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RNA and Protein Synthesis
Chapter 12-3
How are proteins made?
• In molecular terms, genes are coded
DNA instructions that control the
production of proteins within the cell.
(test question)
• The first step in decoding these
genetic messages is to copy part of
the nucleotide sequence from DNA
into RNA, or ribonucleic acid.
• These RNA molecules contain coded
information for making proteins.
There are three main differences
between RNA and DNA:
• The sugar in RNA is ribose
instead of deoxyribose (test question)
• RNA is generally singlestranded
• RNA contains uracil in place of
thymine.
Three Types of RNA
• The assembly of amino acids
into proteins is controlled by
RNA.
• messenger RNA
• ribosomal RNA
• transfer RNA.
Most genes contain instructions
for assembling amino acids
into proteins. The RNA
molecules that carry copies of
these instructions are known
as messenger RNA (mRNA)
because they serve as
“messengers” from DNA to the
rest of the cell.
Proteins are assembled
on ribosomes.
Ribosomes are made up
of several dozen
proteins, as well as a
form of RNA known as
ribosomal RNA (rRNA).
• a third type of RNA
molecule transfers each
amino acid to the ribosome
as it is specified by coded
messages in mRNA. These
RNA molecules are known
as transfer RNA (tRNA).
(test
question)
Ribosome
Transcription
RNA molecules are produced
by copying part of the
nucleotide sequence of
DNA into a complementary
sequence in RNA, a
process called
transcription.
(test question)
transcription
• Codon A codon is a group of three
nucleotides on messenger RNA that
specify a particular amino acid. (test question)
Because there are four different bases,
there are 64 possible three-base codons (4 × 4 × 4 = 64).
Genetic code
(test question)
Translation
• The decoding of an mRNA
message into a polypeptide chain
(protein) is known as translation.
• Translation takes place on
ribosomes.
• During translation, the cell
uses information from
messenger RNA to produce
proteins.
(test question)
Assignment
• Page 306 1-4