RNA and Protein Synthesis
VOCABULARY
1. gene: sequence of DNA that codes for a protein and thus determines a trait
2. mRNA: RNA molecule that carries copies of instructions for the assembly of amino acids into proteins from
DNA to the rest of the cell
3. rRNA: type of RNA that makes up the major part of ribosomes
4. tRNA: type of RNA molecule that transfers amino acids to ribosomes during protein synthesis
5. transcription: process in which part of the nucleotide sequence of DNA is copied into a complementary
sequence in RNA
6. RNA polymerase: enzyme similar to DNA polymerase that binds to DNA and separates the DNA strands
during transcription
7. promoter: region of DNA that indicates to an enzyme where to bind to make RNA
8. intron: intervening sequence of DNA; does not code for a protein
9. exon: expressed sequence of DNA; codes for a protein
10. codon: three-nucleotide sequence on messenger RNA that codes for a single amino acid
11. translation: decoding of a mRNA message into a polypeptide chain
12. anticodon: group of three bases on a tRNA molecule that are complementary to an mRNA codon
DNA vs RNA
Deoxyribose nucleic acid
1. Double stranded
2. ATGC bases
3. Deoxyribose sugar
Ribose nucleic acid
1. Single stranded
2. AUGC bases
3. Ribose sugar
Types of RNA
Messenger RNA (mRNA)
carries copies of instructions for the
assembly of amino acids into
proteins from DNA to the rest of the
cell; carries codons
Transfer RNA (tRNA)
Ribosomal RNA (rRNA)
transfers amino acids to ribosomes
during protein synthesis; carries
anticodons
site of protein production; makes up
the major part of ribosomes
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.
RNA polymerase binds only to regions of DNA known as promoters
 have specific base sequences
 signals in DNA that indicate to the enzyme where to bind to make RNA.
RNA Editing
Many RNA molecules require a bit of editing before they are
ready to go into action.
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
because they are “expressed” in the synthesis of proteins.
When RNA molecules are formed, both the introns and the
exons are copied from the DNA.
The introns are cut out of RNA molecules while they are still in
the nucleus.
The remaining exons are then spliced back together to form the
final mRNA.
Then, a cap and tail are added to form the final RNA molecule.
Some RNA molecules may be cut and spliced in different ways in different tissues
 makes it possible for a single gene to produce several different forms of RNA.
Introns and exons may also play a role in evolution.  makes it possible for very small changes in DNA sequences to
have dramatic effects in gene expression
THE GENETIC CODE
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The language of mRNA instructions
Consist of 20 different amino acids
With 64 possible codons
 Codon: consist of 3 consecutive nucleotides that
specify a specific amino acid (3 bases long)
 Proteins are made by joining amino acids into long
chains called polypeptides. The property of a protein
is determined by the order in which different amino
acids are joined together to form polypeptides
TRANSLATION
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The decoding of an mRNA message into
a polypeptide chain (protein)
Takes place on ribosomes in the
cytoplasm
 Begins when mRNA in the
cytoplasm attaches to a ribosome
 Each codon of the mRNA moves
through the ribosome
 Proper amino acid is brought into
the ribosome by tRNA
 Amino acid is transferred to
growing polypeptide chain in the
ribosome
 Each tRNA carries only one kind of
amino acid
 Each tRNA has 3 unpaired bases called anticodons which are complementary to one mRNA codon
 Works like an assembly line
 Polypeptide chain continues to grow until the ribosome reaches a stop codon
 Polypeptide chain is released  Protein
PROTEIN SYNTHESIS
PROTEINS
Protein
Enzymes that catalyze and regulate chemical reactions
Act as microscopic tools to build or operate a component of a living cell
Genes code for proteins that in turn determine genetic traits
MUTATIONS
Mutation: Changes in the genetic material
Effect on organism
 Most effects are neutral
 Some effects are deadly
 Some lead to greater genetic variability in a species
Causes
 Random mistakes during DNA replication or RNA transcription
 Prolonged exposure to excessive radiation or harmful chemicals
Types of Mutations
 Point mutation: gene mutations involving changes in one or a few nucleotides
Occur at a single point in the DNA sequence
Include substitutions, insertions and deletions
 Substitution: one base is changed to another
 Insertions: base is inserted into the DNA sequence
 Deletion: Base is deleted from the DNA sequence
 Frameshift mutation: mutations that shift the “reading” frame of genetic message by inserting or
deleting a nucleotide.
May change every amino acid that follows the point of mutation
Protein may be altered so much that it is unable to perform its normal function
May lead to termination of organism (death)
 Chromosomal mutation: involves changes in the number or structure of chromosomes
May change the locations of genes on chromosomes
DELETIONS: involve the loss or all or part of a chromosome
DUPLICATION: produce extra copies of parts of a chromosome
INVERSION: reverse the direction of parts of a chromosome
TRANSLOCATION: part of one chromosome breaks off and attaches to
another
Significance of Mutations
 Most are neutral
 Some are harmful
Cause genetic disorders
Cause many types of cancer
Some lead to greater genetic variability in a species
Polyploidy: organism has extra sets of chromosomes; can cause plants to be stronger and larger
CHROMOSOMAL MUTATIONS
GENE MUTATION