Chapter 4 Genes and DNA
Section 1+2
Pages 84-101
What does DNA look like?
• Pieces of the Puzzle:
1. DNA must be able to
give instructions for
building and
maintaining cells.
2. DNA must be able to
be copied each time a
cell divides, so each
cell contains identical
genes.
Nucleotides: Subunits of DNA
• A nucleotide consists of
a sugar, a phosphate,
and a base. Nucleotides
are identical except for
their base.
• There are 4 bases:
Adenine, Thymine,
Guanine, and Cytosine
• All four bases have a
different shape.
Chargaff’s Rules
• Guanine and Cytosine
always occur in equal
amounts in DNA, as do
Adenine and Thymine
Franklin’s Discovery
• Used X Ray diffraction
to make images of DNA
molecules
• Suggested the spiral
shape of DNA
Watson and Crick’s Model
• After seeing Franklin’s
image, Watson and
Crick concluded that
DNA must look like a
long, twisted ladder.
• This helped explain how
DNA is copied and how
it functions in the cell.
DNA’s Double Structure
• Double Helix, two sides
of the ladder are made
of alternating sugar
parts and phosphate
parts.
• The rungs of the ladder
are made of a pair of
bases:
Adenine-Thymine
Guanine-Cytosine
Animated DNA
• http://highered.mcgrawhill.com/sites/0072943696/student_view0/ch
apter3/animation__dna_replication__quiz_1_
.html
Making Copies of DNA
• Pairing the bases allows
the cell to replicate or
make copies of DNA
• The pairs are
complementary since
they always pair A-T
and G-C
How are copies made?
• During replication, a DNA
molecule is split down the
middle, where bases meet.
• The bases on each side of the
molecule are used as a pattern
for the new strand.
• As the bases on the original
molecule are exposed,
complementary nucleotides are
added to each side of the ladder.
• Two DNA molecules are formed.
• Half of each of the molecules is
old DNA, half is the new DNA
Unraveling DNA
• DNA is often wound
around proteins, coiled
into strands, and
bundled up even more.
• Cell’s without a nucleus
the DNA forms loose
loops within the cell.
• Cell’s with a nucleus the
DNA and proteins are
bundled into
chromosomes.
When are copies made?
• DNA is copied every time a cell divides.
• The job of unwinding, copying and re-winding
the DNA is done by proteins within the cell.
Unraveling DNA
• The structure of DNA allows
it to hold information.
• The order of the bases is
the code that carries the
information.
• A gene consists of a string
of nucleotides that give the
cell information about how
to make a specific trait.
• Humans have over 30,000
genes.
• 2003 Human Genome
Project
Unraveling DNA- Quiz
• Where is the DNA in
your cells?
• How does so much DNA
fit into the nucleus?
• What is the name for
strands of DNA wound
around proteins?
• When do chromosomes
become visible in cells?
• What are chromatids?
• In the nucleus
• It is coiled up tightly
around proteins
• Chromatin
• When the cell is about
to divide
• Two identical copies of
a chromosome that is
about to divide
Genes and Proteins
• DNA code is read like a
book, from one end to the
other and in one direction.
• Bases form the alphabet of
the code.
• Groups of 3 bases are code
for the amino acid profile.
(example: AGC)
• A long string of amino acids
forms a protein.
• Each gene is usually a set of
instructions for making a
protein.
Proteins and Traits
• Proteins are found
throughout cells and
cause most of the
differences that you see
among organisms.
• Proteins act as chemical
triggers and messengers
for many processes within
the cell.
• A single organism may
have thousands of genes
that code for thousands
of proteins.
Help from RNA
• RNA (ribonucleic acid) a
molecule that is present
in all living cells and
that plays a role in
protein production
• Helps in the process of
changing the DNA code
into proteins
Making of a Protein
• Step 1: A copy is made
of one side of the DNA
segment where a
particular gene is
located. This copy is
transferred to the
cytoplasm.
Making of a Protein
• Step 2: This mirror like
copy of a DNA segment
is called messenger RNA
(mRNA).
Messenger RNA copies
the coded message from
DNA in the nucleus , and
carries the message to the
ribosome in the
cytoplasm.
Making of a Protein
• Step 3: Each group of
three bases on the
mRNA segment codes
for one amino acid.
Making of a Protein
• Step 4: The mRNA
segment is fed through
the ribosome. A
ribosome is a cell
organelle composed of
RNA and protein.
Making of a Protein
• Step 5: Molecules of
transfer RNA (tRNA) deliver
amino acids from the
cytoplasm to the ribosome.
Transfer RNA (tRNA)
transfers amino acids to the
ribosome and adds them to
the growing protein.
Making of a Protein
• Step 6: The amino acids
are dropped off
at the ribosome.
Making of a Protein
• Step 7: The amino acids
are joined to make a
protein. Usually, one
protein is produced for
each gene.
Animated mRNA
• http://highered.mcgrawhill.com/sites/0072943696/student_view0/ch
apter3/animation__mrna_synthesis__transcri
ption___quiz_1_.html
How is RNA different from DNA?
• RNA: one strand
contains uracil instead of
thymine
A, G, C, U
• DNA: two strands
A, G, C, T
Changes in Genes
•
•
•
•
•
•
•
Mutation: a change in the
nucleotide-base sequence of a gene
or DNA molecule
Either deletion, insertion or
substitution
Causes an improved trait, no change
or harmful trait
If the mutation occurs on the sex
cells, the mutation can be passed to
the next generation
Mutations happen often
Mutagens are any physical or
chemical agent that can cause the
mutation (examples: UV radiation, X
rays, cigarette smoke)
Examples are Cystic Fibrosis, Sickle
Cell Anemia, Hemophilia, Down
Syndrome
Example of Substitution
• Sickle Cell Anemiaaffects red blood cells.
When Valine is
substituted for glutamic
acid in a blood protein.
The change in shape
isn’t good for the cell to
carry oxygen and clot in
vessel (very painful).
Genetics
• Genetic Engineering: Manipulate individual genes to
create new products, such as foods, drug or fabrics
• Genetic Identification: DNA is your unique fingerprint,
only identical twins share DNA
Clone: a new organism that has an exact copy of another
organism’s genes.
• Selective breeding: A technique to produce offspring
with desirable traits.
Inbreeding: cross two genetically similar (male/female
plump turkey)
Hybridization: cross two genetically different (mcintosh
and red delicious apple to get an empire)
Web sites…..
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
DNA and Genetics:
http://www.pbs.org/wnet/dna/episode1/index.html#
http://www.pbs.org/wgbh/aso/tryit/dna/
http://learn.genetics.utah.edu/content/begin/dna/
http://www.biology.arizona.edu/human_bio/activities/karyotyping/karyotyping.html
http://www.mesacc.edu/~tinhw34501/psquare.pdf
http://www.nature.ca/genome/05/051/0511/0511_m205_e.cfm
http://www.pbs.org/wgbh/nova/body/sequence-DNA-for-yourself.html
http://www.pbs.org/wgbh/aso/tryit/dna/shockwave.html
Genetics:
http://pbskids.org/dragonflytv/games/game_dogbreeding.html
http://www.worldwildlife.org/sites/inner-animal/index.html
http://anthro.palomar.edu/mendel/mendel_2.htm
http://www.athro.com/evo/gen/punexam.html
http://www2.edc.org/weblabs/Punnett/punnettsquares.html
http://biology.clc.uc.edu/courses/bio105/geneprob.htm
http://www.cellsproject.org/examples/sc/page23.html
http://glencoe.mcgraw-hill.com/sites/0078778066/student_view0/chapter5/math_practice.html
http://anthro.palomar.edu/mendel/mendel_1.htm
http://www.biology.arizona.edu/Mendelian_genetics/mendelian_genetics.html
http://www.ndsu.edu/pubweb/~mcclean/plsc431/mendel/mendel1.htm
http://www.pbs.org/wgbh/nova/body/cracking-the-code-of-life.html