2. Pieces of the Puzzle
Genes
determine the traits of an organism
are passed on from one generation to another
located on chromosomes
Chromosomes are made of
protein
DNA= deoxyribonucleic acid
3. What a Gene Has to Be Able to Do
Supply instructions for cell processes and
building cell structures
Be copied each time a cell divides
4. The Subunits of DNA
DNA is made of only four subunits which
are called nucleotides
Each nucleotide consists of
a sugar
a phosphate
a base
Nucleotides are identical except for the
base
5. The Four Bases
Thymine
Adenine
Guanine
Cytosine
They each have a slightly different shape.
The base is usually referred to by the first
letters in their names: A, T, G, C.
6. Chargraff’s Rules
In the 1950’s, Erwin Chargraff found that
the amount of adenine in DNA always
equals the amount of thymine.
Also the amount of guanine always equals
the amount of cytosine.
These findings are known as Chargraff’s
rules.
7. A Picture of DNA
Rosalind Franklin was able to create
images of DNA molecules using a process
known as X-ray diffraction.
The images that Franklin created
suggested that DNA has a spiral shape.
8. Eureka!
James Watson and Francis Crick were
also investigating the structure of DNA.
Based on Franklin’s image, they
concluded that DNA resembles a twisted
ladder shape known as a double helix.
They used their DNA model to predict how
DNA is copied.
9.
10.
11. Making Copies of DNA
One side of DNA is complementary to the
other.
DNA splits down the middle where the two
bases meet.
The bases can be used as a pattern for a
new complimentary side.
12.
13.
14. More About Traits
Incomplete dominance
Sometimes one trait is not completely
dominant over another
These traits don’t blend together but each
allele has its own degree of influence
15. More About Traits
Genes Influence Traits
Sometimes one gene influences more than
one trait
Some traits are the result of several genes
acting together
16. More About Traits
Importance of Environment
Many things in your environment influence
how you grow and develop
Healthy diet
Exercise
You may have the genes to grow tall but
you won’t reach your full potential height
without the proper nutrients
17. Think/Pair/Share
List and describe the parts of a nucleotide.
Which bases pair together in a DNA
molecule?
If a sample of DNA were found to contain
20 percent cytosine, what % of guanine
would be in this sample? Why?
19. Unraveling DNA
DNA is often wound around proteins,
coiled into strands, and then bundled up
even more. In a cell that has a nucleus,
the strands of DNA and proteins are
bundled into chromosomes.
A gene consists of a string of nucleotides
that give the cell information about how to
make a specific trait.
20.
21. Genes and Proteins
Proteins act as chemical triggers for many
of the processes within cells. Proteins help
determine traits.
Another type of molecule that helps make
proteins is called RNA, or ribonucleic acid.
RNA is so similar to DNA that RNA can
serve as a temporary copy of a DNA
sequence.
22. Protein Synthesis: Transcription
The first step in making a protein is to
copy one side of the segment of DNA
containing a gene. This copy is called
messenger RNA (mRNA).
This copy is identical to the original section
except instead of copying thymine, the
copy has uracil.
After being made, the mRNA moves from
the cell’s nucleus into the cytoplasm.
24. Protein Synthesis: Translation
The mRna is then fed through a ribosome.
The ribosome reads three bases of the
mRNA at a time.
These groups of three bases code for a
specific amino acid. The groups are called
codons.
Transfer RNA (tRNA) delivers amino acids
from the cytoplasm to the ribosome
25. Protein Synthesis: Translation
The amino acids are dropped off at the
ribosome.
As more mRNA is fed through the
ribosome, tRNA brings more amino acids
to drop off. As they are dropped off they
join together.
26. Protein Synthesis: Translation
The ribosome starts reading the mRNA at
the START codon. AUG is almost always
the START codon, especially for
eukaryotes.
Once the ribosome reads the STOP
codon, the amino acids that are joined
together form the protein that the mRNA
was coded to make.
28. Changes in Genes
Changes in the number, type, or
order of nucleotide bases on a
piece of DNA are known as
mutations.
Insertion: Base is added that
wasn’t in original sequence
Substitution: Base that was in
original sequence is replaced
by another
Deletion: Base from original
sequence is removed
30. Mutations
There are three possible consequences to
changes in DNA: an improved trait, no
change, or a harmful trait.
Mutations happen regularly because of
random errors when DNA is copied. Any
physical or chemical agent that can cause
a mutation in DNA is called a mutagen.
Examples: X-rays, UV radiation, asbestos,
chemicals in cigarette smoke
31. Mutants Among Us?
Mistakes during DNA replication are
estimated to occur in 1 of every 10,000
base pairs.
We have built-in DNA checking
mechanisms that catch most of these
mutations and correct them. The final
error rate is as low as 1 in 1 billion.
32. Example of Substitution
A mutation, such as a substitution, can be
harmful because it may cause a gene to
produce the wrong protein.
A simple change in an amino acid can
cause a disease such as sickle cell
anemia. Sickle cells are not as good at
carrying oxygen and also are more likely
to cause dangerous blood clots.
33.
34. Uses of Genetic Knowledge
Scientists can manipulate individual genes
within organisms. This kind of
manipulation is called genetic engineering.
Your DNA is unique, so it can be used like
a fingerprint to identify you. DNA
fingerprinting identifies the unique patterns
in an individual’s DNA. Its two main uses
are identifying evidence in criminal cases
and determining whether people are
35.
36.
37. Think/Pair/Share
What is the function of the ribosome in
protein synthesis?
What are the three types of mutations? What
is a mutagen?
Explain the relationship between genes and
proteins.
What is a codon?
