Transcription, Translation, and Mutations

From DNA to ProteinsGenes 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 RNA Double Stranded Single Stranded

Sugar is Deoxyribose Sugar is RiboseAdenine, 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 -

3 Types of RNA that help to build proteins1. Messenger RNA (mRNA) – takes information from the DNA in the nucleus to the

ribosome2. 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 RNA1. An enzyme, RNA polymerase, unzips the molecule of DNA2. 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 Proteins are built from amino acids

1

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

TranslationFrom 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 ribosome2. tRNA carrying a specific amino acid approach the ribosome3. tRNA anticodon pairs with mRNA codon5. 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 codon7. 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 MutationsMutation: A Change in DNA

2

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 Mutations1. 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 Mutations1. 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 temperaturesRepairing DNA When mistakes do occur repair mechanisms fix mutations

3

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.

Transcription, Translation, and Mutations

4

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 RNA

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) –

2. Ribosomal RNA (rRNA) –

3. Transfer RNA (tRNA) – Transcription Transcription –

5

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 ____________.

The Genetic Code

Proteins are built from __________ __________

6

______ 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 ________, ________, ________

TranslationFrom mRNA to Protein

Translation –

Takes place at the _______________

tRNA

One end of tRNA carries __________ __________

Other end carries ______-__________ which complements the codon

Ex: mRNA – tRNA –

Translating the mRNA Code

Steps of Translation

1. The first codon of the mRNA strand attaches to a _______________

7

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

9

MutationsMutations: A Change in DNA

Mutation –

10

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.

Chromosomal Mutations

Chromosomal Mutations –

They occur in all living organisms, but are especially common in ____________

11

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

4 Types of Chromosomal Mutations

1. Deletion –

2. Duplication –

3. Inversion –

4. Translocation –

12

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

Trisomy –

Ex:

13

Monosomy –

Ex:

Tetraploid –

Polyploids –

Is rare in ____________ and almost always results in ____________.

14