Transcript teachers.oregon.k12.wi.us

Transcription
a.k.a “The RNA Lecture”

Genes in the DNA sequence encode
information about proteins and how those
proteins are assembled
nucleus
– DNA is stored in the _______________
ribosome
– Proteins are made at the ____________
Does anyone see a problem?

DNA never leaves the nucleus and the ribosomes never
enter the nucleus.
NUCLEUS
DNA
Ribosome

Key Point: If the cell wants the information stored in
DNA to be expressed as protein, we need to have a
messenger take the information from the nucleus to
the ribosome.

The messenger that the cell uses is called
RNA

Ribonucleic Acid

BASES
a. Cytosine
b. Guanine
c. Adenine
d. Uracil

SUGAR
Ribose
Yes, there is
still a phosphate


# of strands =
1

DIFFERENCES BETWEEN DNA AND RNA
Strands
Sugar
Bases
Where in a
cell?
DNA
RNA
2
1
Deoxyribose
Ribose
A, T, C, G A, U, C, G
Only in
nucleus
Nucleus,
cytoplasm,
ribosome

HOW IS RNA MADE?
Transcription – video link

What must be present during transcription?
a. DNA gene
gene – DNA sequence which
codes for a protein
b. ribonucleotides
c. RNA Polymerase

What are the steps of transcription?
a. DNA separates at gene
b. RNA polymerase
transcribes gene
strand to RNA
c. DNA strands
reconnect; RNA
leaves for ribosome
A–T
T–A
G–C
A–T
C-G
DNA is
A
T
A– U
-T
T
A
T– A
-A
G
C
G– C
-C
A
T
A– U
-T
C
G
C– G
-G
Gene
unzipped
Copy
Gene strand is
transcribed
A–T
T–A
G–C
A–T
C-G
DNA strands
reform
double helix
Where does transcription take place?
In the nucleus
How does RNA Polymerase know
where to start and stop transcription?
Starts at a DNA sequence called the “promoter”
Stops at a DNA sequence called the “terminator”
Promoter
Video Links –
Gene
original
new
Terminator
Where does RNA go after transcription?
Heads to ribosome so the code can be used to build
protein
What types of RNA does a cell make?
1. mRNA – messenger RNA; copy of DNA gene
sent to ribosome
2. rRNA – Let’s come back to the rest
later
3. tRNA –
What happens to RNA after it
leaves the nucleus?
The rest of protein synthesis
What happens to mRNA after it leaves
the nucleus and how does mRNA
actually help a cell make proteins?
Translation –
Let’s go to the
animation!
What’s “Met” and “Arg”?
Amino Acids
What are the main steps in translation?
1. mRNA reaches
ribosome
2. Ribosome scans for
a place to start –
“start codon”
Codon – 3
bases in
mRNA which
code for 1
amino acid
ACG =
CGA =
UCG =
What is a codon?
Codon – 3
bases in
mRNA which
code for 1
amino acid
GAU =
AUG =
UAG,
UGA,
UAA =
What is a codon?
What are the main steps in translation?
3. tRNA with correct anticodon brings amino acid to
ribosome
tRNA – transfer RNA; brings
amino acids to ribosome
Anti-codon – 3 bases in tRNA;
complimentary to codon
Ex. Anti-codon = AUG, codon =
UAC
What are the main steps in translation?
4. tRNA with correct
anticodon for next
codon brings its
amino acid into place
5. Peptide bond forms
between amino acids
What are the main steps in translation?
6. Process continues
until ribosome
reaches a stop codon
What happens to proteins after they are
synthesized?
Proteins for inside of cell:
- Folded into correct shape in cytoplasm
Proteins for outside of cell:
- Folded into correct shape in ER
- Further processed by Golgi Body
- Exported from cell by exocytosis