DNA

1 DNA

This lecture will discuss various factors relating to the structure, properties, and uses of deoxyribonucleic acid (DNA).

Purpose

Structure

Replication

Applications
- DNA Fingerprints
- Genetic Diseases
- Cloning
- Genetically-Modified Foods

2 Size considerations

The following is known about human DNA.

If stretched out, the DNA in a single cell would be ~ 2 meters long.

DNA is divided between 23 chromosomes

Our DNA contains ~ 30,000 genes
- (Based on Human Genome Project - text states ~ 100,000)

3 DNA's Purpose

DNA contains our ``genetic code'' - inherited physical traits.

What is known.
Certain nucleotide sequences carry the ``code'' for synthesis of proteins

What is unknown.
98% DNA is either ``junk'' or (more likely) we don't what is does.

See article by Tom Bethell in The American Spectator, April 2001.

4 Nucleotides

Nucleotides are composed of one of four different nucleic acid bases, a sugar derivative, and a phosphate group.

5 DNA Structure

DNA is composed of four types of nucleotides:

For more information, see Nucleic Acids Handout.

6 Base Pairs

Adenine is always paired with Thymine (A-T pair).

Cytosine is always paired with Guanine (C-G pair).

7 Double Helix

8 Polymerase Chain Reaction

PCR is a method for synthesizing identical copies of DNA from a very small sample.

The General procedure is as follows.

A DNA molecule is heated to separate into two strands.

Free nucleotides (and primer) added to synthesize complementary strands.

Repeat as needed.

9 DNA Fingerprinting

Collect DNA from ``crime scene''.

Use PCR to create large quantities of identical copies of DNA.

Cut into small pieces using Restriction Enzymes

Separate pieces based on size using Gel Electrophoresis

10 DNA Fingerprint Sample

See also text Figure 12.15 (p. 479)

11 RNA

RNA is used primarily for protein synthesis.

There are three different types of RNA.

messenger RNA (mRNA) - transcribes (copies) genetic code from DNA.

transfer RNA (tRNA) - transports amino acids to the site of protein synthesis.

ribosomal RNA (rRNA) - responsible (along with some protein) for translating the DNA code into an amino acid sequence for protein synthesis.

12 Protein Coding

Problem:

Only four nucleotides to code for 20 amino acids

Solution:

Use more than one.

(Analogous to 26 letter alphabet ® all known word)

It requires a three-nucleotide sequence to code for all 20 amino acids.

(There are actually 64 ways to arrange three nucleotides)

13 Genetic Disease

Relatively rare

Error in DNA ® synthesis of ``bad'' protein

Usually ``triggered'' by something

Examples include Down's syndrome, ALS, ...

14 Insulin Production

Insulin contains 51 amino acids.

Laboratory synthesis too difficult.

Insulin obtained from:

Cows

Pigs

Bacteria (See text Figure 12.12, page 472)

15 Cloning

A clone is, genetically speaking, an exact duplicate. The DNA of clones is identical.

Laboratory Procedure

Extract nucleus (containing DNA) from egg cell.

Replace with DNA from ``source''

Allow egg cell to grow normally

16 Why Clone?

Pro

Excellent ``controls'' for laboratory experiments

Production of organisms with desirable properties.

Con

Hard

DNA used is ``old'' (adult DNA different than infant DNA)

ethical ?

17 Genetically-Modified Organisms

Less drastic than cloning.

Pro

Confers desirable properties on organism

Con

Health effects unknown

File translated from T_EX by T_TH, version 3.02.
On 13 Nov 2001, 15:45.