1. Structure & Replication
DNA
Structure & Replication

2. DNA Facts
A single strand of human DNA = about 1 meter long (uncoiled). The total DNA in each cell = about 2m.
The nucleus of a typical cell has a diameter of mm = in
A single strand of DNA contains about 3 billion base pairs.
If the DNA sequence of a person was compiled in books, it would take the equivalent of 200 telephone books, each 1000 pages.

3. Function of DNA
Stores & transmits genetic info from one organism to next generation
Instructs cells on work to do

4. DNA in other organelles? Why?

5. DNA Structure Deoxyribonucleic Acid Building blocks - nucleotides
5-Carbon Sugar (deoxyribose)
Phosphate Group
Nitrogen Base

6. 4 nitrogen bases Adenine (A) & Guanine (G)  purines
Cytosine (C) & Thymine (T)  pyrimidines

7. DNA Strand Nucleotides bond together  polymer
Sugar & Phosphate attached by covalent bonds
Nitrogen bases point outward & attach to each other by hydrogen bonds (weaker)

8. DNA Double Helix Nucleotide Hydrogen bonds Sugar-phosphate backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)

9. Erwin Chargaff Same amount of A&T and C&G
A pairs only w/T – (2 H-bonds)
C pairs only w/G – (3 H-bonds)
Complementary base pairing rule
Source of DNA A T G C
Streptococcus
Yeast
Herring
Human

11. Twisted Ladder
B/C Sugar & Phosphate groups do not line up exactly

12. Double Helix Discoveries
Rosalind Franklin – X-ray diffraction showed DNA helix was 2-3 strands
Watson & Crick – 1953 – exact structure double helix held together by nitrogen bases

14. Anti-parallel
The 2 strands of DNA are arranged in opposite directions (anti-parallel). The strands are identified (named) by the numbered carbon located at the end of the strand.
5’ is read as 5 prime, 3’ is read as 3 prime

15. Chromosome
Supercoils
Coils
Nucleosome
Histones/proteins
DNA
double
helix

16. More DNA Facts
If DNA were the thickness of a clothesline, the length would be 8km (5mi) long.
In bacteria, nucleotides are replicated at a rate of about 500 per second; in mammals, about 50 per second.
During DNA replication, only about one error occurs for every one billion nucleotides made.

17. ENZYMES made of Proteins
100s to 1000s of chemical rxn in human body
Enzymes speed up rxn by millions and even billions of times
Single enzyme molec. acts on about 1000 substrate molecules/second.

18. IMPORTANCE OF ENZYMES Enzymes are biological catalysts.
Lower the amount of energy needed for rxn
Not changed by rxn
Not used up by rxn

19. They lower the amount of energy needed for a reaction.
Reaction pathway
without enzyme
Activation energy
Activation
energy
with enzyme
Reactants
Products

20. Responsible for metabolism:
Catabolism: breaking apart molecules (hydrolysis)
Anabolism: building molecules (dehydration synthesis/condensation rxn)

21. Most enzymes are named after the substrate they work on (usually ending in “-ase”).
Lipase-lipids
Protease-proteins
Sucrase-sucrose

23. DNA Replication Cells copy info for each new cell Occurs in nucleus
3 steps

24. 1. Unzip
DNA Helicase unzips (uncoils) part of DNA strand, breaking H-bonds btwn bases

25. 2. Complementary Base Pairing
DNA Polymerase pairs up free nucleotides with complementary bases (forming new H-bonds)

26. 3. Joining nucleotides
Ligase – joins nucleotides (S+P) w/covalent bonds  2 identical DNA strands, each w/1 new strand & 1 old strand
Semi-conservative replication

28. Checking for Errors DNA polymerases are also “proofreaders”
Only add nucleotides to growing chain, if previous base is correctly paired
Backtracks to correct mistake
Only about 1 error for every one billion nucleotides made

29. DNA Replication Animation

30. Chromosome
Supercoils
Coils
Nucleosome
Histones/proteins
DNA
double
helix