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Genes and DNA
Chapter 6 page 144-154
DNA
• DNA-deoxyribonucleic acid. Is a molecule
that is present in all living cells and that
contains the information that determines
the traits that a living thing inherits and
needs to live
• Nucleotide found in a nucleic acid chain
that contains a sugar, a phosphate group
and a nitrogenous base
DNA
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4 Nucleotides of DNA
A. Adenine
B. Thymine
C. Cytosine
D. Guanine
Chargaff’s rules
• % of thymine will equal adenine for they
always pair together
• % of cytosine will equal guanine
• This was found in the 1950’s by Erwin
Chargaff
Franklin’s work
• Was able to make images of DNA by x-ray
diffraction thus by this process was able to
say that DNA has a spiral shape.
Watson and Crick
• After looking at chargaff’s work and
Franklin’s work. They came to the
conclusion that “DNA must look like a
long, twisted ladder. This lead to the
explanation on how DNA is copied and
how it functions in the cell.
Copying DNA
• Done by a process called replication
• Pairs of bases are complementary to each
other
• Example the sequence CGAC will always
bind with GCTG
Process of Replication
• DNA is split down the middle where the
bases meet. Thus the bases on each side
is now used as a pattern for the new
strand. So when this action of replication
is done you will have one side of old DNA
and one side of new DNA for each
complementary strand.
When does replication occur?
• Replication occurs every time a cell
divides.
How DNA works
• A. A typical skin cell has a diameter of
about 0.0025 cm. The DNA is found in the
nucleus.
• B. The DNA in the nucleus is a part of the
material called chromatin.
• C. A single strand of chromatin is made up
of a long strand of DNA that is coiled
around proteins.
How DNA works (cont)
• D. Each strand of DNA contains two
halves that are connected in the middle
and twisted in a double helix.
• E. When a cell is ready to divide, it
packages the chromatin into chromatids.
Two identical chromatids make up a
chromosome that is ready to divide
How DNA works (cont)
• E. Just before division, each human cell
contains 46 chromosomes. These
chromosomes contain two identical copies
of all of the cell’s genetic material.
Making of Protein
• 1. A copy is made of one side of the DNA
segment where a particular gene is
located. Then it is transferred to the
cytoplasm.
• 2. This mirrorlike copy of a DNA segment
is called messenger RNA or mRNA.
Making of a protein
• 3. Each group of three bases on the
mRNA segment codes for one amino acid
• 4. The mRNA segment is fed through the
ribosome
• 5. Molecules of tRNA deliver amino acids
from the cytoplasm to the ribosome.
Making of a protein
• 6. The amino acids are dropped off at the
ribosome
• 7. The amino acids are joined to make a
protein. Usually one protein is produced
for each gene.
Mutations
• Mutations are changes in the number, type
or order of bases on a piece of DNA
• Types are deletion, insertion, substitution
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