Transcription, Translation, and Mutations

Transcription, Translation, and Mutations

From DNA to Proteins

Genes and Proteins

J Proteins are key cell structures and regulators of cell functions

J Sequence of amino acid makes proteins

J The sequence of nucleotides makes amino acids

RNA

J RNA – ribonucleic acid

J 3 Differences Between DNA and RNA

DNA RNA

Double Stranded Single Stranded

Sugar is Deoxyribose Sugar is Ribose

Adenine, Guanine, Cytosine, Thymine Adenine, Guanine, Cytosine, Uracil

DNA cannot leave the nucleus 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 -

J 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

J Transcription – make an RNA copy of a portion of a DNA strand

J The process of transcription is similar to replication except

J Transcription makes a single strand of RNA

J Does not transcribe the entire strand of DNA

J 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.

The Genetic Code

J Proteins are built from amino acids

J 20 different amino acids

J Codon – a set of 3 nitrogen bases that represents an amino acid.

J The order of nitrogen bases in DNA determines the type and order of amino acids in a protein

J 64 different combinations

J 61 code for amino acids

J 3 signal to stop protein synthesis

J more than 1 codon can code for the same amino acid

J Start codon is AUG (methionine)

J Stop codons are UAA, UAG, UGA

Translation

From mRNA to Protein

J Translation – the process of converting mRNA into a sequence of amino acids

J Takes place at the ribosome

J tRNA

J transfers amino acids to ribosome

J one end of molecule carries amino acid

J other end carries anti-codon which complements the codon

J Ex: mRNA – A-C-A

tRNA –U-G-U

Translating the mRNA Code

J 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

Mutations

Mutation: A Change in DNA

J Mutation – any change in a DNA sequence

J Mutations in Reproductive Cells

J Mutation in egg or sperm can be passed on to offspring

J Sometimes the mutation is so severe that the embryo does not survive

J In rare cases a gene mutation may have positive effects

J Mutations in Body Cells

J This mutation would not be passed on to offspring

J But the mutations can cause harm to the individual

DNA Mutations

1. Point Mutation

J A change in a single base pair in DNA

J A change in a single letter can change the amino acid, thus changing the protein made

2. Framshift Mutation

J A single base is added or deleted from DNA

J Can cause nearly every amino acid in the protein to be changed.

Chromosomal Mutations

J Chromosomal Mutations – changes in chromosomes during replication.

J They occur in all living organisms, but are especially common in plants

J Chromosomal mutations are rarely passed on to the next generation because:

J The zygote usually dies

J The mature organism is usually sterile

J 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

J Spontaneous Mutations – a mistake in base pairing during DNA replication. It occurs at random.

J Mutagen – any agent that can cause a change in DNA

J Ex. Chemicals, radiation, high temperatures

Repairing DNA

J When mistakes do occur repair mechanisms fix mutations

J Proofreading enzymes – reads the DNA strand and checks it for mistakes

J Repair enzymes – fixes any mistakes in the DNA strand

Mistakes in Meiosis

J Sometimes accidents occur during meiosis and chromosomes fail to separate correctly

J Nondisjunction – failure of homologous chromosomes to separate

J 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

J Trisomy – 1 extra chromosome (47)

J Ex: extra chromosome on pair number 21 – down syndrome

J Monosomy – missing 1 chromosome (45)

J Ex: missing chromosome on pair number 23 – turner syndrome

J Tetraploid – 2 extra chromosomes (48)

J Polyploids – organisms with more than the usual number of chromosome sets

J Is rare in animals and almost always results in death.

Transcription, Translation, and Mutations

From DNA to Proteins

J Occurs in two steps – ______and ______

Genes and Proteins

J ______are key cell structures and regulators of cell functions

J The sequence of ______makes amino acids

J Sequence of ______makes proteins

RNA

J RNA –

J Differences Between DNA and RNA

DNA / RNA

DNA A – C – G – T – G – A – A – G – C – T – G – T – A – C – A – G – T – C

RNA

J 3 Types of RNA that help to build proteins

1. Messenger RNA (mRNA) –

2. Ribosomal RNA (rRNA) –

3. Transfer RNA (tRNA) –

Transcription

J Transcription –

J The process of transcription is similar to replication except

J Transcription makes a ______strand of RNA

J 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 ______.

The Genetic Code

J Proteins are built from ______

J ______different amino acids

J Codon –

J The order of nitrogen bases in DNA determines the type and order of amino acids in a protein

J ______different combinations

J ______code for amino acids

J ______signal to stop protein synthesis

J more than 1 codon can code for the same ______

J Start codon is ______(methionine)

J Stop codons are ______, ______, ______

Translation

From mRNA to Protein

J Translation –

J Takes place at the ______

J tRNA

J One end of tRNA carries ______

J Other end carries ______-______which complements the codon

J Ex: mRNA –

tRNA –

Translating the mRNA Code

J 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

Mutations

Mutations: A Change in DNA

J Mutation –

J Mutations in Reproductive Cells

J Mutation in egg or sperm can be passed on to ______

J Sometimes the mutation is so severe that the embryo does not ______

J In rare cases a gene mutation may have ______effects

J Mutations in Body Cells

J This mutation would ______be passed on to offspring

J But the mutations can cause harm to the individual

DNA Mutations

1. ______Mutation

J A change in a single letter can change the ______, thus changing the ______made

2. ______Mutation

J Can cause ______amino acid in the protein to be changed.

Chromosomal Mutations

J Chromosomal Mutations –

J They occur in all living organisms, but are especially common in ______

J Chromosomal mutations are rarely passed on to the next generation because:

J 4 Types of Chromosomal Mutations

1. Deletion –

2. Duplication –

3. Inversion –

4. Translocation –

Causes of Mutations

J Spontaneous Mutations –

J Mutagen –

J Ex.

Repairing DNA

J When mistakes do occur repair mechanisms fix mutations

J Proofreading enzymes –

J Repair enzymes –

Mistakes in Meiosis

J Sometimes accidents occur during meiosis and chromosomes fail to separate correctly

J Nondisjunction –

J 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

J Trisomy –

J Ex:

J Monosomy –

J Ex:

J Tetraploid –

J Polyploids –

J Is rare in ______and almost always results in ______.