GENE EXPRESSION TRANSCRIPTION, TRANSLATION AND MUTATIONS.

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GENE EXPRESSION TRANSCRIPTION, TRANSLATION AND MUTATIONS

Transcript of GENE EXPRESSION TRANSCRIPTION, TRANSLATION AND MUTATIONS.

Page 1: GENE EXPRESSION TRANSCRIPTION, TRANSLATION AND MUTATIONS.

GENE EXPRESSION

TRANSCRIPTION, TRANSLATION AND

MUTATIONS

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HOW DOES DNA, AS A GENE, GET EXPRESSED?

• DNA codes for specific proteins to be made

• proteins are assembled from amino acids

• amino acids are selected based on the genetic code

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Amino Acids will be bonded together to form long chains. These long chains are proteins.

•There are 20 different amino acids

•The DNA code dictates the sequence of acids

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DNA to Proteins

• The process of making the proteins from DNA instructions is called PROTEIN SYNTHESIS

• Protein Synthesis has 2 major steps:– Transcription– Translation

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TRANSCRIPTION

Trans= Across Script= writing

Writing across= RNA is being made (or written) using DNA

Starts in the nucleus with the chromosome which contains the gene that will be expressed.

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As with replication--• DNA unzips, but this time only in the gene location

• mRNA forms instead of another piece of DNA

• Uracil is substituted for Thymine

• only one strand is transcribed- called the “sense” strand- other strand is called the “nonsense” strand

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A gene is a section of a chromosome which codes for a specific trait

WHAT IS A GENE?

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After the DNA code is copied into the mRNA language, Transcription ends with the mRNA leaving the nucleus. (DNA is too big)

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RNA

• needed to assist in the synthesis of proteins

• 3 types– Messenger RNA (mRNA)– Transfer RNA (tRNA)– Ribosomal RNA (rRNA)

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RNA STRUCTURE & Differences from DNA

• 1.) Uracil instead of Thymine

• 2.) Single stranded

• 3.) Sugar is a Ribose Sugar

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The strand of mRNA that forms is set up in 3-base code words.

Formed from nitrogen bases

These are called

CODONS

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Transcribe This DNA

• DNA

• ACTCAGACTATGACCTAGGATCAT

• TGAGTCTGATACTGGATCCTAGTA

• Consider bottom row as sense strand

• What will the 8 codons be in mRNA?

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TRANSLATION

• Translating RNA into proteins• Where are proteins made??• RIBOSOMES• Begins when mRNA travels to and enters

the ribosomes• Transfer RNA (tRNA) is out in the

cytoplasm searching for amino acids• Ribosomal RNA (rRNA) is in the

ribosomes, helping place the mRNA in position

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Fig. 14.11, p. 230

Each codon (mRNA) indicates which amino acid the tRNA is suppose to bring to the ribosomes.

Scientists use a chart like this to translate the protein.

Example:

codon = ACA

AA = threonine

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Fig. 14.12, p. 231

codon in mRNA

anticodon

amino acid OH

amino acidattachment site

anticodon

tRNA MOLECULE

amino acid attachment site

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CG anticodon 1A

UG anticodon 2C

CU anticodon 3C

GA anticodon 4A

GC anticodon 5C

UC anticodon 6G

AU anticodon 7C

Once mRNA is at the ribosome, tRNA matches amino acids to the codons using

ANTICODONS

**Each tRNA carries a different amino acid

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Amino acid chain

tRNA

mRNAcodons

ribosome

anticodon

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Binding site for mRNA

P (first

binding site for tRNA)

A (second binding site for tRNA)

Fig. 14.14a, p. 232

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Fig. 14.14b, p. 233

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• Because there are only 20 amino acids, they are often called by their first three letters

mRNA codons AUG CCG GAU UAGamino acids Met Pro Asp stop

*not all codons will code for an AA, some will be stop codons to tell translation to stop

start codon

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