Structure and Function of DNA

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RNA, what’s different from DNA?

The RNA sugar has 2 OH groups vs 1 in DNA

(Instead of thymine (T) in DNA)

(Ribose vs deoxyribose)

RNA has the base uracil (U)

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Complementary = DNA: A-T, C-G; RNA: A-U, C-G

Names of structures?

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What are the structures?

And, which is which?

Complementary = DNA: A-T, C-G; RNA: A-U, C-G

Name of structure?

What type of bond is this?

Learning check

1. Along one strand of a DNA double helix is the nucleotide sequence GGCATAGGT.

Want is the sequence for the other DNA strand?

___ ___ ___ ___ ___ ___ ___ ___ ___

2. A molecule of DNA contains 2 polymer strands called _________ made by bonding many monomers called ____________ together. Each monomer contains 3 parts: __________, _________ and _________.

3. DNA and RNA are polymers of _______ monomers.

4. What type of bond joins the bases of complementary DNA strands?

What is the flow of Genetic Information?

From DNA

To RNA

To Protein

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In 2 stages

DNA is transcribed

The result is mRNA

mRNA is then translated

The result is a sequence of amino acids in a polypeptide

But, what is the correspondence…

Between nucleotides of an RNA

What are the 4 types of nucleotides?

DNA: ATCG RNA: AUCG

And the amino acids of a polypeptide

How do we get to protein?

There are 20 amino acids in protein

How do the 4 nucleotides specify 20 amino acids?

Each designated by a single letter

Amino acids are identified by triplets of bases which

What are the triplets of bases called?

Codons

Specify all the amino acids

The genetic code is

The relationship between nucleotide sequence

And amino acid sequence

One DNA codon (3 nt) => one RNA codon (3 nt) => one amino acid

How is this read?

1. How many nucleotides are necessary to code for a polypeptide that is 100 amino acids long?

2. An organism’s 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.

Learning check

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

Mixing genes from various species

Tobacco plant

The code is the same in different species

After genes have been transferred,

They can be transcribed and translated

(one species to another)

What does this allow for?

expressing firefly gene

All 20 amino acids are common to all living systems

Overview: What is the flow of genetic information?

DNA RNA Protein

In eukaryotic cells where does transcription occur?

Where is mRNA synthesized?

The nucleus

The nucleus

Where does translation occur?The cytoplasm

What happens to protein as it is made?

It coils

It folds

It forms a 3-D shape

And, several polypeptide chains bind together

How do genes control structures and activities of cells?

Via transcription & translation processes

What are each of these shapes called?

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 ___________.

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

Cancer causing genesFirst 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

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)

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

They are proteins that stimulate cell division

What do these growth factors do??

Or, are others that affect the cell cycle

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

Proto-oncogene

Gene mutation Multiple gene copies

Gene location moved

oncogene

Normal growth stimulating protein, but in excess!

Hyperactive! Growth stimulating protein

New promoter

In all cases, normal gene expression is changed => cell division

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 pathwaysThen see full-fledged cancer cells

Typical colon cancer progression - mutations

Normal cell

Count the mutations…

What do the mutations lead to?

Increased cell divisionAnd, structure of cell grossly altered

Malignant cell

What are the cellular

changes?

DNA changes?

Increased cell

division

Growth of benign tumor

Growth of malignant

tumor

Oncogene activated

Tumor-suppressor

gene inactivated

2nd Tumor-suppressor

gene inactivated

Typical colon cancer progression – oncogene & TSG

What are cancer causing agents called?

Carcinogens

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What is the carcinogen for these cancers?

UV radiation

Tobacco

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Microscopic changes that happen when a person smokes

Normal lung tissue

• Ciliated columnar epithelia• H = cilia sweep mucus• J = goblet cell produces

mucus• L = basal layer of cells

Abnormal lung tissue

• Columnar cells becoming crowded out• Displaced by basal cells• Fewer cilia, reduced

capability• Chemicals in tobacco

toxic to cilia, paralyzing• Smokers cough

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