Transcription Notes
Transcription
• Information in DNA is used to
make proteins (specifically in
the bases – A, T, G or C)
• DNA is found in the nucleus
• Proteins are made in the
ribosomes
• DNA is double-stranded and is
too big to leave the nucleus
How does the information on
DNA get to the ribosomes?
• This is where RNA comes in:
• RNA = Ribonucleic acid
• RNA is single-stranded, so it is
smaller and can fit out of the
nucleus
• DNA’s information is copied onto
mRNA (messenger RNA) and
mRNA takes the message to the
ribosome to make proteins
Definition of Transcription
• The process of copying DNA
onto mRNA in order to get
the information from the
nucleus to the ribosomes to
make proteins
Picture of Transcription
Cell Membrane
Nucleus
DNA
mRNA
Ribosomes
RNA VS. DNA
• Single – Stranded Double – Stranded
• Sugar – Ribose
Sugar –
• 4 Bases:
4 Bases:
–
–
–
–
Adenine (A)
Guanine (G)
Cytosine (C)
Uracil (U)
Deoxyribose
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
How is information
copied onto mRNA?
• This process is similar to
replication
• RNA Complementary Base
Pairs are a little different
than DNA Base Pairs
– G–C
– A – U (instead of T)
Steps of Transcription
• Step 1:
• DNA must unwind and unzip.
• The weak Hydrogen bonds
that hold the DNA strand
together in the middle are
broken by an enzyme.
Steps of Transcription
• Step 1 (Picture):
A-T
T-A
C -G
Enzyme unzips
G
C
DNA at the
A
T
WEAK
G
C hydrogen bonds
G
C
Steps of Transcription
• Step #2:
• The DNA strand pulls apart and
free RNA nucleotides (that are
floating around in the nucleus)
begin to pair up with their
complementary nucleotide on
ONE side of the DNA strand with
the help of an enzyme.
Steps of Transcription
• Step #2 (Picture):
A
U
G
A
T
C
G
A
G
G
DNA
A-T
U-A
C-G
G-C
A-T
C
C
mRNA DNA
G
Free RNA
nucleotides
floating in
the nucleus
U
A
C
Steps of Transcription
• Step #3:
• After copying the desired
section of DNA, the mRNA
separates from the DNA strand
• The mRNA (which is singlestranded) now leaves the
nucleus and goes to the
ribosomes to make proteins
Steps of Transcription
• Step #3: (Picture)
A
U
C mRNA single-stranded
G
A
G
G
Steps of Transcription
• Step #4:
• The original DNA zips back
together and stays in the
nucleus
Steps of Transcription
• Step #4 (Picture):
A- T
T– A
C– G
G– C
A -T
G –C
G -C
Original DNA strand
Transcription
Animations
• http://www.stolaf.edu/people/gia
nnini/flashanimat/molgenetics/tr
anscription.swf
• http://wwwclass.unl.edu/biochem/gp2/m_bio
logy/animation/gene/gene_a2.ht
ml
Transcription Simulation
Make sure Biological
Simulations CD is in the
drive