RNA AND PROTEIN
SYNTHESIS
RNA vs DNA
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RNA
5 – Carbon sugar (ribose)
Phosphate group
Nitrogenous base
Single stranded
Uracil base
DNA
5 – Carbon sugar (deoxyribose)
Phosphate group
Nitrogenous base
Double stranded
Thymine base
RNA MOLECULE
TYPES OF RNA
Messenger RNA (mRNA)
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Carries copies of instructions for
the assembly of amino acids
into proteins from DNA to the rest
of the cell
Ribosomal RNA (rRNA)
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Makes of the major part of a ribosome
Transfer RNA (tRNA)
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Transfers amino acids to ribosomes
during protein synthesis
TRANSCRIPTION
• Transcription
 The process of producing
RNA molecules by copying
part of the nucleotide
sequence of DNA into a
complementary sequence
in RNA
 Requires the enzyme
RNA polymerase
• Binds to and separates the
DNA strands
• Uses one strand of DNA as a
template to form RNA
• Binds to regions of DNA known
as promoters which have
specific base sequences
• Promoters are signals in DNA
that indicate to the enzyme
where to start and stop making
RNA
GENE: coded DNA instructions that control the production of
proteins in the cell
RNA Editing
RNA molecules have sections called…
• Introns: sections not coded for
making proteins
 “cut” out or edited while still in
the nucleus
• Exons: sections coded for making
proteins
 “spliced” back together to form
final mRNA
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
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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
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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
• 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
• Causes of genetic disorders
• Causes of many types of cancer
 Some lead to greater genetic variability in a species
• Polyploidy: organism has extra sets of chromosomes (3N or 4N)
• Can cause plants to be stronger and larger