The History of DNAIn 1953, Watson & Crick

used theX-ray diffraction pictures

made by Franklin to determine the structure of DNA & build a model of its

structure.

What this lead to• 1959: The first human chromosome abnormality, Down

Syndrome, is identified• 1969: Isolated the first gene• 1984: Jeffreys develops genetic fingerprinting• 1989: genetic screening of embryos for their gender• 1993: the first human embryos are cloned• 1994: the first genetically modified food is sold• 1995: PCR and DNA fingerprinting play a role in OJ’s

trial• 1997: Dolly, the sheep, is cloned• 2002: The first cat is cloned

DNA: deoxyribonucleic acid, controls the production of

proteins in the cell.

DNA & RNA are bothpolymers

The repeating subunits of DNA

& RNA

A phosphate

group

A 5 carbon sugar called deoxyribose.

A nitrogen base

The sugar and the

phosphate groups form

the backbone of the DNA molecule

DNA looks like a twisted

ladder. The sides of the ladder are

made of sugar & phosphate.

The “rungs” of the ladder are

bonded pairs of nitrogen bases. The bases are

bonded together by

weak hydrogen bonds.

In RNA only!

The bases on one strand of the DNA molecule are the exact

compliment of the bases on the other strand. Thus, they are

called complimentary strands.

1. Replication begins when the enzyme DNA HELICASE attaches to the DNA molecule

2. DNA helicase unzips the DNA by breaking the hydrogen bonds between the bases.

3. The DNA is separated into 2 strands.

4. The unpaired bases on each strand attract the unpaired complimentary bases that float around in the nucleus.

5. They then form new hydrogen bonds.

6. Two new DNA molecules result from replication, with the EXACT same code.

7. Each is one half of the ORIGINAL DNA double helix.

1. Replication occurs at MANY points of the DNA molecule at once.

A. If not, it would take 3 days

for one DNA molecule to replicate.

B. This way, it only takes 3 minutes to replicate.

DNA contains the information to MAKE proteins but does not actually make it – RNA

does….

Look… no T’sThey are replaced

by U’s

Notice… only one strand…not two like DNA – not a double

helix.

RNA’s sugar is RIBOSE, not

deoxyribose like DNA

mRNA – MESSENGER RNA is a single strand of RNA that copies DNA information during protein

synthesis.

It serves as a TEMPLATE for assembling amino acid

sequences to make proteins.

tRNA – TRANSFER RNA is a single strand of RNA that is folded back on itself like a

hairpin.

There are 20 forms of tRNA that correspond to each of the 20 amino acids which bind to

them.

rRNA – RIBOSOMAL RNA, is RNA in a globular form. They

are ribosomes!Total function is unknown…….

•Is the formation of protein using the information coded on DNA and carried out by RNA

•Protein synthesis has 2 parts: transcription & translation

DNA

RNA

Proteins

To transcribe means to COPY or to write something down.RNA is transcribed from DNA

through this process…..

1. First, the enzyme RNA POLYMERASE opens up the

DNA molecule.

2. Next, RNA polymerase attaches RNA bases floating around in the nucleus to the

DNA bases.

3. The transcription process stops when a termination CODE is reached on the DNA molecule.

4. RNA is then released & the DNA closes back up……..

•All three types of RNA are made this way.

•RNA then leaves the NUCLEUS and enters the cytoplasm.

•joins up with RIBOSOMES and proteins are made.

•The GENETIC code is the system that contains information needed by cells for proper functioning.

•A CODON is a group of 3 sequential mRNA bases that recognize a specific amino acid

•Codons are UNIVERSAL.•Every organism has the same genetic code for proteins………

•For example, UUU is the codon for the amino acid phenylalanine in

mice, men, & bacteria.

Amino acids must be in the proper sequence for proteins to

function properly.

The number of different kinds of proteins varies with the

COMPLEXITY of an organism.

1. MRNA enters the cytoplasm from the nucleus and finds a ribosome to hook up with.

2. tRNA’s then bring specific amino acids to the ribosomes.

3. The ribosome attaches to an AUG (start codon) on

mRNA.

4. TRNA attaches itself to the mRNA and passes its amino

acid off to the growing protein chain.

5. TRNA leaves and another tRNA takes its place with a

new amino acid.

This process continues until a STOP codon is reached and

the protein chain is complete and falls off.

Protein Synthesis Animation

Protein Synthesis Video

http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a3.html

http://vcell.ndsu.edu/animations/transcription/movie-flash.htmhttp://vcell.ndsu.edu/animations/translation/movie.htm

Video