DNA Structure Replication DNA Facts n A single

DNA Structure & Replication

DNA Facts n. A single strand of human DNA = about 1 meter long (uncoiled). The total DNA in each cell = about 2 m. n The nucleus of a typical cell has a diameter of 0. 00034 mm = 0. 000013 in n A single strand of DNA contains about 3 billion base pairs. n If the DNA sequence of a person was compiled in books, it would take the equivalent of 200 telephone books, each 1000 pages.

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

DNA in other organelles? Why?

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

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

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

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

Erwin Chargaff n Same amount of A&T and C&G – A pairs only w/T – (2 H-bonds) – C pairs only w/G – (3 H-bonds) n Complementary base pairing rule Source of DNA A T G C Streptococcus 29. 8 31. 6 20. 5 18. 0 Yeast 31. 3 32. 9 18. 7 17. 1 Herring 27. 8 27. 5 22. 2 22. 6 Human 30. 9 29. 4 19. 9 19. 8

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

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

Nucleosome Chromosome DNA double helix Coils Supercoils Histones/proteins

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

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

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

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

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

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

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

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

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

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

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

DNA Replication Animation

Nucleosome Chromosome DNA double helix Coils Supercoils Histones/proteins