Transcription, Translation, and Mutations
From DNA to Proteins
Genes and Proteins
 Proteins are key cell structures and regulators of cell functions
 Sequence of amino acid makes proteins
 The sequence of nucleotides makes amino acids
RNA
 RNA – ribonucleic acid
 3 Differences Between DNA and RNA
DNA
Double Stranded
Sugar is Deoxyribose
Adenine, Guanine, Cytosine, Thymine
DNA cannot leave the nucleus
RNA
Single Stranded
Sugar is Ribose
Adenine, Guanine, Cytosine, Uracil
RNA can leave the nucleus
DNA - A – C – G – T – G – A – A – G – C – T – G – T – A – C – A – G – T – C
RNA  3 Types of RNA that help to build proteins
1. Messenger RNA (mRNA) – takes information from the DNA in the nucleus to the
ribosome
2. Ribosomal RNA (rRNA) – what ribosomes are made of
3. Transfer RNA (tRNA) – transports amino acids to the ribosome
Transcription
 Transcription – make an RNA copy of a portion of a DNA strand
 The process of transcription is similar to replication except
 Transcription makes a single strand of RNA
 Does not transcribe the entire strand of DNA
 Steps of Transcription From DNA to RNA
1. An enzyme, RNA polymerase, unzips the molecule of DNA
2. As the DNA molecule unzips, RNA polymerase adds on RNA nucleotides to one
strand of the DNA.
3. Transcription continues until RNA polymerase reaches a special stop sequence.
4. mRNA molecule breaks away, leaves the nucleus.
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The Genetic Code
 Proteins are built from amino acids
 20 different amino acids
 Codon – a set of 3 nitrogen bases that represents an amino acid.
 The order of nitrogen bases in DNA determines the type and order of amino acids in
a protein
 64 different combinations
 61 code for amino acids
 3 signal to stop protein synthesis
 more than 1 codon can code for the same amino acid
 Start codon is AUG (methionine)
 Stop codons are UAA, UAG, UGA
Translation
From mRNA to Protein
 Translation – the process of converting mRNA into a sequence of amino acids
 Takes place at the ribosome
 tRNA
 transfers amino acids to ribosome
 one end of molecule carries amino acid
 other end carries anti-codon which complements the codon
 Ex: mRNA – A-C-A
tRNA –U-G-U
Translating the mRNA Code
 Steps of Translation
1. The first codon of the mRNA strand attaches to a ribosome
2. tRNA carrying a specific amino acid approach the ribosome
3. tRNA anticodon pairs with mRNA codon
5. The first codon on mRNA is AUG which codes for amino acid methionine.
AUG is the start codon for protein synthesis.
6. A new tRNA carrying an amino acid will pair with the next mRNA codon
7. As the process continues a chain of amino acids is made until it reaches a stop
codon on the mRNA UAA, UAG, UGA.
DNA
T–A–C–A–G–G –T–C–G –T–T–A–C–G–G–A–C–T
mRNA
tRNA
Amino
Acids
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Mutations
Mutation: A Change in DNA
 Mutation – any change in a DNA sequence
 Mutations in Reproductive Cells
 Mutation in egg or sperm can be passed on to offspring
 Sometimes the mutation is so severe that the embryo does not survive
 In rare cases a gene mutation may have positive effects
 Mutations in Body Cells
 This mutation would not be passed on to offspring
 But the mutations can cause harm to the individual
DNA Mutations
1. Point Mutation
 A change in a single base pair in DNA
 A change in a single letter can change the amino acid, thus changing the
protein made
2. Framshift Mutation
 A single base is added or deleted from DNA
 Can cause nearly every amino acid in the protein to be changed.
Chromosomal Mutations
 Chromosomal Mutations – changes in chromosomes during replication.
 They occur in all living organisms, but are especially common in plants
 Chromosomal mutations are rarely passed on to the next generation because:
 The zygote usually dies
 The mature organism is usually sterile
 4 Types of Chromosomal Mutations
1. Deletion – a fragment of a chromosome breaks off, it can be lost
2. Duplication – a chromosome fragment attaches to its homologous
chromosome, which will then carry two copies of a gene.
3. Inversion – fragment reattaches to the original chromosome in the reverse
orientation.
4. Translocation – a fragment may join a nonhomologous chromosome.
Causes of Mutations
 Spontaneous Mutations – a mistake in base pairing during DNA replication. It
occurs at random.
 Mutagen – any agent that can cause a change in DNA
 Ex. Chemicals, radiation, high temperatures
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Repairing DNA
 When mistakes do occur repair mechanisms fix mutations
 Proofreading enzymes – reads the DNA strand and checks it for mistakes
 Repair enzymes – fixes any mistakes in the DNA strand
Mistakes in Meiosis
 Sometimes accidents occur during meiosis and chromosomes fail to separate
correctly
 Nondisjunction – failure of homologous chromosomes to separate
 During meiosis I one chromosome from each pair is supposed to move to opposite
poles but occasionally both chromosomes of a pair move to the same pole
 Trisomy – 1 extra chromosome (47)
 Ex: extra chromosome on pair number 21 – down syndrome
 Monosomy – missing 1 chromosome (45)
 Ex: missing chromosome on pair number 23 – turner syndrome
 Tetraploid – 2 extra chromosomes (48)
 Polyploids – organisms with more than the usual number of chromosome sets
 Is rare in animals and almost always results in death.
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Transcription, Translation, and Mutations
From DNA to Proteins
 Occurs in two steps – ______________ and _____________
Genes and Proteins
 ____________ are key cell structures and regulators of cell functions
 The sequence of _______________ makes amino acids
 Sequence of __________ __________ makes proteins
RNA
 RNA –
 Differences Between DNA and RNA
DNA
DNA
RNA
A–C–G–T–G–A–A–G–C–T–G–T–A–C–A–G–T–C
RNA
 3 Types of RNA that help to build proteins
1. Messenger RNA (mRNA) –
2. Ribosomal RNA (rRNA) –
3. Transfer RNA (tRNA) –
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Transcription
 Transcription –
 The process of transcription is similar to replication except
 Transcription makes a ____________ strand of RNA

 Steps of Transcription From DNA to RNA
1. An enzyme, _______ _______________, unzips the molecule of DNA
2. As the DNA molecule unzips, RNA polymerase adds on _______ ____________
to ________ strand of the DNA.
3. Transcription continues until RNA polymerase reaches a special ___________
sequence.
4. mRNA molecule breaks away, leaves the ____________.
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The Genetic Code
 Proteins are built from __________ __________
 ______ different amino acids
 Codon –
 The order of nitrogen bases in DNA determines the type and order of amino acids in
a protein
 ______ different combinations
 ______ code for amino acids
 ______ signal to stop protein synthesis
 more than 1 codon can code for the same __________ __________
 Start codon is ________ (methionine)
 Stop codons are ________, ________, ________
Translation
From mRNA to Protein
 Translation –
 Takes place at the _______________
 tRNA

 One end of tRNA carries __________ __________
 Other end carries ______-__________ which complements the codon
 Ex: mRNA –
tRNA –
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Translating the mRNA Code
 Steps of Translation
1. The first codon of the mRNA strand attaches to a _______________
2. ________ carrying a specific amino acid approaches the ribosome
3. tRNA anticodon pairs with __________ __________
4. The first codon on mRNA is _________ which codes for amino acid
_______________. AUG is the __________ codon for protein synthesis.
5. A new tRNA carrying an amino acid will pair with the next mRNA codon
6. As the process continues a chain of amino acids is made until it reaches a
________ codon on the mRNA; ________, ________, & ________.
DNA
T–A–C–A–G–G –T–C–G –T–T–A–C–G–G–A–C–T
mRNA
tRNA
Amino
Acids
8
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Mutations
Mutations: A Change in DNA
 Mutation –
 Mutations in Reproductive Cells
 Mutation in egg or sperm can be passed on to _______________
 Sometimes the mutation is so severe that the embryo does not __________
 In rare cases a gene mutation may have _______________ effects
 Mutations in Body Cells
 This mutation would _________ be passed on to offspring
 But the mutations can cause harm to the individual
DNA Mutations
1. ______________ Mutation

 A change in a single letter can change the ____________ __________, thus
changing the ___________ made
2. _______________________ Mutation

 Can cause ___________ amino acid in the protein to be changed.
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Chromosomal Mutations
 Chromosomal Mutations –
 They occur in all living organisms, but are especially common in ____________
 Chromosomal mutations are rarely passed on to the next generation because:


 4 Types of Chromosomal Mutations
1. Deletion –
2. Duplication –
3. Inversion –
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4. Translocation –
Causes of Mutations
 Spontaneous Mutations –
 Mutagen –
 Ex.
Repairing DNA
 When mistakes do occur repair mechanisms fix mutations
 Proofreading enzymes –
 Repair enzymes –
Mistakes in Meiosis
 Sometimes accidents occur during meiosis and chromosomes fail to separate
correctly
 Nondisjunction –
 During meiosis I one chromosome from each pair is supposed to move to opposite
poles but occasionally both chromosomes of a pair move to the same pole
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 Trisomy –
 Ex:
 Monosomy –
 Ex:
 Tetraploid –
 Polyploids –
 Is rare in ____________ and almost always results in ____________.
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