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Structure and Function of DNA
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RNA, whats different from DNA?
RNA has the base uracil (U)
(Instead of thymine (T) in DNA)
The RNA sugar has 2 OH groups vs 1 in DNA
(Ribose vs deoxyribose)
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Names of structures?
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Complementary DNA A-T, C-G RNA A-U, C-G
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What are the structures?
And, which is which?
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Name of structure?
What type of bond is this?
Complementary DNA A-T, C-G RNA A-U, C-G
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Learning check

• Along one strand of a DNA double helix is the
  nucleotide sequence GGCATAGGT.
• Want is the sequence for the other DNA strand?
• ___ ___ ___ ___ ___ ___ ___ ___ ___
• A molecule of DNA contains 2 polymer strands
  called _________ made by bonding many monomers
  called ____________ together. Each monomer
  contains 3 parts __________, _________ and
  _________.
• DNA and RNA are polymers of _______ monomers.
• What type of bond joins the bases of
  complementary DNA strands?

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What is the flow of Genetic Information?
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From DNA
To RNA
To Protein
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In 2 stages
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DNA is transcribed
The result is mRNA
mRNA is then translated
The result is a sequence of amino acids in a
polypeptide
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But, what is the correspondence
Between nucleotides of an RNA
And the amino acids of a polypeptide
What are the 4 types of nucleotides?
DNA ATCG
RNA AUCG
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How do we get to protein?
There are 20 amino acids in protein
Each designated by a single letter
How do the 4 nucleotides specify 20 amino acids?
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Amino acids are identified by triplets of bases
which
Specify all the amino acids
What are the triplets of bases called?
Codons
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The genetic code is

• The relationship between nucleotide sequence
• And amino acid sequence

One DNA codon (3 nt) gt one RNA codon (3 nt) gt
one amino acid
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How is this read?
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Learning check

1. How many nucleotides are necessary to code for a
   polypeptide that is 100 amino acids long?
2. An organisms genetic information is stored
   within the sequence of ___________.
3. The genetic information is transcribed into a
   sequence of ____________.
4. (the answer to 3) are then translated into a
   sequence of ______________.
5. The nucleotide sequence of a DNA codon is GTA.
   The mRNA complementary sequence codon is _____.
6. The above codon codes for the _________ amino
   acid.

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• Did you know that the genetic code is shared by
  all organisms?

All 20 amino acids are common to all living
systems
The code is the same in different species
After genes have been transferred,
(one species to another)
They can be transcribed and translated
What does this allow for?
Mixing genes from various species
Tobacco plant
expressing firefly gene
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Overview
What is the flow of genetic information?
DNA? RNA? Protein
In eukaryotic cells where does transcription
occur?
The nucleus
Where is mRNA synthesized?
The nucleus
Where does translation occur?
The cytoplasm
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What happens to protein as it is made?
It coils
It folds
It forms a 3-D shape
And, several polypeptide chains bind together
What are each of these shapes called?
How do genes control structures and activities of
cells?
Via transcription translation processes
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Learning check

1. Information in a gene is a specific linear
   sequence of ____________ in DNA.
2. The gene serves as a template in ____________.
3. The gene produces a ___________ strand of mRNA.
4. mRNA specifies a linear sequence of ___________.

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The Genetic Basis of Cancer
In recent years, scientists have learned more
about the genetics of cancer
What have they identified?
That cells escape from control mechanisms
This causes changes in some of the cells genes
Or changes in the way certain genes are expressed
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Cancer causing genes
First discovered in a chicken virus
What is a (chicken) virus?
Molecules of DNA or RNA
Surrounded by protein
How do they work?
Become a permanent resident in host cells
And, insert their nucleic acid into DNA
Of host chromosomes
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What happens when they insert into a host cell?
They make the host cell cancerous
Is there something unique about the virus nucleic
acids?
They contain a gene that causes cancer
Called an oncogene (tumor gene)
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In many cases we all have some of these genes
They are called proto-oncogenes
They are normal genes that can become oncogenes
They are found in many animals
They code for growth factors
What do these growth factors do??
They are proteins that stimulate cell division
Or, are others that affect the cell cycle
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What happens when these proteins malfunction?
Uncontrolled cell growth - cancer
What causes the proto-oncogene to malfunction?
A mutation must occur
Several types of mutations can occur
A mutation within a gene
An error in DNA replication many gene copies
The normal location of the gene is changed
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Proto-oncogene
Multiple gene copies
Gene location moved
Gene mutation
oncogene
New promoter
Normal growth stimulating protein, but in excess!
Hyperactive! Growth stimulating protein
In all cases, normal gene expression is changed
gt cell division
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Which cancer is one of the best understood?
Colon cancer
What is the progression of colon cancer?
Begins as an unusually frequent division of
normal-looking cells in the colon lining
Several (4 or more) mutations are needed
Activation of cellular oncogene
And inactivation of 2 tumor-suppressor genes
These mutations result in altered signal
transduction pathways
Then see full-fledged cancer cells
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Typical colon cancer progression - mutations
Count the mutations
Normal cell
Malignant cell
What do the mutations lead to?
Increased cell division
And, structure of cell grossly altered
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Typical colon cancer progression oncogene TSG
Increased cell division
What are the cellular changes?
Growth of benign tumor
Growth of malignant tumor
Tumor-suppressor gene inactivated
2nd Tumor-suppressor gene inactivated
Oncogene activated
DNA changes?
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What are cancer causing agents called?
Carcinogens
What is the carcinogen for these cancers?
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Tobacco
UV radiation
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Microscopic changes that happen when a person
smokes
Normal lung tissue
Abnormal lung tissue

• Ciliated columnar epithelia
• H cilia sweep mucus
• J goblet cell produces mucus
• L basal layer of cells

• Columnar cells becoming crowded out
• Displaced by basal cells
• Fewer cilia, reduced capability
• Chemicals in tobacco toxic to cilia, paralyzing
• Smokers cough

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Exam 3
Next Tuesday, 11/20/07
The exam covers
Chapter 8, Mitosis Meiosis
Chapter 10 Structure / Function of DNA
Some cancer
Pages 128-129 211-215