Transcript RNA & Protein Synthesis

RNA & Protein Synthesis
Genes
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The double helix structure explains how DNA can
be copied, but it does not explain how genes work.
Genes are coded DNA instructions that control the
production of proteins within the cell.
Genetic messages can be decoded by copying part
of the nucleotide sequence from DNA into RNA.
RNA contains coded information for making
proteins.
Ribonucleic Acid, RNA
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RNA is a single-stranded nucleic acid involved in
protein synthesis.
RNA is a copy of DNA that goes out into the
cytoplasm to tell the cell what to do in order to stay
alive.
You can think of an RNA molecule as a disposable
copy of a segment of DNA.
The ability to copy a single DNA sequence into RNA
makes it possible for a single gene to produce
hundreds or even thousands of RNA molecules.
The Structure of RNA
There are three main differences between RNA and DNA:
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The sugar in RNA is ribose instead of deoxyribose; one more atom
of O2 than the sugar in DNA.
RNA is generally single-stranded.
RNA contains uracil in place of thymine, A-U.
Protein Synthesis
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RNA plays an important role in protein synthesis.
Protein Synthesis – assembly of new protein molecule
from amino acids.
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Protein molecules are made by the cell.
Takes place in the ribosome, which are made up of
proteins and ribosomal RNA (rRNA).
Protein Synthesis (Cont.)
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Before protein synthesis can occur, genetic information
from the nucleus must be moved from the nucleus to the
ribosome.
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This action is carried out by a “messenger” molecule,
messenger RNA (mRNA).
mRNA sends messages from DNA to the cytoplasm.
Messenger RNA (mRNA) carries copies of instructions for
assembling amino acids into proteins.
Transcription
DNA
strand unzips, and one strand is
used as a template to create an mRNA
molecule. (Similar to replication.)
 Match up bases to one side of a gene in
DNA
 mRNA detaches from the DNA
 mRNA moves out of the nucleus and
into the cytoplasm
Transcription only copies specific genes.
RNA:
A binds U
C binds G
Codons
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After transcription, the mature molecule undergoes
splicing or merging.
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Portions of the mRNA strand that do not code for proteins
are elimated.
What remains? Codons
Codons: set of three nucleotides that code for the
production of a protein.
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Three-letter “words” tell the ribosome the order in which
amino acids should be arranged in the new protein.
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Can be arranged in 64 ways.
Anticodons
During
protein construction,
transfer RNA (tRNA) transfers
each amino acid to the ribosome to
be assembled into new proteins
during translation.
The
trio of bases are called
anticodons.
The
mRNA codons forms base
pairs with tRNA anticodons.
A
–U
C – G
Translation
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As the ribosome moves from the codon to codon along
the mRNA, amino acids carried by the tRNA are added,
forming a strand of amino acids – a new protein
molecule.
This process of creating a new protein by “reading” the
code in mRNA is called translation.
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Translation is the decoding of an mRNA message into a
polypeptide chain (protein).
Translation takes place on ribosomes.
During translation, the cell uses information from messenger
RNA to produce proteins.
Phenylalanine
Methionine
Ribosome
mRNA
Start codon
tRNA
Lysine
Copyright Pearson Prentice Hall
Read your mRNA codon  CCU
Find the tRNA anticodon  GGA
Find 1st base on the left, 2nd base on the top, 3rd base on the right.
Find where they all cross in the chart.
Read your amino acid.  Glycine