Download 8.4 Transcription

8.4
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8.4 Transcription
2.1 Atoms, Ions,
and Molecules
•Topic: 8.4 Transcription
1.
2.
•Essential Question:
1. What is the central
dogma?
2. Why can an mRNA
strand made during
transcription, be
thought of as a mirror
image of the DNA
strand from which it
was made?
What is the central dogma?
Why can an mRNA strand made during
transcription, be thought of as a mirror image of
the DNA strand from which it was made?
KEY CONCEPT
Transcription converts a
gene into a singlestranded RNA molecule.
8.4 Transcription
On Your OWN: The Central Dogma
P.4
Draw fig 8.10 (pg.239)- color code
• Red
• Blue
• Green
Make a double-bubble map
comparing and contrasting
DNA and RNA (239-240)
3.2 Cell Organelles
REVIEW:
rough endoplasmic
reticulum
Have bumps called
ribosomes which
link amino acids together
to form
proteins
8.4 Transcription
Proteins are used for movement, eyesight,
and digestion and practically everything
else you do.
8.4 Transcription
KEY CONCEPT
Transcription converts a gene into a single-stranded
RNA molecule.
RNA
DNA
8.4 Transcription
Connect
• Suppose you want to play skeeball at a arcade. The
game only takes tokens, but you only have quarters.
What do you do?
– You exchange your quarters for tokens.
• In a similar way, your cells cannot
make proteins from DNA.
• They must convert the DNA into
RNA in order to make proteins
• This process is known as transcription
8.4 Transcription
RNA carries DNA’s instructions.
• The central dogma
states that
information flows in
one direction from
DNA to
RNA to
proteins.
8.4 Transcription
•
The central dogma includes three processes.
1. Replication
•
Copies DNA
replication
2.Transcription
•
•
•
Converts DNA into
RNA
RNA is a link between
DNA and proteins
“quarters tokens”
transcription
translation
3.Translation
•
Interprets an RNA
message into a string
of amino acids that will
make up a protein
8.4 Transcription
• Protein Synthesis: the process whereby biological cells
generate new proteins. Includes DNA replication,
transcription, and translation.
8.4 Transcription
Location of Protein Synthesis
• Prokaryotic cells: replication, transcription, and
translation all occur in the cytoplasm (remember there is
no nucleus), at approx the same time
• In Eukaryotic cells, where DNA is located inside the
nucleus, these processes are separated by location and
times.
– Replication and transcription occur in the nucleus
– Translation occurs in the cytoplasm
8.4 Transcription
• RNA differs from DNA in three major ways.
RNA
Ribose Sugar
Uracil (U)
Single-Stranded
Please add a
drawing to each
side of your
double-bubble
map
DNA
Deoxyribose Sugar
Thymine (T)
Double-Stranded
8.4 Transcription
• RNA is similar to DNA in a few ways
– Both are a chain of nucleotides
– Each is made of a sugar, a phosphate group, and a
nitrogen containing base
– Each has A, C, & G
8.4 Transcription
Protein Synthesis Video
• Transcription 2m50s
8.4 Transcription
• Transcription copies specific genes from DNA to make a
complementary strand of RNA.
– Only a gene, NOT the entire DNA strand is transcribed
8.4 Transcription
To transcribe is to make a copy of DNA into a complementary
messenger RNA strand
8.4 Transcription
Get out 3 Colors and MAKE A KEY on the top of your
handout
-DNA
-RNA
- Transcription Complex (RNA Polymerase)
8.4 Transcription
1. RNA polymerase and other proteins, (which we call a
transcription complex) recognize the start of a gene and
unwind a segment of it.
transcription complex
start site
nucleotides
8.4 Transcription
Why must the DNA strands unwind and separate before
transcription can take place?
– The bases must be exposed so that the DNA can be read
transcription complex
start site
nucleotides
8.4 Transcription
2. RNA polymerase, using the DNA as a template, strings
together a “complementary” strand of RNA
• Uracil bonds with Adenine U=A (no Thymine)
• The DNA helix winds again as the gene is transcribed.
RNA
DNA
RNA polymerase
moves along the DNA
8.4 Transcription
How does the base sequence of the RNA transcript being
formed compare with the sequence on the template strand?
• It is complementary
RNA
DNA
RNA polymerase
moves along the DNA
8.4 Transcription
Transcription Practice
Transcribe this DNA strand into a mRNA strand
*Remember: No Thymine. Instead use Uracil. A=U
DNA
AAA TAG GAT ATC GGA TAC AGT
RNA
UUU AUC CUA UAG CCU AUG UCA
8.4 Transcription
3. The RNA strand detaches from the DNA once the gene is
transcribed.
• The transcription complex falls apart
• DNA re-zips
RNA
8.4 Transcription
Where will the RNA transcript go after it separates from the
DNA in step 3?
• It is processed and LEAVES the nucleus, heads to the
cytoplasm
RNA
8.4 Transcription
• Transcription makes three types of RNA.
– Messenger RNA (mRNA) which has been transcribed
from the DNA, carries the message that will be
translated to form a protein.
– Ribosomal RNA (rRNA) forms part of ribosomes where
proteins are made.
– Transfer RNA (tRNA) brings amino acids from the
cytoplasm to a ribosome.
make a Replication vs. Transcription Double
8.4Please
Transcription
Bubble (bottom of pg. 4)
Pg. 242 in book
• Transcription and replication are similar, but have different
end results. Please create a double-bubble map comparing
and contrasting the two processes.
– Replication copies
all of the DNA
– Transcription copies
a specific gene.
one
gene
– Replication makes
one copy (only happens once)
– Transcription can make many
copies (happens almost continuously)
growing RNA strands
DNA
8.4 Transcription
Similarities between DNA replication and Transcription?
•
•
•
•
•
Occur within the nucleus
Both are catalyzed by enzymes
Both unwind DNA
“complementary” base pairing
Highly regulated (very carefully done- we want NO
mistakes)
Differences?
• End results are different
• Replication makes an identical copy of ALL of the DNA
• Happens only once during the cell cycle
• Transcription only makes a complementary strand of segments
of DNA
• Can happen over and over again at anytime
8.4 Transcription
Practice
DNA
A T C G A A A T C G G G A T T
RNA
U A G C U U U A G C C C U A A