1. 12-3 RNA and Protein Synthesis
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Comparing
The transcription process is similar to replication.
Transcription and replication both involve complex enzymes and complementary base pairing.
The two processes have different end results.
Replication copies all the DNA; transcription copies a gene.
Replication makes one copy; transcription can make many copies.
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3. 12–3 RNA and Protein Synthesis
Genes are coded DNA instructions that control the production of proteins.
Genetic messages can be decoded by copying part of the nucleotide sequence from DNA into RNA.
RNA contains coded information for making proteins.
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4. 12–3 RNA and Protein Synthesis
RNA carries DNA’s instructions.
The central dogma states that information flows in one direction from DNA to RNA to proteins.
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5. 12–3 RNA and Protein Synthesis
The central dogma includes three processes.
Replication
Transcription
Translation
RNA is a link between DNA and proteins.
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The Structure of RNA
The Structure of RNA
There are three main differences between RNA and DNA:
The sugar in RNA is ribose instead of deoxyribose.
RNA is generally single-stranded instead of double stranded.
RNA contains uracil in place of thymine.
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Types of RNA
Types of RNA
There are three main types of RNA:
messenger RNA
ribosomal RNA
transfer RNA
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Types of RNA
The three main types of RNA are messenger RNA, ribosomal RNA, and transfer RNA.
Messenger RNA (mRNA) carries copies of instructions for assembling amino acids into proteins.
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Types of RNA
Ribosome
Ribosomal RNA
The three main types of RNA are messenger RNA, ribosomal RNA, and transfer RNA. Ribosomal RNA is combined with proteins to form ribosomes.
Ribosomal RNA (rRNA) forms part of ribosomes where proteins are made.
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Types of RNA
Amino acid
The three main types of RNA are messenger RNA, ribosomal RNA, and transfer RNA.
Transfer RNA
During protein construction, transfer RNA (tRNA) brings amino acids from the cytoplasm to a ribosome.
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11. Protein Synthesis DNA molecule DNA strand (template) 3¢ 5¢
TRANSCRIPTION
mRNA 5¢ 3¢
Codon
TRANSLATION
Protein
Amino acid

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Transcription
Transcription
A transcription complex consisting of RNA and other proteins recognizes the start site of a gene and begins to unwind the DNA.
RNA polymerase reads one side of the DNA template and strings together a complementary strand of RNA nucleotides.
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Transcription
Transcription
The growing RNA strand hangs freely as it is transcribed and detaches completely once the entire gene is transcribed.
DNA Molecule
Nucleotides
Newly synthesized RNA strand
RNA polymerase
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Transcription
RNA
RNA polymerase
DNA
During transcription, RNA polymerase uses one strand of DNA as a template to assemble nucleotides into a strand of RNA.
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The Genetic Code
The Genetic Code
The genetic code is the “common language” of mRNA instructions and is shared by almost all organisms.
The code is written using four “letters” (the bases: A, U, C, and G).
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The Genetic Code
A codon consists of three consecutive nucleotides on mRNA that specify a particular amino acid.
The start codon signals the start of translations and the amino acid methionine.
The stop codon is three codons that signal the end of a chain of amino acids.
A codon is a group of three nucleotides on messenger RNA that specify a particular amino acid.
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The Genetic Code
The genetic code shows the amino acid to which each of the 64 possible codons corresponds. To decode a codon, start at the middle of the circle and move outward.
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The Genetic Code
The genetic code matches each codon to its amino acid or function.
three stop codons
one start codon, codes for methionine
The genetic code shows the amino acid to which each of the 64 possible codons corresponds. To decode a codon, start at the middle of the circle and move outward.
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Translation
Translation
Translation is the decoding of an mRNA message into a polypeptide chain (protein).
Ribosomes are the site of protein synthesis; made of rRNA and proteins
Catalyzes the formation of peptide bonds between amion acids
During translation, the cell uses information from messenger RNA to produce proteins.
Nucleus
mRNA
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Reading frame
Codon
A reading frame is the series of 3 nonoverlapping nucleotides read, in order, by a cell.
3 different reading frames are possible for each mRNA molecule.
Codons must be read in the correct reading frame for the correct protein to be made.
This diagram illustrates how information for specifying the traits of an organism is carried in DNA. 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, and proteins play a key role in producing an organism’s traits.
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Anticodon
Amino acids are linked to become a protein.
An anticodon is a set of three nucleotides that is complementary to an mRNA codon.
An anticodon is carried by a tRNA.
Transfer RNA (tRNA) is a type of RNA that carries amino acids from the cytoplasm to the ribosome. One end has a specific anticodon, the other end attaches to a specific amino acid.
This diagram illustrates how information for specifying the traits of an organism is carried in DNA. 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, and proteins play a key role in producing an organism’s traits.
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Ribosomes
Ribosomes consist of two subunits
The large subunit has three binding sites for tRNA.
The small subunit binds to mRNA.
This diagram illustrates how information for specifying the traits of an organism is carried in DNA. 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, and proteins play a key role in producing an organism’s traits.
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Translation Process
1. Ribosome assembles at the start codon; complementary tRNA molecule pair with the exposed codon.
Lysine
Phenylalanine
tRNA
Methionine
Ribosome
During translation, or protein synthesis, the cell uses information from messenger RNA to produce proteins. The cell uses all three main forms of RNA during this process.
mRNA
Start codon
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Translation
Protein Synthesis-ribosome helps bond the new amino acid to the start codon and breaks the bond between the amino acid and the first tRNA.
Lysine
tRNA
During translation, or protein synthesis, the cell uses information from messenger RNA to produce proteins. The cell uses all three main forms of RNA during this process.
mRNA
Translation direction
Ribosome
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Translation
3. Ribosome pulls the RNA strand the length of one codon; first tRNA returns to the cytoplasm; another codon is exposed for tRNA binding. The process continues until the ribosome reaches a stop codon.
Polypeptide
Ribosome
tRNA
During translation, or protein synthesis, the cell uses information from messenger RNA to produce proteins. The cell uses all three main forms of RNA during this process.
mRNA
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26. Amino acids within a polypeptide
Genes and Proteins
Codon
Codon
Codon
DNA
mRNA
Protein
Single strand of DNA
Codon
Codon
Codon
mRNA
This diagram illustrates how information for specifying the traits of an organism is carried in DNA. 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, and proteins play a key role in producing an organism’s traits.
Alanine
Arginine
Leucine
Amino acids within a polypeptide
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27. Amino acid (Start codon methionine)
Polypeptide bond
Large subunit
tRNA
codons
Small subunit
mRNA
anticodon

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12–3
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12–3
The role of a master plan in a building is similar to the role of which molecule?
messenger RNA
DNA
transfer RNA
ribosomal RNA
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12–3
A base that is present in RNA but NOT in DNA is
thymine.
uracil.
cytosine.
adenine.
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12–3
The nucleic acid responsible for bringing individual amino acids to the ribosome is
transfer RNA.
DNA.
messenger RNA.
ribosomal RNA.
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12–3
A region of a DNA molecule that indicates to an enzyme where to bind to make RNA is the
intron.
exon.
promoter.
codon.
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12–3
A codon typically carries sufficient information to specify a(an)
single base pair in RNA.
single amino acid.
entire protein.
single base pair in DNA.
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