Download Notes 4-3 continued, DNA

Notes 4-3 continued…
DNA
Scientists
• 1952- Rosalind Franklin used X-ray method to
take photographs of DNA
• 1953- Watson and Crick use the photographs
and discovered the structure of DNA is a
double helix (twisted ladder)
• DNA is found inside the nucleus of cells
Structure of DNA
• The DNA molecule, supported
by proteins, is shaped like a
twisted ladder.
Chromosomes
• DNA coils around proteins, then coils up some
more, and condenses into chromosomes
DNA
• Deoxyribonucleic Acid
• Belongs to the organic molecule group known
as “nucleic acids” that we discussed in chap 3
• Sides of the ladder are made up of molecules
of sugar called deoxyribose and phosphate
molecules
• The rungs of the ladder are made up of 2
nitrogen bases
Nitrogenous bases
• DNA has 4 possible nitrogen bases: Adenine,
thymine, guanine, and cytosine
• They are represented by the capital letters A,
T, G, C
• In DNA, A always pairs with T and G always
pairs with C
• Look at the DNA molecule on the next slide to
see what I mean
• Draw this in
your notes
• Notice the base
pairs in the
rungs, A-T and
C-G
• Notice the
alternating
sugars and
phosphates on
the sides
Replication of DNA
• Happens inside the nucleus during interphase
• An enzyme (a protein) comes and “unzips” the
DNA ladder between its base pairs
• New bases are then added to the old strand
• As a result, you end up with 2 identical strands of
DNA
• This is an important part of the cell cycle, as each
new daughter cell needs a copy of DNA, since
DNA holds the instructions for making proteins
Replication of DNA
• Because of the way in which the nitrogen
bases pair with one another, the order of the
bases in each new DNA molecule exactly
matches the order in the original DNA
molecule.
Problem:
• If the left side of the ladder has the following
sequence of base pairs: A-C-T-G-G-T-G-C-G-A-C-T,
what would the sequence on the right side of the
ladder be? Write down your answer….
T-G-A-C-C-A-C-G-C-T-G-A