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Protein Synthesis
Objectives:Students will be successful if they can………1)Explain how messenger RNA, Ribosomal RNA, and transfer RNA are involved in protein synthesis.2)Summarize the role of RNA polymerase in the synthesis of messenger RNA3)Describe how the code of DNA is translated into messenger RNA and is utilized to synthesize a particular protien.
Lets take a look at some examples of Proteins
Keratin: A hard durable protein found in Hair and Nails/Claws
Proteases: Protiens that help digest proteins (meat)
Actin /Mysosin: Proteins that are used in muscle fibers.
Collagen: Found in connective tissue
PSD-95: Protein that builds connections between synapses
How are these Proteins Made?
The Central Dogma
DNA → RNA → ProteinThis chain of events occurs in all living things,
from bacteria to humans, DNA codes for RNA, which guides the synthesis of Proteins.
The Evolutionary Significanceof the
Central DogmaRemember Ribozymes!!!The first forms of life were made up of RNA…….The DNA molecule evolved after RNAWe have to convert DNA back into RNA before
we make proteins because of this evolutionary history.
The machinery we use to make proteins still reads the ancient form of information, RNA.
Transcription
• The first step of the Central Dogma involves transcription.
• In Protein Synthesis we are transcribing a single gene of the DNA molecule in specific type of RNA, called messenger RNA or mRNA for short.
Steps of Transcription
Step 1. Transcription factors bind to the TATA box at the beginning of a gene.
Step 2. RNA polymerase bind to the transcription factors and begins transcription.
Step 3. RNA polymerases use ATP to add nucleotides of RNA (A,U,C,G’s), copying the gene. Nucleotides are added in the 5’ to 3’ direction of the mRNA strand.
The DNA strand being transcribed is referred to as the template strand, and is read from 3’ to 5’
Nuclear Pores
Once the mRNA strand is synthesized it’s free to leave the nucleus through a nuclear pore.
The single stranded mRNA strand is skinny enough to leave the nucleus, a double stranded DNA molecule can not.
This way your DNA molecule doesn’t have to leave the nucleus.
Translation
mRNA: Out into the Cytoplasm• Once the mRNA strand leaves the nucleus
through a nuclear pore. It can be processed by a ribosome to make a protein, by the process of Translation.
http://www.youtube.com/watch?v=5bLEDd-PSTQ&NR=1
Ribosomes The Site of Protein Synthesis
• Ribomsomes are constructed of Proteins and Ribosomal RNA (rRNA)
• Each ribosome has a large ribosome subunit and a small ribosome subunit, that wraps around a mRNA molecule to translate the mRNA code.
Translating the mRNA code
• The mRNA code is read by the ribosome in the 5’ to 3’ prime direction.
• The genetic code is read in codons.• Codons are three base pairs long, and each
codes for a particular amino acid.
The Code
• The code is read in messenger RNA language (mRNA).
• The code is redundant, multiple codons read for the same amino acid.
• There is a possibility of 43 (64) different possible codons, but only 20 different amino acids, as well as a start codon (methionine) and stop codons.
What would be the 3 letter codon for the amino acid Methionine (the start codon)
• Every single gene starts with the codon AUG.• The adding of the amino acid Methionine is
referred to as methylation.
How do Amino Acids get to Ribosome?
• Amino acids are carried by transfer RNA (tRNA) to ribosome to be sequenced in the correct order of the mRNA strand.
• The tRNA has a three nucleotide sequence, called the anti-codon that pairs up to the codon of the mRNA strand.
The A site, P site, and E siteof the Ribosome
• The A site: Where amino acids enter into the ribosome.
• The P site: Where the amino acids are linked together by polypeptide bonds to form long chains of amino acids called proteins.
• The E site: Where the tRNA molecule exits from the ribosome, leaving its protein behind. The tRNA can then return to be activated by attaching another specific amino acid to it.
The Poly-peptide chaina Protein
• Each amino acid is linked together by a polypeptide bond, creating the primary structure of the protein.
