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Chromosomes and DNA
• Each chromosome contains a long
strand of DNA
• Body cells contain 23 pairs of
chromosomes
Chromosomes and DNA
DNA carries the code that controls
what cells are made of and what they do
• The rungs of the DNA
ladder are made from pairs
of bases
• There are four bases
• These bases always pair together in the
same way
• How do you think the four bases pair
up?
A always pairs with T
C always pairs with G
DNA and Protein Synthesis
• DNA contains the genetic
information to
make amino acids
• Amino acids combine to make
proteins
• These proteins determine the
physical traits
of an organism and control cellular
functions.
DNA and Protein Synthesis
• Codon: three bases code for a specific protein:
ex: AAA = Lysine
• The codons code for 20 amino acids
• Just like the alphabet has 26 letters to make all
the words we know, the 20 amino acids make
all the different proteins found in living
organisms
• The codons are the template for protein synthesis,
which takes place on the ribosomes (rRNA) in the
cytoplasm
DNA and Protein Synthesis - Transcription
Transcription:
1) DNA unzips
2) mRNA (messenger ribonucleic acid) copies info
from DNA using base pairings
•
RNA is different from DNA
a) Single stranded, not double stranded
b) Instead of deoxyribose, it has ribose
c) instead of Thymine, it uses Uracil
3) Carries the genetic code from the nucleus to the
ribosome in the cytoplasm
 The amino acids join together to form a
protein
 We need proteins to make and repair
cells
 Proteins are made in the cytoplasm
DNA and Protein Synthesis
• Amino acids are linked together in the same
order as the codons , creating a protein chain
• Just like linking letters to make words, linking
amino acids makes proteins
mRNA
CUA AUG UGC
Amino
Acid
Amino
Acid
Amino
Acid
DNA Mutations

What is a mutation?
1)
Change in the DNA of a gene.
2) When a cell puts its genetic code into action it is
making precisely the proteins it needs for its
structure and function.
3) If something changes a gene’s code words, the
resulting protein may change.
4) If the protein is central to the cell’s architecture
then a mutation could result in an abnormal cell.
DNA and Mutations
Mutations are any changes that take place in DNA:
• Can be spontaneous or caused by mutagens
• ex: Chemicals, high temperatures, UV light,
radiation
• Can change the genetic code, and be replicated
when forming new body cells.
• In sex cells, can be passed on to offspring.
• Mutations can be neutral, beneficial, or harmful
• ex: Blue eyes – a mutation that occurred 610,000 years ago, can be traced back to one
ancestor
• what kind of mutation is that?
Types of Gene
Mutations
1) Substitution- can be a simple substitution in one base
of the gene sequence.
For example:
Original: CAC GCC ATT GCG ATG
Mutation: CAC GCC ATG GCG ATG
One amino acid will replace another in this type of
mutation thereby altering the resulting protein.
DNA and Mutations – Lets looks at different mutations
THE DOG BIT THE CAT
DNA and Mutations - Substitution
THE DOG BIT THE CAT
• Substitution - Replace just one letter:
THE DOG BIT THE CAR
Types of Gene
Mutations
1) A Substitution is a Point Mutation
Because it occurs at only one base in the DNA Strand.
Types of Gene Mutations
Remember that DNA sequences are read in groups of
three (codons) so we can use a simple sentence to
demonstrate a substitution.
Original –
The Fat Cat Ate The Wee Rat
Substitution – The Fat Hat Ate The Wee Rat
Where did the substitution occur?
The letter “C” in Cat was changed to an “H”
Gene Mutations –
Substitutions: Sickle Cell
Anemia
Sickle Cell Anemia is a disease of red blood cells.
Codon for glutamic acid has been changed to code for valine
because of a substitution in one codon in the gene for the
protein hemoglobin.
Four hemoglobin proteins carry oxygen inside red blood cells.
The change in the amino acid causes the hemoglobin to fold
abnormally causing a sickle shaped red blood cell.
Sickle Cell Anemia
The mutation affects the folding and
stability of the hemoglobin protein
Frameshift MutationsInsertions and Deletions
1)
Insertions and Deletions can be point
mutations
2) One or several base pairs are inserted into a
gene or deleted from it.
3) This results in a shift in the reading frame or
“frameshift”.
4) Therefore insertions and deletions are called
“frameshift mutations”
DNA and Mutations - Deletion
THE DOG BIT THE CAT
• Deletion: Delete just one letter (T):
THE DOG BIT HEC AT
DNA and Mutations-Insertions
THE DOG BIT THE CAT
• Insertion - Add just one letter (E):
THE DOE GBI TTH ECA T
Cells have “proof reading” proteins that constantly
check the DNA and fix errors, so most are corrected
Frameshift Mutations
Frame- Shift Mutation in DNA can be demonstrated
with a simple sentence.
Original –
Frame Shift –
The Fat Cat Ate The Wee Rat
The Fat CaA teT heW eeR at.
Which letter (base) was deleted?
The letter “t” in CAT.
Deletions
Some times whole sections of genes are deleted.
Original –
Deletion–
The Fat Cat Ate The Wee Rat
The Fat Ate The Wee Rat
Where did the deletion occur?
The word “Cat” was deleted.
Insertions (Duplications and Tandem
Repeats)
Sometimes whole sections of genes are inserted.
Original – The Fat Cat Ate The Wee Rat
Insertion–
The Fat Cat Cat Ate The Wee Rat
a duplication or….
Original – The Fat Cat Ate The Wee Rat
Insertion– The Fat Cat Cat Cat Ate The Wee Rat
….a tandem repeat (duplication continues through several
generations)
How do Mutations Occur?
1) Can occur spontaneously when
copying errors occur (replication is
fast and there are lots of free
nucleotides around during
replication.)
2) Exposure
to mutagens – mutation
causing agents in the environment
Types of Mutagens
1) Ultraviolet radiation in sunlight –
Skin cancer may result!!!
Types of Mutagens
2)
X-rays
Types of Mutagens
3)


Environmental Agents
Natural or manmade chemicals in the
environment
Many carcinogens or cancer-causing
agents disrupt DNA.
How are mutations fixed?
 Proofreading- cells have built in mechanisms that
catch and repair most of the changes that occur
in DNA.
 Mutations in eukaryotic cells are rare.
 In somatic cells any good or bad consequences will
not be passed on to offspring.
 If a mutation occurs in a gamete it may be passed
to the next generation.
Mutation and Evolution
 A mutation and the protein made from the
mutated gene that is passed from generation to
generation (inherited) can have a beneficial,
harmful, or neutral effect on an organism’s ability
to survive in its prevailing environment.
 Therefore, gene mutations provide the
foundation for change in a population of organisms
– mutations provide the foundation for evolution
by natural selection.
Mutation Practice
Original DNA: TAC CTC GTA AAC CCT TAA GGG ACT
Mutation 1:
TAC CTC GTA CAC CCT TAA GGG ACT
Circle all that apply: Deletion, Addition, Substitution,
Inversion, Duplication