Protein

Gene

• An organic compound made up of one or

more polypeptides

• Composed of a combination of amino acids

• Each type of protein consists of a different

number of and a different combination of

the 20 known amino acids

• Important structural components of cells

• Enzymes are proteins that control the

chemical reactions of the body and regulate

cell growth

• A segment of DNA that controls the

production of a protein

Gene Expression

• The process of transferring genetic material

from DNA into a protein

– Turning the “code” into something

2 Parts:

1. Transcription

– Information on a DNA molecule is copied onto

an RNA molecule

2. Translation

– RNA molecule directs the synthesis of a protein

Check out the cool video animation entitled:

“Transcription”

Transcription

Reading Frame

• Copying the info of a segment of DNA (a

single gene referred to as the transcription

unit) onto a messenger RNA (mRNA)

molecule that can be used in the cytoplasm

• The way in which DNA is “read”

• The genetic code on DNA must be ordered

in such a way that it can be read accurately

and consistantly

• Genetic info is encoded in DNA as a

sequence of non – overlapping base

triplets

• Sequence must remain constant with a

recognizable starting and ending point

Step #1:

Initiation

1. Transcription Factors bind to the

TATA Box in the promoter region (also

called enhancer region) located just before

the gene to be transcribed (the transcription

unit)

2. RNA Polymerase recognizes the promoter

region and binds to the Transcription

factors forming a transcription complex

3. RNA Polymerase will bind to ONE strand

of the double stranded DNA

– This strand is called the template or

anti – sense strand and is transcribed

– The other strand is called the coding or sense

strand and is not transcribed BUT it will have

the same base sequence as the RNA

Step #2:

Elongation

1. RNA Polymerase reads the DNA in

groups of 3 nucleotides called DNA

triplets

2. RNA Polymerase reads the DNA in the 3’

to 5’ direction and creates the mRNA in

the 5’ to 3’ direction

3. RNA Polymerase will then synthesize a

series of complimentary “triplets” of RNA

nucleotides called codons

– Each codon is a code for a specific amino acid

that will go into the protein once it’s assembled

– The order of the codons determine the order of

the amino acids in the protein

– In many cases, a specific amino acid is coded

for by more than one codon

4. RNA Polymerase moves along the reading

frame of the DNA template reading 3 bases

at a time and adding RNA nucleotides to

the growing mRNA molecule

5. As the mRNA molecule grows it peels

away from the DNA template strand and

the DNA recoils behind it.

Step #3:

Termination

• Transcription will continue until the RNA

Polymerase reaches a “termination site”

on the DNA template

• This sequence will cause the creation of the

codons:

UAA UAG or UGA

• These are stop codons

Step #4:

mRNA processing

• RNA Polymerase and mRNA separate from

the DNA template

• A special nucleotide sequence is added to

both ends of the new mRNA

• A complex of enzymes and nucleic acids cut

out all of the introns and joins the ends of

the exons

• The finished mRNA is then transported from

the nucleus into the cytoplasm

Want to see Transcription in Real Time?Check out the cool video animation entitled:

“Transcription

In Real Time”