Download Transcription and Translation

Transcription and Translation
Gene Expression
• Information from
DNA is used to
make protein
Gene Expression
• What is the purpose of transcribing DNA
into mRNA?
– mRNA carries the DNA sequence from the
nucleus out into the cytoplasm where protein
is made
• Why do we need to make protein?
– Protein makes up most of the cell’s structure
and machinery to make things work
RNA
• Copied from DNA in the nucleus
• Has ribose instead of deoxyribose
• Complementary bases
– G pairs with C
– A pairs with U
• Single stranded
• Leaves the nucleus to go out into the
cytoplasm
Composition of RNA
• Nitrogen bases
– Adenine
– Cytosine
– Guanine
– Uracil
• Ribose
• Phosphate group
• Sugar-phosphate backbone
Type of RNA
Messenger
RNA
(mRNA)
Ribosomal
RNA
(rRNA)
Function
• Copies the DNA sequence
• Carries the message from the
nucleus out to the cytoplasm where
the protein synthesis occurs
• Central component of ribosomes
• Machinery that makes protein from
the message encoded by mRNA
• Small RNA chain that transfers a
Transfer RNA specific amino acid to the growing
(tRNA)
polypeptide chain during protein
synthesis
RNA Transcription
• Transcription is the
process by which DNA
is copied into mRNA .
• RNA polymerase
makes the mRNA.
• Transcription happens in
the nucleus .
Process of Transcription
•
RNA polymerase has 3 jobs
1. Attach to the DNA
2. Open DNA
3. Add complimentary base pairs to one strand
of the DNA molecule
•
•
The subunits added have ribose instead
of deoxyribose
The subunits added have Uracil in place
of Thymidine
Transcription
• Black strand: coding strand
• Blue strand: template to make mRNA
• Red Strand: newly synthesized mRNA
5’
3’
3’
3’
5’
• Result:
5’
Transcription
• For example:
DNA:
mRNA:
AG C C T G T GAAC
Transcription
• For example:
DNA:
mRNA:
AG C C T G T GAAC
U
Transcription
• For example:
DNA:
mRNA:
AG C C T G T GAAC
UC
Transcription
• For example:
DNA:
mRNA:
AG C C T G T GAAC
UCG
Transcription
• For example:
DNA:
mRNA:
AG C C T G T GAAC
UCGG
Transcription
• For example:
DNA:
mRNA:
AG C C T G T GAAC
UCGGA
Transcription
• For example:
DNA:
mRNA:
AG C C T G T GAAC
UCGGAC
Transcription
• For example:
DNA:
mRNA:
AG C C T G T GAAC
UCGGACA
Transcription
• For example:
DNA:
mRNA:
AG C C T G T GAAC
UCGGACAC
Transcription
• For example:
DNA:
mRNA:
AG C C T G T GAAC
UCGGACACU
Transcription
• For example:
DNA:
mRNA:
AG C C T G T GAAC
UCGGACACUUG
Transcription animation
Transcription Review
• What is transcription?
• Name 3 things that are different between
DNA and RNA.
• What does uracil pair with?
• What is the function of mRNA?
Translation
(Protein Synthesis)
Translation
• the process of making protein from mRNA
– the mRNA sequence determines the amino acid
sequence in the protein
– the protein synthesis machinery includes mRNA,
ribosome and tRNA
Translation
• Takes place in the cytoplasm
• tRNA (transfer RNA) brings amino acids to the ribosome
nucleus
ribosome
Codon
Anticodon
Translation
• Ribosome
– machinery that strings amino acids together to
make protein
• Amino acid
– basic building block of protein
• Peptide bond
– Covalent bond between amino acids in a
peptide (string of amino acids)
Translation
• tRNA – short
strand of RNA
• Codon
– A 3-nucleotide code on the mRNA that
determines the amino acid at that position
• Anticodon
– the complementary 3-nucleotide code on the
tRNA
Translation animation
Read the Codon Wheel
• Start codon – AUG (codes for methionine)
• 3 stop codons
• Start codon – AUG (codes for methionine)
• 3 stop codons - UAG
• Start codon – AUG (codes for methionine)
• Stop codon – UAG, UAA,
Translation
• Start codon – AUG (codes for methionine)
• Stop codon – UAG, UAA, UGA
Process of Translation
1. The mRNA leaves the nucleus through
pores in the nuclear membrane into the
cytoplasm
2. A ribosome attaches to mRNA
3. The ribosome moves along the mRNA to
find the first AUG codon
4. The correct tRNA has the anticodon that
will bind to the codon on the mRNA
5. The correct tRNA bring the amino acids
Process of Translation
6. The codon AUG starts the protein
synthesis, and therefore, methionine is
the first amino acid
7. A tRNA with the UAC anticodon carries
the amino acid methionine
8. The ribosome moves to the next codon
4. The correct tRNA has the anticodon that
will bind to the codon on the mRNA
5. The ribosome
Protein Synthesis
• Determine the amino acid sequence of the
following mRNA using the codon wheel
mRNA:
C GAU GACAC U U UAGAAC
Hint: Find the start codon
Protein Synthesis
• Determine the amino acid sequence of the
following mRNA using the codon wheel
mRNA:
C GAU GACAC U U UAGAAC
Protein Synthesis
• Determine the amino acid sequence of the
following mRNA using the codon wheel
mRNA:
C GAU GACAC U U UAGAAC
Met
Protein Synthesis
• Determine the amino acid sequence of the
following mRNA using the codon wheel
mRNA:
C GAU GACAC U U UAGAAC
Met
-
Thr
- Leu
Protein Synthesis
• Determine the amino acid sequence of the
following mRNA using the codon wheel
mRNA:
C GAU GACAC U U UAGAAC
Met
-
Thr
- Leu
(stop)
• The amino acid chain is released from
ribosome when a stop codon is reached
Protein Synthesis
• Why do we need to make protein?
• How are the amino acids put together in
the correct order?
• How does translation start?
• How does translation end?
Gene Expression