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I. History of DNA
• T.H. Morgan showed that differences
in chromosomes determined fly traits
• What are chromosomes made of???
DNA and Protein.
Many other experiments showed
DNA, not the protein, contains info.
The DNA in one cell has ALL the info
needed to make you!
Watson and Crick discovered that
DNA looks like a spiral staircase
and called it a Double Helix
Lots and
lots of math
X-ray diffraction
3D model
Review:
What is a polymer? Monomer?
Review:
Molecules make chains (polymers) too
One
nucleotide =
monomer
Many nucleotides
= DNA = polymer
Review:
Which molecules make chains?
DNA – chain of nucleotides
RNA – chain of nucleotides
Protein – chain of Amino acids
II. What is DNA
Shape: Double Helix - made of two chains
of nucleotides; referred
to as “strands”
- chains are twisted
together in a spiral
II. What is DNA
Structure:
DNA Nucleotides are made up of:
A sugar - deoxyribose
A Nitrogen base – A,
T, G or C
A phosphate
Nucleotide
II. What is DNA
Structure:
The order of the bases in the chain
is called the sequence.
A
G
T
C
How many
nucleotides?
How many
chains?
II. What is DNA
Everyone has a unique sequence!
A
G
T
C
II. What is DNA
Structure:
Once a chain is built is it used as a
template to build a second chain
A
T
G
C
T
A
C
G
II. What is DNA
Structure:
MUST FOLLOW CERTAIN RULES!
A
T
G
C
T
A
C
G
II. What is DNA
Structure:
Bases that pair up are called
complementary
A
T
G
C
T
A
C
G
II. What is DNA
Structure:
Strong covalent bonds hold nucleotides
together.
A
T
G
C
T
A
C
G
II. What is DNA
Structure:
Weak hydrogen bonds hold the chains
together
A
T
G
C
T
A
C
G
III. Replication
• Making an exact
copy of ALL of the
DNA
• Every time a cell
divides to make
more cells, it must
copy its DNA
III. Replication
Before replication….
Think of DNA as a Closed zipper.
Covalent bonds
Hydrogen bonds
III. Replication
Step 1: “Unzip the Zipper”
Helicase breaks
Hydrogen Bonds
between chains Opens the zipper
III. Replication
Step 2:
Each chain of
nucleotides is
used to build a
two new chains
using the enzyme
DNA
polymerase
III. Replication
Step 2:
Still must follow
complementary
base pair rules
A binds with T
G binds with C
III. Replication
There are many links to
Replication animations on our
unit resource page!!
Use these to help you
understand!
III. Replication
What are we left with?
- 1 cell with twice as much DNA
as usual
- Now the cell can split into two
and both have all necessary DNA
DNA is used to make RNA, too
So first a little about RNA….
IV. Structure of RNA
• RNA is a nucleic
acid
• RNA is made of
nucleotides
• Single strand (chain)
of nucleotides
A
G
U
C
IV. Structure of RNA
• The sugar in RNA’s
nucleotide is Ribose
• Bases are A, G, C and
Uracil
• RNA contains
information
• RNA contains 1 recipe
A
G
U
C
IV. Structure of RNA
• RNA is temporary and
unstable
A
G
U
C
IV. Types of RNA
• mRNA – messenger RNA;
– Contains the info to assemble proteins
• rRNA – Ribosomal RNA
–Make up part of the ribosome, where
proteins are made
• tRNA – transfer RNA
- brings Amino Acids to ribosome
V. Transcription
• Uses DNA to make a chain of RNA
– Only copies one recipe at a time.
Each recipe is called a gene!
V. Transcription
• Step 1: Open DNA zipper
–Just like replication we first need to
separate the DNA strands
V. Transcription
• Step 2: Make the RNA
–Using same pairing rules copy
one chain of DNA into RNA
–A’s in the DNA will pair with
U’s in the RNA!!
V. Transcription
G
A
C
U
V. Transcription
• Step 3: Chains of DNA pair up again,
RNA gets kicked out
• Now we have a temporary copy of
one of our recipes!
V. Transcription
–Replication and Transcription need
DNA so where do they take place?
- Where do we
Make protein?
V. Transcription
–So if we need the mRNA to make
protein, what has to happen after we
transcribe it?
VI. Genes
Sections of DNA that contain the recipe
for a single protein.
-
A gene is only active if it gets transcribed
into RNA.
Genes that are not transcribed do not
give you any traits.
After transcription we have:
• The directions to make the protein
• The factory to build the protein
• The building blocks to make protein
• All we need is to translate the
information from “nucleotide” to
“amino acid”
VII. Genetic Code:
Think of the genetic code as a
“Nucleotide to Amino acid” dictionary
Codon 1
Codon 2
VII. Genetic Code:
Every three bases of the mRNA is
called a Codon
Codon 1
Codon 2
VII. Genetic Code:
Each Codon translates to a different
Amino Acid.
- cell reads codons to make protein
Codon 1
Codon 2
VII. Genetic Code:
AUG is always the first codon – means
“Start here!”
GGC means “now go get glycine”
UAG means “Stop! You’re done!”
Codon 1
Codon 2
VII. Genetic Code:
There are 20 different amino acids and
64 codons.
So… Some codons “mean” the same
amino acids (GGC and GGG)
Codon 1
Codon 2
VII. Genetic Code:
For each codon there is a tRNA with a
complementary Anticodon
VIII. Translation:
Cell reads codons to make a particular
chain (sequence) of amino acids
- a chain of amino acids is a PROTEIN
VIII. Translation:
Watch the animations and tell me what
is happening
VIII. Translation:
Step 1: mRNA lines up to be read by
ribosome
VIII. Translation:
Step 2: tRNA’s with anticodons that
are complementary to codons line up
AA1
AA2
VIII. Translation:
Step 3: Amino Acid 1 is linked to
amino acid 2 with a peptide bond
AA1 AA2
VIII. Translation:
Step 4: empty tRNA leaves and
Ribosome shifts to a new codon
AA1 AA2
AA3
VIII. Translation:
Step 5: steps repeat until stop codon is
reached
AA1 AA2 AA3
AA4
VIII. Translation:
Step 5: steps repeat until stop is
reached
STOP
AA1 AA2 AA3 AA4
VIII. Translation:
Step 6: protein is released
STOP