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
DNA (deoxyribonucleic acid)a nucleic acid which stores
genetic traits in the proteins it
codes for.
 All living things contain DNA.
 DNA is a nucleic acid.
 Nucleic acids are made of
nucleotide subunits hooked
together.
Nucleotides

Nucleotides- subunits
of DNA made of:
1. Phosphate (PO4)
2. Sugar (deoxyribose).
3. Nitrogen base.
Nitrogen Bases

Four different nitrogen bases
makes four different
nucleotides:
– Guanine
– Cytosine
– Adenine
– Thymine
 These four nucleotides make up
the DNA of almost every single
living thing.
Nucleotides
Chargaff’s Rule

He measured amounts of each base
in various organisms and found:
 % of adenine (A) = % thymine (T)
% of cytosine (C) = % guanine (G)
 Chargaff’s rule told us that A
bonds to T and C bonds to G
 If 20% of strand is A, what %T?
%C?
Structure of DNA

Discovered by Watson and Crick
 Double helix- 2 spiral strands of nucleotides
bonded together
Structure of DNA
Siderail
backbone is the sugar
and phosphates of nucleotides
Rungs are the nitrogen bases of
nucleotides
–A----T
–C----G
Hydrogen
bonds between bases
hold two strands together
What is DNA Replication?
Replicate = make “exact” copies.
 DNA replication- copying of DNA so that a cell
made divide
 All DNA must be
replicated before a
cell can divide. Why?

Enzymes and Replication

Helicase- enzyme that
unwinds DNA
 DNA polymerase-enzyme
that moves along each
strand and brings in bases
for new strand copy
DNA Replication

Can be a mistake in replication
 Mutations-change in DNA
 Mutagens- substances that cause mutations
–
–
–
–
X-rays
Toxins
Drugs
UV light, etc.
Mutations

3 types of mutations that can
occur during DNA
replication:
– Insertions -extra
nucleotides
– Deletions –missing
nucleotides
– Substitutions –placement
of wrong nucleotides
 Can be helpful or harmful
mutations.
Insertion
Deletion
Substitution
Most Destructive Mutation?





The bases, A, C, G, and T can be equated to letters
of a “DNA sentence”
THE DOG WAS HOT IN THE SUN
Substitution:
THE DOG WAS NOT IN THE SUN
Insertion?
THE DOG NWA SHO TIN THE SUN
Deletion?
THE DOG ASH OTI NTH ESU N
Why should I care?
How Much DNA Is In OUR Cells?
 Chromosome-strands of DNA coiled tightly
 Human cell has 46 (23 pairs)
 23 from Mom
 23 from Dad
 Other organisms
have different
numbers of
chromosomes
2 Types of Cells

Somatic cells –all body cells except sex cells
 Diploidchromosomes are in pairs
 46=23 pairs for humans
 1 set (23) from mom, 1 set (23) from dad

Gametes - sex cells
 Egg & sperm
 Haploid no pairs (only 23 single chromosomes)

If all body cells contain the same # of
chromosomes, why are all cells so
different?
 Different cells make different proteins due
to different “active” segments of DNA.
– Heart cells make proteins needed for the heart
to work properly
– Brain cells make proteins needed for the brain
to work properly
What is the Purpose of DNA?

DNA stores the genetic
information that codes for
proteins.
 ALL CELL FACTORIES
MAKE PROTEINS!
What is the Purpose of DNA?
Gene-
a segment of DNA that codes for a
protein.
DNA has 1000’s of
genes to make many
different types of
proteins.
Why are proteins
important?
Protein
- polymer of
amino acids
aa—aa—aa—aa—aa—aa—aa—aa = protein
What is the Purpose of DNA?
RNA (Ribonucleic acid)
_____DNA____ vs._____RNA___
Stores the genetic code in
the nucleus
Double stranded
Sugar of DNA nucleotides
= deoxyribose
A, C, G, T
“DNA is DNA”
Found in nucleus only
Transmits the genetic code
to the rest of the cell
Single stranded
Sugar of RNA nucleotides is
ribose
A, C, G, U (uracil) NO T!
Different forms: mRNA,
rRNA, tRNA
Found all over cell
DNA vs. RNA
Part 1of Protein Synthesis:
Transcription

Transcription- copying of DNA to mRNA that occurs
in the nucleus.
 DNA complementary to mRNA
 ATA-CGG-AAT (DNA)
transcription in nucleus
UAU-GCC-UUA
(RNA)
Transcription
cytoplasm
Translation
Part 2 of Protein Synthesis:
Translation:

Translation- converting mRNA to protein which
occurs at ribosomes in the cytoplasm
 mRNA codons
translation by ribosomes
a.a.---a.a---a.a (protein)
cytoplasm
Part 2 of Protein Synthesis:
Translation:
Codon-three bases
of mRNA that code for an amino acid
UAU-GCC-UUA (3 mRNA codons)
translation by ribosomes
a.a.---a.a---a.a. (protein)
mRNA needs the help of tRNA to bring in the amino acids
to be hooked together
cytoplasm
Whole Process
ATA-CGG-AAT
(DNA)
transcription in nucleus
UAU-GCC-UUA (3 mRNA codons)
translation in cytoplasm at ribosomes
a.a.-a.a-a.a.
(protein)
How do we know what amino acid results?
The Codon Wheel!!!
Part #1
Transcription
cytoplasm
Part #2
Translation
The Codon Wheel
***How do we use the wheel? There are 2 clues.
The Codon Wheel
Whole Process
DNA:
ATA-CGG-AAT
transcription in nucleus
mRNA: UAU-GCC-UUA(3 codons)
translation in cytoplasm
protein:
a.a.-a.a-a.a.
tyrosine-alanine-leucine
Protein Synthesis Animation!
How do we know what amino acid results?
The Codon Wheel!!!
Amino Acids

Where do our cells get
these amino acids to build
the proteins?
 From FOOD!
 We eat proteins, then these
proteins are broken down
(metabolized) into amino
acids in our stomach.
 We reuse these amino acids
to build other proteins.