Molecular Biology

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Molecular Biology
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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.
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Many other experiments showed DNA, not the
protein, contains info. The DNA in one
cell has ALL the info needed to make you!
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Watson and Crick discovered that DNA looks like a
spiral staircase and called it a Double Helix
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Review

• What is a polymer? Monomer?

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Review

• Molecules make chains (polymers) too

One nucleotide monomer
Many nucleotides DNA polymer
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Review

• Which molecules make chains?

DNA chain of nucleotides
RNA chain of nucleotides
Protein chain of Amino acids
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II. What is DNA

• Shape Double Helix -
• - made of two chains of nucleotides referred
  to as strands
• - chains are twisted together in a spiral

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II. What is DNA

• Structure

DNA Nucleotides are made up of
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II. What is DNA

• Structure

The order of the bases in the chain is called the
sequence.
How many nucleotides? How many chains?
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II. What is DNA
Everyone has a unique sequence!
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II. What is DNA

• Structure

Once a chain is built is it used as a template to
build a second chain
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II. What is DNA

• Structure

MUST FOLLOW CERTAIN RULES!
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II. What is DNA

• Structure

Bases that pair up are called complementary
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II. What is DNA

• Structure

Strong covalent bonds hold nucleotides together.
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II. What is DNA

• Structure

Weak hydrogen bonds hold the chains together
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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

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III. Replication

• Before replication.
• Think of DNA as a Closed zipper.

Covalent bonds
Hydrogen bonds
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III. Replication

• Step 1 Unzip the Zipper
• Helicase breaks
• Hydrogen Bonds
• between chains -
• Opens the zipper

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III. Replication

• Step 2
• Each chain of nucleotides is used to build a two
  new chains using the enzyme DNA polymerase

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III. Replication

• Step 2
• Still must follow complementary base pair rules
• A binds with T
• G binds with C

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III. Replication
There are many links to Replication animations on
our unit resource page!! Use these to help you
understand!
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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
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DNA is used to make RNA, too

• So first a little about RNA.

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IV. Structure of RNA

• RNA is a nucleic acid
• RNA is made of nucleotides
• Single strand (chain) of nucleotides

A
G
U
C
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IV. Structure of RNA

• The sugar in RNAs nucleotide is Ribose
• Bases are A, G, C and Uracil
• RNA contains information
• RNA contains 1 recipe

A
G
U
C
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IV. Structure of RNA

• RNA is temporary and unstable

A
G
U
C
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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

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V. Transcription

• Uses DNA to make a chain of RNA
• Only copies one recipe at a time. Each recipe is
  called a gene!

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V. Transcription

• Step 1 Open DNA zipper
• Just like replication we first need to separate
  the DNA strands

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V. Transcription

• Step 2 Make the RNA
• Using same pairing rules copy one chain of DNA
  into RNA
• As in the DNA will pair with Us in the RNA!!

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V. Transcription
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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!

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V. Transcription

• Replication and Transcription need DNA so where
  do they take place?
• - Where do we
• Make protein?

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V. Transcription

• So if we need the mRNA to make protein, what has
  to happen after we transcribe it?

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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.
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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

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VII. Genetic Code
Think of the genetic code as a Nucleotide to
Amino acid dictionary
Codon 1
Codon 2
G
C
G
A
U
A
G
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VII. Genetic Code
Every three bases of the mRNA is called a Codon
Codon 1
Codon 2
G
C
G
A
U
A
G
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VII. Genetic Code
Each Codon translates to a different Amino Acid.
- cell reads codons to make protein
Codon 1
Codon 2
G
C
G
A
U
A
G
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VII. Genetic Code
AUG is always the first codon means Start
here! GGC means now go get glycine UAG means
Stop! Youre done!
Codon 1
Codon 2
G
C
G
A
U
A
G
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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
G
C
G
A
U
A
G
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VII. Genetic Code
For each codon there is a tRNA with a
complementary Anticodon
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VIII. Translation
Cell reads codons to make a particular chain
(sequence) of amino acids - a chain of amino
acids is a PROTEIN
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VIII. Translation
Watch the animations and tell me what is happening
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VIII. Translation
Step 1 mRNA lines up to be read by ribosome
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VIII. Translation
Step 2 tRNAs with anticodons that are
complementary to codons line up
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VIII. Translation
Step 3 Amino Acid 1 is linked to amino acid 2
with a peptide bond
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VIII. Translation
Step 4 empty tRNA leaves and Ribosome shifts to
a new codon
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VIII. Translation
Step 5 steps repeat until stop codon is reached
AA2
AA1
G
G
C
G
A
A
G
U
U
A
G
C
U
A
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VIII. Translation
Step 5 steps repeat until stop is reached
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VIII. Translation
Step 6 protein is released
STOP
C
C
A
G
G
C
G
A
A
G
U
U
G
A
G
C
U