Lesson 4A: Protein Synthesis: Transcription

Question 1

Protein

Answer 1

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

Question 2

Gene Expression

Answer 2

Gene - a segment of DNA that controls the production of a protein

Gene Expression – the process of transferring genetic material from DNA into
a protein

There are two processes involved in gene expression

Transcription – information on the DNA molecule is copied onto an RNA
molecule

Translation – RNA molecule directs the synthesis of a protein

Question 3

Transcription

Answer 3

Copying the information 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.

Occurs in four stages.

Question 4

1. Initiation

Answer 4

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)

RNA Polymerase recognizes the promoter region and binds to the Transcription factors
forming a transcription complex

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

Question 5

2. Elongation

Answer 5

RNA Polymerase will then synthesize a series of complimentary strand of mRNA

RNA Polymerase reads the DNA in the 3’ to 5’ direction and creates the mRNA in the 5’ to
3’ direction

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

As the mRNA molecule grows it peels away from the DNA template strand and the DNA
recoils behind it.

mRNA will always start with the sequence AUG

Question 6

3. Termination

Answer 6

Transcription will continue until the RNA Polymerase reaches a “termination
site” on the DNA template

This sequence will cause the creation of the one of these sequences on the
mRNA:

UAA UAG or UGA

RNA Polymerase and mRNA separate from the DNA template

Question 7

4. mRNA Processing

Answer 7

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