bases bases of of one of strand one the strand other are paired strand. are paired with the withbases the bases in theinother the other strand. strand. Thymine is paired with Adenine (T-A). 2 hydrogen bonds Cytosine is paired with Guanine (C-G). 3 hydrogen bonds

8 The strands are said to be antiparallel because they are upside down in relation to each other. That is, the fifth carbon in deoxyribose points upward in one strand and downward in the other.

9

10 G C Along each strand, the sugars are linked together by a phosophate group. A T Complimentary nitrogenous bases hold the strands to one another through hydrogen bonds. G C

11 C G Notice that the orientation of one strand is opposite to the other. (antiparallel) T A C G

12 G C A T Notice that the orientation of one strand is opposite to the other. (antiparallel) G C

13 C G Notice that the orientation of one strand is opposite to the other. (antiparallel) T A C G

14 These 2 strands of nucleotides are twisted into a right-handed helix that makes one complete turn every 10 nucleotides (a distance of 3.4 nm). 3.4 nm Sugarphosphate backbone in - orientation Sugarphosphate backbone in - orientation Base pairs joined by hydrogen bonds Figure 7 pg. 276

15 3D Model of DNA Animation by: Drew Berry 2003 HHMI The Walter and Eliza Hall Institute Dolan DNA Learning Center

16 Let s hear from Hank Green?

17 If the DNA in one of your cells were laid end to end it would be about 3m in length (6 billion base pairs long). In order to fit this massive amount of information into each cell, the DNA is coiled upon itself to form structures known as chromosomes. rotein molecules called histones act as "spools" on which the DNA molecule coils. These coils (nucleosomes) are then coiled upon themselves to form a chromatin fibre. How does it all fit? histone nucleosome

18 Chromatin condenses during mitosis, at which time it can be seen as a chromosome. centromere chromosome chromatin fibre histone nucleosome Figure 1 pg. 291

19 3D Model of DNA Coiling Animation by: Drew Berry 2003 HHMI The Walter and Eliza Hall Institute Dolan DNA Learning Center

20 Read pgs Do # 1, 3, 4 and 6 pg. 272 Read pgs Do #1-9 pg 279

21 Grade 12 Biology - SB14U1 University reparation All figures are taken from Nelson Biology 12 Mr. Manbodh