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Biology
Biology
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2. 12-3 RNA and Protein Synthesis
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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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The Structure of RNA
The Structure of RNA
RNA consists of a long chain of nucleotides.
Each nucleotide is made up of a 5-carbon sugar, a phosphate group, and a nitrogenous base.
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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.
RNA contains uracil in place of thymine.
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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
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.
Ribosomes are made up of proteins and ribosomal RNA (rRNA).
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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) transfers each amino acid to the ribosome.
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Transcription
What is transcription?
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Transcription
Transcription
RNA molecules are produced by copying part of a nucleotide sequence of DNA into a complementary sequence in RNA. This process is called transcription.
Transcription requires the enzyme RNA polymerase.
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Transcription
During transcription, RNA polymerase binds to DNA and separates the DNA strands.
RNA polymerase then uses one strand of DNA as a template from which nucleotides are assembled into a strand of RNA.
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Transcription
RNA polymerase binds only to regions of DNA known as promoters.
Promoters are signals in DNA that indicate to the enzyme where to bind to make RNA.
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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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RNA Editing
RNA Editing
The DNA of eukaryotic genes contains sequences of nucleotides, called introns, that are not involved in coding for proteins.
The DNA sequences that code for proteins are called exons.
When RNA molecules are formed, introns and exons are copied from DNA.
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RNA Editing
The introns are cut out of RNA molecules.
The exons are the spliced together to form mRNA.
Exon
Intron
DNA
Pre-mRNA
mRNA
Many RNA molecules have sections, called introns, edited out of them before they become functional. The remaining pieces, called exons, are spliced together. Then, a cap and tail are added to form the final RNA molecule.
Cap
Tail
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The Genetic Code
The Genetic Code
The genetic code is the “language” of mRNA instructions.
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.
A codon is a group of three nucleotides on messenger RNA that specify a particular amino acid.
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The Genetic Code
Each codon specifies a particular amino acid that is to be placed on the polypeptide chain.
Some amino acids can be specified by more than one codon.
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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
There is one codon AUG that can either specify the amino acid methionine or serve as a “start” codon for protein synthesis.
There are three “stop” codons that do not code for any amino acid. These “stop” codons signify the end of a polypeptide.
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Translation
What is translation?
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Translation
Translation
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.
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Translation
Messenger RNA is transcribed in the nucleus, and then enters the cytoplasm where it attaches to a ribosome.
Nucleus
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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Translation
Translation begins when an mRNA molecule attaches to a ribosome.
As each codon of the mRNA molecule moves through the ribosome, the proper amino acid is brought into the ribosome by tRNA.
In the ribosome, the amino acid is transferred to the growing polypeptide chain.
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Translation
Each tRNA molecule carries only one kind of amino acid.
In addition to an amino acid, each tRNA molecule has three unpaired bases.
These bases, called the anticodon, are complementary to one mRNA codon.
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Translation
The ribosome binds new tRNA molecules and amino acids as it moves along the mRNA.
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
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
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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The Roles of RNA and DNA
The Roles of RNA and DNA
The cell uses the DNA “master plan” to prepare RNA “blueprints.” The DNA stays in the nucleus.
The RNA molecules go to the protein building sites in the cytoplasm—the ribosomes.
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Genes and Proteins
Genes and Proteins
Genes contain instructions for assembling proteins.
Many proteins are enzymes, which catalyze and regulate chemical reactions.
Proteins are each specifically designed to build or operate a component of a living cell.
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33. Amino acids within a polypeptide
Genes and Proteins
Codon
Codon
Codon
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.
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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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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