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End Show Slide 1 of 39 Copyright Pearson Biology Biology Protein Synthesis: I will understand the general pathway of transcription and translation
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Transcript of End Show Slide 1 of 39 Copyright Pearson Prentice Hall Biology Protein Synthesis: I will understand...
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Biology Biology Protein Synthesis:
I will understand the general pathway of transcription and translation
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12-3 RNA and Protein Synthesis
Protein Synthesis:
“making a protein”
Step 1. Transcription
Step 2. Translation
DNA to mRNA mRNA to protein
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12–3 RNA and Protein Synthesis
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Types of RNA
What are the three main types of RNA?
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Types of RNA
Types of RNA
There are three main types of RNA:
• messenger RNA (mRNA)
• ribosomal RNA (rRNA)
• transfer RNA (tRNA)
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Types of RNA
Messenger RNA (mRNA) carries copies of DNA with instructions to make proteins.
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Types of RNA
During protein construction, transfer RNA (tRNA) transfers each amino acid to the ribosome.
Amino acid
Transfer RNA
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Types of RNA
Ribosomes are made up of proteins and ribosomal RNA (rRNA).
Ribosome
Ribosomal RNA
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12-3 RNA and Protein Synthesis
Protein Synthesis:
“making a protein”
Step 1. Transcription
Step 2. Translation
DNA to mRNA mRNA to protein
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Transcription
What is transcription?
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Transcription
Transcription
- One strand of DNA being copied into one piece of mRNA
- Occurs in the nucleus
- DNA mRNA
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Steps to Transcription
1. Part of DNA
unwinds in nucleus
2. RNA polymerase
binds to promoter (T-A-T-A) (“start”) region
on DNA strand
3. RNA polymerase unzips DNA
strand
4. RNA polymerase makes pre-mRNA by
joining RNA base pair to
DNA
5. RNA polymerase
reaches “stop” region and pre- mRNA released
from DNA
6. Pre-mRNA removes introns
(unwanted mRNA) to make mature mRNA
7. mRNA exits the nucleus
into cytoplasm
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Transcription
RNA
RNA polymerase
DNA
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Translation
What is translation?
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Translation
Nucleus
mRNA
Messenger RNA is transcribed in the nucleus, and then enters the cytoplasm where it attaches to a ribosome.
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Translation
1. Ribosome attaches to mRNA at
AUG codon
2. Ribosome “decodes” codon and brings in
loaded tRNA
3. Ribosome moves and
decodes next codon and brings in loaded tRNA
4. 1st tRNA unloads
amino acid to the 2nd tRNA
5. 1st tRNA then
unbinds from
mRNA
7. Cycle continues until stop
codon reached
6. Results in a chain of amino
acids (protein!)
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Translation
LysinetRNAPhenylalanine
Methionine
Ribosome
mRNAStart codon
The ribosome binds new tRNA molecules and amino acids as it moves along the mRNA.
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Translation
Protein Synthesis
tRNA
Ribosome
mRNA
Lysine
Translation direction
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Genes and Proteins
IN A NUTSHELL:
The sequence of bases in DNA is used as a template for mRNA.
The codons of mRNA specify the sequence of amino acids in a protein.
CodonCodon Codon
Codon Codon Codon
mRNA
Alanine Arginine Leucine
Amino acids within a polypeptide
Single strand of DNA
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The Genetic Code
Q: How do I find the amino acids that link together to form a protein?
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The Genetic Code
A codon consists of three consecutive nucleotides on mRNA that specify a particular amino acid.
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The Genetic Code
AUG = Methionine
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The Genetic Code
AAC = asparagine
