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RNA and Protein Synthesis
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RIBONUCLEIC ACID
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
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8.
9.
promoter: region of DNA that indicates to an enzyme where to
bind to make RNA
intron: intervening sequence of DNA; does not code for a
protein
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
Types of RNA
mRNA
rRNA
tRNA
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.
TRANSCRIPTION
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.
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.
• 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
The Genetic Code
• 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
Translation
 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
TRANSLATION
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 the
genetic message by inserting or deleting a
nucleotide
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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
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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
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Cause genetic disorders
Cause many types of cancer
 Some lead to greater genetic variability in a species
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Polyploidy: organism has extra sets of chromosomes
Can cause plants to be stronger and larger
GENE MUTATION
TYPES OF MUTATIONS
CHROMOSOMAL MUTATIONS